Posted in Orthognathic Surgery

Mandibular Orthognathic Surgery

Introduction

From time immemorial, man has been trying to acquire for himself an appearance that is pleasing and acceptable to the society. Facial features often form a basis for the stereotyping of personality characteristics. Correction of facial deformities has been attempted by many people over the centuries sometimes with success but often with disastrous results.

Orthognathic surgery has become a useful and acceptable treatment modality for patients with skeletal discrepancies in addition to orthodontic problems. Over the past few decades, refinements in surgical techniques and advent of sophisticated instruments have made this surgery safe, easier and predictable.

Historical developments

Hullihen was the first person to correct jaw deformity surgically in 1849, when he corrected an anterior open bite by mandibular subapical osteotomy. The most important early contribution came from Blair in the early 1900s – he described a horizontal osteotomy of the mandibular ramus through the extra-oral route for the correction of mandibular prognathism. Ernst (1932) discussed an intra-oral approach for the same procedure. Blair was the first to classify jaw deformity into five classes as : mandibular prognathism, mandibular retrognathism, alveolar mandibular protrusion, alveolar maxillary protrusion and open bite.

Berger (1897), Babcock (1909), Bruhn & Lindemann (1921), Kostecker (1931) described similar osteotomy method of Blair for correction of mandibular prognathism.

Trauner 1955 described the inverted ‘L’ osteotomy of the ramus for the correction of mandibular prognathism.

Hugo Obwegesser (1955) described the technique of intraoral sagittal split osteotomy for the correction of mandibular problems. This was modified by Dalpont in 1958, Hunsuck in 1968 and Epker in 1977.

Heinz Köle described the procedure of genioplasty 1968 and a technique to correct open bite.

Paceno (1922) published some basic principles of roentgenographic cephalometry, which was later modified and popularised by Broadbent and Holfrath (1935). Burstone et al (1978 & 1980) gave an analysis for the assessment of dentofacial deformity using cephalometric radiographs ” The cephalometric analysis for orthognathic surgery” (COGS).

The first use of bone plating was carried out by Soerensen in 1917 for fracture mandible. Bernd Spiessl 1974 was the first to use rigid fixation after sagittal split osteotomy. Use of rigid fixation to stabilise osteotomised segment was reported by Champy & associates 1976, Mischelet, Leyoness & Desus 1973, Dromer and Luhr 1981, Steinhäuser 1986 etc.  Miniaturised plates were used by Luhr 1981, Steinhäuser 1986 etc. Miniaturised plates by Luhr, 1989 solved the problem of excessive bulk of miniplates for use in midface.

Other contributors were Bruhn, Asher, Perthes (Extra oral vertical osteotomy for mandibular ramus), Picher, Wassmund, Wunderer, (Mandibular osteotomy)

The latest developments in orthognathic surgery is the use of adjunct plastic surgical procedures like rhytidectomy, liposuction, lip correction and the use of the principle of distraction osteogenesis for correction of jaw deformities.

Surgical anatomy

The mandible is the skeletal component of the lower face. It is a single bone with four anatomically distinct regions :- a body, alveolar process, ramus and condyloid process.

The horizontal U-shaped body has

  1. a dense basilar portion that contains the neurovascular bundle and provides for muscle attachments, and
  2. an alveolar portion that is hollowed out by the teeth and is dependent on them for its development and maintenance.

The anterior midline portion of the mandibular body is termed the symphysis. It gives attachment an anchorage to the tongue muscles in the internal (lingual) aspect, and forms the prominence of the chin in the external aspect.

The vertical ramus is a thin, dense structure with little marrow that is entirely sheathed by masticatory muscles. Its antero-superior portion, the coronoid process, provides attachment for the temporalis muscle.

The mandibular condyle rests on the ramus on a thin neck and articulates with a portion of the temporal bone, the glenoid fossa. This temporomandibular joint further consists of a separating articular disc, a joint capsule, and a series of extra-capsular cheek ligaments.

Anatomical position of the mandibular canal

Knowledge of the position of mandibular canal as it courses through the ramus and body of the mandible is crucial in avoiding neurosensory deficits and excessive blood loss. The mandibular foramen lies at a mean distance of 8.3 mm below the tip of the lingula. The lingula is positioned 4.9mm + 3.5mm above the occlusal plane. Therefore the neurovascular bundle generally enters the mandibular foramen inferior to the mandibular occlusal plane.

The mandibular foramen is located about two-thirds of the distance from the anterior to the posterior border of the ramus. Tracing the course of the mandibular canal in relation to the inferior border reveals that it travels forward to the lowest point at the 1st molar region before gradually sloping superiorly to the level of the mental foramen.

Timing of osteotomies

The treatment of dentofacial deformities is based on a careful co-ordination of orthopaedics, orthodontics and surgery. Early treatment using functional appliances and by orthodontic teeth movements may prevent functional and psychological problems, limit he deformity, shorten treatment time, improve results and obtain stability. As a rule of thumb it is better to wait till the skeletal growth is completed before doing orthognathic surgery. There has been report in literature to support the corrective surgical measure even during the growth period, specially if there is compelling psychological need for such intervention in the patient.

Role of pre-surgical orthodontics

Many patients undergoing orthognathic surgery require a period of pre-surgical orthodontics. The goals of pre-surgical orthodontics are

  1. to eliminate dental mal-relationships which prevent surgical repositioning of fragments
  2. to achieve decompensation by undoing the natural compensating tooth alignments. This usually worsens the occlusal relationship but it corrected by surgery.
  3. to create interdental spacing to facilitate segmental osteotomy and
  4. to perform those tooth movements which, if done post-surgically, will spoil the result of surgery.

Surgical approach

When considering the surgical approach to the facial bones, there are a number of important aspects, some of which are mutually antagonistic. They are briefly described as

  1. there must be a safe approach which allows a clear view to be obtained of the bone to be cut and good access to instruments.
  2. the access incision and dissection should avoid important structures like nerves, large blood vessels and teeth.
  3. the incision should be placed in such a way that the scars are relatively well-hidden, if it is not possible to avoid them altogether.
  4. the approach should take into consideration the risk of sterility and post-operative infection.
  5. specific situations like trismus should be taken into account.

Extra-oral approach

The best access to the bones of the face is through the skin. However, this direct approach may lead to visible scars. So the incision should be sited in such a way that the scars are hidden e.g. in submandibular region or in the hairline.

The condylar region

The easiest approach to the mandibular condyle is through a pre-auricular incision. The pre-auricular incision is sited just anterior to the pinna or alternatively around the tragus and at the junction of ear and scalp superiorly. It is then directed obliquely forwards and upwards at a 45° angle. The external auditory meatus is occluded with cotton wool or an antiseptic dressing. After marking out the incision line and infiltrating the area with 1:2,00,000 adrenaline solution subcutaneously, the incision is made through the skin, which is then undermined and sutured forward to the cheek. The posterior branch of the superficial temporal artery is ligated. The anterior superficial temporal vessels and the auriculotemporal nerve are identified and retracted anteriorly. Next, the incision is deepened down to the temporalis fascia and the zygomatic bone, and is then extended inferiorly in the plane between the cartilaginous external auditory meatus and the back of the condyle. Anteriorly, the dissection proceeds deep to the parotid gland until the underlying condyle can be palpated. A ‘T’ shaped incision may be made over the lateral surface of the capsule to expose the condyle.

Al Kayat and Bramley in 1979 described a question-mark shaped incision which avoided the main vessels and nerves. This technique has the added advantage of a wider exposure. After dissection down to the temporal fascia superiorly, the point where the fascia splits into two layers is identified about 2 cm above the zygomatic arch. An incision is made starting at the root of the arch, running at 45°upwards and forwards through the superficial layer of the temporalis fascia. The periosteum of the malar arch is incised and turned forward as a flap, which includes within it the temporal branches of the facial nerve.

If both condyles need to be exposed, the bicoronal flap may be used. This flap has an added advantage that calvarial bone grafts may be harvested through the same approach.

The inferior end of the skin incision should never be extended below the lobe of the ear. This is to minimise the risk of damage to the main branch of facial nerve. While operating on the condyle, a Toller retractor or a Dautery retractor may be placed under the neck of the condyle to prevent injuring the maxillary vessels.

The mandibular ramus

The indications for an extra-oral route of access to the mandibular ramus include severe trismus and severe prognathism that requires large movements. The incision options include

  1. the posterior mandibular vertical incision,
  2. the Risdon incision (submandibular incision one finger breadth below the lower border of the mandible),
  3. skin crease incisions.

