Alpha Angle Values Predict the Severity of Hip Chondral Damage in Patients With Cam-Type Femoroacetabular Impingement Syndrome: A Systematic Review and Meta-analysis

Abstract

To assess the role of alpha angle (AA) in predicting the severity of hip chondral damage in patients with cam-type femoroacetabular impingement (FAI) syndrome. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols guidelines, a systematic review was performed to summarize and critically appraise studies analyzing the prognostic capability of AA values in predicting the severity of intraoperatively evaluated hip chondral damage in patients with cam-type FAI syndrome. The risk of bias was assessed through the Quality In Prognosis Studies tool. Meta-analyses based on groups and individual data from studies with a low risk of bias were conducted. We employed a cumulative link mixed model to analyze the relationship between AA and the ordinal outcome (chondral damage). The model was adjusted for sex, age, and the lateral center-edge angle (LCEA). Interactions between sex and AA were also investigated, and probabilities were calculated. Twelve studies with 4,564 patients were included in a qualitative review (aged 30-39 years, 1,822 women [40%]). Studies with a low risk of bias (n= 4; 2,945 patients) indicated that AA values are significantly smaller (mean difference [95% confidence interval] of 10.5° [6.5°-15°]) in the low-grade chondral damage group (grades 0/I/II) compared with the high-grade chondral damage group (III/IV). The cumulative link mixed model with individual patient data from studies with low risk of bias (n= 3; 1,460 patients) indicated that for each 1° increase in AA, the odds of being in a greater category of chondral damage increased by a factor of 1.04 (odds ratio 1.04, P < .0001). Men were at significantly greater risk (odds ratio 2.11, P < .0001) than women, but no significant interaction between sex and AA was observed (P= .054). We estimate the average probability of having high-grade chondral damage to be greater than 33% when AA values surpass 71° for men and 90° for women, and greater than 50% when 89° for men and 108° for women. However, the heterogeneity observed across studies should be considered. The AA is a significant predictor of hip chondral damage severity in patients with cam-type FAI syndrome, regardless of sex and independently of age and LCEA. In addition, men are at a greater risk of chondral damage than women, and this risk increases with aging but decreases with the magnitude of the LCEA. Level III, systematic review of Level II and III studies.