J . small Anim. Pract. (1979) 20,209-218.
Temporomandibular joint dysplasia in an Irish Setter K . A. JOHNSON Department of Veterinary Clinical Studies, University of Sydney, Sydney, 2006, Australia
ABSTRACT Dysplasia of the temporomandibular joints was diagnosed in an Irish Setter. The condyloid process was mis-shapen and the glenoid fossa flattened, which allowed subluxation of the temporomandibular joints with recurrent locking of the coronoid process on the zygomatic arch with the mouth open. Permanent relief from open mouth jaw locking was given by partial zygomatic arch ostectomy. INTRODUCTION Dysplasia of the condyloid process of the mandible and the mandibular fossa of the temporal bone allows instability and subluxation of the temporomandibular joint. Such dysplasia and subluxation may result in locking of the coronoid process of the mandible on the zygomatic arch, while the mouth is open, as described in Basset Hounds (Robins & Grandage, 1977) and an Irish Setter (Stewart et al., 1975). The subluxation was at first attributed to flattening of the articular surfaces of the mandibular fossa and consequent laxity of the temporomandibular joint (Stewart et al., 1975). However, a more detailed study showed that an abnormality of both the condyloid process and the mandibular fossa, designated as temporomandibular joint dysplasia, could cause the subluxation and allow open mouth locking (Robins & Grandage, 1977). Open mouth locking due to a single traumatic subluxation of one temporomandibular joint with the coronoid process displaced lateral to the zygomatic arch has been reported in a St. Bernard (Culvenor, 1978). This is a report of an Irish Setter with bilateral temporomandibular joint dysplasia, which had a history of frequent open mouth jaw locking. The morpho0020-45 10/79/0400-0209$02.00
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logy of the temporomandibular joints is compared with that of unaffected Irish Setters. CASE R E P O R T History A three and a half year old, male Irish Setter was referred to the University of Sydney Veterinary Hospital and Clinic because it had recurrent episodes of open mouth jaw locking. The first episodes occurred at about 6 months of age and surgery had been performed to tighten both temporomandibular joints. Unfortunately a more detailed account of the technique used was unavailable because the dog was then disposed of to its present owner. The surgery was not effective in the long term because frequent episodes of open mouth jaw locking, usually on the right side, continued for the next 3 years. However, during this time, the jaw was always spontaneously relocated within a few minutes. The dog was fed a diet of fresh meat and commercial dry food and ate normally. About 3 weeks before examination the dog began to eat poorly and lose weight. It had been necessary to use general anaesthesia to effect reduction of the mandible on the last two occasions before being referred for examination. Examination Generalized muscle wasting was evident with the muscles of mastication more severely affected. The external sagittal crest and zygomatic arches were prominent. There was inferior prognathia with a 5 mm gap in the closed bite of the incisor teeth. The dog resented attempts to examine its mouth. When the jaws were opened widely, slight lateral deviation and rotation of the mandible caused the ipsilateral coronoid process to touch the zygomatic arch. As the jaws closed, the mandible progressively deviated up to 1 cm laterally and the coronoid process, which engaged outside the ipsilateral zygomatic arch, was quite prominent as a subcutaneous bulge. During this manoeuvre the two halves of the mandible underwent some independent movement. The mandible on the side which was locking underwent outward rotation. This was facilitated by spreading of the mandibular symphysis, witnessed as a widening of the angle and space between the lower canine teeth. Open mouth locking could be produced on either side, but more easily on the right and resulted in 15 cm of apertognathia. The coronoid process never locked on both sides simultaneously. Some discomfort manifested by ptyalism, swallowing and repeated attempts at opening the mouth was associated with open mouth locking of the jaw. Radiographs of the temporomandibular joints were taken in the lateral, lateral oblique and dorso-ventral projections with the jaws closed and locked open. The lateral oblique view (Fig. l), showed the mandibular fossae were shallow due to a deficiency of the dorsal temporal articular margin. Thejoint space was wider over
T E M P O R O M A N D I B U L A R JOINT D Y S P L A S I A IN A N IRISH SETTER
21 1
FIG. 1. In the oblique lateral view of the left temporomandibular joint with the mouth open there is a deficiency of the dorsal articulating surface of the temporal bone A A A the joint space is wider dorsally A and the retroglenoid process is enlarged AA. The osscous prominence in the dorsal joint space is the contralateral retroglenoid process. A small chip of bone is present on the dorsal caudal t border of the left coronoid process.
