Effect of nonablative laser energy on the joint capsule: An in vivo rabbit study using a holmium: YAG laser

Background and Objective The nonablative application of holmium:yttrium‐aluminum‐garnet (Ho:YAG) laser energy to the joint capsule of patients with glenohumeral instability has been found to shrink capsular tissue and to help stabilize the joint. The purpose of this study was to evaluate the effect of nonablative laser energy on the short‐term histological properties of joint capsular tissue in an in vivo rabbit model. Study Design/Materials and Methods Eighteen mature New Zealand white rabbits were used in this study. One randomly selected stifle was treated with laser energy, and the contralateral stifle was sham‐operated. Animals were euthanized immediately after surgery (day 0), at 7 days postsurgery and 30 days postsurgery. Specimens were processed for histology and transmission electron microscopy. Results Laser‐treated samples at day 0 showed diffuse hyalinization of collagen with nuclear karyorrhexis of fibroblasts. Laser‐treated tissue at 7 days postsurgery revealed fibroblast proliferation around and into acellular hyalinized regions of collagen. At 30 days postlaser treatment, areas of fused collagen were greatly reduced as large reactive fibroblasts migrated and secreted matrix. Conclusion This study illustrates the short‐term in vivo tissue response to nonablative laser treatment, where acellular hyalinized regions of collagen are infiltrated by fibroblasts that have used the treated collagen as the framework for migration and secretion of new collagen matrix in order for tissue repair to proceed. Lasers Surg. Med. 20:164–171, 1997. © 1997 Wiley‐Liss, Inc.