Evaluation of the first experience of intramedullary nail lengthening using PRECICE ® in a South African limb lengthening and reconstruction unit

Limb length discrepancies are often managed by limb lengthening of the long bones. The process of limb lengthening requires stabilisation of bones, followed by osteotomy and subsequently distraction of the limb segment. Various stabilisation methods exist including external fixation, internal lengthening devices and a combined approach. External fixation techniques like the Ilizarov Method have been the gold standard for limb lengthening. Although external fixation devices have numerous benefits and are widely used, it is associated with various complications like pin tract infection, joint contractures and neurovascular impalement. Combined fixation techniques like lengthening over a nail (LON) or lengthening and then nailing (LATN), entails the removal of the external fixation device after the distraction phase. An intramedullary nail then supports the bone during the consolidation phase. This allows for a reduction of the external fixation time and a more comfortable consolidation phase, but this approach has also been associated with some complications. In an attempt to eliminate the associated adverse effects of both the external and combined fixation approaches, internal lengthening nails Abstract


Introduction
Limb length discrepancies are often managed by limb lengthening of the long bones.The process of limb lengthening requires stabilisation of bones, followed by osteotomy and subsequently distraction of the limb segment.Various stabilisation methods exist including external fixation, internal lengthening devices and a combined approach. 1External fixation techniques like the Ilizarov Method have been the gold standard for limb lengthening. 24][5][6] Combined fixation techniques like lengthening over a nail (LON) or lengthening and then nailing (LATN), entails the removal of the external fixation device after the distraction phase.8][9] This allows for a reduction of the external fixation time and a more comfortable consolidation phase, but this approach has also been associated with some complications. 9,10In an attempt to eliminate the associated adverse effects of both the external and combined fixation approaches, internal lengthening nails were introduced.2][13][14] The ILNs are implanted into the intramedullary canal of long bones, and nail distraction then causes bone lengthening through distraction osteogenesis. 1,116][17] A new ILN system, the PRECICE ® Limb Lengthening System (Ellipse Technologies, California, USA), has recently been FDAapproved for clinical use.The PRECICE ® System is a magnetically operated intramedullary nail where the distraction of the tibia or femur can be controlled with precision and accuracy. 18This system uses an external remote control (ERC) technology to non-invasively adjust the required distraction rates. 18The PRECICE ® System is predicted to be more accurate and reliable than previously used ILNs and to minimise the associated complications. 11,19The PRECICE ® System was therefore evaluated in this study for accuracy of distraction and implant-related complications.

Study patients
The study was a retrospective chart analysis of all consecutive PRECICE ® nail patients.A total of nine patients (11 limb segments) underwent a limb lengthening procedure with this device between May 2013 and October 2014.The patients comprised seven males and two females with a mean age of 34 years (25-49 range).Of the lengthened limb segments, ten femoral and one tibial lengthening procedures were documented.Limb length discrepancies can be due to a number of origins, but in this study the aetiology was reported as post-traumatic for seven limb segments.The remaining four segments were lengthened for stature.All the involved patients were informed about the need for surgical removal after the desired target length was achieved and the regenerate had fully united.The appropriate institutional research ethics guidelines were adhered to.

Treatment, surgery and aftercare
The pre-operative assessment comprised clinical assessment as well as calibrated radiographs measured with a commercially available pre-operative planning software package.A newer version of the PRECICE ® nail was introduced during the course of the study and patients received nails at a ratio of 5:6 (PRECICE 1:PRECICE 2).Nail diameter selection was based on the medullary canal diameter with eight and three patients receiving the 10.7 mm and 12.5 mm nails, respectively.The patient was placed on a fracture table under general anaesthesia.The anatomic axis of the bone was marked using fluoroscopic guidance, the nail length was marked on the limb and the osteotomy level was marked on average 12 cm proximal to the tip of the nail.Pre-drilling of the osteotomy site was performed through a 1 cm incision, thus venting the medullary canal.After placement of a guide wire, sequential reaming of the canal was performed to a diameter at least 1 mm larger than the nail diameter.The nail was brought down to the level of the osteotomy and, after completion of the osteotomy, advanced fully before the nail was locked proximally and distally.Nail functionality was tested intra-operatively using the ERC to distract the nail by 1 mm.Distraction of the nail started as an outpatient procedure at around 10 days after surgery (lag period ranging from 5-19 days) and proceeded at the conventional distraction rate of 1 mm/day in a single adjustment.Ongoing physiotherapy rehabilitation was performed and distraction was monitored by clinical and radiographic examinations every 2 weeks.Physiotherapy focused on maintenance of joint mobility and the prevention of contractures.Toe-touch weight bearing was allowed until consolidation was advanced.
Distraction length, follow-up period and implant-related complications were documented (Table I).The distraction length measured radiographically at final follow-up visit was tabulated against the target distraction length (Table I).The complications were listed as observed during clinical and radiographic examinations.The statistical analysis was performed as outlined in Kirane et al. (2014), where the overall accuracy of distraction was calculated. 11The accuracy reflects the relative value of the target length (prescribed distraction) to the achieved distraction length represented as a percentage.

