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 defe cts by either laser or drilling. The purpose of the research was to de termine 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 par tial thickness and full-thickness cartilage defects of standardized si ze with both excimer laser and drilling. Light and scanning electron m icroscopic examinations of the repair tissue showed that healing of os teochondral defects created by laser may be delayed compared with defe cts created by drilling, for at least 6 weeks postoperatively. Even th ough there initially was a considerable delay in healing in the laser group, neither laser nor drilling had any appreciable effects on the m echanical properties of the repair tissue, as demonstrated by biomecha nical testing at 14 weeks. Specifically, the repair cartilage in the d efects 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 thickn ess, 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 bot h types of defects was pooled, and the values were compared with those for contralateral (control) tissue. The control tissue had a 51% grea ter aggregate modulus (0.59 +/- 0.18 MPa, p = 0.0001), 34% less Poisso n'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 inf erior to that of normal control tissue.