EFFECTS OF EXCIMER-LASER ON HEALING OF ARTICULAR-CARTILAGE IN RABBITS

This study examined healing of 1.0 mm diameter defects in rabbit knee articular cartilage for as long as 14 weeks after creation of the defects by either laser or drilling. The purpose of the research was to determine the effects of laser debridement of cartilage on the intrinsic biomechanical properties of the repair tissue. We therefore imitated chondral shaving and subchondral abrasion of cartilage by creating partial thickness and full-thickness cartilage defects of standardized size with both excimer laser and drilling. Light and scanning electron microscopic examinations of the repair tissue showed that healing of osteochondral defects created by laser may be delayed compared with defects created by drilling, for at least 6 weeks postoperatively. Even though there initially was a considerable delay in healing in the laser group, neither laser nor drilling had any appreciable effects on the mechanical properties of the repair tissue, as demonstrated by biomechanical testing at 14 weeks. Specifically, the repair cartilage in the defects in the laser group had the following material properties (mean +/- SD): aggregate modulus, 0.40 +/- 0.24 MPa; Poisson's ratio, 0.37 +/- 0.08; permeability, 3.72 +/- 4.28 x 10(-15) m(4)/N . s ; and thickness, 0.20 +/- 0.06 mm. The corresponding values for the defects in the drilling group were 0.39 +/- 0.23 MPa, 0.34 +/- 0.09, 3.82 +/- 3.44 x 10(-15) m(4)/N . s , and 0.22 +/- 0.09 mm. The repair tissue from both types of defects was pooled, and the values were compared with those for contralateral (control) tissue. The control tissue had a 51% greater aggregate modulus (0.59 +/- 0.18 MPa, p = 0.0001), 34% less Poisson's ratio (0.23 +/- 0.25, p = 0.0001), 48% less permeability (1.94 +/- 0.96 x 10(-15) m(4)/N . s, p = 0.0001), and was 29% thicker (0.27 +/- 0.08 mm, p = 0.0001). Thus, as evidenced by biomechanical testing at 14 weeks, neocartilage in both superficial and osteochondral defects, created by either laser or a drill, exhibited structural integrity inferior to that of normal control tissue.