For group A, the lengthening goal was achieved in 28 (88%) of 32 patients; 2 patients had slow healing and 2 patients had premature consolidation. For group B, the lengthening goal was achieved in 26 (87%) of 30 patients; 2 patients had subluxation (1 knee and 1 hip) and 2 patients had delayed union.
Adverse events are listed in Table 3. Group A had 26/32 (81%) affected segments and developed 58 events: 12 patients had 1 event, 9 patients had 2 events, 2 patients with 3 events, 3 patients had 4 events, and 2 patients had 5 events. Group B had 18/30 (60%) affected segments and a total of 31 events: 8 patients had 1 event, 7 patients had 2 events, and 3 patients had 3 events. Both groups had similar rates of obstacles and complications. The only significant difference between groups was found in the total problems (P<0.001), specifically with pin site/superficial infection (P<0.0001).
Limb lengthening in patients with CFD with/without FH is a challenge to orthopaedic surgeons, especially for severe cases.3 In the literature, femoral lengthening in these patients is associated with an increased incidence of complications compared with patients with other etiologies, regardless of method used for lengthening.14 The goal of our study was to compare the outcomes of femoral lengthening in patients with CFD with/without FH utilizing the external monolateral fixator (LRS) versus the internal IM lengthening nail (PRECICE).
There are several limitations to this study. First, the number of patients in both groups is relatively small. This is due to the rarity of patients with LLD due to CFD with or without FH that undergo lengthening. Second, the mean age and length of follow-up of both groups is significantly different. At our institution, the motorized IM nail has only been used for patients older than 9 years as the procedure requires a trochanteric entry point and also because the 8.5-mm diameter PRECICE nail has only recently became available. Monolateral external fixation can be used in younger children, as young as 3 years. The difference in follow-up between groups is secondary to the fact that the PRECICE nail is new technology. The vast majority of complications occur during the lengthening period and within the first 6 to 12 months after surgery; therefore, it is unlikely that late complications in the IM group would alter the findings of this study. Third, as this is a chart review, the number of complications reported is dependent on the dictation. Despite the possibility that our pin tract infections are likely underreported, it was still shown to be significant in comparison with the motorized IM nail.
Group A did appear to have a slightly better mean length achieved than group B; this is likely due to the 3 group B patients who had to prematurely stop lengthening due to subluxation and delayed union only achieving 53% to 83% of their desired length. Subluxation is always a risk in CFD patients who undergo lengthening procedures. With the external fixator, this is mitigated by spanning the knee with a hinged external fixator construct. With the IM lengthening nails, we rely on dynamic splinting in full extension. The first stage of knee subluxation is the development of a knee contracture; vigilant splinting is crucial. In the CFD population, the most feared risks are hip or knee subluxation. Preoperative preparation of the acetabular coverage by Dega or other pelvic osteotomy usually prevents hip subluxation with the goal to keep the center edge angle above 20 degrees.20,21 For the knee, mild instability can be treated with extension bracing during lengthening. Higher grades of instability are best treated with preoperative anterior cruciate ligament/posterior cruciate ligament reconstruction and bracing.
We found that the CI for group B was 34.7 d/cm (SD±11.2), which is within the range reported by other studies using IM lengthening nails such as the ISKD nail (36 d/cm)22 and the Fitbone nail (45 d/cm).23 We reported a CI of 29.3 d/cm (SD±12.7) for group A patients, which is less than reported by Prince et al1 who used monolateral external fixation (39 d/cm), Catagni and colleagues who used the Ilizarov technique (44.9 d/cm)24 and Horn and colleagues who used the Taylor spatial frame (57 d/cm).23 At our institution, we performed the osteotomy at the middle lower third of the femur, which is a preferable site for healing due to its proximity to the metaphysis.
While preoperative flexion was similar between both groups, a significant difference was observed at the end of lengthening and at consolidation. This phenomenon is supported by various studies in the literature, which have also observed a decrease in ROM with external fixation, although some also report a regain in ROM after removal of the fixator.1,6,8 Others report continued ROM reduction postremoval.24 Group B had an overall better retention of ROM over the course of treatment and after removal, which is supported by prior studies.14,22,23 The difference observed between the 2 methods could be due to the tethering effect that the external fixator pins have on the musculature throughout the treatment, impacting the ability of the knee joint to move properly.6 The IM nail does not have this restricting effect and the musculature can continue to function freely and maintain adequate ROM. Although this difference was observed at the end of lengthening and at the consolidation time point, there was no difference in ROM at final follow-up. These results suggest that ROM is better maintained during the lengthening phase allowing for more efficient rehabilitation and ROM return.
The complication rates that required return to the OR were lower than reported by other studies that used the Paley classification system such as Prince et al1 and Oostenbroek et al25 with rates of 50% and 69%, respectively. There is little data available for comparing complication rates using the Paley classification for the motorized IM nail. In our study, 14/32 (44%) of group A patients and 12/30 (40%) of group B patients had to return to the operating room to treat the complications.
Group A had significantly more adverse events than group B; pin site/superficial infections were the main contributor. Both groups had similar rates of obstacles and complications. The number of adverse events per lengthening session between the 2 groups was significantly different with 1.80 (SD±1.07) events per lengthening session for group A and 1.00 (SD±1.03) events per lengthening session for group B; (P=0.02). Black et al19 used their own classification system to compare circular fixation to the Fitbone IM nail in CFD patients. They reported the number of adverse events per lengthening session to be significant at 2.4±1.3 for circular fixation and 1.2±1.1 for the motorized nail (P=0.02). In their study, no significant difference was reported in the total number of complications, although category I complications (defined as minimal intervention required; treatment goal still achieved such as pin-tract infections and mild joint contractures) were significantly different between the groups. Eleven of 14 (79%) circular fixator patients had category I complications as compared with 5/15 (33%) IM patients (P=0.03), the majority of which were due to pin tract infections.
Delayed union of the regenerate was dynamized in several ways depending on whether it was classified as a problem or an obstacle. If the delayed union was a problem, group A femurs were dynamized with modification of the frame while group B femurs were dynamized by compression of the regenerate by using the ERC. If delayed union was an obstacle, it was dynamized by removing the screws to allow increased load transfer to the regenerate bone.
The distraction index and CI were similar in both groups whereas the ROM was better retained during the lengthening phase and at consolidation. The overall problem complication rate was significantly lower with the IM lengthening nail. These findings in conjunction with patient and surgeon preference can help with decision making in regards to which lengthening technique to use. Further studies will be needed to continue to analyze the various techniques to help determine the best course of treatment for this unique patient population. Another important consideration is age of the patient. The PRECICE nail is not as practical in children with CFD younger than 9 years, whereas the monolateral external fixator can be used as early as 3 years.
In summary, we feel that the IM lengthening nail represents a significant advance in technology for CFD lengthening. The increased potential for knee subluxation must be guarded against by strict bracing protocols, and in cases of preoperative radiographic instability, prophylactic knee ligament reconstruction.
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Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
bone lengthening; intramedullary nail; complication; monolateral external fixation; leg length discrepancy; limb lengthening; magnet