Augmentation of Fracture Healing Using Soft Callus.

Danoff, Jonathan R; Aurégan, Jean-Charles; Coyle, Ryan M; Burky, Robert E; Rosenwasser, Melvin P

OBJECTIVES This study sought to investigate the effect of soft callus removal and reapplication in a rat closed femur fracture model. We hypothesized that removing soft callus will impair fracture healing, whereas reapplication will facilitate healing. METHODS A closed midshaft femur fracture was created in 78 rats and stabilized with an intramedullary wire. Seven days later, rats were equally divided and fractures surgically exposed. In the control group, no callus was removed, whereas in the callus removal group CR(-) group, the callus was removed and in the callus replaced group CR(+), callus was removed and replaced. Half of the rats were killed at 4 and 7 weeks. Fracture healing was graded with radiographs and callus volume measured with micro-CT. Mechanical torsion properties were measured, and histologic analysis was conducted. RESULTS At both end points, evidence of delayed healing was found on radiographs and micro-CT in CR(-) rats (P = 0.0001), whereas CR(+) rats showed normal fracture healing compared with controls. The normalized callus volume was similar in all groups at both end points. At 7 weeks, the maximum stiffness in CR(-) rats was 68% less than control (P = 0.0001). Stiffness increased 55% in CR(+) rats from CR(-) rats (P = 0.0017). Histology supported our findings with complete endochondral ossification in CR(+) rats but wide areas of hyaline cartilage in CR(-) rats at 7 weeks. CONCLUSIONS Removal of soft callus in a rat model delays fracture healing at early and late time points, whereas replacement mitigates these negative consequences. Replacing the soft callus should be considered in all osteosynthesis procedures.