this surface of the condyloid process, particularly when the jaws were open. The retroglenoid process was thicker and enlarged. Dorso-ventral views showed the right (Fig. 2) or left (Fig. 3) coronoid process outside the zygomatic arch, depending upon which side was locked. The contralateral condyloid process was rostrally displaced in relation to the glenoid cavity when the coronoid process was locked on the zygomatic arch. In the dorso-ventral view (Fig. 4) with the X-ray beam centred over the temporomandibular joints, the articular surfaces of the condyloid process were
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FIG.2. In the dorso-ventral view with the mouth open, the right coronoid process is located lateral to the right zygomatic arch v. The right mandible is also rotated outward and the left mandible inwards. The left condyloid process is rostrally displaced from the glenoid cavity and the increase is joint space is evident v w .
abnormally shaped. The medial articular surface occupied thegreater proportion of the width of each condyle and was outside the limits of the glenoid cavity. The axis of the total articular surface of the condyloid process was obliquely disposed, forming an angle of approximately 80" to the midline. In four adult Irish Setters similar in age and weight to the affected dog, radiographs (Fig. 5 ) revealed that the axis through the articulating surface was almost transverse, and the medial and lateral articulating surfaces were equal in
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FIG.3. In the dorso-ventral view with the mouth open, the left coronoid process is located lateral to the zygomatic arch v, but not to the same extent as the right coronoid process in Fig. 2. The right condyloid process is rostrally displaced ~ v The . amount of zygomatic arch which is overlapped by the condyloid process is reduced when compared with the left side.
width and convex in appearance. A similar appearance is to be found in published radiographs of the normal dog (Schebitz & Wilkens, 1968). Surgery and Results A diagnosis of bilateral temporomandibular joint dysplasia with subluxation, allowing the coronoid process to engage the zygomatic arch and cause open mouth jaw locking was made. A bilateral partial zygomatic arch ostectomy was
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FIG 4. In the dorso-ventral view of the affected dog with the mouth closed, the medial articular surfaces occupy a greater proportion of the width of the condyloid process A A A compared with a normal Irish Setter (Fig. 5.). The medial articular surfaces lie outside the width of the glenoid cavity v and the articular surfaces are more obliquely disposed to the transverse plane.
performed. The surgical technique has been described by Stewart et al., (1975) and Robins & Grandage (1977). At the time of surgery the zygomatic arch was exposed and then the coronoid process was engaged outside the zygomatic arch to determine the amount of bone to be removed. It was necessary to remove most of the ventral border of the zygomatic arch, leaving a thin rim of bone along the dorsal edge. Even though the coronoid process could barely touch this remaining portion of zygomatic arch it was preserved in order to maintain some support for the orbit. In the first week post-operatively the right coronoid process would momentarily lock when the dog ate or became excited. However, there was only 6-7 cm of apertognathia when this occurred, which was much less than the fully open position. During the following six months the dog had no recurrence of the problem and gained in body weight, making ostectomy of the full width of the zygomatic arch unnecessary.
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FIG.5. In this dorso-ventral radiograph of a normal Irish Setter, the medial and lateral vv articular surfaces are equal in width. The overall articular surface of both condyloid processes, which have a convex appearance, are in the same transverse plane.