After marking and infiltrating the area with adrenaline solution, the skin is incised and undermined subcutaneously to expose the platysma, which is split in the line of its fibres. The investing layer of deep cervical fascia is now seen. Structures like facial vessels, marginal mandibular nerve and submandibular lymph nodes should be preserved as far as possible. By blunt dissection through the connective tissues, the lower border of the mandible is reached. The periosteum of the lower border is excised and reflected to expose the entire ramus. The masseter is then stripped off the lateral surface and medial pterygoid off the medial surface. With appropriate retraction, the whole of the ramus and the coronoid and condylar processes are all exposed.

Mandibular body and symphysis

The extra-oral approach is now rarely used to access the mandibular body and symphysis. An incision along a skin crease may be considered in cases where major repositioning of lower border is required or when access to the mouth is poor. In the body region, this is performed 1 cm below the lower border and parallel to it. The incision in symphyseal region should be in the submental crease, or 5mm below and posterior to the lower border if there is no crease. Exposure is performed in the same way as for the ramus.

Intra-oral approach

The obvious advantage of no visible scars has encouraged the development of intra-oral approach to the mandible. The visibility and instrumentation through this approach have been made easier by recent improvements in instrument design.

The mandibular ramus

The intra-oral approach for mandibular ramus is most commonly used for performing sagittal split osteotomies. Local anaesthetic with adrenaline is infiltrated in the lingual side of the ramus and in the molar region buccally before putting the incision. The incision may be placed in various ways. The easiest method is to extend the Ward’s incision for third molar surgery anteriorly along the crest of the alveolus and posteriorly up the anterior border of the ramus. Postero-superiorly, it is taken slightly on to the buccal side of the ramus. Subperiosteal dissection is carried out inferolaterally in the body area and posteriorly towards the antegonial notch. On the lingual side of the ramus, the dissection is carried towards the posterior border of the ramus. The inferior dental neurovascular bundle is identified as it enters the bone at the lingula. A little dissection anterior and lingual to the lingula is also required.

The approach for vertical subsigmoid osteotomy or subcondylar osteotomy is by a vertical incision along the anterior border of the ramus and then forward along the external oblique ridge. The periosteum along the lateral surface of the ramus is raised down to the lower border and upwards to the sigmoid notch. Specialised retractors like the Bauer or Le Vasseur Merrill type may be used to obtain adequate visibility and to aid in instrumentation.

Mandibular body

The intra-oral approach for mandibular body is used for body osteotomy of the mandible. This requires bilateral osteotomies at some part of the mandibular body, most often in the premolar region. Since 1st or 2nd premolar teeth are removed, the incision starts at the unattached gingivae opposite the first or second molar tooth, and is continued to the gingival margin just posterior to the papilla of the tooth to be extracted. It is extended around the gingival margin, and continued inferiorly and obliquely forwards towards the base of the buccolabial sulcus. Care should be taken to avoid the mental foramen and the mental nerve. The mucoperiosteal flap is then dissected back widely to the lower border. A lingual mucoperiosteal flap is raised via a gingival margin incision.

If the body osteotomy is being done to close an edentulous space, the incision may be placed over the ridge and flaps retracted buccally and lingually. A modification is to split the ridge mucosa at right angles. In non-extraction cases, the incision may be placed in the buccal sulcus, leaving attached gingiva intact.

Anterior mandible

The incision is commenced at the premolar area on one side at the junction of the attached and the unattached gingivae. It is then brought on to the lip in the canine region. A transverse incision just through the mucosa is continued round to the canine on the opposite side. A mucosal flap is raised initially on the lip, and when the mentalis muscle is reached, this is sectioned down to bone and the mucoperiosteal flap is raised from the alveolus. The anterior portion of the mandible is stripped of periosteum down to the lower border. The dissection is then extended posteriorly, inferior to the mental nerves to allow for extension of the bony cut into the molar region. Anteriorly, the lower genial muscles are left attached to the bone, thus maintaining the blood supply of the lower border fragments.


Osteotomy techniques

The surgical treatment of the deformities of the mandible must be considered in all the three dimensions. A number of osteotomy techniques are now available to correct different types of lower jaw deformities. According to the site of operation, the techniques may be divided into

  1. Ramus osteotomies
  2. Osteotomies of the mandibular body and symphysis
  3. Segmental procedures and

Ramus osteotomies

Osteotomies of the mandibular ramus are used to advance the retrognathic mandible and to retrude the prognathic mandible. They are usually the best procedures in situations where large movements are necessary. Previously done exclusively as extra-oral procedures, they are being increasingly performed through the intra-oral approach now, thanks to recent developments like oscillating saws, fibre-optic lighting systems and specialised retractors.

Condylectomy

Condylectomy is employed in the correction of only a few conditions such as ankylosis, tumours of the condyle and condylar hyperplasia. In ankylosis, removal of a condyle fused to the skull is the first step in its correction, this is followed by a reconstruction of the joint and finally by osteotomies to correct the mandibular retrusion or asymmetry.

The management of condylar hyperplasia depends on the age of the patient. Where active growth is still continuing in the condyle, a condylectomy is necessary. In many patients, the condylar overgrowth ceases towards the end of the growth period, leaving an apparent prognathic and asymmetric deformity. In such cases, the condyle may be left intact and an osteotomy performed on the affected side.

After exposure of the joint capsule by pre-auricular approach, a ‘T’ shaped incision is made on its lateral surface. The horizontal bar of the ‘T’ is placed over the maximum bulbosity of the condyle. A Toller condylar retractor is inserted posterior to the condylar neck and is then brought forward within the capsule medial to the condylar neck. This is to stabilise the condyle and to safe retraction. The bone for removal, as determine by the pre-operative assessment, is marked out with the use of callipers. A simple horizontal section is then made through the neck of the condyle onto the retractor. The deeper portion of the neck may be separated with a chisel after the bone has almost been sectioned through with a bur. After mobilisation of the condyle, it is drawn out of the joint cavity and the lateral pterygoid muscle is stripped off. If the condyle is very deformed or difficult to remove, a bur hole through its lower end and a wire inserted through it will allow traction to be applied to it, and will aid in mobilisation. Any sharp edges of bone in the distal fragment are smoothed. It there has been significant bleeding during the operation, a suction drain is inserted. Closure is done in layers.

When further orthognathic surgery is planned for the correction of residual deformities, it is better postponed for about 3 to 9 months.

Oblique subcondylar condylotomy

The descriptions of subcondylar osteotomies by Jaboulay and Berard (1898) and Kostecka (1931) are among the earliest ones for the correction of mandibular deformities. Access may be gained through a pre-auricular approach. The condylar neck is sectioned obliquely and is mandible is repositioned posteriorly. Simple overlapping of the segments is enough to facilitate bony union. Robinson (1956,1958) described the use of a nasal saw for the osteotomy while Hinds (1958) used no.8 round burs to create grooves and then completed the osteotomy using an osteotome.

The procedure done in most centres now is the one described by Ward (1961) and McKenzie (1961). This ‘blind’ approach has inherent risks of damage to facial nerve and unpredictable haemorrhage from the maxillary vessels. Under general anaesthesia, the mouth is propped wide open, and a line is drawn from a point approximately 1 cm below the ear lobe to the middle of the infra-orbital margin. A Kostecka awl is passed through the skin from the posterior border of the ramus along this line, keeping its tip in close contact with the medial surface of the ramus. It comes out through the skin at the sigmoid notch. A Gigli saw is then passed around the condylar neck using the awl as the guide. The condylar neck is sectioned maintaining an obtuse angle with the saw. Following section of both sides, the mandible is repositioned and intermaxillary fixation is applied up to 6 weeks.

The intra-oral subcondylar osteotomy is a more difficult procedure. It was first described by Winstanley in 1968. Hebert, Kent and Hinds (1970) used a Stryker oscillating saw which allowed for greater visibility. Refinements in technique were described by Massey (1974) and Walker (1977). The bone cut is most easily done with an oscillating saw. Good retraction in the condylar region is necessary by using Obwegeser retractors or Bauer’s retractors. When repositioning the distal fragment, one should make sure that the condylar head remains in the fossa and that the neck fragment overlaps the ramus on its lateral surface.

The vertical subsigmoid osteotomy

Whereas the subcondylar osteotomy may be used only in cases of mild degrees of prognathism, the vertical osteotomy of the ramus is useful in cases where large movements are required. Originally described by Caldwell and Letterman in 1954, this procedure consists of a vertical sectioning of the mandible in a line from the lower aspect of the sigmoid notch downward just posterior to the mandibular foramen to the lower border of the mandible. By decortication of the distal segment, the whole body of the mandible can be repositioned posteriorly to a more normal occlusal and jaw relation.

The chief indications include excessive mandibular prognathism and cases of facial asymmetry where large rotational move of one or more rami is required to achieve correction. This surgery has also been used to treat significant temporomandibular joint complaints, minor anterior open bite and mild degrees of mandibular retrusion.

