37. Fractures of the Mandible
1. The mandible is the largest and also the only moving bone amongst the bones of the face and consists of a large body which is convex anteriorly and has two vertical rami which bear the coronoid processes anteriorly and the condyloid processes posteriorly. Several muscles are attached to the mandible but of them five play a significant role when the mandible fractures. The massetor inserts on the lateral surface of the body of the mandible near the angle and the myelohyoid inserts into the central half of the myelohyoid ridge on the medial surface of its body. The lateral pterygoid inserts on the medial surface of the condyloid process and the tendon of the temporalis is attached to the upper part of the coronoid process both laterally as well as medially. The medial pterygoid attaches to the medial surface of the angle of the mandible (see figures 1 and 2).
These attachments have a bearing on how the fractured fragments will move (see figures 3,4,5).
2. Vehicular accidents, accidental falls or assault are by far the commonest causes for fractures of the mandible which is the most frequently fractured bone in the face. The fractures of the nasal bones are a close second. Gun shots can also cause mandibular fractures. The fracture of the coronoid process as well as a vertical fracture of the ramus are rare. A combination of fractures such as parasymphysis with contralateral body or angle or fractures of the body with fractures of the contralateral condyle are frequently seen. A vast majority of mandibular fractures are compound because they invariably breach the mucosa. They can also be compound externally. The mandible only rarely fractures in the centre at the symphysis. The fractures might be comminuted and may have loose fragments of bone within the fracture line. The fractures of the coronoid process which gets pulled up by the temporalis though rarely treated actively except with immobilization for a short period with elastic bands mounted on wires on each jaw need to be carefully followed up because excessive osteogenic activity around the fracture site can lead to extra-articular hypomobility and even ankylosis of the TM joint.
3. An unusual fracture of the mandible occurs in the condylar process on either side or bilaterally quite often in its intra-capsular part following a blow to the chin or a fall on the chin which results in a small wound on the chin but may or may not have a fracture in the symphyseal area of the mandible (Fig. 6,7). These fractures occur mainly in children, are missed and may lead to ankylosis of one or both temporo-mandibular joints over the years if not treated properly. A wound on the chin should therefore be treated with suspicion and a thorough physical examination as well as proper x-rays needs to be taken if the child complains of pain or is not inclined to open the mouth fully. These fractures because they are enveloped by a thick capsule do not usually get displaced and are best seen on a CT-scan. They are treated with inter-maxillary fixation with elastic bands and/or arch bars and elastic bands for two weeks followed by diligent physiotherapy.
Another unusual fracture occurs on either side of central third of the mandible (see fig. 8) leaving behind a floating piece. This is hazardous in a semi-conscious or an unconscious patient, and the patient may have difficulty in breathing because the tongue falls back. This will require a tongue stitch and all health professionals who give first aid under these circumstances and/or surgeons in trauma units should be aware of this possibility.
4. Physical examination: External swelling as well as sub-mucous and sub-lingual hematoma are common. The fracture might be visible intra-orally and a tooth or teeth might be avulsed, chipped or may be seen to be intruded in the area of the fracture. External palpation may elicit crepitus, reveal a step in the bony outline and sometimes the fractured segments can be moved against each other. Intra-oral bleeding when present collects in the mouth but spitting is difficult and the collection may need to be sucked out so that a proper examination of the oral mucosa and tongue can be done to rule out laceration. Rarely an avulsed tooth might be found lying free in the collected clot. Oral opening is usually restricted. The jaw might show deviation and a step deformity in occlusion may be noticed. A small area on the lower jaw supplied by the mental nerve might show hypoaesthesia.
5. Investigations: In a majority of cases conventional radiological investigations allow a good diagnosis. CT-scans of course are far superior and can pinpoint additional, indistinct, incomplete fracture lines and the degree of comminution as well as small loose fragments. The scans are also more helpful in assessing the damage to the root of teeth. CT-scans also help pinpoint damage to the rest of the facial skeleton which occurs in major trauma and helps in the overall treatment.
6. Anaesthesia: Usually surgical treatment can begin 48 hours after the accident which allows the initial oedema to subside. General anesthesia is preferred because it is difficult to give local blocks in the midst of the swelling and the hematoma that might be present. Intra-nasal intubation will allow freedom around the oral cavity for the two jaws to be fixed with inter-dental wiring. Care must be taken to see that the patient is in a very light plane of anaesthesia or almost completely awake by the time he or she is extubated, particularly when he or she is obese, respiratory compliance is poor and the neck is short. Sometimes inter-dental fixation is not completed till extubation is performed and only when the patient is fully awake are the wires between the jaws are joined and tightened.
