Poorer clinical outcomes after THA in patients with a spinal scoliotic deformity: a case-control study of 268 patients assessed with PROMS.

Introduction: Spinal deformities can lead to specific complications after total hip arthroplasty (THA), such as functional leg length discrepancy due to a fixed pelvic obliquity, as well as an increased risk of prosthetic instability due to a lack of adaptive pelvic mobility, but these issues were not investigated in large comparative series. Therefore a retrospective case-control study was done aiming: 1) to analyze the impact of a preoperative scoliotic deformity on the functional outcomes of patients who underwent THA with a minimum 1-year follow-up, 2) to measure the prevalence of scoliosis in both the case and control groups 3) to screen other factors that may be correlated with poorer clinical outcomes in patients who underwent THA, including age, gender, Body Mass index (BMI), American Society of Anesthesiologists (ASA) score, primary THA etiology and postoperative complication occurrence.

Hypothesis: The presence of scoliosis would have a negative impact on THA outcomes as assessed by PROMs.

Materials and methods: A case-control study was conducted using prospectively collected data including 268 patients who underwent THA between January 2009 and December 2021 through a direct anterior approach by the same senior surgeon. Cases were identified based on a 1-year follow-up modified Harris Hip score (mHHS) lower than 81 while controls were defined as patients with an excellent 1-year follow-up mHHS score (equal to or higher than 81). Three controls were randomly matched with each case based on the surgery period. To assess the impact of a concurrent scoliosis on clinical outcomes, a mathematical univariate and multivariate logistic model was used, including other confounding factors (age, gender, ASA score, BMI, Complication occurrence, etiology), to calculate the adjusted odds-ratio.

Results: In the multivariate analysis, scoliosis was found to be a significant risk factor, with a three-fold higher adjusted odds-ratio of lower mHHS score (adjOR = 3.1; 95 CI:1.4-7, [p < 0.01]). The mean mHHS score was significantly lower in the scoliosis group compared to the non-scoliosis group (77 vs. 84 [p = 0.01]) as well as the mean Oxford Hip Score (36 vs. 43 [p < 0.001]). Among the other assessed risk factors, only the occurence of a postoperative complication was associated with an increased odds ratio of poorer mHHS scores (adjOR = 7.1; 95 CI: 2.78-18.24, [p < 0.001]). The prevalence of scoliosis in our practice was 19%.

Discussion: Given the prevalence of 19% found in our study, we recommend screening for scoliosis in all patients scheduled for THA. Our results indicate that patients who had scoliosis experienced lower PROMs scores compared to those who had not. Surgeons should consider delivering this information to patients who have scoliosis undergoing THA to mitigate patient dissatisfaction.

Level of evidence: III; retrospective case-control study.