Hip–spine relationship in total hip arthroplasty: Concepts, clinical relevance, and future perspectives

Dislocation remains a leading cause of revision in total hip arthroplasty (THA). While Lewinnek's “safe zone” for acetabular component placement has historically guided surgical orientation, dislocations still occur within this range, highlighting its limitations. Recent research has emphasized the importance of spinopelvic dynamics, particularly the relationship between pelvic tilt and spinal alignment, in influencing functional component orientation and dislocation risk. Patients with spinal stiffness, prior fusion, or spinopelvic imbalance are at higher risk for instability after THA. Several spinopelvic classification systems have been developed to stratify risk and guide implant positioning. However, these systems often rely on static imaging and fail to capture post-operative or age-related changes in spinopelvic mobility. Furthermore, they do not account for femoral motion or multidirectional impingement. Virtual range of motion (VROM) simulation offers a dynamic, patient-specific alternative by modeling critical movements, such as flexion, extension, and rotation, relative to the functional pelvic plane. This enables pre-operative planning of impingement-free zones tailored to individual pelvic and femoral alignment. Even in patients with altered spinopelvic dynamics, implants planned within these parameters may achieve stability without depending solely on sagittal spinopelvic classification. Although spinopelvic classification systems contribute valuable insights, their clinical utility is limited by post-operative variability and omission of femoral alignment. Patient-specific, VROM-based planning may offer clinical relevant implant orientation, improving THA stability and outcomes through individualized functional alignment strategies. • Spinopelvic mobility influences implant stability in total hip arthroplasty. • Static classification systems have key limitations in long-term clinical application. • Virtual range of motion planning ensures impingement-free motion in daily functional postures. • Supine functional pelvic plane offers a reliable reference for implant orientation.