The chief contra-indication to the vertical subsigmoid osteotomy is significant retrognathism of the lower jaw. Even moderate advancement of the distal segment have been found to cause problems like non-union and TMJ disturbances. This should be considered when facial asymmetry is treated, since advancement on side might occur inadvertently. Recent condylar fracture is another relative contra-indication.

Surgical technique

The procedure may be done through extra-oral or intra-oral approaches. Using the extra-oral approach, a skin crease / submandibular incision is made and the lower border of the mandible is exposed. The whole of the lateral surface of the ramus is then stripped of periosteum and of the attachments of the masseter. Using the Rayne subsigmoid retractor or Thompson ramus retractor, it is then possible to visualise the entire lateral surface of the ramus. The medial pterygoid insertion is reflected off the deep surface. A small bony thickening on the lateral surface of the ramus (antelingula) acts as a guide to the position of the lingula. Using an oscillating saw or a Lindemann or an Ash surgical fissure bur, a vertical bony cut is made a few millimetres posterior to the antelingula from the sigmoid notch down to a point 3 to 4 mms anterior to the posterior border of the mandible. It is better to divide the bone in a slightly oblique angle anteroposteriorly. The mandible is very thin in the sigmoid notch area and relatively thick at the lower border. When the bur / saw meets no resistance, penetration through the medial surface has been achieved. The sectioning is then completed with sharp chisel and mallet.

When the cut has been completed on both sides, the mandible is retropositioned and intermaxillary fixation is applied. Sometimes a small wedge of bone needs to be cut out of the sigmoid notch area to allow the condylar fragment to lie flush against the rest of the ramus. An interosseous wiring may be done to stabilise the position and to maintain good bony contact.

Where a greater movement is planned, a coronoidectomy or coronoidotomy is usually necessary. This may be done with a bur by sectioning obliquely from the anterior border of the mandibular ramus to the sigmoid notch. This makes it easier to position the mandible posteriorly by preventing development of excessive tension in the temporalis muscle. Decortication of the lateral surface is another procedure done to facilitate large movements.

One or two loose sutures are used to reconstitute the periosteal and muscle sling at the lower border.  A drain may be inserted if there is excessive bleeding. Simple suturing of muscle, deep fascia, platysma and skin are done in steps.

This method has two main disadvantages – it leaves an external scar, and there is risk of damage to the mandibular branch of facial nerve. Recent improvements in visibility and instrumentation in the ramus area have led to the use of intra-oral approach. The mandibular ramus is exposed via a straight-line incision medial to the external oblique ridge, or alternatively via an extended third molar incision. Following a complete subperiosteal dissection of the lateral surface of the ramus and the body s far forward as the distal aspect of the first molar, retractors can be inserted in the lateral side of the ramus. Some stripping of muscle on the medial side and identification of the inferior alveolar bundle may be helpful. With the mandible in closed position, the osteotomy cut is performed with the oscillating saw angled at 120° in a slightly curved fashion. The cut is made from posterior to the mandibular foramen up to the sigmoid notch and down to the antegonial notch. Where major posterior positioning of the ramus is required, a coronoidectomy is often necessary. This may be done through the same incision line after exposure of the lingual side.

Bell et al (1980) recommended that medial pterygoid muscles should not be stripped off to keep the condylar stump in a good position. However, Epker and Wolford (1980) felt that this approach is more likely to lead to relapse. They advocated wiring the proximal fragment to ensure that the condyle is seated in its fossa. Mucoperiosteal flaps are closed in the usual way after intermaxillary fixation.

Horizontal ramus osteotomy

The horizontal osteotomy of the mandibular ramus was first proposed by Blair in 1907. His technique consisted of passing a Blair needle or a Gigli saw through a short skin incision at the posterior border of the ramus, introducing the saw to the medial surface of the ramus and making a section. Numerous complications like injury to the facial nerve, maxillary artery bleed, inferior alveolar nerve damage, parotid gland injury and relapse have been attributed to this technique by various authors.

The original technique was modified by many surgeons till sagittal split was introduced in 1950s. One of the first modifications was the blind Gigli saw procedure, offered by Hensel in 1937. Moose in 1945 proposed an intra-oral direct visualisation osteotomy, done with an orthopaedic power-driven saw. He also endorsed a handsaw suggested by Sloan in 1951. In 1941, Kazanjian advocated horizontal osteotomy above the mandibular foramen by the Risdon approach and used a surgical bur for the bony cut. In 1951, he recommended an incision through the bone at an angle using a sharp osteotome. He believed that ‘bevelling in this fashion allowed for greater area of contact of the cut ends, promoting early consolidation’. This may have been the initial conception of the Obwegeser-Dalpont sagittal splitting procedure.

The disadvantages of horizontal ramus osteotomies include

  1. a tendency to produce open bite anteriorly by the power of masticatory muscles and the counter-action of depressor muscles
  2. non-union produced by minimal bone apposition and
  3. requirement of long periods of immobilisation.

The sagittal split and its modifications

The bilateral sagittal split osteotomy (BSSO) is an indispensable surgical procedure for the correction of lower jaw deformities. It is a highly versatile technique that allows for mandibular repositioning over large distances in many directions. The indications are many and include horizontal mandibular excess, deficiency and asymmetry. It is the operation of choice for mandibular advancement. The BSSO is very useful for mandibular setback of small to moderate magnitude.

History

A surgical procedure resembling the sagittal split was described in 1942 in the German literature by Schuchardt. Trauner and Obwegeser (1957) described a horizontal osteotomy of the mandibular ramus made through the medial cortex, just superior to the mandibular foramen, followed by a vertical cut taken down the anterior border of the ramus, and an oblique cut made through the lateral cortex towards the angle of the jaw. Though very satisfactory for mandibular excess, there was relatively little bone contact in mandibular retrusion. Dalpont (1961) suggested that this problem could be overcome by advancing the oblique cut towards the molar region, and making it vertical through the lateral cortex. Hunsuck (1968), modified the technique, advocating a shorter, horizontal medial cut, just past the lingula, to minimise soft tissue dissection, while maintaining the anterior vertical cut. In 1977, Epker suggested several modifications, including minimal stripping of masseter. Bell and Schendel (1977) established the biologic basis of BSSO and showed that with minimal detachment of the pterygomasseteric sling, complications could be reduced. Several other modifications have come up over the years, but the basic technique remains the same.

Surgical technique (Epker modification of Obwegeser-Dalpont technique)

The BSSO is usually done as an intra-oral procedure. After the injection of a vasoconstrictor in to the soft tissues of the third molar both lingually and buccally, an incision is made just lateral to the crest of the alveolus. Alternatively, an extended Ward’s incision may be used. The incision is extended up the anterior border of the ramus and anteriorly along the external oblique ridge. The incision is carried as far anterior s the surgeon has planned to make the anterior vertical cut through the lateral cortex, usually as far as the 2nd or 1st molar tooth. A subperiosteal dissection is done laterally over the body of the mandible down to and under the lower border. On the lingual side of the ramus, the subperiosteal dissection is extended up to the posterior border, identifying the lingula and the neurovascular bundle in the process. The anterior dissection is carried forward over the internal oblique ridge. An Obwegeser channel retractor or a similar instrument may be used to expose the lower border. Exposure of the coronoid process by stripping of the temporalis muscle may be necessary.

A retractor is inserted medially to prevent damage to the neurovascular bundle. The lingual cortex is then divided from just posterior to the lingula to the anterior border of the ramus using an Ash fissure bur. This bur cut is extended down along the anterior border of the ascending ramus just medial to the external oblique ridge. When the anterior limit of the bone cut has been reached, it is then taken downwards through the lateral cortex to the lower border. It must be ensured that the cortex is completely cut through, but not so deeply that the neurovascular bundle is injured. The anterior vertical cut is then extended right through the lower border with burs and fine chisels.

The lateral-lower border fragment may be split from the medial portion with a fine chisel, which can be used to separate the two fragments. The chisel is moved along the entire bony cut including the ramus section, keeping it in close contact with the lateral fragment. Gentle levering is done to separate the two cortical plates. As they separate, attention should be paid to the neurovascular bundle which should lie in the medial segment. If it lies in the lateral segment, it will need to be separated from that cortex. In mandibular setbacks for prognathism, a portion of the lateral cortex of bone will need to be removed, and the medial pterygoid must be stripped off to allow posterior positioning.

After both the sides have been similarly split, it should be possible to place the body of the mandible in the new desired position. In order to prevent relapse, it should be made sure that there is no rotational movement of the proximal segment. Some minor trimming of the fragments may required to obtain flush contact. An inter-osseous wire is placed at the upper border or at the anterior end of the ramus to hold the bone ends in the correct position. Then the final tightening and positioning of the wires is done with the teeth in the new relationship to ensure a passive repositioning of the fragments. The incision is closed either with black silk or with a resorbable suture. With the fixation in place, it would take at least 6 weeks to obtain adequate healing.

