Mechanical Axis Following Staple Epiphysiodesis for Limb-Length Inequality

Background: Staple epiphysiodesis is an option for the treatment of limb-length discrepancies, but it is not without complications. The purpose of this study was to review the outcomes of staple epiphysiodesis, including changes in the mechanical axis. Methods: The study included patients who underwent, between 1990 and 2005, staple epiphysiodesis of the femur or tibia, or both, to address limb-length discrepancy. We reviewed preoperative, postoperative, and final long standing anteroposterior radiographs of fifty-four patients to assess limb-length discrepancy, shifts in the mechanical axis, changes in the mechanical axis zone, and changes in the anatomic lateral distal femoral angle and the medial proximal tibial angle. Postoperative radiographs were also reviewed to assess the adequacy of staple placement. Results: Three staple epiphysiodesis groups were identified: fifteen patients who underwent a distal femoral staple epiphysiodesis, eighteen who underwent a proximal tibial procedure, and twenty-one who underwent combined distal femoral and proximal tibial procedures. Fifty percent (twenty-seven) of the fifty-four patients showed a shift in the mechanical axis of >= 1 cm as compared with the preoperative measurement. Eighty-nine percent of these large shifts were varus in nature. The proximal tibial and combined epiphysiodeses resulted in significantly larger shifts in the mechanical axis (p = 0.002 and p = 0.006, respectively) and zone changes (p = 0.009 and p = 0.006, respectively) than did the distal femoral procedures. Six patients ultimately underwent a high tibial osteotomy to correct a post-stapling varus deformity. The proximal-lateral aspect of the tibia was by far the most common location for inadequate staple placement. Conclusions: Mechanical axis deviation is common following staple epiphysiodesis for the treatment of limb-length discrepancy. Proximal tibial and combined distal femoral and proximal tibial staple epiphysiodeses, even if done well technically, lead to clinically relevant shifts in the mechanical axis of the lower extremity more than half of the time. Distal femoral staple epiphysiodesis may still be a safe option for the treatment of limb-length discrepancy, but we advise caution when utilizing proximal tibial staple epiphysiodesis to treat limb-length inequality.