Abstract
Orthopaedic surgeons have recently adapted the hol mium:yttrium-aluminum-garnet (YAG) laser for the shrinkage of capsular tissues for treatment of glenohu meral instability. The molecular mechanism of capsular shrinkage has not been documented to date. This study examined the effects of heating on bovine calf knee capsule and subsequent shrinkage of the cap sule. Capsule specimens were placed in a saline bath at temperatures ranging from 55° to 75°C for 1, 3, 5, and 10 minutes. Shrinkage was quantified by digital imaging, and the tissue was examined by light and polarized light microscopy. Tissue contraction was not measurable at or below 57.5°C. At 60°C, tissue shrink age occurred with corresponding basophilic staining and loss of birefringence in collagen fibers. For speci mens heated at 60°C and 62°C, shrinkage directly correlated with duration of thermal exposure. Maximal shrinkage of approximately 50% in length occurred at and above 65°C with thermal exposures of 1 minute or greater. This study demonstrates that thermal shrink age of bovine knee capsule correlates with denatur ation of collagen fibers and depends on both time and temperature. Capsular shrinkage treatments may be performed with any energy source that is capable of well-controlled heating of capsular tissue and does not depend on the special properties of laser light.
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