Objectives: This study compared callus formation in distal femur fractures stabilized with locking plates and intramedullary nails to test the hypothesis that locking plates induce less fracture callus than IM nails.

Design: Retrospective case matched study.

Setting: Two orthopaedic trauma centers.

Patients: 174 distal femur fracture were reviewed to extract cases treated with retrograde IM nails (NAIL group, n=12). These were then individually matched to cases treated with locking plates (Plate group, n=12).

Intervention: Retrograde IM nailing or locking plate fracture fixation.

Outcome Measures: Periosteal callus was measured on lateral and antero-posterior radiographs taken at 12 weeks after injury using validated software to objectively extract the size of peripheral callus from digital radiographs.

Results: The NAIL group had 2.4 times more callus area per location (231 ± 304 mm2) than the PLATE group (95 ± 109 mm2, p=0.028). Compared to the PLATE group, the NAIL group had 3.4 times more callus anteriorly (p=0.31), 2.6 times more callus posteriorly (p=0.25), and 2.3 times more callus medially (p=0.16). At 12 weeks after injury, no or minimal callus for secondary bone healing (<20 mm2) was present in 20% of callus locations in the NAIL group and in 54% of callus locations in the PLATE group.

Conclusion: Significantly less periosteal callus formed in fractures stabilized with locking plates than with IM nails. This result is likely multifactorial and further study of the interaction between construct stiffness and fracture healing in the distal femur is warranted.