Biomechanical analysis of distal femur fracture fixation: fixed-angle screw-plate construct versus condylar blade plate.

OBJECTIVE: The objective of this study is to establish the relative strength of fixation of a locking distal femoral plate compared with the condylar blade plate.

METHODS: Eight matched pairs of fresh-frozen cadaveric femurs were selected and evaluated for bone density. A gap osteotomy model was used to simulate an OTA/AO A3 comminuted distal femur fracture. One femur of each pair was fixed with the blade plate; the other, with a locking plate. After 100 N preload and 10,000 cycles between 100 N and 1000 N, total displacement of each specimen was assessed. After completion of cyclic loading, maximum load to failure was tested.

RESULTS: Significantly greater subsidence (total axial displacement) occurred with the blade plate (1.70 +/- 0.45 mm; range, 1.21-2.48 mm) than with the locking plate fixation (1.04 +/- 0.33 mm; range, 0.67-1.60 mm) after cyclic loading (P = 0.03). In load-to-failure testing, force absorbed by the locking plate before failure (9085 +/- 1585 N; range, 7269-11,850 N) was significantly greater than the load tolerated by the blade plate construct (5591 +/- 945 N; range, 3546-6684 N; P = 0.001). Variability in bone mineral density did not affect the findings (fixed angle distal femoral plate r = 0.1563; condylar blade plate r = 0.0796).

CONCLUSIONS: The locking screw-plate construct proved stronger than the blade plate in both cyclic loading and ultimate strength in biomechanical testing of a simulated A3 distal femur fracture. Although differences were small, the biomechanical performance of the locking plate construct over the blade plate may lend credence to use of the locking plate versus the blade plate in the fixation of comminuted distal femur fractures.