Eventhough it is a very versatile method, the BSSO has some limitations. When an open bite is present, there is a tendency to relapse. Also, in cases of mandibular retrusion where the ramus height is short, it is of little value.

Inverted ‘L’ and ‘C’ osteotomies

Originally described by Trauner and Obwegeser in 1957 as an intra-oral procedure, the inverted ‘L’ osteotomy is a blend of the vertical subsigmoid ostyeotomy and the BSSO techniques. It can also be accomplished through the submandibular approach. It is a safe and relatively simple operation for the treatment of severe mandibular retrusion. It allows for lengthening of the ramus, for which a bone graft is required to fill the defect. For large (>12 mm) advancements, concern over adequate bony interface between the segments and the concomitant problem of stability after BSSO are eliminated. For large mandibular setbacks, it bypasses the need for coronoidectomy. There is also less risk of condylar sag when compared to the vertical subsigmoid osteotomy. This procedure is well suited for secondary correction of proximal segment malrotation following BSSO, as well as for simultaneous advancement and lengthening of ramus in cases of severe ramus underdevelopment.

The extra-oral technique is similar to that used for the vertical subsigmoid osteotomy. A vertical bony cut is made downwards from a point just a few mms above and behind the lingula. The horizontal cut is made from the upper extremity of the vertical cut in a forward direction to end in the anterior border of the ramus. This may be done with either a bur or a saw. Extensive stripping of temporalis muscle is unnecessary. Bone grafts should be carefully shaped to fit the defect created following the application of intermaxillary fixation. Usually, the grafts are harvested from the iliac crest and are held in place with rigid fixation. Where the technique is used for treating mandibular prognathism, the proximal fragment should be trimmed back to allow for posterior positioning. Often the inferior end of the fragment will need to be removed.

The intra-oral technique is similar to BSSO in the initial incision and dissection. After identification of the lingula and the neurovascular bundle, the bicortical horizontal osteotomy is done just superior to, but as close as possible to the foramen. This is done with either a reciprocating saw or a Lindemann bur. The cut should stop a few millimetres posterior to the lingula. Exposure of the lateral ramus and the vertical cut are similar to the intra-oral vertical subsigmoid osteotomy, except that the bicortical vertical cut ends just superior to the level of the lingula.

In cases where extensive movement is required, the soft tissue tension limits mobilisation. Extensive stripping of soft tissue from the distal segment, scoring of the periosteum, division of the temporalis tendon and release of suprahyoid musculature may be necessary to achieve passive mobilisation. The placement of bone grafts is much more difficult in the intra-oral technique.

The ‘C’ osteotomy is basically a modification of the inverted ‘L’ osteotomy.  Instead of bringing the vertical subsigmoid ‘cut’ down to the lower border, it is brought forwards, below the level of the mandibular canal, in a horizontal direction. It is completed by making a short vertical cut anteriorly through the lower border. This method allows the mandible to be advanced, often without the need for bone grafting, but produces a defect in the ramus.

The arcing ramus osteotomy described by Epker and Wolford in 1980 is similar to the ‘C’ osteotomy. In this technique, the inferior alveolar nerve is preserved by cutting a window in the region of the lingula and following the nerve through in its canal in the anterior direction. The bony cuts follow a smooth arc rather than a simple joining of vertical and horizontal cuts. The use of ‘C’ or arcing osteotomy allows the mandible to be advanced in cases of steep mandibular plane angle, while leaving the pterygoid muscles totally attached to the proximal segment.

Mandibular body osteotomies

The mandibular body osteotomy was first described by Blair in 1907 as an extra-oral procedure. In 1912, Harsha corrected prognathism by excising a rhomboid shaped bone from the 3rd molar area using ‘bone-cutting forceps and rongeurs’. New and Erich (1941) favoured ostectomy in the bicuspid or the 1st molar regions, and preferred an open (combined extra-oral and intra-oral) approach. In 1944, Dingman described a two-stage method of ostectomy in which he overcame the disadvantage of compounding the extra-oral wound intra-orally, and also avoided injury to the mandibular nerve. This operation was widely used in 1940s and early 1950s. Thoma (1969) recommended intra-oral osteotomy using bone drills and osteotomes.

Now, almost all cases of mandibular prognathism are treated with ramus osteotomies. The present indications of body osteotomy are

  1. to utilise space from planned extraction sites or already missing teeth,
  2. in gross mandibular prognathism in combination with a ramus procedure,
  • in prognathic cases where the body is long in relation to the ramus,
  1. anterior openbite restricted to the anterior dento-alveolar segment,
  2. transverse excess of mandible (combined with genioplasty) and
  3. surgical correction of curve of Spee.

The technique for the body osteotomy is variously performed. In mandibular prognathism, where a premolar is planned to be removed, a buccal periosteal flap is raised. The mental nerve is identified and the tooth at the osteotomy site is extracted. A small lingual flap is raised, extending this slightly posteriorly. Using a template, the bone to be removed is marked out with a thin bur. The line of the mandibular canal is marked out on the lateral cortex using burs. The area of bone immediately above the canal is cut and removed with a chisel. The outer cortex overlying the canal is then divided, a rectangular portion is removed, and the nerve and vessels identified. The lower border segment is now removed completely as a wedge from below the canal. Keeping the lingual strut intact, the other side is operated upon in a similar way. Then the neurovascular bundle is lifted away from the lingual strut, and the latter is removed using burs and chisels. A lower border or cortical wire in the midbody area is inserted on both sides, but not tightened. The mandibular segments are then repositioned with the help of previously fabricated splints, and intermaxillary fixation is applied. After this, any gap that may be present is filled with cancellous bone taken from the removed bone pieces, and the interosseous wires are tightened.

When this procedure is used to correct mandibular deficiency, it is better to use a step osteotomy, with the step directed anteriorly. It is usually possible to put a wire across two stepped portions and for the gaps to be filled in with cortico-cancellous bone grafts. The mucoperiosteal flaps should be adequately mobilised to provide for good closure of soft tissue over bone.

The step sliding osteotomy and the horizontal ‘L’ sliding osteotomy are modifications of the procedure, intended to aid in anterior positioning of the distal segment and to increase the bony interface.

The disadvantages of the procedure include high risk of mental nerve paresthesia and loss of teeth. Since the mandibular angle is not interfered with, some patients show poor post-surgical cosmetic result. Removal of a large segment of bone results in imperfect bone end apposition, or excessive medial rotation of the proximal fragments.

Segmental (subapical) procedures

Osteotomies of the mandibular ramus are the oldest procedures used to correct jaw deformities. Initially described in 1849 by Hullihen, a procedure similar to a subapical osteotomy was used to treat a case of ‘elongation of lower jaw’ secondary to a burn injury. In 1910, Babcock described an extra-oral operation to accomplish forward movement of a mandibular segment. Modifications of the intra-oral procedure were later described by Hofer (1936, 1942) and Köle (1959), who popularised this surgical option.

Before the widespread use of maxillary osteotomies, subapical osteotomy of the mandible was advocated for correction of anterior micrognathia. The subapical osteotomy avoids the detrimental forces placed on the mandible by the suprahyoid musculature since the bony cuts are placed superior to these muscle attachments.

The indications for subapical procedures include

  1. malocclusion caused by a mandibular dento-alveolar deformity with appropriately positioned maxillary and mandibular skeletal bases,
  2. non-skeletal openbite (often combined with maxillary subapical osteotomy)
  • posterior and lateral apertognathia, not amenable to orthodontic correction,
  1. as a substitute for orthodontic levelling and
  2. specific cases requiring intrusion of mandibular incisors where proclination of these teeth would be detrimental.

Anterior mandibular subapical osteotomy

The anterior subapical osteotomy can be used as a single isolated procedure, or more frequently, in conjunction with other surgical procedures. This technique can be used to effect extrusion, intrusion, uprighting or anterior or posterior positioning of the anterior mandibular dento-alveolar segment.

After infiltrating the lower labial mucosa with vasoconstrictor, the anterior mandible is approached through a bucco-labial flap. The incision extends from first bicuspid to first bicuspid, and is first carried only through the mucosa, to further dissect in an oblique fashion through the mentalis down to the periosteum. The periosteum is incised, and the anterior mandible is degloved to the inferior border. The dissection proceeds posteriorly at that level and the mental foramen and nerve are identified. Since the vitality of the osteotomised segment is predicated on the lingual mucoperiosteum, inadvertent tearing or detachment of this pedicle should be strictly avoided. Once the nerve is visualised and protected, the mucosal incision can be extended posteriorly as dictated by the proposed osteotomy site. If an extraction is planned, it can be done at this stage. The labial periosteum is elevated superiorly to the crest of the ridge to expose the osteotomy site.

