The mechanism of joint capsule thermal modification in an in vitro sheep model

The purpose of this study was to understand the mechanism responsible for j oint capsule shrinkage after nonablative laser application in an in vitro s heep model. Femoropatellar joint capsular tissue specimens harvested from 2 0 adult sheep were treated with one of three power settings of a holmium:yt trium-aluminum-garnet laser or served as a control. Laser treatment signifi cantly shortened the tissue and decreased tissue stiffness in all three las er groups, whereas Failure strength was not altered significantly by laser treatment. Transmission electron microscopic examination showed swollen col lagen fibrils and loss of membrane integrity of fibroblasts, A thermometric study revealed nonablative laser energy caused tissue temperature to rise in the range of 64 degrees C to 100 degrees C, Electrophoresis after trypsi n digestion of the tissue revealed significant loss of distinct alpha bands of Type I collagen in laser treated samples, whereas alpha bands were pres ent in laser treated tissue without trypsin digestion, The results of this study support the concept that the primary mechanism responsible for the ef fect of nonablative laser energy is thermal denaturation of collagen in joi nt capsular tissue associated with unwinding of the triple helical structur e of the collagen molecule.