DISCUSSION The mandible of the dog is capable of moving at the temporomandibular joints in more than a simple hinge motion. This is facilitated by the limited movement which occurs at the mandibular symphysis. The mandibular symphysis is jointed by fibrocartilage along the rostrodorsal edge and below this by fibrous cruciate ligaments. Independent movement of the two halves of the mandible is allowed by squeezing or stretching the fibrocartilage band and rotation on the cruciate
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FIG.^. Open mouth jaw locking produced in the normal skull shows the coronoid process engaged lateral to the zygomatic arch AA. The mandible is outwardly rotated on the same side A A A and the contralateral condyloid process is rostrally subluxated A.
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ligaments, although the cruciate ligaments limit the lateral spread of the symphysis. Normal opening and closing of the jaw does not require movement of the mandibular symphysis, but it is necessary for chewing (Scapino, 1965). During normal jaw opening the lateral part of the condyloid process swings forward and downward, placing stress on the lateral temporomandibular ligament (Scapino, 1965).When the articular surfaces are more obliquely disposed to the midline, as was seen in this dog (Fig. 4),the lateral part of the condyle moves even further out of the glenoid cavity causing stretching and laxity of the lateral temporomandibular ligament (Robins & Grandage, 1977). The earlier attempts to tighten the lateral temporomandibular ligament failed in this case and another (Robins & Grandage, 1977) due to this stress placed on the ligament during normal opening of the mouth. Open mouth jaw locking can only occur when movement at the mandibular symphysis allowing rotation of the two halves of the mandible is combined with laxity and subluxation of the temporomandibular joint (Fig. 6). The aetiology of the dysplasia of the condyloid process and mandibular fossa, which gives rise to the laxity and subluxation of the temporomandibularjoint, is not known. Robins & Grandage (1977) suggested that dysplasia of the temporomandibular joints was the primary problem and either congenital or acquired in origin. The presence of inferior prognathia may be responsible for increased laxity of the mandibular symphysis. It does necessitate either a change in the angle of the condyloid process to conform to the glenoid cavity or an alteration in the normal biomechanics of the temporomandibular joint. Inferior prognathia or increased laxity of the mandibular symphysis may be a primary problem leading to development of temporomandibular joint dysplasia. In man, temporomandibular joint dysplasia does occur and a shallow glenoid fossa with an underdeveloped temporal eminence, together with a lax joint, does give rise to recurrent subluxation (Sheppard & Sheppard, 1977). However, due to the anatomical differences of man from the dog, the shorter coronoid process does not lock on the zygomatic arch. Coronoid process hyperplasia causes restriction of oral opening by contact with the zygomatic arch and this acts against dislocation. Thus in man subluxation of the temporomandibular joint, even when combined with coronoid process hyperplasia, is unlikely to produce open mouth jaw locking as seen in dogs (Stacy, 1978; personal communication). The severity of laxity and subluxation which occurs in a temporomandibular joint may be correlated with the amount of displacemnt which the contralateral coronoid process can undergo. The degree of stretching of the temporomandibular joint and fibrous mandibular symphysis may increase progressively since open mouth jaw locking, which the dog could reduce unattended, did occur for a long period of time prior to locking which required veterinary attention. Also, some time may be necessary for a space to develop outside the zygomatic arch in which the coronoid may completely engage, as this site is normally well covered by the origin of the masseter muscle.