7. Principles of surgical treatment: The key to proper reduction and later inter-maxillary fixation of fractures of the mandible lies in restoration of normal occlusion of teeth (class 1) where upper anterior, maxillary teeth with a slight overjet partially cover the mandibular teeth and the mandibular molars show no medial or lateral shift while opposing their maxillary counterparts. This type of class one occlusion is prevalent in a vast majority of the population. However a small number of patients may not have a class one occlusion and this can be diagnosed on the table by way of telltale marks on the corresponding teeth along their opposing borders. Occasionally a non clinical family photograph taken earlier will reveal the nature of such an occlusion. In communited fractures loose bony fragments with or without attachment to the mucosa are best preserved within the area whatever the form of fixation because they serve as natural, local bone grafts.
8. Fractures of the mandible have been traditionally treated with inter-maxillary fixation by way of wires when the maxilla is intact or, if it is fractured, then after it is stabilized. A stainless steel wire of gauge 26G of adequate length is twisted into a loop and passed around both the maxillary and mandibular teeth in an equi-distant series facing each other and tightened with a twister. The loops are then fixed to each other after the fracture has been reduced and this wire is again twisted to get a rigid fixation (Figs. 9-12).
However, this method has now been almost completely replaced by arch bars (which themselves have flat curved hook like flanges) which are fixed to the mandibular and maxillary teeth with wires and the arch bars are then fixed to each other also by wires and are then tightened by a twister after the fracture has been reduced (Fig. 13-21).
A further advance in the treatment of these fractures has come about with the development of small plates of varying lengths with holes which straddle the fractured bone fragments and are fixed with mini screws resulting in rigid fixation with almost complete elimination of rotational forces between fractured segments (Fig. 21, lower right). While plates and screws themselves suffice to heal a fracture, usually an additional measure of wiring the jaw together for a couple of weeks to give rest to the operated part and relief of pain is frequently employed. When fractures are treated by inter-dental wiring alone the wires are left in place for six weeks which is the normal time for the healing of these fractures.
Access: Access to the fractures of the mandible can be achieved without incisions in the skin orally through the buccal sulcus for most fractures of the body of the mandible and through the retro-molar area for fractures at the angle of the mandible and some sub-chondylar fractures. This avoids scars (see figures below 22-29).
In the past when the technique of plating was not available, and inter-dental fixation was kept for six to eight weeks, feeding posed some troublesome problems and oral hygiene was difficult to maintain and proper instructions had to be given to the patient on how to brush and gargle safely.
9. While the incidence of non-union of the fractures of the mandible has reduced considerably after the advent of the technique of plating of fractured fragments, the problem is not entirely solved because these fractures are commonly compound on the buccal side and the teeth might not be healthy, and when such teeth are nearer the fracture site, insidious infection can retard osteogenesis. In established cases of non-union diagnosed clinically and proved by CT-scans, the infected teeth around the fracture site might need to be treated (extracted), the original plates and screws if used need to be removed, the ununited fracture will have to be debrided and its edges excised, loose ununited fractured small pieces of bone will have to be removed and cancellous bone grafts will have to be placed in the recreated defect and then a new sometimes longer plate might need to be employed in addition to inter-maxillary fixation. Persistent non-union after such treatment is rare in fractures of the mandible.
10. Malunion: A malunited fracture of the mandible has the opposite problems to that of an ununited fracture. The osteogenic capacity of the bones in the area of the fracture has been proved but the effort involved in breaking the malunion is time consuming even with power driven cutting instruments and the roots of teeth might be exposed. In the event unless problems with occlusion are of such a nature that they interfere with chewing or deglutition or the malunited fractured fragments result in abnormal spaces where food collects, treatment might not be undertaken. Rarely such malunited fractures might affect the jawline disturbing the symmetry of the face and show an abnormal hollow and/or a swelling. Patients when they seek a surgical procedure for such a blemish deserve surgical intervention only after explaining to them the major nature of surgery.
11. Fractures of the edentulous mandible: In these fractures more often than not the bone has been reabsorbed. Since this situation is common in the older age group, the vascularity in view of the atrophy is also not normal. In the event any fixation with plates is hazardous. If the patient was wearing a denture, then the same denture is fitted after the fracture is reduced and then circum-orally wired to keep it in place. If there is a denture in the upper jaw as well, then the same procedure is performed and the two dentures are then wired to each other as shown in the earlier figures (Fig. 9-12).
The compiler of these short notes, Ravin Thatte gratefully acknowledges the contribution of Bharati Khandekar, a plastic surgeon from Dombivali in Maharashtra and Nisheet Agni, maxillofacial surgeon from Mumbai for the illustrations, patients photographs and theoretical inputs.