Biomechanical comparison of different double plate constructs for distal supracondylar comminuted femur fractures (AO/OTA 33-A3).

Abstract

Dual plating for distal femoral fractures, especially with a metaphyseal comminution, is biomechanically superior compared to single lateral plating, promotes fracture union and prevents complications. However, the optimal placement and length of the additional medial plate are still unknown. Thus, we aimed to biomechanically compare three different double plate constructs for distal femoral fractures. A distal femoral fracture with a metaphyseal comminution (AO/OTA 33-A3) was created in synthetic femora and stabilized according to the following groups of 6 specimens each: Single lateral plate (SP), double plate with anteromedial oblique locking plate (DPOB), double plate with parallel medial locking plate with 4 screws (DP4S) and double plate with parallel medial locking plate with 6 screws (DP6S). Afterwards, the femora were tested axially with a quasi-static load of 400 N as well as torsionally with 5 Nm of internal and external rotation. Interfragmentary motion and rotation were measured with an optical 3D motion analysis system. Fracture gap motion and varus-valgus tilt under axial testing were significantly lower with DPOB, DP4S and DP6S than with SP (p = 0.02) without a significant difference between the double plate constructs. DP4S and DP6S showed a significant lower anteroposterior tilt under axial loading than SP (p = 0.02), whereas DPOB showed no significant difference compared to SP but had a significantly higher anteroposterior tilt than DP6S (p = 0.02). Under internal and external rotation testing, anteroposterior shift was significantly different, and axial rotation was significantly lower with DPOB, DP4S and DP6S compared to SP (p = 0.02) without a significant difference between the double plates. Dual plating is biomechanically superior under axial and torsional loading compared to the traditional single lateral plating for distal femoral fractures with metaphyseal comminution. A parallel arrangement of double plates is biomechanically more effective in resisting anteroposterior tilt, whereas the length of parallel medial plates (with 4 or 6 screws) has no influence on the biomechanical performance.