Acute and long-term response of the meniscus to partial meniscectomy using the holmium: YAG laser

The purpose of this study was to evaluate the histological effects of holmium:YAG laser partial meniscectomy in an in vivo rabbit model and compare it with scalpel partial meniscectomy at selected time intervals. Twenty-four adult male New Zealand rabbits underwent bilateral partial medial meniscectomies through the avascular zone. In the right knee, partial medial meniscectomy was performed using a standard surgical blade; in the left knee, an anatomically similar partial medial meniscectomy was performed using a Ho:YAG laser (Coherent, Santa Clara, CA). All animals were randomized and three animals were killed at postoperative days I and 3, and postoperative weeks 1, 2, 3, 4, 6, and 10. Samples of all medial and lateral menisci, with attached synovium and vascular rim, from both knees were harvested and submitted for histological and/or ultrastructural examination. The results indicate that (1) at all time periods, laser cut menisci had more cell loss and matrix degradation; (2) synovial necrosis was more common in laser-treated knees; (3) the Ho:YAG laser creates three zones of damage in the meniscal fibrocartilage: a zone of fibrin and debris at the incision site, a zone of necrosis characterized by degeneration of the collagen and loss of viable cells, and a zone of thermal change characterized by collagen degeneration. The zone of thermal change, with its histological injury was thought at the time of surgery to be the viable border. The zone of thermal change may act as a barrier to delay healing, and the scalpel produced a consistently straighter cut.