The vertical osteotomy is performed with rotary instruments or appropriate microsaws. If the vertical cut is at or proximal to the mental foramen, it will be necessary to reposition and retract the mental nerve. The lingual soft tissues should be protected using a Howarth periosteal elevator during the osteotomy. The horizontal osteotomy cut is made at least 5 mm below the root apices of the teeth to prevent devitalisation. This cut joins inferior extent of the vertical cuts, and should be perpendicular to the bone surface. The remainder of the osteotomy may be completed with thin osteotome or spatula chisel.

After mobilising the segment and removing any interfering bone ends, it is repositioned to the planned post-surgical site with the help of pre-formed surgical splints. The segment is secured by trans-osseous wires, or preferably semi-rigid fixation. While closing the wound, it is important that the mentalis muscle is approximated to its original anatomic location. Following this, closure is done in at least two layers.

Posterior mandibular segmental osteotomy

The posterior subapical osteotomy is done in cases requiring intrusion of the posterior dento-alveolar segment. This procedure requires isolation of the whole length of the inferior dental nerve in relation to that segment and retention of soft tissue pedicle in the lingual aspect. To maintain the apical blood supply, at least 5mm of bone should be present below the root apices. This is a difficult procedure to perform and is mainly of only academic interest.

Total mandibular subapical osteotomy

The total mandibular subapical osteotomy was described by MacIntosh (1974) and Booth et al (1976). However, as early as in 1961, Dalpont had described a similar procedure that included an oblique retromolar osteotomy and a total or a partial sagittal osteotomy of the mandibular ramus. This procedure may be used for advancement of the whole of the lower arch where it is retroposed but the mandible is in normal shape. It could also be helpful in increasing the vertical height of the lower jaw and for levelling procedures.

When combined with a sagittal split, a horizontal subapical cut is made below the teeth and below the mandibular canal, from the third molar region on one side to the opposite side. This is then joined to a vertical cut through the lateral cortex which extends superiorly to the crest of the alveolus and then posteriorly up the ramus of the mandible as in a sagittal split osteotomy. On the ramus, it is finished just beyond the lingula. After making it sure that the horizontal division of the main body of the mandible is complete, the ramus is split as in BSSO. The segment is mobilised and repositioned as necessary using pre-fabricated splints and intermaxillary wires.

When performed alone (not combined with a ramus split), the buccal cortical bone is cut above and below the mandibular canal and the cortex removed. The horizontal osteotomy is done above the level of the canal and below the apices of the teeth, taking care not to injure the lingual soft tissues. Segmentalisation of the alveolus is completed by performing vertical osteotomies at the 3rd molar extraction site or between adjacent teeth. For setbacks, some amount of bone may need to be removed from the third molar or retromolar regions.

Genioplasties

Anatomically, chin is the area below the labiomental fold. It is one of the most prominent facial features. Chin deformities can manifest in three dimensions, but the vast majority are in the horizontal plane. The term genioplasty implies all surgical procedures performed on the bony chin. These are often used in associated with other operations of the jaws. By segmentalising the chin while maintaining the lingual pedicle, it can be moved in all three dimensions of space.

History

The horizontal sliding osteotomy of the chin was first described by Hofer (1942), who used an extra-oral approach and achieved fixation with trans-osseous wires. Converse in 1950 discussed the feasibility of bone grafts introduced through an intra-oral approach. Trauner and Obwegeser (1957) used the horizontal osteotomy through an intra-oral incision. Converse and Wood-Smith in 1964 described various applications for the horizontal osteotomy. In 1965, Reichenbach et al proposed wedge osteotomy for vertical shortening of chin. Hinds and Kent (1969) discussed the importance of maintaining the soft tissue pedicle along the inferior segment.

Surgical technique

The incision and flaps are very similar to those used for anterior segmental surgery. The periosteum is stripped off the anterior surface of the mandible and care is taken to avoid any damage to mental nerves. An extension of periosteal stripping is required below the mental foramina and back to the 1st molar region.

The bone cut is made using an Ash surgical fissure bur or an oscillating saw, 5mm below the apices of teeth. The cut is angled in such a way that the chin prominence is brought up or down in anterior or posterior slides. It is essential to leave a good lingual soft tissue pedicle. Periosteum may be stripped off the distal part of the segment, but in the midline always the geniohyoid and often the digastric muscles should be left attached to the lower border. After repositioning the segment, fixation is obtained with carefully placed inter-osseous wires, and closure is in two layers. A pressure dressing is applied to minimise chances of haematoma formation, and to facilitate soft tissue reattachment.

Horizontal advancement

The inferior segment is brought forwards and its lingual cortex is fixed with wires to the buccal cortex of the main body of the mandible. An alternative is to place suitably bent miniplates. In this procedure, the advancement is limited to the overall thickness of the symphysis. Occasionally, the chin is so deficient that a double sliding horizontal osteotomy must be used. The technique involves the creation of a stepped intermediate wafer of bone between the mandible and the inferior fragment, which is also advanced to provide bony contact between the upper and lower fragments. Alternatively, a sandwich bone graft may be used to get good interface and to ensure a predictable contour.

Horizontal setback

The proximal tips of the mobilised fragment are reduced to ensure a smooth transition along the inferior border. Also, the surgeon must be aware of the possible loss of vertical dimension of the chin.

The tenon technique

Michelet et al in 1974 described the ‘tenon’ technique of genioplasty. A ‘U’ shaped monocortical osteotomy is created centrally in the symphysis. Lateral extensions are developed below the mental nerves, which connect to the superior limbs of the ‘U’. Full thickness osteotomies are completed on the lateral extensions but only through the lingual cortex on the superior aspect of the ‘U’. The resultant full thickness of bone behind the tenon allows for better positioning and lag screw fixation. When posterior movement is desired, the ‘U’ is inverted and the tenon is in the inferior fragment.

Vertical reduction

The vertical height changes can be effected by altering the angle of the osteotomy. The magnitude of vertical dimensional change is proportional to the amount and direction of the horizontal movement. If it is desired to shorten the chin without horizontal changes, a wedge reduction is indicated, which may be performed using horizontal osteotomy or tenon technique. It is technically easier to do the wedge ostectomy from the superior stable fragment.

Vertical augmentation

This is indicated when the lower facial height is to be increased, when the deficit is in the mandibular alveolus or the symphysis. Vertical augmentation is accomplished by altering the angle of the horizontal cut or by interpositional grafting or alloplastic implant placement between the osteotomised segments.

Diagnosis-based treatment

Before embarking on attempts to correct dento-facial deformities, it is essential to have an accurate diagnosis of the existing problem. Clinical examinations, cephalometric measurements and model analysis are useful to this count. A treatment plan should be arrived at on the basis of this diagnosis and should include the osteotomy planned, amount and direction the segments are to be moved and movement of teeth using pre-surgical or post-surgical orthodontics. Often there will be a particular treatment that provides the best result, but ideally the treatment plan of each patient should be individualised as no two deformities are ever alike.

Mandibular prognathism

Before attempting correction of mandibular prognathism, it is necessary to assess whether the condition is a true mandibular excess or a case of midface retrusion. Most patients with mandibular prognathism presents with a long lower jaw, Class III malocclusion, excessive facial height and a high FM angle.

Mandibular prognathism may be corrected using a wide variety of surgical manoeuvres. Previously popular procedures included conylotomy, subcondylar osteotomy, Obwegeser sagittal split and mandibular body osteotomies. Now most patients are treated by some form of ramus osteotomy like the BSSO, vertical ramus osteotomy or inverted ‘L’ osteotomy. As required, an advancement or reduction genioplasty in horizontal or vertical dimension may be performed as an adjunctive procedure.

Mandibular retrognathism / micrognathia

The treatment of mandibular retrognathism is difficult owing to the tendency to relapse and problems with bone grafting. The BSSO and vertical ramus osteotomies are useful only for moderate cases. The inverted ‘L’ osteotomy may be a better procedure in such cases. In some cases, a long genioplasty is required to correct chin retrusion.

The problems of relapse have been solved to a good extent with rigid fixation and bone grafting. The distraction osteogenesis technique is fund to be valuable tool in the correction of mandibular retrognathism

Bimaxillary protrusion

The term bimaxillary dento-alveolar protrusion refers to a condition in which the maxilla and mandible both are so severely protruded that the lips cannot be closed without strain. The condition may or may not accompany relative protrusion of the jaws themselves. Since bimaxillary protrusion is compatible with good occlusal relationship, the patient’s problems are primarily aesthetic.

Orthodontic correction of bimaxillary protrusion can be carried out quite successfully in both growing children and non-growing adults. The main disadvantage of orthodontic correction is that due to anchorage loss, the space available cannot be used to its full extent for retraction.

In its simplest form, surgical treatment of bimaxillary protrusion involves maxillary and mandibular segmental osteotomies following extraction of first or second premolars, to retract and frequently to intrude protruding maxillary and mandibular incisors. In many instances, an adjunctive augmentation genioplasty is also required to achieve a good facial profile. Other procedures often required for the correction of severe bimaxillary protrusion are LeFort I osteotomy and mandibular body/ramus osteotomies.

