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

OBJECTIVES: Temporomandibular pain is often accompanied by pathologic chang es to joint retrodiscal tissues, The substantial representation of females in this condition has encouraged hypotheses which link genetic or hormonall y induced abnormalities in tissue composition (type III collagen, type I co llagen, type III/type I ratio) to the development of temporomandibular diso rders. As this condition is often associated with a history of orofacial tr auma, we investigated the functional impact of retrodiscal trauma on the co mposition and biomechanics of retrodiscal tissues. DESIGN AND METHODS: Retrodiscal tissue of female goats received trauma or s ham 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 w ere assayed for collagens I and III, RESULTS: Thirty days after surgical section of retrodiscal tissues, the tis sue had reformed, but the composition and biomechanics were substantially c hanged. Healed tissue manifested less than half the strength of normal tiss ue (P = 0.02), In addition, the development of tissue strain shifted from a relatively even distribution to a confined region near the retrodiscal-dis cal 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 col lagen (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 i nterface of the disc and retrodiscal tissue, and that this shift dramatical ly weakens the tissue and increases the probability of reinjury, inflammati on and pain.