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Instability and subluxation of any joint will often result in secondary osteoarthritis (Salter, 1970). It may be expected that secondary osteoarthritis of the temporomandibular joints would occur eventually, since ostectomy of the zygomatic arch only removes one of the components of locking and does not correct the subluxation. Alternatively, partial ostectomy of the locking portion of the coronoid process may be performed in order to preserve the integrity of the zygomatic arch. This could be achieved with minimal interference to the attachment of the temporal muscle. In man, procedures which have been attempted to correct instability of the temporomandibular joint include injection of sclerosing solutions around the joint, passage of a sling of temporal fascia through a hole drilled in the condyle and attachment of the sling deep to the temporal muscle, plication of the capsular ligaments, excision of the intra-articular cartilage, grafting to enlarge the flattened temporal eminence (Sheppard & Sheppard, 1977), condylectomy to allow formation of intracapsular scar tissue and condylotomy to change the position of the condyle (Macalister, 1973). ACKNOWLEDGMENTS
The author wishes to acknowledge the advice given by Associate Professor G. C. Stacy, Department of Oral Medicine and Oral Surgery, University of Sydney and Dr C. R. Bellenger, Department of Veterinary Clinical Studies, University of Sydney, in the preparation of the manuscript; Mr I. Bell of Sydney for referring the case and the secretarial assistance of Mrs L. Scott. REFERENCES CULVENOR, J.A. (1978) What Is Your Diagnosis? J. Am. uet. rned. Ass. 172(6), 719. MACALISTER, A.D. (1973) The Dislocating Jaw. Trans. Int. Con$ Oral Surgs. 4, 17. G. AND GRANDAGE, J. (1977) Temporomandibular Joint Dysplasia and Open-Mouth Jaw ROBINS, Locking in the Dog. J. Am. vet med. Ass. 171(10), 1072. SALTER R.B. (1970) Textbook of Disorders and Injuries of the Musculosketetal System. Williams and Wilkins Company, Baltimore. SCAPINO, R.P. (1965) The Third Joint of the Canine Jaw. J. Morph. 116,23. H. (1968) Atlas of Radiographic Anatomy of Dog and Horse. Paul SCHEBITZ, H. AND WILKENS, Parey, Berlin and Hamburg. SHEPPARD, I.M. AND SHEPPARD, S.M. (1977) Subluxation of the temporomandibular joint. J. Oral Surg., Oral Med., Oral Path. 44(6), 821. STEWART, W.C., BAKER,G.J. AND LEE,R. (1975) Temporomandibular subluxation in the dog: A case report. J. small Anim. Pract. 16, 345.
Temporomandibular joint dysplasia in an Irish Setter K . A. JOHNSON Department of Veterinary Clinical Studies, University of Sydney, Sydney, 2006, Australia
ABSTRACT Dysplasia of the temporomandibular joints was diagnosed in an Irish Setter. The condyloid process was mis-shapen and the glenoid fossa flattened, which allowed subluxation of the temporomandibular joints with recurrent locking of the coronoid process on the zygomatic arch with the mouth open. Permanent relief from open mouth jaw locking was given by partial zygomatic arch ostectomy. INTRODUCTION Dysplasia of the condyloid process of the mandible and the mandibular fossa of the temporal bone allows instability and subluxation of the temporomandibular joint. Such dysplasia and subluxation may result in locking of the coronoid process of the mandible on the zygomatic arch, while the mouth is open, as described in Basset Hounds (Robins & Grandage, 1977) and an Irish Setter (Stewart et al., 1975). The subluxation was at first attributed to flattening of the articular surfaces of the mandibular fossa and consequent laxity of the temporomandibular joint (Stewart et al., 1975). However, a more detailed study showed that an abnormality of both the condyloid process and the mandibular fossa, designated as temporomandibular joint dysplasia, could cause the subluxation and allow open mouth locking (Robins & Grandage, 1977). Open mouth locking due to a single traumatic subluxation of one temporomandibular joint with the coronoid process displaced lateral to the zygomatic arch has been reported in a St. Bernard (Culvenor, 1978). This is a report of an Irish Setter with bilateral temporomandibular joint dysplasia, which had a history of frequent open mouth jaw locking. The morpho0020-45 10/79/0400-0209$02.00
209
01979 BSAVA
210
K . A . JOHNSON
