Increased stiffness with medial column screw supplementation of lateral locking plate for distal femur fractures: a biomechanical study

Introduction: We propose and assess the biomechanical stability of medial column screw supplementation in a synthetic distal femur fracture model.

Materials and methods: Twenty-four low density synthetic femora modeling osteoporotic, intraarticular distal femur fractures with medial metaphyseal comminution were split into two fixation groups: (1) lateral locking distal femur plate (PA- plate alone) and (2) lateral locking distal femur plate with a 6.5 mm fully threaded medial cannulated screw (PWS- plate with screw). Cyclic biomechanical testing included 5 steps of 10,000 cycles with each step increasing axial loads starting at 0.5xBW (BW = 80 kg) up to 2.5xBW. Discrete stiffness was calculated for each step and cumulative stiffness was calculated across the entire protocol. Outcomes of interest included cumulative stiffness, discrete stiffness, and instrumentation failure.

Results: Seven of the PA models had failure during testing. No failures were seen in the PWS group. PWS had 19.8% higher cumulative stiffness compared to PA (676.3 N/mm vs 809.8 N/mm; P = 0.014). Discrete stiffness showed < 1% differences at lower loads, but increasing loads found the PWS group with 12% greater discrete stiffness than the PA group (879.1 N/mm vs 983.8 N/mm; P = 0.028).

Conclusion: This is the first study to evaluate the contribution of a medial column screw in a distal femur fracture model. PWS had superior stiffness and few failures compared to PA. Applied clinically, a medial column screw can increase construct stability in the setting of complex distal femur fractures with minimal increase in operative time, patient morbidity and cost.