Evaluation of the rate of post-operative dislocation in patients with ipsilateral valgus knee deformity after primary total hip arthroplasty.

PURPOSE: There is scant literature on the evaluation of dislocation after total hip arthroplasty (THA) in patients with ipsilateral valgus knee deformity. This study aimed to investigate the post-operative dislocation rate in patients with valgus knee deformity who underwent ipsilateral THA and identify whether ipsilateral valgus knee deformity increases the dislocation rate after THA. METHODS: We retrospectively reviewed patients with valgus knee deformity who underwent ipsilateral THA in our institution from January 2016 to December 2018. Each hip with ipsilateral valgus knee deformity was matched with a hip without valgus knee deformity according to sex, affected side, and date of surgery. The primary outcome was the dislocation rate after THA. Univariate analyses were initially used to compare data between the dislocation group and the non-dislocation group. Independent risk factors for dislocation were determined using multivariate logistic regression. RESULTS: There were 257 THAs with ipsilateral valgus knee deformity (valgus knee group) and 257 THAs without valgus knee deformity (control group). The valgus knee group showed a significantly higher dislocation rate than the control group (9.7% versus 1.6%, p < 0.001). Older age (p = 0.020) and malposition of the acetabular cup (p = 0.048) were independent risk factors of post-operative dislocation. CONCLUSION: Patients with valgus knee deformity have a higher risk of dislocation after ipsilateral THA. If ipsilateral THA and total knee arthroplasty must be performed successively, total knee arthroplasty may have an earlier priority than THA.

Risk Factors for Early Dislocation Following Primary Elective Total Hip Arthroplasty.

BACKGROUND: Dislocation following total hip arthroplasty (THA) continues to be one of the most common reasons for revision THA. The purpose of this study is to measure the current rate of dislocation following THA in the United States. A secondary goal is to identify patients at highest risk of instability after THA. METHODS: The Nationwide Readmissions Database was used to identify cases of elective primary THA between 2012 and 2014. All readmissions associated with dislocations were identified. Kaplan-Meier curves were used to assess the time to dislocation in the study population. A multivariate logistic regression was modeled to assess risk factors associated with readmission for dislocation. RESULTS: A total of 207,285 THAs were identified between 2012 and 2014. Of the total, 2842 dislocation-associated readmissions (1.4%) were identified, at a median of 40 days post-THA. A history of spinal fusion was the strongest independent predictor of dislocation (odds ratio [OR], 2.45; 95% confidence interval [CI], 1.97-3.04; P < .0001). Parkinson's disease was also significantly associated with dislocation (OR, 1.63; 95% CI, 1.05-2.51; P = .03), as well as dementia (OR, 1.96; 95% CI, 1.13-3.39; P = .02), depression (OR, 1.28; 95% CI, 1.13-1.43; P < .0001), and chronic lung disease (OR, 1.2; 95% CI, 1.07-1.33; P = .001). Inflammatory arthritis and avascular necrosis were independent risk factors for dislocation (OR, 1.56; 95% CI, 1.25-1.97; P < .0001; OR, 1.67; 95% CI, 1.45-1.93; P < .0001). CONCLUSION: THA is a highly effective procedure with a low overall rate of instability. A history of spinal fusion was the most significant independent risk factor for dislocation within the first 6 months following THA.