Purpose: Anterior cruciate ligament (ACL) injuries in siblings are commonly observed in the clinic. One, possibly genetic, factor contributing to the pathogenesis of sibling injuries may be narrow intercondylar notches, which are well recognized as predisposing to ACL injury. This study aimed primarily to: (1) assess the incidence of ACL injuries in siblings within an existing study cohort, (2) compare intercondylar notch width size in injured compared to matched uninjured control siblings and (3) compare the number of injured versus control sibling pairs sharing a narrow notch.
Methods: Twenty-four ACL-injured siblings from 10 families were matched for age, gender, family composition and sports activity, with 24 uninjured siblings from another 10 families. Intercondylar radiographs were taken to calculate anterior and posterior notch width indices (NWI). Notch size and the number of narrow notches in sibling pairs were compared between groups.
Results: Thirteen of 72 ACL-study participants had siblings with torn ACLs. Mean anterior NWI was 0.18 and 0.24 (p < 0.001), and mean posterior NWI was 0.26 and 0.3 (p = 0.006) for injured and uninjured siblings, respectively. Sixty percent of injured sibling pairs shared a narrow notch, while no uninjured sibling pairs did so (p = 0.003).
Conclusion: This study showed that siblings (and often sibling pairs) with injuries do have significantly narrower notches than those without. This could partly explain the prevalence of ACL injuries in siblings. To reduce ACL-injury rates, we advise that siblings of ACL-injured athletes with narrow notches, be radiologically screened, and if necessary, cautioned and counselled regarding preventative training.
Level of evidence: Case-control study, Level III.
Keywords: Anterior cruciate ligament; Family predisposition; Notch shape; Notch width index; Sibling.