A biomechanical comparison of conventional versus cable pin fixation for transverse patellar fractures

Background: Transverse patellar fractures require fixation that anatomically restores continuity of the knee extensor complex and resiliency to the loads of early postoperative knee mobilization. The objective of this study was to evaluate the biomechanical fixation strength of three patellar osteosynthesis techniques. Methods: Transverse osteotomies were created in 24 custom fourth-generation composite left patellae, randomized into three equal groups for osteosynthesis fixation: Group I, modified anterior tension wiring; group II, cannulated lag screws with anterior tension wiring; group III, cable pin fixation system. All patellae were loaded in simulated 60-degree knee flexion at 15 mm/min until complete failure. Results: Mean load to failure for group I (415.14±150.10 N) was significantly less than the load for group II (814.37±281.98 N), P=0.023 and group III (1103.64±358.70 N), P<0.0001. Mean stiffness for group II and group III were 51.60±5.01 N/mm and 46.53±3.09 N/mm, respectively, and statistically higher (P<0.0001) than group I (23.86±7.02 N/mm). Mean medial gapping in group III (10.33±6.50 mm) was statistically higher (P=0.041) than that in group II (4.59±3.19 mm). Conclusions: Greater compression across the fracture site was likely in the more robust constructs of cannulated lag screws with anterior tension wiring (group II) and cable pin fixation (group III), which may allow more timely and aggressive postoperative mobilization.