Impact of the hip-spine relationship and patient-perceived leg length discrepancy after total hip arthroplasty: A retrospective study.

PURPOSE:Patient-perceived leg length discrepancy (PLLD) is one of the major postoperative complications of total hip arthroplasty (THA). This study aimed to identify factors that cause PLLD following THA. MATERIALS AND METHODS:This retrospective study included a series of consecutive patients who underwent unilateral THA between 2015 and 2020. Ninety-five patients who underwent unilateral THA with postoperative radiographic leg length discrepancy (RLLD) ≤1 cm were classified into two groups according to the direction of preoperative pelvic obliquity (PO). Standing radiographs of the hip joint and whole spine were obtained before and one year after THA. The clinical outcomes and the presence or absence of PLLD was confirmed one year after THA. RESULTS:Sixty-nine patients were classified as having type 1 PO (rising toward the unaffected side) and 26 were classified as having type 2 PO (rising toward the affected side). Eight patients with type 1 PO and seven with type 2 PO had PLLD postoperatively. In the type 1 group, patients with PLLD had larger preoperative and postoperative PO values and larger preoperative and postoperative RLLD than those without PLLD (p = 0.01, p < 0.001, p = 0.01, and p = 0.007, respectively). In the type 2 group, patients with PLLD had larger preoperative RLLD, larger amount of leg correction, and a larger preoperative L1-L5 angle than those without PLLD (p = 0.03, p = 0.03, and p = 0.03, respectively). In type 1, postoperative PO was significantly associated with postoperative PLLD (p = 0.005), but spinal alignment was not an indicator of postoperative PLLD. The area under the curve (AUC) for postoperative PO was 0.883 (good accuracy) with a cut-off value was 1.90° CONCLUSION: Rigidity of the lumbar spine might lead to postoperative PO as a compensatory movement, resulting in PLLD after THA in type 1. Further research on the relationship between flexibility of the lumbar spine and PLLD is needed.