What causes buckling of the Temporomandibular Joint (TMJ)?

TMJ Buckling: Etiology and Pathophysiology

TMJ "buckling" most commonly refers to condylar deformity and structural collapse resulting from chronic inflammatory arthritis (particularly juvenile idiopathic arthritis), traumatic injury, or degenerative osteoarthritis that leads to progressive bone remodeling and eventual structural failure of the mandibular condyle.

Primary Pathophysiological Mechanisms

Inflammatory Arthritis-Induced Structural Changes

• TMJ arthritis directly impacts mandibular growth and development, with the severity of structural deformity depending on the timing of arthritis onset in relation to growth trajectory and whether involvement is unilateral or bilateral 1.
• JIA-induced dentofacial deformities and condylar structural changes can occur early in the disease course, though the relationship between arthritis severity and the degree of structural deformity is indirect and incompletely understood 1.
• Untreated synovitis leads to progressive cartilage damage, bone erosion, and joint deformity over time, which can manifest as condylar collapse or "buckling" 2.
• In juvenile patients specifically, TMJ synovitis affects mandibular growth and development, potentially causing asymmetric condylar development and structural compromise 2.

Degenerative and Biomechanical Factors

• Parafunctional clenching may result in degeneration that first manifests as trabecular sclerosis of the mandibular condyle, eventually progressing to structural compromise 3.
• TMJ osteoarthritis affects all joint structures including the subchondral bone, with abnormal bone remodeling initially characterized by loss of bone mass, followed by reparative mechanisms that lead to stiffness and thickening of the condylar osteochondral interface 4.
• Chondrocyte loss, extracellular matrix degradation, and subchondral bone remodeling are critical factors in TMJ OA that can lead to structural failure 4.
• The articular surfaces are dynamically modified periosteum with healing and regenerative capability, but when overwhelmed by disease or trauma, structural collapse can occur 3.

Traumatic and Developmental Causes

• Traumatic arthritis following injury can lead to progressive structural changes and condylar deformity 5.
• Developmental anomalies including condylar hypoplasia represent intrinsic structural weakness that may manifest as progressive deformity 5.
• Fractures of the condyle or joint structures can result in malunion or nonunion with subsequent structural compromise 5.

Clinical Context and Differential Diagnosis

Important Diagnostic Considerations

• Only 5% of TMJ disorders represent true intra-articular pathology, though these cases are typically more severe and complex 5.
• Approximately 50% of patients presenting with TMJ-region symptoms have complications unrelated to the TMJ itself, emphasizing the critical importance of accurate differential diagnosis before attributing symptoms to structural joint pathology 5.
• MRI is the gold standard for detecting synovitis and evaluating soft tissue structures, while CT/CBCT is preferred for evaluating bone lesions and structural deformities 2.

Critical Pitfall to Avoid

The relationship between TMJ inflammation and symptoms is not always direct—some patients with significant structural changes may be relatively asymptomatic while others with minimal structural pathology may have severe symptoms 2. This disconnect means that imaging findings of condylar deformity must be correlated with clinical presentation rather than treated based on imaging alone.

Progressive Nature and Timing

• After achieving posterior functional occlusion (around 16 months of age), biomechanics assumes control of facial growth, development and adaptation, meaning that pathological processes affecting the TMJ during growth have compounding effects on structural development 3.
• The severity of dentofacial deformity and degree of skeletal maturity is a major factor in decision-making regarding disease management, as structural changes in skeletally immature patients have different implications than in mature patients 1.