logy of the temporomandibular joints is compared with that of unaffected Irish Setters. CASE R E P O R T History A three and a half year old, male Irish Setter was referred to the University of Sydney Veterinary Hospital and Clinic because it had recurrent episodes of open mouth jaw locking. The first episodes occurred at about 6 months of age and surgery had been performed to tighten both temporomandibular joints. Unfortunately a more detailed account of the technique used was unavailable because the dog was then disposed of to its present owner. The surgery was not effective in the long term because frequent episodes of open mouth jaw locking, usually on the right side, continued for the next 3 years. However, during this time, the jaw was always spontaneously relocated within a few minutes. The dog was fed a diet of fresh meat and commercial dry food and ate normally. About 3 weeks before examination the dog began to eat poorly and lose weight. It had been necessary to use general anaesthesia to effect reduction of the mandible on the last two occasions before being referred for examination. Examination Generalized muscle wasting was evident with the muscles of mastication more severely affected. The external sagittal crest and zygomatic arches were prominent. There was inferior prognathia with a 5 mm gap in the closed bite of the incisor teeth. The dog resented attempts to examine its mouth. When the jaws were opened widely, slight lateral deviation and rotation of the mandible caused the ipsilateral coronoid process to touch the zygomatic arch. As the jaws closed, the mandible progressively deviated up to 1 cm laterally and the coronoid process, which engaged outside the ipsilateral zygomatic arch, was quite prominent as a subcutaneous bulge. During this manoeuvre the two halves of the mandible underwent some independent movement. The mandible on the side which was locking underwent outward rotation. This was facilitated by spreading of the mandibular symphysis, witnessed as a widening of the angle and space between the lower canine teeth. Open mouth locking could be produced on either side, but more easily on the right and resulted in 15 cm of apertognathia. The coronoid process never locked on both sides simultaneously. Some discomfort manifested by ptyalism, swallowing and repeated attempts at opening the mouth was associated with open mouth locking of the jaw. Radiographs of the temporomandibular joints were taken in the lateral, lateral oblique and dorso-ventral projections with the jaws closed and locked open. The lateral oblique view (Fig. l), showed the mandibular fossae were shallow due to a deficiency of the dorsal temporal articular margin. Thejoint space was wider over
T E M P O R O M A N D I B U L A R JOINT D Y S P L A S I A IN A N IRISH SETTER
21 1
FIG. 1. In the oblique lateral view of the left temporomandibular joint with the mouth open there is a deficiency of the dorsal articulating surface of the temporal bone A A A the joint space is wider dorsally A and the retroglenoid process is enlarged AA. The osscous prominence in the dorsal joint space is the contralateral retroglenoid process. A small chip of bone is present on the dorsal caudal t border of the left coronoid process.
this surface of the condyloid process, particularly when the jaws were open. The retroglenoid process was thicker and enlarged. Dorso-ventral views showed the right (Fig. 2) or left (Fig. 3) coronoid process outside the zygomatic arch, depending upon which side was locked. The contralateral condyloid process was rostrally displaced in relation to the glenoid cavity when the coronoid process was locked on the zygomatic arch. In the dorso-ventral view (Fig. 4) with the X-ray beam centred over the temporomandibular joints, the articular surfaces of the condyloid process were
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FIG.2. In the dorso-ventral view with the mouth open, the right coronoid process is located lateral to the right zygomatic arch v. The right mandible is also rotated outward and the left mandible inwards. The left condyloid process is rostrally displaced from the glenoid cavity and the increase is joint space is evident v w .
abnormally shaped. The medial articular surface occupied thegreater proportion of the width of each condyle and was outside the limits of the glenoid cavity. The axis of the total articular surface of the condyloid process was obliquely disposed, forming an angle of approximately 80" to the midline. In four adult Irish Setters similar in age and weight to the affected dog, radiographs (Fig. 5 ) revealed that the axis through the articulating surface was almost transverse, and the medial and lateral articulating surfaces were equal in
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FIG.3. In the dorso-ventral view with the mouth open, the left coronoid process is located lateral to the zygomatic arch v, but not to the same extent as the right coronoid process in Fig. 2. The right condyloid process is rostrally displaced ~ v The . amount of zygomatic arch which is overlapped by the condyloid process is reduced when compared with the left side.
