High genetic contribution to anterior cruciate ligament rupture: Heritability ∼69%

Objectives: We aimed to determine the lifetime genetic risk for anterior cruciate ligament (ACL) rupture. Methods: We used a twin study approach, linking the Swedish Twin Register with national healthcare data to form a 30 year, population wide, longitudinal twin cohort. We studied ACL rupture in this cohort of 88 414 identical and fraternal twin pairs, aged ≥17 years, to determine the familial risk and heritability of ACL rupture. Results: The incidence rate of ACL rupture was 70 (95% CI 66 to 74) per 100 000 person years. The familial risk, which is the excess risk ratio (RR) of the second twin having ACL rupture given that the first twin has had such a rupture, was higher in identical twin pairs (RR=8.6, 95% CI 6.2 to 11.0) than in fraternal twin pairs (RR=1.9, 95% CI 0.9 to 3.0). The overall heritability of ACL rupture was high, 69% (95% CI 47 to 91), increasing from 60% at age 17 years to 80% at age 60 years. Women and men had similar familial risk and heritability of ACL rupture. Conclusion: The genetic contribution to ACL rupture of ∼69% is high and suggests strong familial clustering. If clinicians recognise the high genetic risk of such injury, they may be better able to counsel athletes whose near relatives have had ACL rupture.