Effect of absorbable poly-D, L-lactide acid rod on development of rabbit epiphyseal plate / 第二军医大学学报

ABSTRACT

Objective: To assess the influence of absorbable poly-D, L-lactide acid (PDLLA) rods on the development of epiphyseal plate after implanted into the distal femoral epiphysis in skeletally immature New Zealand white rabbits. Methods: Seventy-five New Zealand white rabbits were evenly randomized into 3 groups according to the diameter of rods 1.5 mm PDLLA rod group, 2.2 mm PDLLA rod group, and 3.2 mm PDLLA rod group. The absorbable PDLLA rods were placed into a drill hole of equal size in the intercondylar portion of the right femur, crossing the central portion of epiphyseal plate; empty drill holes of same size were made across the left femoral physis, which served as a control. The area of injured epiphyseal plates was calculated before operation. The animals were sacrificed at 3, 6, 9, 12 and 24 weeks after operation. Measurement of femur bone length, radiographic measurement of both knee joint valgus angles, histology sections and transmission electron microscopic examination of the physis and adjacent bones were performed to evaluate the influence of implanted rods on epiphyseal plate. Results: The proportions of injured area caused by the drill holes in 1.5 mm group, 2. 2 mm group, and 3.2 mm group were (1.86±0.10)%, (4.03±0.52)% and (7.52±1.02)%, respectively. At 24 weeks after operation, femur bone lengths (mm) of experimental and control sides were 90.60±0.55 and 90.27±0.84 in 1.5 mm group,87.53±0.67 and 87.06±0.78 in 2.2 mm group, and 85.30±1.39 and 84.91±1.40 in 3.2 mm groups, respectively; their knee joint valgus angles (°) were 7.863±1.26 and 8.110±1.18 in 1.5 mm group, 8.858±1.30 and 9.453±1.95 in 2.2 mm group, and 11.90±2.80 and 14.448±5.17 in 3.2 mm group, respectively. There was no significant difference in femur lengths and valgus angles between 2 sides in each group (P>0.05). Both femur bone lengths in 3.2mm group were shorter than those in the 1.5 mm and 2.2 mm groups. No abnormalities of cartilage cells were observed, without obvious histological evidence of inflammation; only nonspecific foreign body reaction and macrophage infiltration were noticed. Conclusion: PDLLA rod itself does not cause any disturbance to the development of the epiphyseal plate. The growth disturbance of epiphyseal plate depends on the area of injured epiphyseal plate; a injured area over 7% of epiphyseal plate may cause the growth disturbance of epiphyseal plate.