Long Term Changes of the Axis of the Lower Limb After Chiari Pelvic Osteotomy—A Retrospective Analysis of 111 Osteotomies After 34 Years

<b>Background/Objectives</b>: The Chiari pelvic osteotomy (CPO) creates a bony roof by medialization of the acetabulum, thus improving the biomechanics of dysplastic hip joints. Long-term results have already been examined in various studies. However, the impact on the axis of the lower limb has not been investigated yet. The aim of this study was the analysis of changes in the alignment of the lower limb and leg length caused by a CPO and, consecutively, the impact on conversion total hip arthroplasty and primary knee arthroplasty. <b>Methods</b>: A total of 85 patients with 111 CPOs were clinically examined, patient reported outcome measures collected, and long leg standing radiographs analysed according to Paley. <b>Results</b>: The patients were examined an average of 34 years (±7.8; 23-53) after CPO. Unilaterally operated patients (N = 59 hips) showed a pathological MAD in 71% (N = 42) on the operated side (90% valgus, 10% varus). On the unaffected side, we could identify 56% (N = 33 hips) pathological cases (70% valgus, 30% varus). When patients underwent CPO bilaterally (N = 52 hips), the MAD was abnormal in 34 operated hips (65%; 97% valgus, 3% varus). If a leg length discrepancy occurred after the operation, the pelvis and the femur contributed the most to the total leg length discrepancy. <b>Conclusions</b>: Shifts in the mechanical axis following a CPO must be considered in order to inform patients appropriately preoperatively and quantified postoperatively by performing long leg standing radiographs in order to plan following joint replacement therapy adequately and maximize the chance of a successful long-term outcome on a functional level as well as for the patient's satisfaction.