An Analysis of Characteristics Associated With Bilateral Versus Unilateral Anterior Cruciate Ligament Injuries: A National Database Analysis.

BACKGROUND

Anterior cruciate ligament (ACL) injuries are common, yet the specific risk factors that distinguish patients who sustain bilateral injuries from those with unilateral injuries remain poorly characterized. Identifying these factors is crucial for targeted prevention strategies.

PURPOSE: To identify demographic and clinical factors associated with bilateral ACL injuries compared with unilateral ACL injuries.

STUDY

DESIGN

Case-control study; Level of evidence, 3.

METHODS

This retrospective cohort study utilized the PearlDiver database to identify patients with unilateral (ACL-ALONE; n = 359,491) or bilateral (ACL-BOTH; n = 3115) ACL injuries. A 2-stage analytical approach was employed. First, demographics and comorbidities were compared between cohorts in the entire population. Second, the analysis was restricted to the female subpopulation to evaluate the specific role of amenorrhea. Multivariable logistic regression models were constructed for both stages to identify factors independently associated with bilateral injury, controlling key confounders.

RESULTS

Analysis of the full cohort (N = 362,606) revealed that patients with bilateral ACL injuries were significantly younger than those with unilateral injuries (28.8 vs 31.0 years; P < .001). In the full cohort multivariable model, significant independent risk factors for bilateral injury included the 15- to 19-year age group (adjusted odds ratio [aOR], 1.62; 95% CI, 1.35-1.94; P < .001), tobacco use (aOR, 1.24; 95% CI, 1.13-1.35; P < .001), vitamin D deficiency (aOR, 1.31; 95% CI, 1.14-1.50; P < .001), and hypermobility (aOR, 1.83; 95% CI, 1.18-2.82; P = .006). In the female-specific analysis (n = 179,923), amenorrhea was a significant independent factor (aOR, 1.39; 95% CI, 1.16-1.64; P < .001), while hypermobility showed a strong, nonsignificant trend (aOR, 1.65; 95% CI, 0.99-2.77; P = .05).

CONCLUSION

This study identifies a distinct and multifactorial risk profile for bilateral ACL injury. Independent risk factors in the overall population include younger age (15-19 years), tobacco use, vitamin D deficiency, and hypermobility. In the female subpopulation, amenorrhea emerged as a significant sex-specific risk factor, associated with a 39% increase in the adjusted odds of bilateral injury. The association for hypermobility, while significant in the full cohort, demonstrated a strong, nonsignificant trend in the female-only analysis, suggesting a complex interaction. These findings indicate that bilateral ACL injury etiology extends beyond biomechanics, implicating a confluence of demographic, endocrine, constitutional, and modifiable lifestyle factors.