bubble_chart Overview

Temporomandibular joint ankylosis refers to the restricted or complete inability of mandibular movement due to fibrous scarring or bony adhesions in the temporomandibular joint, surrounding joint areas, or intermaxillary regions.

bubble_chart Etiology

The most common cause of temporomandibular joint ankylosis is trauma. Injury to the joint structures, muscles, and adjacent tissues can lead to bleeding and inflammation, followed by fibrosis and bone formation, resulting in permanent movement restriction. At birth, trauma can be caused by the direct application of forceps to the joint area or forceps applied to other parts of the mandible or breech delivery. Subsequent trauma can also lead to joint ankylosis, often due to a blow to the chin, indirectly causing joint injury. Extra-articular ankylosis may result from factors such as coronoid process trauma, depressed zygomatic fracture, burn scars, or cautery treatment for oral cancer.

Inflammation caused by infection is another significant cause. Primary infection of the temporomandibular joint is rare, as infections usually spread from adjacent areas, such as odontogenic infections. In such cases, extra-articular tissues are more likely to be affected. In the past, otitis media often led to chronic infections of the temporomandibular joint, but since the use of antibiotics, this complication has become rare. Microorganisms that can cause osteomyelitis may spread through the bloodstream to the temporomandibular joint, forming new lesions and leading to joint ankylosis and growth arrest.

Joint ankylosis can also result from radiation therapy, and rheumatoid arthritis may also cause joint ankylosis.

bubble_chart Clinical Manifestations

Clinically, it is classified into three types:

① True ankylosis: The lesion involves the joint itself, forming fibrous or bony adhesions between the condyle and the glenoid fossa, resulting in loss of joint mobility.

② Pseudoankylosis: Scar adhesions in the oral or maxillofacial tissues cause contracture of the jaws, leading to difficulty in opening the mouth, but the joint structure itself remains normal.

③ Mixed ankylosis: A combination of intra-articular and extra-articular lesions causing joint ankylosis.

The common features of temporomandibular joint ankylosis include joint fixation, progressive difficulty in opening the mouth, and in severe cases, complete inability to open, resulting in trismus. The severity depends on the type of lesion and disease duration. Due to the complete loss of mandibular movement, patients experience difficulty eating, relying only on the retromolar space and interdental gaps to squeeze and suck soft food, which affects chewing function, oral hygiene, and physical development. This can lead to mandibular developmental deformities, malocclusion, and loss of condylar mobility.

bubble_chart Diagnosis

(1) Clinical Features If there is no condylar growth arrest or tissue loss, ankylosis will not be accompanied by facial asymmetry. In such cases, diagnostically significant features include: in unilateral incomplete ankylosis, the midline of the chin deviates toward the affected side during mouth opening, which is caused by the descent or forward sliding of the contralateral condyle while the affected condyle remains relatively immobile. By placing both fingers in the external auditory canal or in front of the tragus and instructing the patient to open and close their mouth, significantly reduced or lost mobility of the affected condyle can be detected. X-rays usually reveal positive findings, such as unclear joint structure, with the condyle and joint space occupied by a large, irregular radiopaque area.

If ankylosis is accompanied by growth arrest or tissue loss, clinical deformities become evident. In unilateral cases, the midline of the chin deviates toward the affected side in the closed-mouth position; if the patient can achieve Grade I mouth opening, the deviation of the mandible toward the affected side becomes more pronounced. The affected side appears fuller in the masseter region due to the shortened ramus, and the antegonial notch is deeper compared to the contralateral side. In bilateral cases, significant chin retraction and shortening of the lower third of the face are observed, and reduced or lost mobility of the affected condyle can be detected. X-rays also reveal pronounced mandibular deformities, including a thickened condylar neck, enlarged and elongated coronoid process, shortened ramus, and a prominent contrast between the increased mandibular angle and deepened antegonial notch.

A preliminary diagnosis can be made based on obvious and typical clinical signs, but preoperative confirmation with X-rays is essential to formulate a reasonable treatment plan.

bubble_chart Treatment Measures

The treatment of intra-articular ankylosis and extra-articular ankylosis generally requires surgical intervention. Before performing the surgery, an accurate diagnosis is essential. First, it is necessary to determine whether the ankylosis is intra-articular, extra-articular, or a mixed type; whether the nature of the ankylosis is fibrous or bony; whether the condition is unilateral or bilateral, as well as the location and extent of the lesion. Only then can an appropriate surgical plan be formulated. During the operation, care must be taken not to confuse the affected side, as this would cause unnecessary suffering to the patient. Depending on the extent and severity of the condition, local anesthesia may be used. If general anesthesia is necessary, awake intubation should be performed to prevent the risk of airway obstruction due to tongue retraction. The tracheal tube should not be removed until the patient is fully awake after the surgery.

bubble_chart Prognosis

For any type of temporomandibular joint ankylosis, the issue of postoperative recurrence has always been a widely concerned yet unresolved problem. According to domestic and international data, the postoperative recurrence rate varies significantly, ranging approximately between 10% and 55%. The recurrence rates for true and false ankylosis are roughly similar, while the long-term efficacy for mixed ankylosis is even poorer.

There are many factors contributing to recurrence, and current perspectives are not entirely consistent. It is generally believed to be related to the following factors.

bubble_chart Differentiation

Since the surgical approaches for intra-articular and extra-articular ankylosis differ, accurate differentiation is essential. The key diagnostic points are presented in Table 1.

Table 1 Differential Diagnosis of Intra-articular and Extra-articular Ankylosis

Differentiation Points	Intra-articular Ankylosis	Extra-articular Ankylosis
Medical History	History of suppurative sexually transmitted diseases, injuries, etc.	History of oral ulcers, maxillofacial fractures, burns, or radiation therapy
Intermaxillary Scarring	Absent	Present
Lower Facial Development	Severe deformity (not evident if onset occurs in adulthood)	Mild deformity (no impact if onset occurs in adulthood)
Occlusal Relationship	Severe malocclusion (not evident if onset occurs in adulthood)	Grade I malocclusion (no impact if onset occurs in adulthood)
X-ray Findings	Loss of joint space, bony fusion forming a spherical mass (fibrous ankylosis shows preserved but blurred joint space)	Normal joint appearance, narrowed space between the maxilla and mandibular ramus with increased density