Outcomes following femoral lengthening

Patients and Methods

This study was subject to an institutional Research and Development Department review (Research and Development registration number SE.14.038). We performed a retrospective review of all skeletally mature patients who underwent femoral lengthening between September 2009 and October 2014 (n = 84). Patients with nonunion, concurrent deformity correction, lengthening of congenital limb deficiencies, lengthening below an unstable hip and patients who had undergone previous lengthening procedures were excluded (n = 51).

No cases were lost to follow-up. This left 33 femoral lengthening procedures in 22 patients for review with 11 patients undergoing bilateral procedures. Patients who underwent bilateral femoral lengthenings were reviewed as separate cases, whether the lengthenings were simultaneous or consecutive. The first 20 consecutive Precice nail femoral lengthenings performed in our unit were compared to a preceding cohort of 13 cases of lengthening using the LRS external fixator. The Precice procedures were performed by one of the two consultant limb reconstruction surgeons (PC or DG). All the LRS operations were performed by the same consultant limb reconstruction surgeon (PC).

The characteristics of the study groups are summarised in Table I. In the Precice group two patients (four cases) had non-syndromic short stature. A total of four patients (seven cases) with skeletal dysplasia included Léri-Weill dyschondrosteosis, Robinow syndrome and two patients with spondylo-epipyseal dysplasia (one patient only had one femur lengthened as part of this cohort). Three cases (three patients) of post-traumatic leg length discrepancy (LLD) were treated. The other causes for acquired leg length discrepancies included spinal dysraphism in two cases (two patients) and following treatment of adolescent Blount’s disease (one patient). The cause of limb length discrepancy was unknown in three cases (three patients). In the LRS group the diagnosis was short stature in six patients (12 cases). This was syndromic in two patients (one case of Turner’s syndrome and one of Klippel-Feil’s syndrome) and due to stunted growth following chemotherapy for leukaemia in one patient. The cause was unknown in three patients (six cases). One case of post-traumatic LLD was treated.

The mean length of follow-up was 14.7 months (6 to 30) in the Precice group and 28.8 months (10 to 53) in the LRS group.

Pre-operative clinical information was obtained from the hospital records. Pre-lengthening knee range of movement (ROM) was recorded on a proforma. All radiographs were taken in a standard fashion, including erect bipedal length and alignment views.

Results

The groups were comparable with respect to age and gender (Table I).

The results of lengthening are summarised in Table II. The mean lengthening was 59.7 mm (50 to 70) in the Precice and 51.4 mm (25 to 68) in the LRS group. The mean rate of lengthening was greater in the Precice group (0.93mm/day versus 0.83 mm/day with LRS). This was due to more patients in the LRS group having soft-tissue complications.

We had no cases of ‘inadequate’ regenerate in either group. The modified healing index in the Precice group was significantly shorter than seen in the LRS group (31.3 days/cm compared with 47.1 days/cm; p < 0.001). This was mostly due to a shorter consolidation phase in the Precice group (mean 101 days, 42 to 153 versus LRS group mean 204 days, 97 to 329) where the regenerate seemed to form at a faster rate. There were no cases of premature consolidation or regenerate fractures in either group.

We encountered a change in MAD of > 2 mm in eight Precice cases, and regenerate deformity leading to a shift of > 2 mm in MAD in six of the LRS cases. There were no cases with a change in MAD of > 10 mm in either group.

Patients who had been treated by the LRS rail were permitted to weight-bear as tolerated, but no patients were actually able to bear full weight immediately. The Precice group were only permitted to weight-bear once lengthening had been completed and some regenerate was visible, increasing loading depending on the appearance of the regenerate. Overall however, the Precice group were actually able to achieve full weight-bearing without aids earlier than the LRS group (3.6 months, 2 to 7 versus 4.8 months, 3 to 7; p = 0.02).

