Changes in sagittal spinal alignment and pelvic parameters in patients undergoing a total hip arthroplasty

BACKGROUND: The relationship of the spine to the pelvis has been widely studied. However, the role of the hip joint in maintaining sagittal balance remains poorly understood. We aimed to examine if radiographic sagittal spine and pelvic parameters change after Total Hip Arthroplasty (THA), and to evaluate the postural effects on these parameters in standing, sitting, and supine positions. MATERIALS AND METHODS: 36-inch anteroposterior and lateral standing, sitting and supine radiographs in patients undergoing a unilateral THA pre and post THA were obtained. Standard pelvic and spinal alignment parameters were measured. RESULTS: There were 31 cases with complete radiographic information. Pre-THA SVA was 35.7mm, improving to 24.9mm post-THA. Lumbar lordosis was 50.6° standing and 33.8° sitting; maintained post-THA at 50.6° standing and 36.4°sitting. Pelvic incidence remained unchanged in all positions pre and post-THA (49.1° to 51.2°). Pre-THA sacral slope was 36.9° standing, 23.3° sitting and 40.9° supine. This was maintained post-THA (36.0° standing, 22.9°sitting and 39.7°supine). Pre-THA pelvic tilt was 14.5° standing, 27.8° sitting and 8.8° supine. This was maintained post-THA (15.3° standing, 28.2°sitting and 12.0°supine). Lumbar lordosis was significantly less, and pelvic tilt was significantly greater in sitting position than in standing and supine positions, representing the pelvis moves posteriorly as a patient goes to a seated position,CONCLUSION: This study establishes baseline values for the normal standing, sitting and supine sagittal spine and pelvic parameters patient's undergoing THA. THA does not seem to lead to substantial changes in sagittal spine and pelvic radiographic parameters.