Sex, Age, and Graft Size as Predictors of ACL Re-tear: A Multivariate Logistic Regression of a Cohort of 503 Athletes

OBJECTIVES: The minimum size required for a successful quadrupled hamstring autograft ACL reconstruction remains controversial. The risks of ACL re-tear in younger patients who tend to participate in a higher level of sports activity, and female athletes who have numerous predisposing factors, are poorly defined. Purpose: To identify risk factors for graft re-tears within 2 years of ACL surgery. The hypotheses are that female sex, a smaller size graft, and younger patients will increase the odds of failure. Study Design Cohort Study. Level of evidence, 3. METHODS: A cohort of 503 athletes undergoing primary, autograft hamstring ACL reconstruction, performed by a single surgeon using the same surgical technique and rehabilitation protocol, between September-December 2012, was followed for a total duration of 2 years. Return to play was allowed between 6 and 12 months post-surgery upon completion of functional testing. Exclusion criteria included infections, revisions, double bundle techniques, multi-ligament injuries, non-compliance, BTB/allografts/hybrid grafts. Primary outcome consisted of binary data (ACL graft re-tear or no tear) as measured on physical exam (Lachman and pivot shift) and MRI. Multivariate logistic regression statistical analysis with model fitting was used to investigate the predictive value of sex, age, and graft size on ACL re-tear. Secondary sensitivity analyses were performed on the adolescent subgroup, age and graft size as categorical variables, and testing for interactions among variables. Sample size was calculated based on the rule of 10 events per independent variable for logistic regression. RESULTS: The mean age of the 503 athletes was 27.5 (SD 10.6; range = 12-61). There were 235 females (47%) and 268 males (53%) with a 6% rate of re-tears (28 patients; 17 females). Mean graft size was 7.9 (SD 0.6; range = 6-10). Univariate analyses of graft size, sex, and age only in the model showed that younger age (odds ratio [OR] = 0.86; 95% confidence interval [CI] = 0.80-0.93; P = .001] and smaller graft size (OR = 0.36; 95% CI = 0.18-0.70; P = .003) were significantly predictive of re-tear. Female sex was correlated with re-tear but was not significant (OR = 1.8; 95% CI = 0.84-3.97; P = .13). Multivariate analysis with all 3 variables in the model showed similar significant results. Graft size < 8 mm (OR = 2.95; 95% CI = 1.33-6.53; P = .008) and age < 25 (OR = 7.01; 95% CI = 2.40-20.53; P = .001) were significantly predictive of re-tear. Entire model was statistically significant (Omnibus test P = .001; Hosmer-Lemeshow statistic P = .68; Receiver Operating Curve [ROC] = 0.8). CONCLUSION: Surgeons should counsel their patients who are female, younger than 25 and with a graft size less than 8 mm accordingly and consider modifying their surgical or rehabilitation techniques to mitigate these re-tear risks.