Patient perception of leg length after total hip arthroplasty does not correlate with sagittal lumbar spine stiffness, history of spinal pathology or fusion

Purpose Although spinal pathology or fusion can change patients’ posture and pelvic orientation, their correlation with perception of limb length discrepancy (LLD) after total hip arthroplasty (THA) is not well understood. We hypothesised that LLD perception after THA would not correlate with a history of spinal pathology, fusion or sagittal lumbar spine stiffness among patients who underwent THA. Methods Four hundred consecutive patients who underwent THA and had a complete set of anteroposterior and lateral EOS® imaging in standing and sitting positions were included in this retrospective case–control study. All patients underwent THA between 2011 and 2020. Sagittal lumbar spine stiffness was measured by changes in lumbar lordosis and sacral slope from the standing to the sitting position (lumbar spine stiffness: standing sacral slope-sitting sacral slope < 10°). Anatomical and functional lower extremity length, change in the centre of hip rotation, coronal and sagittal knee alignment, and hindfoot height were measured. Multiple logistic regression was used to investigate the correlation between patient perceptions of LLD, and the variables found to be significant in the univariate analysis. Results There was a substantial difference between the patients with and without LLD perceptions regarding axial pelvic rotation ( p = 0.001), knee flexum-recurvatum ( p = 0.007) and hindfoot height ( p = 0.004). There was no significant difference between patients with and without LLD perceptions regarding differences in femoral length ( p = 0.06), history of spine pathology or fusion ( p = 0.128) and lumbar spine stiffness ( p = 0.955). Conclusions Our study found no significant correlation between perceptions of LLD after THA and spinal fusion or lumbar spine stiffness. Changes in the position of the centre of hip rotation can affect the functional leg length. Surgeons should consult patients regarding other factors, such as knee alignment or hind-/midfoot pathologies, as well as compensatory mechanisms, such as axial pelvic rotation, that could affect perceptions of LLD.