Hemipelvis malrotation deformity leading to instability: The need for careful preoperative radiographic evaluation in total hip arthroplasty.

Postoperative instability remains one of the main causes of early revision after total hip arthroplasty (THA), often occurring within the first 5 years. While factors such as implant design, surgical technique, and spinopelvic alignment have been widely studied, hemipelvis malrotation-a subtle, often unrecognized unilateral pelvic deformity-has received limited attention. This condition can lead to apparent implant malposition despite adherence to standard surgical protocols. A review of current literature suggests that hemipelvis malrotation may significantly influence postoperative hip stability, yet it is frequently missed on standard anteroposterior (AP) pelvic radiographs. A clinical case is presented in which a patient experienced recurrent anterior dislocation after primary THA, even though the acetabular and femoral components appeared well positioned on routine imaging. Further evaluation with advanced imaging revealed a pronounced unilateral hemipelvis malrotation that had altered the true functional orientation of the acetabulum. Revision surgery incorporating correction of this underlying deformity successfully restored joint stability and resolved the patient's symptoms. This case highlights the limitations of traditional 2-dimensional imaging and underscores the need for a more comprehensive, multiplanar, and dynamic preoperative assessment. Recognizing hemipelvis malrotation as a distinct contributor to THA instability may improve surgical planning and reduce the risk of dislocation and early revision. Collaboration between orthopedic surgeons and radiologists is essential to identify subtle pelvic asymmetries that can compromise component alignment and long-term functional outcomes.