Complications and re-operations are summarised in Table III. All the pin site infections in the LRS group responded to oral antibiotics. No pins required removal or exchange. There were no cases of deep infection in either group. In one LRS case lengthening was abandoned after 70 days, 10 mm short of the 60 mm goal due to loss of knee ROM that did not respond to treatment. The same patient was diagnosed with a deep vein thrombosis (DVT) when lengthening was stopped which required anticoagulation with warfain. Due to difficulty controlling his anticoagulation, and the associated increased bleeding risk, surgical release was not undertaken and his knee ROM remained reduced at final follow-up with an arc of movement from 0° to 90°. A total of two patients developed fixed flexion deformities at the knee and another four patients had reduced knee flexion following LRS lengthening which responded to a manipulation under anaesthetic with return to full pre-lengthening ROM. In the Precice group three patients required soft-tissue releases due to contractures. In all, two required releases of the ilio-tibial band (ITB) for hip abduction contractures and a third required both hamstring and ITB releases for a fixed flexion deformity (FFD) of the knee which did not respond to physiotherapy. Knee ROM at final follow-up had returned to the pre-lengthening range in all Precice cases and in 12 of 13 LRS cases. There were no implant failures with the Precice nail. A total of two out of 39 distal locking bolts backed out of the nail, both required removal after completion of lengthening due to soft-tissue irritation. In one patient the distracting pin clamp of the LRS seized which required manipulation and adjustment under general anaesthetic.

The pain score during the distraction phase (4.4 versus 8.1; p < 0.001), the pain score during the consolidation phase (2.2 versus 5.3; p < 0.001), and the cosmetic scar rating (3.0 versus 7.5; p < 0.001) were all significantly better in the Precice group (Table IV).

Discussion

The aims of limb lengthening are to achieve the desired length with the fewest complications and as rapid a return to normal function as possible. To compare external fixation and intramedullary implants is difficult due to the contrasting methods. We attempted to compare similar cases of ‘simple’ lengthening without concurrent deformity correction, despite various aetiologies. We feel that these cases would have been suitable to either treatment options and a comparison would be useful to inform future practice.

All cases in the Precice group achieved the desired length and 12 from 13 LRS cases. The mean modified HI was found to be significantly shorter (31.3d/cm versus 47.1d/cm, p < 0.001) in the Precice group. This shorter HI suggests that the regenerate formed more rapidly in the Precice group. The mean time to actual full weight bearing was also significantly shorter in the Precice cases (3.6 months versus 4.8 months, p = 0.02). Although weight bearing is partly dependant on the instructions from the treating surgeon and influenced by whether cases are uni- or bilateral, we feel that the ability to walk unassisted with a normal gait pattern is an indication of restoration of normal function to a limb which allows comparison between the groups.

We used the same low energy technique to perform the corticotomy in both groups. Some authors have expressed concern that intramedullary reaming might destroy endosteal blood supply⁴ which has been thought to be important for regenerate formation in distraction osteogenesis.² It has been noted that preservation of the periosteum was key to producing bone.^4,11,13 We speculate that the shorter HI in the Precice group is due to the bone grafting effect following intramedullary reaming. The inherent stability of the intramedullary device may also be a contributing factor. A histological study might help to compare the regenerate between the two techniques. Conclusions on the difference in regenerate should be interpreted with caution as all the corticotomies where not performed at exactly the same level which could influence regenerate quality.

One of the perceived problems with an intramedullary lengthening device is that the femur is lengthened along the anatomical axis, theoretically leading to medialisation of the knee joint.¹⁸ Previous authors suggested that the mechanical axis moves laterally by 1 mm for every 1 cm lengthened.¹⁸ This observation was not consistent with the results in our series. A change of the MAD of < 2 mm was considered inconsequential, as suggested by previous authors.¹⁸ This was due to the potential for errors in measurement and also because the mechanical axis would remain within the intercondylar eminence of the tibia (Fig. 1). We only encountered a change in MAD of > 2 mm in eight from 20 Precice cases. Paley et al⁴ have suggested that only a change of > 10 mm in the MAD is clinically significant. There were no cases with a change in MAD of > 10 mm in our series. An external fixation system allows lengthening along either the anatomical or mechanical axis of the femur. Mechanical axis lengthening with a monorail device requires very long pins at the distal fixation, which can easily bend leading to deformation of the regenerate into varus.^9,26 For this reason we elected to lengthen along the anatomical axis. We encountered regenerate deformity leading to a shift of > 2 mm in MAD in six from 13 LRS cases, and none were clinically significant (Fig. 2). We did not routinely assess sagittal alignment of the whole limb, only the segment (femur) involved. With both devices the lengthening is in a straight line, not matching the anterior bow of the femur in the sagittal plane. As such, sagittal alignment would therefore likely to be affected in a similar fashion by both devices.

Figs. 1a - 1b

a) Radiographs of a 17-year old male patient with short stature due to Léri-Weill dyschondrosteosis. An anteroposterior (AP) whole leg alignment view pre-lengthening demonstrating the mechanical axis. b) AP whole leg alignment view post-lengthening of 65 mm of both femurs performed sequentially demonstrating no marked change in the mechanical axis of either limb.

