Micromotion at a femoral osteotomy stabilized with a retrograde interlocking intramedullary nail.

Abstract

Retrograde nails are becoming used increasingly in the trauma setting and the indications are expanding. The goal of this study was to evaluate micromotion at fracture sites in the proximal half of the femur stabilized with a retrograde intramedullary nail to determine the effects of fracture location, canal fill, and screw configuration. Composite femurs were loaded in simulated single-leg stance while measurements of micromotion were made using linear variable differential transducers and motion analysis. Part one of the study compared differences by fracture location (subtrochanteric vs. proximal third vs. mid-shaft). Part two determined the effects of canal fill (13 vs. 10 mm nail) and proximal interlocking screw configuration on micromotion in the setting of subtrochanteric fracture. Subtrochanteric fracture location led to significantly more axial displacement compared to the other locations (p < 0.05). Reduced canal fill led to more coronal rotation (p < 0.05) and likely more axial displacement (p = 0.06). Screw configuration was important for axial displacement (p < 0.05), particularly in the non-canal filling condition where the proximal screw configuration with only one screw in the more proximal location had increased micromotion compared to one distal. Fracture location, nail size, and proximal locking screw configuration are all important to the stability of the fracture construct. In subtrochanteric fractures, surgeons should consider using a canal filling nail with either two screws or the distal screw only, or using a different nail design.