Total hip arthroplasty (THA) effectively provides pain relief and improves function and health-related quality-of-life dimensions for patients with symptomatic osteoarthritis (OA) [[1], [2], [3]]. However, leg length discrepancy (LLD) following THA causes low back pain, gait disorders, and neurological dysfunctions and can lead to gross dissatisfaction and morbidity in patients [4,5]. Any discussion on LLD should include both radiographic LLD (R-LLD) and perceived LLD (P-LLD). Orthopedic surgeons generally plan surgery to correct preoperative R-LLD; however, inconsistency is often observed between postoperative R-LLD and P-LLD. Previous studies have reported a 30% rate of P-LLD after THA [6]. While it has been reported that R-LLD ≤10mm is acceptable, it has also been reported that P-LLD occurs when the R-LLD is ≥ 5 mm after THA [7,8]. However, we found that patients who had undergone THA complained about P-LLD despite no postoperative R-LLD.

Pelvic tilt and lumbar flexibility have been reported to be related to P-LLD after THA. In addition, degeneration and imbalance of the lumbar spine caused by LLD in OA may be related to postoperative P-LLD [9]. R-LLD and P-LLD are inconsistent in cases of OA with a large pelvic tilt angle and long R-LLD [10]. However, factors that affect P-LLD after THA have not been evaluated. Therefore, we investigated the factors that caused the inconsistency between R-LLD and P-LLD in cases where the R-LLD was unchanged after THA.

The purpose of this study was to investigate the following: (1) if there are any incidences where P-LLD occurs even when there is no R-LLD and (2) risk factors associated with residual P-LLD.