Fig. 2

An anteroposterior whole leg alignment radiograph of an 18-year old male patient with short stature during the consolidation phase of simultaneous bilateral femoral lengthening of 60 mm with the use of the LRS system. It demonstrates the typical varus angulation and translation deformity due to the cantilever effect of the soft tissue.

Despite advances in limb lengthening procedures, complications remain a problem.²⁷ Early studies on the Precice nail have suggested high accuracy and few complications.¹ In the Precice group we observed soft-tissue complications in three patients. These cases were all early in our series and all were lengthenings of > 60 mm. Subsequently we started performing prophylactic release of the ITB at time of insertion if the planned lengthening was > 40 mm. Anecdotally, this appeared to be the length when patients complained most of muscle and joint tightness. We also instituted earlier and more regular physiotherapy. There were no further soft-tissue complications after introducing these measures. All cases in the Precice group regained full knee ROM. Other authors have also shown an improved ROM of the knee during lengthening with intramedullary lengthening, preventing muscle contractures and joint subluxations.^4,22,28,29 There were more soft-tissue complications in the LRS group. These results are in keeping with the work of previous authors that showed a permanent loss of more than 15% of pre-operative knee flexion in 8% of external fixator lengthening cases.⁷ We agree that the soft-tissue complications are due to transfixing of the soft tissues¹⁴ and the dragging effect of the pins. Supracondylar corticotomies are thought to result in more loss of knee flexion during lengthening.¹⁵ We only performed two supracondylar corticotomies in retrograde nailing cases with no knee contractures in either case, however the number is too small to draw any significant conclusions.

In two Precice cases, one of the locking bolts backed out during lengthening. The locking bolts are only proximally threaded to allow a thicker core and more strength. Some of the earlier generation lengthening nails reported high rates of uncontrolled lengthening or failure to lengthen.¹⁹ We did not observe this problem with the Precice nail and the mean rate of lengthening was 0.93 mm/day. We had one hardware complication in the LRS group. The distraction unit fused and the subject had to be taken to theatre for adjustment of the LRS and replacement of the distraction unit.

There are no validated patient reported outcome measures specific for limb lengthening. We have attempted to quantify the patients experience and implant tolerance with a number of observations. Patients were significantly happier with the cosmetic appearance of their scars in the Precice group (mean score 3.0 versus 7.5 out of 10, p < 0.001). We retrospectively asked all subjects to rate their pain. Previous authors found significant correlations between the mean contemporaneous scores and the single retrospective scores for pain with the VAS.³⁰ Nevertheless we treat these findings with caution due to the risk of recall bias. Subjects experienced significantly less pain both during lengthening and consolidation (p < 0.001) in the Precice group. More cases in the Precice group indicated that they were able to perform their activities of daily living, including washing, dressing themselves and using the lavatory. All the cases in the Precice group indicated that they would choose to have the treatment again compared to only 68% of cases in the LRS group.

One potential issue with the Precice nail is the cost involved, being approximately 2.5 times more expensive than the LRS system. Although unable to provide a direct comparison, like other authors we can speculate that some of the increased cost is mitigated by fewer complications and re-operations.² The difference in cost may be further offset by the savings due to shorter rehabilitation time after intramedullary lengthening. An accurate analysis is needed to assess the cost effectiveness.

We believe our study is the first in which femoral lengthening with a Precice nail has been compared to an alternative technique. We acknowledge that there are several limitations to our study. Firstly, the two groups were not matched. However, variables such as age, aetiology and lengthening achieved were similar and we attempted to compare cases of lengthening with similar difficulty. Secondly, all data were reviewed retrospectively. A pain diary might have been more accurate than the retrospective application of the VAS, especially in the LRS group who undertook the questionnaire much later, after completion of treatment, than the Precice group. Thirdly, because the series was performed consecutively, the follow-up period in the Precice group is much shorter that the LRS group and does include the surgeons’ learning period for a new implant. This is however a preliminary study and at the time of writing only eight out of the 20 Precice nails had been removed as advised by the manufacturer. Late complications following removal of the device might still occur.

We conclude that we achieved a significantly lower HI and encountered fewer complications with a Precice nail femoral lengthening. Patients experienced better implant tolerance and were more satisfied with their treatment in the Precice group.

Take home message: The Precice nail should now be the method of choice for simple femoral lengthenings.