Apertognathia

Apertognathia (open bite) is more of a neuromuscular rather than anatomic problem. Development of severe open bite is related to positioning of mandible relative to maxilla, and is usually associated with differential growth of different dento-alveolar segments. There are three general influences in the aetiology of open bite deformity. They are

  1. genetic
  2. sucking habits in childhood and
  3. tongue posture and positioning

Orthodontic treatment of open bite deformity is based on redirection of growth (headgear, chin cap and functional appliances), habit control and tooth movements. It is among the least successful of all orthodontic treatments.

The commonly used surgical procedures for correction of alveolar open bite are

  1. anterior maxillary subapical osteotomy for extrusion,
  2. anterior mandibular subapical osteotomy for extrusion,
  3. mandibular body V, Y or step osteotomy,
  4. bilateral sagittal split osteotomy (mild open bite),
  5. posterior maxillary osteotomy for intrusion,
  6. LeFort I osteotomy with differential superior impaction of posterior segment (combined with anterior maxillary osteotomy),
  7. combination of any of these and
  8. adjunctive procedures like inferior turbinectomy and tongue mass reduction.

Köle procedure

The Köle procedure consists of a standard anterior mandibular subapical osteotomy, following which a portion of the lower border is removed as in genioplasty. The lower border segment is stripped of all its periosteum and muscle. Its ends and edges are then trimmed and it is inserted into the gap produced by raising the anterior segment. The new lower border will need to be shaped to give a more normal outline to the chin prominence. When a genioplasty is thought to be inappropriate, a bone graft or alloplastic material may be used to fill the gap.

Facial asymmetry

Facial asymmetry is among the most difficult of all the facial deformities to treat. Accurate diagnosis of the problem and meticulous treatment planning is very important in its treatment. The mandibular procedures commonly used to correct facial asymmetry are ramus osteotomies including BSSO and lateral sliding genioplasties.

Although no face is perfectly symmetrical, minimal discrepancies are often not noticed. The common instances where a significant degree of facial asymmetry is seen are

  1. unilateral condylar hyperplasia / hypoplasia
  2. unilateral ankylosis of the temporomandibular joint
  3. hemifacial microsomia / macrosomia and
  4. unilateral masseteric hypertrophy (rare)

Condylar hyperplasia

The condylar hyperplasia typically occurs during late adolescence and is accompanied by elongation of the condylar head and neck. When it presents before the growth has ceased, there may be additional skeletal and dental compensations that also affect the upper jaw. Very often, there is a bowing of the inferior border of the mandibular body.

The management of condylar hyperplasia depends on the age at which it presents. When active growth is still continuing in the condyle, a condylectomy is necessary, but in cases where there has been a continual downgrowth of maxilla to compensate for changes in the mandible, other operations may be necessary. In many patients, this overactivity ceases after the growth period, leaving an apparent asymmetric prognathic deformity. In these cases, the condyle may be left behind, and an osteotomy performed on the affected side. Maxillary levelling procedure commonly performed is a LeFort I with differential superior impaction of affected side. For mandibular correction, a subcondylar or subsigmoid osteotomy is usually done. An inferior border corticotomy of the mandibular body on the affected side may be required. Where there has been some rotation of the chin, a lateral sliding genioplasty may be done.

TMJ ankylosis / condylar hypoplasia

The surgical correction of jaw deformities secondary to TMJ ankylosis generally follows the same principles of condylar hyperplasia correction. If ankylosis release and costochondral grafting is done at an early age, the growth of the grafted part compensate the deficiency to a good extent. If done at a later stage, the defect would already have become severe and combined maxillary and mandibular procedures with massive repositioning f the segments. An adjunctive genioplasty is often required.

Hemifacial microsomia

Hemifacial microsomia (first arch syndrome) usually presents as facial asymmetry characterised by under development of TMJ, mandibular ramus, muscles of mastication, maxillary and malar bones, parotid gland and external ear. The relative retrusion of the mandible and its asymmetric development results in a compensatory slanting of the already hypoplastic maxilla, causing a significant slanting of the occlusal cant.

The earliest treatment attempted is soft tissue replacement of the auricular tracts and sinus tracts. Surgical correction of asymmetry and malocclusion requires complete maxillary and mandibular repositioning. The maxillary surgery usually performed is LeFort I with differential superior impaction of the unaffected side. The mandibular surgeries include bilateral sagittal splits and genioplasties. Prediction tracing, model surgeries and the use of prefabricated splints are essential in this procedure. Camouflage procedures like genioplasty and augmentation of the deficient parts may also be done. Materials used for augmentation include autogenous bone and alloplastic materials.

Transverse mandibular deficiency

Transverse mandibular deficiency is commonly managed by the orthodontic correction of the resultant crowding, which may be by extractions, interproximal reduction of tooth mass and dental compensations. Surgery is often required to correct the basal bone problem. This is especially true in narrow and tapered arch forms, in complete telescopic bites (Brody’s syndrome, Pierre-Robin syndrome etc) and in those whose crowded teeth have already been treated by orthodontic therapy. These patients might benefit from surgically assisted rapid mandibular expansion.

The technique involves a vertical osteotomy in the symphyseal area and the use of a Haas expansion appliance. The appliance is placed a few days before surgery. A horizontal genioplasty cut is combined with the vertical osteotomy placed between the roots of lower anterior teeth. Once the osteotomy is completed, a guide pin is inserted into the appliance and activated. The activation is continued every 48 hours until the expansion is completed.

Transverse mandibular excess

Transverse excess of the mandible is usually seen in association with true mandibular excess (with or without prognathism). Other conditions that present for treatment include masseteric hypertrophy and bilateral condylar hyperplasia.

True mandibular excess

The transverse deformity associated with true mandibular excess has been surgically treated in various ways. Most procedures involved extraction of 1st or 2nd premolar teeth and reduction in the symphyseal / parasymphyseal areas. The options include

  1. a mandibular body ‘step’ osteotomy, in which the ostectomy in the 1st premolar region is curved forward to proceed downward anterior to the mental foramen.
  2. a connected subapical osteotomy and symphyseal reduction, which could be combined with or without ramus osteotomies like BSSO.
  • if mandibular intercanine width is greater than maxillary intercanine width, a vertical interdental osteotomy or ostectomy of the anterior part of the mandible may be done.
  1. if there is a concomitant posterior cross-bite, a differential ostectomy at the medial cortex of the symphysis allows for narrowing of mandible by medial rotation of the right and left halves, with rotation occurring in the vertical axis of the condyles. If combined with ramus osteotomies, the stress on condyles is reduced.

Masseteric hypertrophy

Masseteric hypertrophy is characterised by a combination of masseter muscle enlargement and skeletal deformity in the region of angle of the mandible. The skeletal deformity is a combination of extremely acute gonial angle, lateral flaring of the mandibular angle and a reverse slope of the ascending ramus.

The medical treatment of the condition is intramuscular injection of dilute botulinum toxin. Surgical treatment consists of reduction of muscle mass and ostectomy of mandibular angle. It is usually done as an extra-oral procedure, but using angled oscillating saws and other specialised instruments, it is now possible to do it intra-orally.

Short mandibular ramus

Short mandibular ramus deformities are characterised by a lack of posterior facial height. This is frequently associated with anterior maxillary hyperplasia and always with a posterior maxillary hypoplasia. The mandible is small and retrusive and the chin lacks anterior projection.

Surgical correction is directed to elongation of posterior facial height and increased projection of lower face. Maxillary correction is accomplished by a LeFort I osteotomy. The posterior facial height is then increased by bone grafting. At the same time, the anterior maxillary excess is resected and the anterior face height shortened. The chin deformity is corrected by a combined advancement / vertical reduction genioplasty. The actual problem in the ramus may be treated with sagittal split and advancement. Large ramus deformities need to be corrected through an extra-oral approach using a ‘V’ or inverted ‘L’ osteotomy.

Obstructive sleep apnoea

Obstructive sleep apnoea (OSA), originally described by Burwell as pickwickian syndrome, is the most common sleep related breathing disorder, with a reported incidence of 1% to 3% in industrialised countries. The incidence is higher in elderly and male population. Patients commonly present complaining of excessive daytime somnolence (EDS), insomnia, headache, loud and obnoxious snoring, decreased cognitive functioning during waking hours and physical and sexual dysfunction.

Studies have revealed that the pathology of the disorder is an anatomical and physiological obstruction in the oropharynx, specifically collapse of the lateral and posterior pharyngeal walls in most cases. This propensity towards airway collapse is increased in the presence of redundant tissues or decreased posterior airway space as a result of a retropositioned tongue base. Obstruction of the upper airway during sleep results in significant cardiopulmonary and central nervous system dysfunction. Apart from clinical examination, cephalometric radiographs and nocturnal polysomnographs are helpful in diagnosis.

