Sagittal plane deformity after temporary epiphysiodesis of the distal femur for correcting limb length discrepancy.

BACKGROUND: Outcome of the temporary epiphysiodesis procedure for limb length discrepancy (LLD) is commonly evaluated in the coronal plane. The purpose of this study was to investigate implant position and complications of the distal femur and patella in the sagittal plane after the temporary epiphysiodesis. METHODS: We retrospectively reviewed 27 patients with LLD who underwent temporary epiphysiodesis of the distal femur using staples (11 patients) or eight-plates (16 patients) between 2007 and 2015. The mean age was 9.7 years (range, 6.3-13.8) at the time of epiphysiodesis. The implants were removed after a mean period of 2.6 years (range, 0.8-4.8) from the epiphysiodesis. Correction amount of LLD was measured on anteroposterior long leg standing radiographs. Implant position, extension deformity of the distal femur (>5° from epiphysiodesis to removal of implant) and patella baja (the epiphyseal line midpoint method < 1.0) were evaluated using lateral knee radiographs. RESULTS: The average correction amount of LLD was 17.4 mm (range, 2-34). The average implant position was 43.1% (range, 35-55) from the anterior edge of the distal femoral epiphysis. At removal surgery, 16 patients (59%) had extension deformity of the distal femur and 14 patients (52%) showed patella baja. There were significant correlations between implant position and extension deformity (r = -0.51, p < 0.01) and as well as between correction amount of LLD and patella baja (r = -0.64, p < 0.01). CONCLUSION: After temporary epiphysiodesis for the treatment of LLD, extension deformity of the distal femur and patella baja occurred frequently. Anterior placement of the implants is associated with extension deformity of the distal femur. The implant should be placed in the center of distal femoral physis, not the center of femoral shaft. Excessive correction of LLD should be avoided due to a risk of patella baja.