Locked Plating of Distal Femur Fractures Leads to Inconsistent and Asymmetric Callus Formation

OBJECTIVES: Locked plating constructs may be too stiff to reliably promote secondary bone healing. This study used a novel imaging technique to quantify periosteal callus formation of distal femur fractures stabilized with locking plates. It investigated the effects of cortex-to-plate distance, bridging span, and implant material on periosteal callus formation. DESIGN: Retrospective cohort study. SETTING: One Level I and one Level II trauma center. PATIENTS: Sixty-four consecutive patients with distal femur fractures (AO types 32A, 33A-C) stabilized with periarticular locking plates. INTERVENTION: Osteosynthesis using indirect reduction and bridge plating with periarticular locking plates. MAIN OUTCOME MEASUREMENT: Periosteal callus size on lateral and anteroposterior radiographs. RESULTS: Callus size varied from 0 to 650 mm2. Deficient callus (20 mm2 or less) formed in 52%, 47%, and 37% of fractures at 6, 12, and 24 weeks postsurgery, respectively. Callus formation was asymmetric, whereby the medial cortex had on average 64% more callus (P=0.001) than the anterior or posterior cortices. A longer bridge span correlated minimally with an increased callus size at Week 6 (P=0.02), but no correlation was found at Weeks 12 and 24 postsurgery. Compared with stainless steel plates, titanium plates had 76%, 71%, and 56% more callus at Week 6 (P=0.04), Week 12 (P=0.03), and Week 24 (P=0.09), respectively. CONCLUSIONS: Stabilization of distal femur fractures with periarticular locking plates can cause inconsistent and asymmetric formation of periosteal callus. A larger bridge span only minimally improves callus formation. The more flexible titanium plates enhanced callus formation compared with stainless steel plates.