Holmium:YAG laser-assisted capsular shift in a canine model: intraarticular pressure and histologic observations.

The purpose of this study was to determine the initial effects of Holmium:YAG laser energy on the shoulder joint capsule. A new surgical procedure to correct shoulder joint instability uses Holmium:YAG laser energy to cause "shrinkage" of joint capsular tissues. To date there has been no information concerning an intraoperative measurable end point for the application of laser energy at surgery or the resultant depth and degree of tissue alteration. Seven greyhound dogs were used in this study. Preoperative intraarticular pressures (IAP) were measured on entry and after injection of 10 ml of solution. Laser energy was applied to the cranial medial glenohumeral ligament and joint capsule of all right shoulders with arthroscopic visualization. The unoperated left shoulders served as the control group. Six weeks after surgery pressure measurements were performed on both shoulders. A "second look" arthroscopy was performed on the shoulders. After euthanasia was performed, the anterior capsular tissues were harvested from both shoulders for histologic examination. The specimens were inspected by three blinded examiners. After 6 weeks the postoperative laser-treated IAP were higher than the same joint preoperative IAP in four of six dogs for both static nondistension and 10 ml distension measurements. At this same interval the marked tissue damage of the treated capsule was easily discerned by blinded observers. On histologic evaluation the laser-treated capsule showed synovitis and pericapsular tissue reactivity. The depth of the injury was beyond the joint capsule into the pericapsular tissue. It was not possible to determine the end point of the capsular "shrinkage" operation by combined pressure/volume intraoperative measurements. There was no uniform joint capsule compliance at 6 weeks. The histologic changes were extensive in both magnitude and depth. Future studies in this animal should include decreased laser energy plus other means of monitoring the intraoperative effects of laser use.