Histological differences between various methods of hemiepiphysiodesis: is guided growth really different?

Growth modulation of angular deformities with a novel constant force implant concept-preclinical results

PURPOSE

Varus-valgus deformities in children and adolescents are often corrected by temporary hemi-epiphysiodesis, in which the physis is bridged by an implant to inhibit growth. With standard implant solutions, the acting forces cannot be regulated, rendering the correction difficult to control. Furthermore, the implant load steadily increases with ongoing growth potentially leading to implant-related failures. A novel implant concept was developed applying a controlled constant force to the physis, which carries the potential to avoid these complications. The study aim was to proof the concept in vivo by analyzing the effect of three distinct force levels on the creation of varus deformities.

METHODS

The proposed implant is made of a conventional cerclage wire and features a twisted coil that unwinds with growth resulting in an implant-specific constant force level. The proximal medial tibial physes of 18 lambs were treated with the implant and assigned to three groups distinct by the force level of the implant (200 N, 120 N, 60 N).

RESULTS

The treatment appeared safe without implant-related failures. Deformity creation was statistically different between the groups and yielded on average 10.6° (200 N), 4.8° (120 N) and 0.4° (60 N) over the treatment period. Modulation rates were 0.51°/mm (200 N), 0.23°/mm (120 N) and 0.05°/mm (60 N) and were constant throughout the treatment.

CONCLUSION

By means of the constant force concept, controlled growth modulation appeared feasible in this preclinical experiment. However, clinical trials are necessary to confirm whether the results are translatable to the human pathological situation.

Proximal Femoral Growth Modification: Effect of Screw, Plate, and Drill on Asymmetric Growth of the Hip

BACKGROUND

Guided growth has long been used in the lower extremities but has not been applied to varus or valgus deformity in the hip, as may occur in children with cerebral palsy or developmental dysplasia of the hip. The purpose of this study was to determine if screw, plate, or drilling techniques decreased the femoral neck-shaft angle (NSA) and articular trochanteric disease (ATD), as well as describe growth plate structural changes with each method.

METHODS

Twelve 8-week-old lambs underwent proximal femoral hemiepiphysiodesis (IACUC approved) using either a screw (n=4), plate (n=4), or drilling procedure (n=4). Postoperative time was 6 months. Radiographs taken after limb harvest were used to measure NSA and ATD. Differences between treated and control sides were determined by 1-tailed paired t tests and Bonferroni (α=0.05/3). Histology was obtained for 1 limb pair per group. Proximal femurs were cut in midcoronal plane and the longitudinal growth plates were examined for structural changes.

RESULTS

The mean NSA measured 7 degrees less than controls in this model using the screw technique, and this difference was statistically significant. Differences between the control and the treated groups did not reach statistical significance for either the plate or the drill group. Differences in ATD were not statistically significant, although there was a trend for larger ATD measurements using the screw technique. Histologically, physeal changes were observed on the operative sides in screw and plate specimens, but not drill specimens, compared with contralateral sham control. The screw specimen exhibited the most severe changes, with growth plate closure over half the section. The plate specimen showed focal loss of the physis across the section, but with no evidence of closure.

CONCLUSIONS

This study builds on previous work that indicates screw hemiepiphysiodesis can effectively alter the shape of the proximal femur, and result in a lower neck-shaft ankle (or lesser valgus). This study suggests that implantation of a screw is likely to be more effective than a plate or drilling procedure in decreasing the NSA in skeletally immature hips.

CLINICAL SIGNIFICANCE

If further preclinical, and later clinical, studies demonstrate reproducible efficacy, guided growth of the proximal femur may eventually become a viable option for treatment or prevention of hip deformity in select patients.

Failure of tension band plating: a case series

Growth modulation with tension band plates (TBP) has been shown to be a very useful method for the treatment of angular deformities in growing children. Recently, we have observed cases of failure where the epiphyseal screw was drawn through the physis into the metaphysis. This study describes a series of children who developed this complication. Patients who developed TBP failure after operative treatment of lower limb angular deformities were identified from the databases at four institutions over a 5-year period. The medical records were reviewed to record demographics, primary diagnoses, details of the operative procedure, development of physeal arrest, and recurrence of the original deformity. Six patients (five girls) with nine implant failures were identified. The mean age of the children at the time of implant insertion was 7.2 years (range, 4-10 years). The primary diagnoses included hypophosphatemic rickets (n=7), congenital pseudoarthrosis of the tibia associated with neurofibromatosis 1 (n=1), and post-traumatic malunion after distal tibial fracture (n=1). Of the nine TBP that presented with the complication, four were inserted into the medial distal femur (one bilateral case), two into the medial proximal tibia (one bilateral case), two into the lateral distal tibia, and one into the medial distal tibia. None of these patients developed physeal growth arrest at the last follow-up as assessed on the latest radiographs. The use of TBP for guided growth in patients younger than 10 years old with rickets, neurofibromatosis, or other conditions that produce osteopenia leads to an increased risk for implant failure. In these cases, it is important to confirm that the epiphyseal screw has good purchase. Patients with these features should be monitored closely for early detection of this complication.