Synovial regeneration in the equine carpus after arthroscopic mechanical or carbon dioxide laser synovectomy.

OBJECTIVE: To compare synovial regeneration in the equine carpus after mechanical or CO(2) laser synovectomy. STUDY DESIGN: Arthroscopic partial synovectomy was performed in the radiocarpal and intercarpal joints. SAMPLE POPULATION: Twelve horses, 3 to 6 years of age, were randomly divided into 3 groups. METHODS: The antebrachiocarpal and intercarpal joints in each horse were randomly assigned a treatment such that each horse had one joint treated as a control (arthroscopic lavage), one in which a mechanical or CO(2) laser partial dorsal carpal synovectomy was performed, and one in which a combination of the mechanical and laser techniques was performed. The groups were euthanized for collection of specimens, respectively, at 1, 3, and 6 months postoperatively. The synovial membrane was evaluated grossly, histologically, and by transmission and scanning electron microscopes (TEM and SEM). RESULTS: The synovial villi failed to regenerate in all groups. At 1 month, the intimal cell layer was incomplete and the surface was still granulating. At 3 months, intimal regeneration was complete but more mature in the CO(2) laser synovectomy groups than in the mechanical synovectomy groups. Intimal regeneration was complete in all groups at 6 months. The subintima was replaced with fibrous tissue that separated the original subintimal vascular bed from the regenerated synovial surface. The CO(2) laser required preliminary training to operate effectively, and the air environment altered the intraoperative evaluation of the synovectomy site. CONCLUSIONS: Villous regeneration does not occur in horses after surgical synovectomy. All synovial membranes healed with a fibrous subintima and less populated intima. The CO(2) laser is capable of performing a more superficial synovectomy than that achieved with mechanical synovectomy using a motorized arthroscopic synovial resector. CLINICAL RELEVANCE: Mechanical or CO(2) laser synovectomy may be performed in the horse; however, additional evaluation is needed to determine the physiological significance of the lack of villus regeneration in this species. A combination of the resection techniques is not advised because of the increased risk of full-thickness capsular defects.