Postoperative longer leg on surgical side and high riding greater trochanter worsen forgotten joint score after unilateral total hip arthroplasty.

Leg length discrepancy (LLD), offset, and anatomical abnormalities such as a high-riding greater trochanter are key factors that may influence the outcomes of total hip arthroplasty (THA). Understanding how these factors affect patient-reported outcomes (PROs) is crucial for optimizing surgical techniques and improving patient satisfaction. This study investigated whether preoperative and postoperative LLD, offset, and a preoperative high-riding greater trochanter influence PROs in unilateral THA. A questionnaire survey was conducted targeting 1,010 individuals who underwent primary THA. Of the 652 respondents (62%), 203 with healthy contralateral sides were included. PROs were assessed using the Forgotten Joint Score-12 (FJS-12), Oxford Hip Score (OHS), and Visual Analogue Scale (VAS)-Satisfaction. Anteroposterior radiographs taken before and one week after surgery were used to measure LLD, femoral offset, acetabular offset, global offset, and articular trochanteric distance (ATD). A high-riding greater trochanter was defined as an ATD < 0 mm. Multivariable analyses revealed that a longer leg on the surgical side postoperatively (P = 0.0004) and a preoperative high-riding greater trochanter (P = 0.01) were negative factors for FJS-12. Older age (P = 0.0004) and higher body mass index (P = 0.04) were negative factors for OHS. Male sex negatively affected VAS-Satisfaction (P = 0.04). This study is the first to reveal that a longer postoperative leg on the surgical side and the presence of a high-riding greater trochanter leads to a decrease in the FJS-12 score independently. Therefore, to improve joint stability, it may be more beneficial to increase offset rather than extend leg length.