A large preoperative pelvic oblique angle affects perception of leg length discrepancy after total hip arthroplasty

Background: In some cases, patients feel a perceived leg length discrepancy (P-LLD) despite no radiographic leg length discrepancy (R-LLD) after total hip arthroplasty (THA). We aimed to investigate the rate of postoperative P-LLD and the factors that cause postoperative P-LLD. Methods: A retrospective study was conducted on 100 patients with R-LLD <= 5 mm after THA. Patients were classified into two groups based on P-LLD post-THA: group P (with P-LLD) and group E (without P-LLD). Relevant data on the general characteristics and radiological findings between the two groups were compared. Results: We observed that 25 & 75% of patients belonged to group P and group E, respectively, with no significant difference in patient background. Postoperative Japanese Orthopedic Association (JOA) classification of pain and activities of daily living scores were significantly lower in group P than in group E (37.2 +/- 3.9 vs. 39.1 +/- 2.2, respectively; P = 0.013, and 16.2 +/- 4.2 vs. 18.2 +/- 2.2, respectively; P = 0.011). The preoperative pelvic oblique angle (POA) was significantly larger in group P than in group E (3.3 +/- 2.3 degrees vs. -0.2 +/- 2.1 degrees; respectively; P < 0.01). The pelvis tilted toward the surgical side was significantly higher in group P than in group E(88% vs 57%; respectively; P = 0.013). The preoperative C7 coronal vertical axis (C7 CVA) was significantly larger in group P than in group E (6.7 +/- 14.7 mm vs. -0.2 +/- 10.3 mm; respectively; P = 0.028). Multivariate logistic analysis revealed that preoperative POA (OR, 3.71; 95% CI: 1.86-8.12; P < 0.01) and the pelvis tilted toward the surgical side (OR, 4.14; 95% CI: 2.07-9.71; P = 0.022) were independent risk factors for P-LLD after THA. Conclusion: Even though there was no postoperative R-LLD, 25% of patients had P-LLD. A large preoperative POA and the pelvis tilted toward the surgical side were independent risk factors for P-LLD after THA.