The biologic response to laser thermal modification in an in vivo sheep model

The purpose of this study was to evaluate the effect of nonablative laser e nergy on mechanical, histologic, ultrastructural, and biochemical propertie s of joint capsular tissue in an in vivo sheep model. Femoropatellar joint capsule was treated with the holmium:yttrium-aluminum-garnet laser via an a rthroscope, and tissues were harvested immediately after surgery, or at 3, 7, 14, 30, 60, 90, and 180 days after surgery (n = 8/group). Laser treatmen t caused significant decreases in tissue stiffness from 0 to 7 days after s urgery, then stiffness gradually increased after 14 days. Tissue strength w as lowest 3 days after laser treatment. Histologic examination revealed imm ediate collagen hyalinization and cell necrosis, followed by active cellula r response characterized by extensive fibroblast migration and capillary sp routing. Tissue appeared to be normal histologically 60 days after surgery; however, collagen fibrils remained uniformly small. This study showed an a ctive tissue response secondary to thermal modification with concomitant re covery of mechanical properties by 30 days after surgery. Whether the shrin kage or joint stability was maintained with time remains to be evaluated. T o clarify the advantages and disadvantages of this technique, a carefully c ontrolled clinical trial with long term followup should be performed.