Temporomandibular joint (TMJ) pseudoankylosis is characterized by limited mouth opening and mandibular movements, resulting from factors outside the joint. The authors present a case of TMJ pseudoankylosis caused by congenital zygomatic malformation and hyperplasia of the coronoid process. Treatment with coronoidectomy and postoperative physiotherapy achieved favorable results.
Pseudoankylosis of the temporomandibular joint (TMJ) is much less frequent than intracapsular (true) ankylosis. It is characterized by mandibular hypomobility caused by a pathology extrinsic to the joint. The level of hypomobility associated with the condition may vary from limitation of mandibular lateral excursions to complete trismus. Normally, there is no pain. Some facial deformity may be present, according to the volumetric increase.
Diagnosis may be complemented by extra-oral radiographs (panoramic, submentovertex and Waters incidence). Computed tomography (CT) provides higher image quality, particularly when sagittal multiplane reconstructions are available. Magnetic resonance imaging (MRI) may be indicated when fibrous tissue formation is suspected.
Treatment usually involves unilateral or bilateral coronoidectomy. Different approaches, such as intraoral, preauricular or submandibular, have been described. The intervention should be made as early as possible after diagnosis is confirmed, particularly in unilateral cases, to avoid the need for bilateral coronoid resection, in case prolonged mandibular hypomobility results in contralateral hypertrophy. The masticatory muscles may also become adapted to the restrictive condition, resulting in limitation of the results or the need for temporal and masseter myotomy. Aggressive physiotherapy should be started immediately after surgical intervention to prevent recurrence. Extra-oral approaches have been recommended, with removal of the lower bundles of the temporal muscle, to prevent recurrence.
Zygomatic malformations are not frequent, but may result from intrauterine trauma or be associated with syndromes such as Treacher-Collins or Nager. They are also seen in some patterns of facial clefts, and should be corrected through zygoma osteoplasty, bone grafting or alloplastic implants, according to the severity of functional or aesthetic compromise.
A 20-year-old female patient was referred in March 2004 because of limited mouth opening ( Fig. 1 ), which had been developing since adolescence. She was a twin and during pregnancy had been in an unfavourable intrauterine positioning with her sibling’s knee compressing her face. The patient had moderate scoliosis for which she was undergoing orthopaedic therapy. No previous history of facial trauma was reported. Although reporting difficulty in mouth opening for dental treatment, she had undergone restorations, orthodontic treatment and a third molar extraction. In 2003, she had been diagnosed, at a different center, with disk displacement without reduction and had undergone arthocentesis and open surgery of the right TMJ. The trismus did not improve.
Limited mouth opening was observed on clinical examination (12 mm recorded inter-incisal), with limited lateral and protrusive excursions. Zygomatic deficiency was apparent on the right midface.
MRI of the TMJ suggested disk displacement without reduction but by the time this surgery was performed, CT scans showed hyperplasia of the right coronoid process and malformation of the right zygomatic bone, positioned lower and backward to the normal contralateral side. Previous TMJ open surgery did not affect limited mouth opening. The left coronoid process presented a moderate volumetric increase, probably due to the prolonged mandibular hypomobility ( Fig. 2 ).
In January 2005, the patient underwent surgery under general anaesthesia and fibrolaryngoscopy entubation. After anaesthesia, mouth opening did not improve. Coronoidectomy was performed by intraoral access, on the right side, with complete resection of the coronoid process ( Fig. 3 ). Intraoperative mouth opening reached 30 mm. Histopathological analysis of the fragment removed revealed normal bone structure.
Clinical evolution was favorable. The patient underwent physiotherapy on the second postoperative day, with mouth opening movements and other forced mandibular lateral excursions. In August 2005, the patient reported satisfaction with the resulting mouth opening of 35 mm, and showed no interest in any type of correction of the zygomatic malformation ( Fig. 4 ).