width and convex in appearance. A similar appearance is to be found in published radiographs of the normal dog (Schebitz & Wilkens, 1968). Surgery and Results A diagnosis of bilateral temporomandibular joint dysplasia with subluxation, allowing the coronoid process to engage the zygomatic arch and cause open mouth jaw locking was made. A bilateral partial zygomatic arch ostectomy was
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FIG 4. In the dorso-ventral view of the affected dog with the mouth closed, the medial articular surfaces occupy a greater proportion of the width of the condyloid process A A A compared with a normal Irish Setter (Fig. 5.). The medial articular surfaces lie outside the width of the glenoid cavity v and the articular surfaces are more obliquely disposed to the transverse plane.
performed. The surgical technique has been described by Stewart et al., (1975) and Robins & Grandage (1977). At the time of surgery the zygomatic arch was exposed and then the coronoid process was engaged outside the zygomatic arch to determine the amount of bone to be removed. It was necessary to remove most of the ventral border of the zygomatic arch, leaving a thin rim of bone along the dorsal edge. Even though the coronoid process could barely touch this remaining portion of zygomatic arch it was preserved in order to maintain some support for the orbit. In the first week post-operatively the right coronoid process would momentarily lock when the dog ate or became excited. However, there was only 6-7 cm of apertognathia when this occurred, which was much less than the fully open position. During the following six months the dog had no recurrence of the problem and gained in body weight, making ostectomy of the full width of the zygomatic arch unnecessary.
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FIG.5. In this dorso-ventral radiograph of a normal Irish Setter, the medial and lateral vv articular surfaces are equal in width. The overall articular surface of both condyloid processes, which have a convex appearance, are in the same transverse plane.
DISCUSSION The mandible of the dog is capable of moving at the temporomandibular joints in more than a simple hinge motion. This is facilitated by the limited movement which occurs at the mandibular symphysis. The mandibular symphysis is jointed by fibrocartilage along the rostrodorsal edge and below this by fibrous cruciate ligaments. Independent movement of the two halves of the mandible is allowed by squeezing or stretching the fibrocartilage band and rotation on the cruciate
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FIG.^. Open mouth jaw locking produced in the normal skull shows the coronoid process engaged lateral to the zygomatic arch AA. The mandible is outwardly rotated on the same side A A A and the contralateral condyloid process is rostrally subluxated A.
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ligaments, although the cruciate ligaments limit the lateral spread of the symphysis. Normal opening and closing of the jaw does not require movement of the mandibular symphysis, but it is necessary for chewing (Scapino, 1965). During normal jaw opening the lateral part of the condyloid process swings forward and downward, placing stress on the lateral temporomandibular ligament (Scapino, 1965).When the articular surfaces are more obliquely disposed to the midline, as was seen in this dog (Fig. 4),the lateral part of the condyle moves even further out of the glenoid cavity causing stretching and laxity of the lateral temporomandibular ligament (Robins & Grandage, 1977). The earlier attempts to tighten the lateral temporomandibular ligament failed in this case and another (Robins & Grandage, 1977) due to this stress placed on the ligament during normal opening of the mouth. Open mouth jaw locking can only occur when movement at the mandibular symphysis allowing rotation of the two halves of the mandible is combined with laxity and subluxation of the temporomandibular joint (Fig. 6). The aetiology of the dysplasia of the condyloid process and mandibular fossa, which gives rise to the laxity and subluxation of the temporomandibularjoint, is not known. Robins & Grandage (1977) suggested that dysplasia of the temporomandibular joints was the primary problem and either