The forward dislocation is practically the only one to which the jaw is subject. Dislocations in other directions are apt to be accompanied by fractures. An understanding of the mechanism of the production and reduction of this dislocation requires a knowledge of the movements of the jaw, and the influences which the ligaments and muscles exert in limiting them. The normal movements of the jaw have already been discussed.

The ligaments which limit the movements of the jaw are those forming the capsular ligament. This is made up of four parts: anterior, posterior, internal lateral, and external lateral. The anterior is very weak, hence pus in the joint is most apt to make its exit forwards. It is readily ruptured in dislocations. The posterior ligament, though stronger, may also be torn. The two lateral ligaments, the outer being the stronger, become tense when the condyle slips forward on the articular eminence. In dislocation they remain attached to the mandible and are not ruptured (see Fig. 76).

Dislocation occurs when the mouth has been widely opened and the condyles are forward on the articular eminences. Some sudden jar accompanied by contraction mainly of the external pterygoid muscle causes the condyle to slip forward just in front of the articular eminences. The pterygoid muscles and the superficial fibres of the masseter muscles aid in producing the luxation. As the condyle leaves the articulation to jump forward, it will be noted that it does so by an extensive movement, which is one of rotation on a transverse axis passing across in the region of the mandibular foramina. The condyle once out of its socket is kept out by the contraction of the temporal, masseter, and internal and external pterygoid muscles.

Reduction Of Dislocation Of The Lower Jaw

In reducing the dislocation, the condyles must be depressed and pushed back. This can be done by one of two ways: viz., the thumbs of the surgeon, being protected by wrapping with a towel or bandage, are placed on the last molar teeth, and the jaw firmly grasped with the fingers beneath it. The back part of the jaw is then pressed downward, the chin tilted upward, and the condyles slid back into place.

Fig. 77.   Fracture of the mandible through the symphysis (author's sketch).

Fig. 77. - Fracture of the mandible through the symphysis (author's sketch).

The other method is to place two corks, one on each side, or a piece of wood, transversely, between the last molar teeth, then raise the chin and push it backward.

The undetached lateral ligaments are put on the stretch when the condyle is luxated forward. Lewis A. Stimson believes that in attempting reduction the jaw should first be opened wider to relax these and then pushed back, but we are not prepared to admit that so doing does relax these ligaments. He has, however, shown that the interarticular cartilage may become displaced and, by filling up the articular cavity, prevent a proper reduction. In rare instances the catching of the coronoid process beneath the malar bone may hinder replacement.