Precision of the PRECICE internal bone lengthening nail

Abstract

Background: Previous designs of internal bone lengthening devices have been fraught with imprecise distraction, resulting in nerve injuries, joint contractures, nonunions, and other complications. Recently, a magnet-operated PRECICE nail (Ellipse Technologies, Inc, Irvine, CA, USA) was approved by the FDA; however, its clinical efficacy is unknown.

Questions/purposes: We evaluated this nail in terms of (1) accuracy and precision of distraction, (2) effects on bone alignment, (3) effects on adjacent-joint ROM, and (4) frequency of implant-related and non-implant-related complications.

Methods: We reviewed medical and radiographic records of 24 patients who underwent femoral and/or tibial lengthening procedures using the PRECICE nail from August 2012 to July 2013 for conditions of varied etiology, the most common being congenital limb length discrepancy, posttraumatic growth arrest, and fracture malunion. This group represented 29% of patients (24 of 82) who underwent a limb lengthening procedure for a similar diagnosis during the review period. At each postoperative visit, the accuracy and precision of distraction, bone alignment, joint ROM, and any complications were recorded by the senior surgeon (SRR). Accuracy reflected how close the measured lengthening was to the prescribed distraction at each postoperative visit, while precision reflected how close the repeated measurements were to each other over the course of total lengthening period. No patients were lost to followup. Minimum followup from surgery was 3 weeks (mean, 14 weeks; range, 3-29 weeks).

Results: Mean total lengthening was 35 mm (range, 14-65 mm), with an accuracy of 96% and precision of 86%. All patients achieved target lengthening with minimal unintentional effects on bone alignment. The knee and ankle ROM were minimally affected. Of the complications requiring return to the operating room for an additional surgical procedure, there was one (4%) implant failure caused by a nonfunctional distraction mechanism and six (24%) non-implant-related complications, including premature consolidation in one patient (4%), delayed bone healing in two (8%), delayed equinus contracture in two (8%), and toe clawing in one (4%).

Conclusions: We conclude that this internal lengthening nail is a valid option to achieve accurate and precise limb lengthening to treat a variety of conditions with limb shortening or length discrepancy. Randomized, larger-sample, long-term studies are required to further confirm clinical efficacy of these devices, monitor for any late failures and complications, and compare with other internal lengthening devices with different mechanisms of operation.

Level of evidence: Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.

Fig. 1

The PRECICE^® nail of the selected size and diameter is assembled by connecting the two telescopic nail pieces as per manufacturer guidelines.

Fig. 2

The internal architecture of the PRECICE^® nail consists of a permanent rare earth magnet that is connected to a gear box and screw shaft assembly.

Fig. 3A–B

(A) The internal magnet within the nail is localized intraoperatively using a wire under fluoroscopic guidance. (B) The external controller unit is placed directly over the internal nail magnet under fluoroscopy and the location is marked on the skin using a marker pen.

Fig. 4

Distraction of the nail is initiated during the early postoperative period, typically Day 5 for the femur and Day 7 for the tibia. The external remote controller unit is applied on the skin marking corresponding to the location of the internal nail magnet. Distraction is performed at the rate of 1 mm/day split into 0.33 mm three times a day or 0.25 mm four times a day.

Fig. 5A–C

AP (left) and lateral (right) radiographs show distraction measurements and consolidating bone regenerate in selected representative case examples. (A) A 14-year-old boy underwent anterograde femoral lengthening for a 3.8-cm congenital leg length discrepancy and 20° external rotation deformity. (B) A 30-year-old man underwent retrograde femoral lengthening for a 3.6-cm leg length discrepancy, 7° genu valgum, and 10° external rotation deformity due to posttraumatic growth arrest. (C) A 41-year-old man underwent tibial lengthening for 4.0-cm shortening from bone loss and tibiotalocalcaneal arthrodesis. Radiographs also show additional screw stabilization across the proximal tibia-fibula joint (green arrow), a lateral blocking screw to prevent valgus malalignment (red arrow), and a posterior blocking screw to prevent procurvatum deformity (black arrow).

Fig. 6

The accuracy and precision of distraction of the PRECICE^® nail were calculated by comparing performed distraction to achieved lengthening. The plot shows the mean and SD of multiple postoperative measurements of distraction versus lengthening for all femoral and tibial lengthenings combined (n = 25).