congenital or acquired in origin. The presence of inferior prognathia may be responsible for increased laxity of the mandibular symphysis. It does necessitate either a change in the angle of the condyloid process to conform to the glenoid cavity or an alteration in the normal biomechanics of the temporomandibular joint. Inferior prognathia or increased laxity of the mandibular symphysis may be a primary problem leading to development of temporomandibular joint dysplasia. In man, temporomandibular joint dysplasia does occur and a shallow glenoid fossa with an underdeveloped temporal eminence, together with a lax joint, does give rise to recurrent subluxation (Sheppard & Sheppard, 1977). However, due to the anatomical differences of man from the dog, the shorter coronoid process does not lock on the zygomatic arch. Coronoid process hyperplasia causes restriction of oral opening by contact with the zygomatic arch and this acts against dislocation. Thus in man subluxation of the temporomandibular joint, even when combined with coronoid process hyperplasia, is unlikely to produce open mouth jaw locking as seen in dogs (Stacy, 1978; personal communication). The severity of laxity and subluxation which occurs in a temporomandibular joint may be correlated with the amount of displacemnt which the contralateral coronoid process can undergo. The degree of stretching of the temporomandibular joint and fibrous mandibular symphysis may increase progressively since open mouth jaw locking, which the dog could reduce unattended, did occur for a long period of time prior to locking which required veterinary attention. Also, some time may be necessary for a space to develop outside the zygomatic arch in which the coronoid may completely engage, as this site is normally well covered by the origin of the masseter muscle.
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Instability and subluxation of any joint will often result in secondary osteoarthritis (Salter, 1970). It may be expected that secondary osteoarthritis of the temporomandibular joints would occur eventually, since ostectomy of the zygomatic arch only removes one of the components of locking and does not correct the subluxation. Alternatively, partial ostectomy of the locking portion of the coronoid process may be performed in order to preserve the integrity of the zygomatic arch. This could be achieved with minimal interference to the attachment of the temporal muscle. In man, procedures which have been attempted to correct instability of the temporomandibular joint include injection of sclerosing solutions around the joint, passage of a sling of temporal fascia through a hole drilled in the condyle and attachment of the sling deep to the temporal muscle, plication of the capsular ligaments, excision of the intra-articular cartilage, grafting to enlarge the flattened temporal eminence (Sheppard & Sheppard, 1977), condylectomy to allow formation of intracapsular scar tissue and condylotomy to change the position of the condyle (Macalister, 1973). ACKNOWLEDGMENTS
The author wishes to acknowledge the advice given by Associate Professor G. C. Stacy, Department of Oral Medicine and Oral Surgery, University of Sydney and Dr C. R. Bellenger, Department of Veterinary Clinical Studies, University of Sydney, in the preparation of the manuscript; Mr I. Bell of Sydney for referring the case and the secretarial assistance of Mrs L. Scott. REFERENCES CULVENOR, J.A. (1978) What Is Your Diagnosis? J. Am. uet. rned. Ass. 172(6), 719. MACALISTER, A.D. (1973) The Dislocating Jaw. Trans. Int. Con$ Oral Surgs. 4, 17. G. AND GRANDAGE, J. (1977) Temporomandibular Joint Dysplasia and Open-Mouth Jaw ROBINS, Locking in the Dog. J. Am. vet med. Ass. 171(10), 1072. SALTER R.B. (1970) Textbook of Disorders and Injuries of the Musculosketetal System. Williams and Wilkins Company, Baltimore. SCAPINO, R.P. (1965) The Third Joint of the Canine Jaw. J. Morph. 116,23. H. (1968) Atlas of Radiographic Anatomy of Dog and Horse. Paul SCHEBITZ, H. AND WILKENS, Parey, Berlin and Hamburg. SHEPPARD, I.M. AND SHEPPARD, S.M. (1977) Subluxation of the temporomandibular joint. J. Oral Surg., Oral Med., Oral Path. 44(6), 821. STEWART, W.C., BAKER,G.J. AND LEE,R. (1975) Temporomandibular subluxation in the dog: A case report. J. small Anim. Pract. 16, 345.
