How Spinopelvic Movements Affect Hip Function After Total Hip Arthroplasty

Total hip arthroplasty (THA) is a widely accepted surgical procedure that effectively alleviates pain, enhances mobility, and improves physical function in patients with hip osteoarthritis. However, improper placement of implants during surgery can lead to complications such as abnormal edge loading, early wear of polyethylene components, ceramic insert fractures, or hip dislocations, often requiring early revision surgeries. While Lewinnek's "safe zone" (30°-50° inclination and 5°-25° anteversion for the acetabular component) has traditionally been used as a guideline, recent studies have reported significant dislocation rates even within these parameters, highlighting spinopelvic movement abnormalities as a critical factor. Normal spinopelvic-hip mechanics allow for adaptive changes in the pelvis and acetabulum during positional transitions, thereby preventing anterior or posterior impingement in the hip joint. However, patients with restricted lumbosacral mobility are at a greater risk of impingement-related symptoms. To address these challenges, advanced metrics such as sacral slope difference (ΔSS), pelvic-femoral angle (PFA), and combined sagittal index (CSI) have been introduced to better define functional safe zones and assess risks of hip impingement and dislocation. While the relationship between CSI and hip dislocations is established, its impact on hip function remains unclear. This study aims to evaluate the effect of spinopelvic movement on hip function in individuals who have undergone THA. By identifying and preventing complications such as hip pain, mobility restrictions, and dislocations, the research seeks to provide meaningful contributions to the literature and improve patient outcomes.