The OSA patients are treated by medical or surgical therapies, but more often by a combination of the two. Medical management of OSA includes weight loss, changes in sleep position, pharmacologic options, oral appliances and continuous positive airway pressure (CPAP). Surgical options include tracheostomy, uvulo-palato-pharyngoplasty, maxillomandibular advancement and various combinations of these. Additionally, septoplasty, hyoid advancement and tongue reduction are utilised as adjunctive procedures.

For maxillomandibular advancement, models are prepared and two splints are fabricated. The first splint is a registration of the occlusion after the mandible is advanced 8 to 10mm, and the second splint is that of the final occlusion after maxillary model has been moved to centric occlusion with respect to the new mandibular position. The mandible is first advanced via BSSO and IMF is placed using the first splint as a guide. The mandible is then fixed using bicortical screws and IMF is released. Then the maxilla is advanced via a LeFort I osteotomy and IMF is applied again, this time using the second splint. Maxillary fixation is accomplished using two specially designed miniplates. Bone can be secured into the advancement gap and secured with a miniplate or lag screw. The septum is fixed to the anterior nasal spine using 2-0 Vicryl. While closing the wound, an attempt should be made to return the alar base to the pre-operative width.

The goal of maxillomandibular advancement is to maximise upper airway space and to reduce upper airway resistance. It is successful because the airway is increased at multiple levels. Advancing the maxilla pulls the soft tissues of the palate forward and upward, brings the palatoglossus forward and opens the nasal valve. Moving the mandible forward results in a more anterior position of the tongue base and a more favourable position of the hyoid.


Fixation techniques

After adequate repositioning of the segments, it is important to hold them rigidly in their new positions. Traditionally this has been achieved with intermaxillary fixation using arch bars or cast silver cap splints. Two advantages of using archbars are that they can be applied quickly and have lugs available for use during IMF. However, archbars may loosen during elastic traction or placement of IMF, leading to improper positioning of osteotomised segments. Additionally, tooth movement might occur due to non-passive adaptation of the archbar.

A better method of controlling occlusion before, during and after orthognathic surgery is with the use of orthodontic appliances. Lugs are desirable to be incorporated into these appliances. Different types of surgical lugs available are soldered lugs, crimp-on lugs and Kobayashi ties.

In addition to intermaxillary fixation, traditional methods of fixation included trans-osseous wiring, circum-dental wiring, circum-ramal wiring and circum-mandibular wiring using stainless steel wires. These methods, when used along with IMF, provided good immobilisation of segments.

Over the past several decades, many devices for rigid internal fixation (RIF) have been developed, and it has now become the most popular form of fixation during orthognathic surgery. Stainless steel, Vitallium, pure titanium and titanium alloy are the materials commonly used for rigid fixation. Though titanium is the most popular material because of its superior biocompatibility, Vitallium is the strongest of these options.

The advantages of RIF are

  1. improved intra-operative control over bony segments,
  2. occlusion can be evaluated upon completion of surgery,
  3. allowance for intra-operative strategic flexibility,
  4. better post-operative patient comfort, leading to enhanced speech, hygiene, nutrition and psychological state
  5. faster bony healing, rapid and safer recovery
  6. early mobilisation of the jaw and a more rapid return of jaw function

The disadvantages of RIF are

  1. more instrumentation is necessary
  2. technically more difficult to perform
  • chances of condylar malpositioning, causing TMJ pain or dysfunction
  1. improper fixation would lead to post-surgical problems
  2. increased risk of infection
  3. more expensive
  • a second surgery is required for hardware removal.

Rigid fixation may be accomplished using lag screws or miniplates. Several different screw and plating techniques are useful for stabilising the variety of mandibular osteotomies.

True lag screws have threads only at the distal end of the screw. The outer hole in the lateral cortex is drilled larger than the diameter of the screw threads. This leads to a compressive force between the proximal and distal segments when tightened. Though this might enhance bone healing, there is a disadvantage that any gap present at the osteotomy site may lead to lateral displacement of the condyle. Position screws engage both proximal and distal segments. In this situation, the hole is drilled equivalent to the diameter of screw threads in both cortices. The screws may be placed trans-orally or percutaneously.

Miniplate fixation is another form of RIF option in orthognathic surgery. The plate is attached only to the lateral cortex (monocortical), thus minimising the risk of inferior alveolar nerve damage. Single plate fixation and double parallel plate fixation has been tried after BSSO. For vertical ramus osteotomies, miniplates offer sufficient strength, but percutaneous approach is required. Subapical and body osteotomies are easily fixed with miniplates, but one must take care not to damage the tooth roots. The symphyseal osteotomies are now routinely fixed with lag screws or miniplates at the lower border to prevent relapse.

In 1991 Foley & Beckman compared the rigidity of three rigid internal fixation techniques after mandibular advancement. The fixation techniques were

  1. Three 2.0 mm Champy screws placed bicortically in an inverted ‘L’ pattern.
  2. Two 2.7 mm Wurzburg screws placed bicortically 1 cm apart, parallel to occlusal plane.
  3. A single 4 holed miniplate secured with monocortical screws.

The results showed no significant difference in rigidity between inverted L group and miniplate group while two 2.7 mm bicortical screws had less rigidity.

In 1996 Shetty et al showed that use of both miniplate and bicortical screws showed better results than using them alone.

Post-operative care

Post-operatively, the patient should be observed closely for at least 24-48 hours. Often the endotracheal tube will be retained for several hours post-operatively and sometimes until the following morning. This would prevent the distressing waking and sleeping episodes due to obstruction of the nasal and oral airways. Since many of the patients will have intermaxillary fixation, vomiting and restlessness should be avoided by suitable medication. Also, a suction apparatus as well as emergency instruments including a tracheostomy set, wire cutters and scissors should be kept ready at the bedside.

As the patient has been deprived of fluids for several hours even prior to surgery, the daily requirements may be furnished by intravenous infusion during the day of surgery. If excessive blood loss has occurred, part of the replacement may be in the form of whole blood. Though saline infusions may be used, the bulk of fluid replacements is usually in the form of 5% glucose in distilled water or Ringer’s lactate solution.

Once the patient is fully conscious and the blood pressure normal, the head is raised to 30° to reduce facial oedema. High doses of steroids such as methyl prednisolone or dexamethasone tend to reduce the soft tissue swelling and a regimen should be instituted immediately before or during the operation. Post-operative use of suction drains, ice packs, pressure dressings and continuation of steroid therapy for a few days tend to reduce oedema and haematoma. Routine antibiotic therapy is a matter of judgement, but it is mandatory in intra-oral operations. Pain may be controlled by administration of appropriate analgesics.

Care of the lips is important as minor trauma may occur at the commissures due to excessive stretching during the operation over prolonged period of time. Any gross swelling of the lips may be reduced by the use of vaseline or steroid creams for a few days.

If the patient has not voided within 6 to 8 hours after surgery, catheterisation is indicated. If normal bowel movements have not returned by the 3rd day, an enema should be ordered. Early ambulation hastens recovery.

Non-absorbable sutures are removed on the 5th post-operative day. Careful oral hygiene and use of antiseptic mouthwash help in reducing incidence of infection. Adequate nutrition during the post-operative period is essential for rapid recovery and bone healing.

The intermaxillary fixation is released after 4 to 6 weeks, after which post-surgical orthodontics is started.

Complications

Haemorrhage

Intra-operative life threatening haemorrhage is a rare complication of orthognathic surgery. Bleeding during BSSO is almost always diffuse immediately after the split and often diminishes spontaneously after a few minutes. However, one might encounter significant haemorrhage from inferior alveolar artery, masseteric artery or retromandibular vein. The bleeding that occurs during vertical ramus osteotomy is from maxillary vessels. The body osteotomies might be encountered by bleeding from inferior alveolar artery or facial artery

If the bleeding is from a large vessel that can be visualised, immediate clamping and ligation may be done. Otherwise, simple packing is done for some minutes. If this does not control bleeding, ligation of the external carotid artery may have to be resorted to.

Haematoma formation is a complication in condylar resections and genioplasties. It is a potential risk in ramus and body osteotomies as well. Post-operative pressure dressings may aid in controlling minor soft tissue bleeding and prevent haematoma formation, but cannot substitute for good intra-operative hemostasis.

Nerve injury

This is one of the most common complications of mandibular surgery. The incidence of post-operative dysfunction of inferior alveolar nerve is greatest in body osteotomies, but it is seen to a lesser degree in sagittal split, and even more rarely in vertical ramus osteotomies. The causes of nerve trauma are cutting too close to the mandibular foramen, bruising / transecting the nerve, pressure on the nerve while repositioning the segments, and direct injury to the nerve while applying rigid fixation. In bilateral sagittal split, excessive traction on the nerve superior to the lingula and unfavourable spilts are the primary causes.

