Callus Patterns in Femoral Lengthening over an Intramedullary Nail

Abstract

Our objectives were to evaluate callus patterns seen in femoral lengthening over an intramedullary nail by Li classification regarding shape and type and to predict the result while using the nail to reduce the external fixation period and its complications. Eight hundred digital radiographs of 15 patients with 15 segments of femur shortening who underwent femoral lengthening with a monolateral external fixator over an intramedullary nail were analyzed retrospectively by four observers. Each radiograph was studied for callus shape, feature type, and callus density using pixel values. The classification was tested for concurrence and reproducibility by interobserver studies and callus patterns were compared with treatment indices to evaluate how they correlated with the outcome. Mean length gained was 4.5 cm (range: 2-8 cm). External fixator index (EFI) was 21.68 days/cm. Average distraction consolidation index (DCI) was 48.49 days/cm. Fusiform callus was seen in three cases, cylindrical in seven, and lateral in five. The homogenous pathway had higher DCI (43.7) than the heterogeneous pathway (32.9), and mixed pathways making up the rest had a DCI of 50.1. Pixel value of callus showed gradual increase in density until 20-24 weeks, then density gradually fell for 8 weeks, again increased after 32 weeks, again gradually fell, and was comparable to adjacent normal bone by 44-48 weeks. Our results suggest that the Li classification can be satisfactorily applied to lengthening procedures over intramedullary nails. The radiologic pattern and pixel value of regenerate can be correlated with the clinical outcome and can be an aid of prognostic value for the surgeon. (C) 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29: 1106-1113, 2011