Fitbone vs Precice: Is There a Difference in Regenerate Healing?

The use of intramedullary lengthening nails (ILN) is now an accepted limb reconstruction technique. The most popular motorised systems enable optimal conditions for lengthening, namely stability, sub-millimetre accurate lengthening or retraction and an avoidance of common complications associated with external fixators, such as pin site infections, muscle tethering and regenerate deformity or fracture. The fitbone stainless steel implant utilises an electrical current transmitted by a subcutaneous antenna to drive the motor. The precise intramedullary system, made of titanium, is lengthened by a rotating magnet driven by an electronic remote controller. To prevent nail breakage or deformity, protected partial weight-bearing is initially advised and weight-bearing permitted when sufficient regenerate has formed in the distraction gap. Purpose: The aim of our study was to evaluate and compare the regenerate formation following lengthening using two different motorised ILN. Methods: A retrospective review identified 13 patients (13 nails) who underwent femoral lengthening using the fitbone and 14 patients (16 nails) lengthened with the precise. Patients were matched for age, sex, aetiology and length achieved.Regenerate analysis was undertaken using the pixel ratio value (PVR), calculated on the radiographs when at the desired length, followed at 4, 8, and 12 weeks. The mean of the two highest ratio values were also assessed, as an indicator that full weight-bearing would be permitted. Complications were recorded in relation to bone, soft tissues and implant. Results: Seven males and 6 females underwent 10 antegrade and 3 retrograde fitbone lengthening. Nine male and 5 female underwent 14 antegrade and one retrograde precise lengthening. The mean age at surgery was 36 years in both groups. Mean length in the fitbone group was 41.7, and 46.8 mm in the precise group. All except one fitbone patient reached the desired length (6 mm short). The regenerate fully consolidated in all patients.There was no statistical difference between the PVR measurements of the cortices at any time interval. There was no difference seen in the time for full weight-bearing or a difference seen in the mean PVR measured at this particular time. There were complications seen in the fitbone group including bolt migration, premature consolidation, and soft tissue irritation from the antenna requiring early surgical removal. There were no complications recorded in the precise group. Discussion: This study has demonstrated no difference between the regenerate formation following femoral lengthening, with either the fitbone or precise ILN. All patients had full bone consolidation and there was no difference seen in time to full weight-bearing following completion of lengthening. The rate of complications seen in the fitbone group may be explained by the learning curve of a new implant.There are several limitations including a retrospective review of a small cohort of patients. However, we conclude that both implants successfully lengthen and form excellent regenerate bone. We would recommend that the choice of implant should not be determined by the potential regenerate formation. How to cite this article: Calder P, Robertson A, Tissingh EK,