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.