Early Weight-bearing Accelerates Regenerate Bone Mineralisation: A Pilot Study Comparing Two Post-operative Weight-bearing Protocols Following Intramedullary Limb Lengthening Using the Pixel Value Ratio

Introduction: Limb lengthening is increasingly accomplished by internal lengthening nails. Previous versions of the magnetic lengthening nails made from titanium alloy allowed limited weight-bearing. In contrast, the newer nails made of stainless steel allow increased weight -bearing. An objective comparison of the rate of healing of the regenerate bone based on the weight-bearing capabilities of these two types of lengthening nails has not been evaluated. The hypothesis for the study is that earlier commencement of full weight-bearing in patients treated with the stainless steel STRYDE (R) nail will lead to faster healing of the regenerate bone during intramedullary limb lengthening compared with those treated with the titanium PRECICE (R) nail.Materials and methods:Thirty patients, divided into two groups of 15 each, underwent antegrade intramedullary lengthening of the femur using a magnetic lengthening nail between May 2017 and November 2020. The pixel value ratio (PVR) obtained from serial digital radiographs was used to quantitatively determine the regenerate bone's mineralisation rate. We compared the rate of healing of the regenerate bone in both groups of patients using the PVR.Results: Patients treated with the STRYDE (R) nail achieved unassisted full weight-bearing significantly earlier than patients treated with the PRECICE (R) nail (12 weeks vs 17 weeks for STRYDE (R) and PRECICE (R) nail-lengthened patients, respectively, p = 0.003). There was no difference in the PVR between both groups of patients at the time of full weight-bearing (p = 0.0857). However, patients treated with the STRYDE (R) nail attained a PVR of 1 significantly earlier than those treated with the PRECICE (R) nail (0.0317).Conclusion: The STRYDE (R) nail provides an earlier return of function and full weight-bearing compared with the PRECICE (R) lengthening nail. Earlier commencement of weight-bearing ambulation leads to more rapid mineralisation of the regenerate bone in patients undergoing intramedullary limb lengthening.