In the natural course of osteonecrosis of the femoral head (ONFH), collapse of the femoral head occurs depending on the size and location of the necrotic lesion [1]. The presence of a collapsed lesion in the weight-bearing portion of the femoral head often results in further collapse progression [2], followed by secondary osteoarthritis that eventually necessitates total hip arthroplasty (THA) no matter how young the patient. On the other hand, necrotic lesions located at the non-weight-bearing portion of the femoral head do not collapse [3]. Accordingly, femoral osteotomies may serve as effective joint-preserving surgeries for post-collapse ONFH by transposing the collapsed necrotic lesion to the non-weight-bearing portion [4].

Transtrochanteric curved varus osteotomy (CVO) is one of the femoral osteotomies performed for post-collapse ONFH, and is indicated when the lateral articular surface is intact [5], which corresponds to type B or C1 ONFH in the classification system of the Japanese Investigation Committee of Health and Welfare (JIC) [6]. Several case series have reported the results of CVO for ONFH, with a 10-year hip survival rate of around 80–90% [[7], [8], [9]]. On the other hand, no studies have compared the results of CVO with the natural course of post-collapse ONFH with type B or C1 necrotic lesions.

This study assessed the 10-year hip survival rate and patient-reported outcome measures (PROMs) of CVO for ONFH compared with those of conservatively managed cases with type B or C1 necrotic lesions.