Locking plates and their effects on healing conditions and stress distribution: A femoral neck fracture study in cadavers.

Background: Implants are used to stabilize femoral neck fractures to achieve successful fracture healing, but there is still a high rate of fracture non-unions. We compared micromotions in femurs with fractured femoral necks stabilized with three screws with or without a locking plate. We also investigated whether osteoporosis was associated with micromotion magnitudes, and explored the influence of implants on load distribution in the upper femur.

Methods: Twelve pairs of human cadaver femurs with femoral neck fractures (AO/OTA 31-B1) were allocated to fracture fixation by three locked screws or three individual screws. All femurs underwent dual energy X-ray absorptiometry. Physiological subject-specific axial load and torque was applied for 10,000cycles. Micromotion of the head fragment was measured every 100cycles with high-resolution optical motion detection. Load distribution was measured with strain-gauge rosettes attached to the lateral and medial proximal diaphysis.

Findings: The locking plate group showed reduced micromotion about the femoral neck axis (P=0.035, effect size=0.62). No differences were found in valgus-varus or antegrade-retrograde rotations, or in the three translations. Micromotion magnitudes were not associated with osteoporosis. The overall micromotions of the upper femur and the load distribution in the proximal diaphysis were not influenced by fixation type.

Interpretation: The locking plate group showed increased resistance to shear forces compared with the screw group. This effect was not associated with a diagnosis of osteoporosis. The locking plate did not affect the load distribution in the proximal femur.