What causes subluxation of the temporomandibular joint (TMJ)?

Causes of Temporomandibular Joint (TMJ) Subluxation

TMJ subluxation is primarily caused by excessive mouth opening, structural joint instability, and muscle dysfunction that allows the condyle to move anterior to the articular eminence but still remain within the joint capsule.

Anatomical and Structural Factors

• Abnormal Joint Morphology:

  • Shallow articular eminence
  • Flattened or eroded condyle
  • Lax joint capsule and ligaments 1
  • Inadequate adaptation of prosthetic components (in cases of TMJ replacement) 1

• Muscle-Related Factors:

  • Insufficient muscular stability 1
  • Imbalance between elevator and depressor muscles
  • Sectioning of the pterygomasseteric sling during surgery 1

Precipitating Events

• Trauma:

  • Direct trauma to the mandible
  • Indirect head and neck trauma 2
  • Surgical trauma (e.g., during TMJ replacement procedures) 1

• Iatrogenic Causes:

  • Anesthetic procedures:
    • Succinylcholine-induced muscle relaxation 3
    • Excessive mouth opening during intubation or extubation 4
    • Jaw manipulation during airway management 3
  • Removal of the coronoid process during surgery 1
  • Incorrect positioning of condyle/fossa components during TMJ replacement 1

• Habitual Factors:

  • Prolonged wide mouth opening (e.g., during dental procedures)
  • Repetitive behaviors like daily chewing of Qat for several hours 5
  • Excessive yawning, laughing, or speaking 5

Pathophysiological Mechanism

During normal TMJ function, the condyle leaves the fossa with maximal opening, which can occur in some individuals with as little as 35mm of opening 6. This movement becomes problematic when:

1. The condyle moves anterior to the articular eminence
2. The elevator muscles (masseter, temporalis, medial pterygoid) cannot return it to normal position
3. The condyle becomes trapped anterior to the eminence but remains within the joint capsule (subluxation) or moves outside the capsule (dislocation)

Risk Factors

• Patient-Specific Factors:

  • History of TMJ instability or previous subluxation 3
  • Connective tissue disorders affecting ligament integrity
  • Female gender (higher incidence of metal hypersensitivity in TMJ replacements) 1

• Surgical Risk Factors (for TMJ replacement patients):

  • Misalignment of stock condyle in the center of the fossa 1
  • Posterior displacement of condyle component causing impingement 1
  • Releasing masticatory muscles during surgery 1

Prevention Strategies

• Preoperative screening for TMJ instability before anesthetic procedures 3
• Careful positioning of prosthetic components during TMJ replacement 1
• In custom-made prostheses, incorporating a posterior stop on the fossa component 1
• Avoiding simultaneous coronoidectomy and masticatory muscle release 1

Understanding these causative factors is essential for proper diagnosis, prevention, and management of TMJ subluxation to improve patient outcomes and quality of life.