Results
The patients had a mean target distraction length of 45.18 mm (15 to 65 mm range).The distraction length that was achieved at final follow-up was 44.64 mm (14 to 75 mm range), leading to a mean difference between the target length and the actual distraction length of −0.55 mm (−25 to 10 mm range).The accuracy of distraction was calculated at 103% ± 18%.The average follow-up period was 266 days (81 to 517 days range).
All the regenerates showed satisfactory healing at final assessment.This was based on radiographic analysis showing the presence of neocorticalisation of the regenerate on two views.Two complications were reported.

Variable Value
Target distraction length (mm)* 45.The first complication occurred due to a protrusion of the tip of the nail through the femoral cortex and the nail was subsequently replaced with a trauma nail to stabilise the regenerate until union.This occurred because the tip of the PRECICE ® nail ended in a previously lengthened part of the bone.The previous lengthening was performed with an external fixator and was done to reconstruct a large segmental bone defect in the femur.Due to the nail tip ending within a softer regenerate area, cortical resistance was lost and the distraction force pushed the nail through the cortex.The second complication was the failure of nail distraction in a femoral lengthening, in which case the nail was exchanged and distraction proceeded uneventfully.In this case it is suspected that under-reaming and a too tight interference fit of the nail prevented distraction and that additional reaming might have prevented this complication.
All complications were successfully treated, and there were no other major complications.
The nails were sized so that their tips ended up around 12 cm away from the osteotomy.For the femoral cases the osteotomy was in the proximal part, resulting in a nail that would end just distal to the midshaft region, as can be seen in Figure 1.The telescopic section of the nail is straight and this means that the nail cannot follow the natural sagittal curvature of the femur.This is another reason why the lengthening nail will not fill the whole length of the femur as is the case in trauma nails.Generally the regenerate formation was very satisfactory and consolidation occurred reliably and predictably (Figure 2).

Discussion
Various internal fixation devices have been developed to overcome the current limitations of external fixation in limb lengthening.Most of these devices (Albizzia ® , Fitbone ® and ISKD, etc.) have also been associated with implant-related complications.4][25] It also does not have the capability to back up the nail which is available with the PRECICE ® Limb Lengthening System and useful in cases of poor regenerate formation or over distraction, although this was never required during this study.6][17] The recently FDA-approved PRECICE ® Limb Lengthening System is a magnetically operated intramedullary nail where distraction can be controlled with precision and accuracy via an external remote controller. 18The PRECICE ® System is predicted to be more accurate and reliable than previously used ILNs and to minimise the associated complications. 11,19][13][14] This small study comprised only nine patients with 11 limbs that required lengthening.This serves as a limitation of this study, as a larger patient pool would have been more significant.Subjects were chosen at random and led to a smaller range of gender and limb segment variance.When comparing the accuracy of the distraction to previous studies, an accuracy of 103% was obtained in this study compared to a previous study showing an accuracy of 96%. 11e showed that in the majority of the cases the required distraction length was achieved and even exceeded in some patients using the PRECICE ® nail.The exceeded distraction length was primarily due to the cosmetic limb lengthening patients exceeding their initial lengthening targets.
When comparing the complications to previous studies investigating the efficacy of the PRECICE ® nail system, the results were found to be similar, with limited implantrelated complications. 11,19In previous cases the nail distraction failure also occurred (non-functional magnet mechanism), in which case the nail was replaced and distraction was successfully continued. 11,19In none of the previous studies or in the current study did any of the patients experience intolerable pain during distraction, as no external or painful rotational manipulation of the limbs was required. 19In a previous study done by Kirane et al. (2014), momentary loss of limb ROM was observed in various patients after surgery, and the original ROM recovered within a few months after surgery. 11This was not the case in the current study, as none of the patients experienced temporary loss of ROM in the limbs.This can possibly be attributed to the aggressive post-operative physiotherapy regimen.Non-implant related complications have been observed in previous studies that included premature osteotomy consolidation, delayed bone healing and toe clawing. 11This study did not show various non-implant related complications, but is limited by the small sample size.The occurrence of implant-related and non-implant related complications limits the efficacy of fixation devices used in limb lengthening surgery.The PRECICE ® nail system may represent an accurate and controllable alternative to the existing intramedullary lengthening nails.