Evaluating the Utility of the Pixel Value Ratio in the Determination of Time to Full Weight-bearing in Patients Undergoing Intramedullary Limb Lengthening

Introduction: Limb lengthening using intramedullary nails is an increasingly popular method of achieving limb length equalisation. Currently, the decision regarding when to commence full weight-bearing (FWB) remains largely subjective. Objective criteria for determining the proper timing of FWB would be helpful to limb lengthening surgeons. This study examines using the pixel value ratio (PVR) as an objective method to determine the time to FWB for patients being lengthened with an intramedullary nail. Materials and methods: A retrospective chart review of 42 patients who underwent unilateral lengthening of the femur was undertaken. The PVR of all four cortices of the regenerate bone was monitored throughout the distraction and consolidation stages to determine the ratio at the time of FWB. Results: Clinically and radiologically determined FWB was achieved at a mean time of 125.7 +/- 30.1 days from surgery. The mean PVR at the time of FWB was 0.94. The medial cortex healed fastest with a mean PVR of 0.96, while the posterior cortex healed slowest with a mean PVR of 0.92. Conclusion: The PVR is a quick and reliable method to objectively assess the state of healing of the regenerate bone during distraction osteogenesis. We observed that there were no adverse effects when subjects commenced FWB when three out of the four cortices had a PVR of at least 0.93.