ENHANCED FIXATION STABILITY IN MEDIAL MALLEOLAR FRACTURES: COMPARISON OF SINGLE VERSUS DOUBLE BICORTICAL SCREWS IN HEALTHY AND OSTEOPOROTIC BONE MODELS

Medial malleolar fractures are common orthopaedic injuries, particularly in osteoporotic populations, and present unique challenges due to reduced bone density and an increased risk of fixation failure. The question of whether bicortical screws, which have demonstrated biomechanical advantages over unicortical constructs, can provide better stability in osteoporotic bone, remains a significant and relevant one. This study aims to investigate the biomechanical performance of single versus double bicortical screw fixation in medial malleolar fractures across healthy and osteoporotic bone models. This study utilized 32 fourth-generation composite Sawbones tibial models, including 16 mimicking healthy bone (17 pcf density) and 16 mimicking osteoporotic bone (7 pcf density). These models were divided into four groups ( n = 8 per group) based on fixation configuration: one or two bicortical screws in healthy or osteoporotic bone. Medial malleolar fractures were simulated and reduced using pointed reduction clamps, followed by fixation in a lag-by-technique fashion. The constructs underwent axial compression testing using a servo-hydraulic system until failure, defined as fracture displacement >5 mm. Load-to-failure and stiffness values were calculated and analyzed using t-tests and ANOVA to compare group differences. Figure 1 shows the experimental set up. Constructs with two bicortical screws demonstrated significantly higher load-to-failure in both healthy (mean: 1747 N vs. 1090 N, p = 0.02) and osteoporotic bone (mean: 935 N vs. 509 N, p = 0.01) compared to single-screw constructs. While higher in the two-screw groups, stiffness values did not reach statistical significance (healthy: 280.42 N/mm vs. 192.19 N/mm; osteoporotic: 178.14 N/mm vs. 134.22 N/mm). Osteoporotic bone exhibited substantially lower biomechanical performance compared to healthy bone across all constructs; however, the use of two screws improved load distribution and reduced fixation failure. This study demonstrates that two bicortical screws provide superior biomechanical performance in medial malleolar fracture fixation compared to one screw, particularly in osteoporotic bone. These findings suggest that surgeons should consider using two bicortical screws to optimize fixation stability and improve outcomes in patients with reduced bone quality. The potential for future research to explore clinical applications and long-term consequences is significant, as it could further validate and enhance the understanding of these findings.