Trauma modifies strength and composition of retrodiscal tissues of the goat temporomandibular joint

OBJECTIVES: Temporomandibular pain is often accompanied by pathologic changes to joint retrodiscal tissues. The substantial representation of females in this condition has encouraged hypotheses which link genetic or hormonally induced abnormalities in tissue composition (type III collagen, type I collagen, type III/type I ratio) to the development of temporomandibular disorderS. As this condition is often associated with a history of orofacial trauma, we investigated the functional impact of retrodiscal trauma on the composition and biomechanics of retrodiscal tissues. DESIGN AND METHODS: Retrodiscal tissue of female goats received trauma or sham trauma. Following a healing period of 30 days, the tissues were pulled to failure on an extensometer. OUTCOME MEASURES: Assessments were made of tissue biomechanical properties (failure force, elastic stiffness, strain distribution). Tissue fragments were assayed for collagens I and III. RESULTS: Thirty days after surgical section of retrodiscal tissues, the tissue had reformed, but the composition and biomechanics were substantially changed. Healed tissue manifested less than half the strength of normal tissue (P= 0.02). In addition, the development of tissue strain shifted from a relatively even distribution to a confined region near the retrodiscaldiscal attachment zone. It appeared that a large increase in the expression of type III collagen (179.6%; P= 0.038) and the ratio of type III/type I collagen (180.9%; P= 0.011) accounted for these functional changes. CONCLUSIONS: We suggest that shifts in collagen expression following injury create shifts in strain development which focus tissue stresses near the interface of the disc and retrodiscal tissue, and that this shift dramatically weakens the tissue and increases the probability of re‐injury, inflammation and pain.