In extra-oral approach, injury to the main trunk or marginal mandibular branch of facial nerve, are likely occurrences.

The neurosensory disturbances are usually transient, lasting for weeks to months. The duration and severity of the problem is directly related to the degree of trauma inflicted on the nerves. Direct nerve injury, such as transection, requires immediate microneuronal repair for optimal recovery.

Unfavourable osteotomy

This complication is most likely to be found in cases of BSSO and the incidence is between 3% and 20%. The unfavourable splits may cause fractures of the proximal or distal segment. The most common factor causing a proximal segment fracture is the failure to cut the inferior border prior to applying chisels to the osteotomy. When this occurs, the fracture line propagates along the buccal aspect of the inferior border. Adverse distal segment fractures may be splits that are short of the lingula, medial splits up the condyle and those occurring just distal to the second molar. The same accident can occur in any osteotomy site if segments are mobilised before adequately deepening the bur/saw cuts.

Strained condylar position

Many procedures involving displacement of the mandibular segments cause the condyles to lie in an abnormal position. The displacements most often noted are condylar sag, anterior displacements and rotations about the vertical axis. These might cause post-operative discomfort and pain.

Poor aesthesis

Even if preceeded by meticulous treatment planning and surgical implementation, orthognathic surgery occasionally produces unexpected aesthetic results. Following reduction genioplasty and correction of severe mandibular prognathism, drooping of soft tissue of the chin may occur. This is most easily corrected by a triangular excision of skin and fat in the submental area. The apex of the triangle is at the symphyseal midline and the lateral incisions are parallel to the lower border of the mandible. The base of the triangle is the submental crease. The incision is closed to produce an inverted ‘Y’ scar. Another option is to attempt submental liposuction.

Unaesthetic scar is an obvious complication of extra-oral approach for any procedure. Unless otherwise deemed necessary, it is always advisable to opt for intra-oral approach.

Malocclusion

Every case of mandibular prognathism or retrognathism requires some period of post-surgical orthodontics to fine-tune the occlusion. In cases of mandibular excess, the occlusal problems noted are

  1. Class II malocclusions or mandibular asymmetry, appearing soon after the function is resumed,
  2. A relapse towards renewed mandibular excess and
  • Lateral open bite developing several months after surgery.

Wound dehiscence

Wound dehiscence is a possible complication in body osteotomies, genioplasties and segmental procedures. This is more common in situations where incision is placed in the buccal vestibule. In order to prevent this, it is important to close the wound without tension especially in advancement cases. Most dehiscences are managed without resuturing, and are left to heal by secondary intention.

Loss of osteotomised segment

This is the direst complication in orthognathic surgery. This can result in genioplasties and in segmental procedures if the lingual soft tissues are not protected, resulting in a decrease of blood supply. Excessive resorption or avascular necrosis can be avoided by maintaining a broad vascularised soft tissue pedicle. This is accomplished by minimal stripping of soft tissues overlying the symphysis and maintaining as much of lingual muscle attachments as possible.

Tooth loss

Though the number of reported cases of tooth loss following surgery is quite low, damage to the teeth with prolonged recovery of tooth vitality is more common. The higher incidence of tooth related complications in mandibular procedures has been attributed to the nature of mandibular vascular and nervous supply, differences in tooth length, the greater difficulty of the procedure in the mandible and the position of the bony cuts.  Teeth adjacent to the osteotomy are most often affected either by loss of vitality or by iatrogenic periodontal defects. It is recommended that the horizontal osteotomies should be placed at least 5 mm from the apices of teeth in order to preserve pulpal circulation.

Relapse

Relapse following mandibular advancement has been well documented. Van Sickels et al (1986) concluded that relapse is to be expected with mandibular advancements greater than 7 mm. The methods recommended for correction or prevention of skeletal relapse include extended periods of skeletal fixation, suprahyoid myotomies and orthodontic overcorrection.

There is evidence that at least five factors affect post-operative stability.

  1. Amount of displacement of the segments. The likely reason for this phenomenon is the excessive tractional forces from the pterygo-masseteric sling and suprahyoid musculature.
  2. Displacement of the condyle.
  3. Rotation of the proximal segment
  4. Type of proximal segment and
  5. Residual growth.

Distraction osteogenesis

Distraction osteogenesis is the slow application of force to a bone gap, resulting in the production of new bone and soft tissues. An osteotomy is made in the area of bone deficiency and an appliance placed and utilised to separate the bone edges. As the bone edges are advanced, the overlying soft tissue envelope is also stretched, inducing hyperplasia of the adjacent soft tissues. The bone gap is initially filled with fibrous connective tissue. If adequate stability of the new generate is maintained, direct ossification of the collagen occurs. Once adequate bone regenerate has been formed, it is held in neutral fixation, allowing for complete ossification of the new bone matrix.

The concept of bone lengthening was first described by Codvilla (1905) for femur lengthening. Gavriel O. Ilizarov (1965) with his colleagues elucidated the rate, rhythm, amount and type of force that optimises the technique in long bones. These basic axioms are commonly referred to as Ilizarov principles. In 1973, Snyder et al studied the application of distraction concepts to the mandible. Michelli and Miotti (1977) demonstrated gradual lengthening in canine mandibles. McCarthy et al in 1992 demonstrated the technique in human mandibles. In 1992, Guerrero and Constasi described in detail the orthodontic principles of mandibular lengthening via distraction osteogenesis.

The distraction osteogenesis protocol includes

  1. Fixation of the distractor and body osteotomy
  2. Latency period of 7 days to allow primary healing of soft tissues
  • Distraction, performed at a rate of 1 mm daily
  1. Stabilisation period of 8 to 12 weeks before any orthodontic movement is started.

Recent advances

Lapori et al (JOMS 1997) performed BSSO in outpatient setting in 90 patients under ambulatory anaesthesia and reported no complications and only three unanticipated admissions.

A new technique for intra-oral inverted ‘L’ osteotomy was described by McMillan et al (BJOMS1999). The procedure included fixing the proximal segment to the maxilla before doing the osteotomy. This is to prevent rotation of the proximal segment after the osteotomy.

Tbaranon (JOMS 1998) compared the rigidity of bicortical screws and a miniplate for fixation of a mandibular setback after a simulated BSSO. The biomechanical stability of 3 bicortical screws with that of a single four holed miniplate after 5mm mandibular setback in cadaver were compared. He found no significant difference between the two.

A technique called ‘extended sliding genioplasty’ was introduced in1995 by Varghese Mani as a camouflage treatment for facial asymmetry secondary to TMJ ankylosis. The advantages of the technique is that while not undertaking complicated double jaw procedures, it maintains the functional occlusion, as well as corrects the asymmetry and the apparent deficiency of mandibular body on the unaffected side.

Intra-oral distraction osteogenesis was first discussed by Guerrero and Bell in 1995. In 1996, Chin and Toth also described the intra-oral procedures. In 1996, Bell, Harper and their colleagues studied the histology of tissues while doing distraction osteogenesis for mandibular widening. In 1997, Guerrero et al compared the efficacy and complications of tooth-supported devices with bone-supported devices. They found that the bone-supported devices have several advantages over the former.

Raghoebar et al (Int J OMS 2000) demonstrated vertical distraction of severely resorbed mandibular alveolus using Groningen distraction device. The device can be snugly attached to the alveolus, and its screws are later replaced by endosseous implants.

Conclusion

Pleasing aesthetic characteristics vary widely among cultures. With the techniques of orthognathic surgery combined with adjunctive procedures, it is now possible to correct facial deformities of any degree. Accurate diagnosis of the problem, assessment of the severity of the deformity, prediction procedures like prediction tracing and model surgery, meticulous treatment planning and surgical implementation and above all, good team effort will all be helpful in achieving a predictable surgical outcome.

References:

  1. Historical developments of orthognathic surgery. W. Steinhauser. Journal of Cranio-Maxillofacial surgery. 1996: 24: 195 – 204.
  2. Mandibular prognathism. David Hall, Ronald Hathaway. Mandibular deficiency. David J. Darab. Modern practice of orthognathic and reconstructive surgery. William H. Bell. B. Saunders company. 1992. Vol. III. 2110 –2140, 2334-2517.
  3. Orthognathic Surgery. edited by J. Betts, T. A. Turvey. In Oral and Maxillofacial Surgery. edited by R. J. Fonseca. W. B. Saunders company. 1992. Vol II.
  4. Surgical Correction of Dentofacial Deformities. Bell, Profitt and White.
  5. Aesthetic Surgery of the face. Varghese Mani
  6. Textbook of Oral and Maxillofacial Surgery. Gustav O. Kruger

 

 

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Author:

I am a practicing maxillofacial surgeon working in India.

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