Abstract
This study aimed to compare the failure rates of two different sizes of plates and screws to stabilize critical-sized (7 mm) femoral defects in male Sprague‒Dawley rats (aged 10 weeks). Femoral defects were stabilized with either a 4-hole plate (length 29 mm, thickness 1 mm, 10 rats, Group 1) and 4 cortical screws (diameter 2 mm) or with a 6-hole plate (length 30 mm, thickness 0.6 mm, 9 rats, Group 2) and 4 cortical screws (diameter 1.5 mm). A polymethylmethacrylate spacer was inserted into the defects to reproduce the first stage of the induced membrane technique. Radiographic evaluations, macroscopic and histologic assessments of the induced membranes were conducted at 1 week and 4 weeks. No implant failure occurred in Group 1 whereas in Group 2, 4/9 (44.4%) implant failures occurred during the follow-up (p = 0.03). On histomorphometry, cell density was higher in Group 1 (4996 ± 716 cells / mm²) than in Group 2 (3500 ± 728 cells/mm²) (p = 0.0195) but the membrane thickness in Group 1 (735 ± 44 μm) was non-significantly lower than in Group 2 (979 ± 165 μm) (p = 0.4). This study suggests that, in rat models of critical-sized femoral defects (7 mm) to study the induced membrane technique, fixation plates with a thickness of 1 mm and four screws (2 mm in diameter) provide stable fixation without implant failure. In contrast, thinner plates (< 1 mm) combined with screws of smaller diameter (1.5 mm) result in a high rate of implant failure.