Generalized joint hypermobility in siblings with anterior cruciate ligament injuries and matched unrelated healthy siblings.

Background And Purpose: Anterior cruciate ligament (ACL) ruptures are common knee injuries, and siblings of individuals with an ACL injury may be at higher risk of ACL injury. Generalized hypermobility may be a familial factor predisposing siblings to ACL injury and may also relate to faulty lower limb alignment. There is a need to determine whether the interaction between hypermobility, family history, and faulty alignment makes siblings with hypermobility at higher risk for ACL injury so that appropriate preventative measures can be taken. This study therefore aimed to (a) compare the prevalence of generalized hypermobility and faulty limb alignment in siblings with and without injury and (b) assess the relationship between generalized hypermobility and lower limb alignment.

Methods: In this case-controlled study, 24 siblings with ACL injuries from 10 families were matched with 24 healthy uninjured siblings from 10 unrelated families. Generalized hypermobility was assessed using Beighton's criteria. Chi-square analyses compared generalized hypermobility and lower limb alignment between siblings and sibling pairs with and without injuries. Spearman's rho was used to assess correlations between generalized hypermobility and lower limb alignment.

Results: There were significant differences between the number of injured and uninjured siblings demonstrating generalized hypermobility when tallied individually (p = .003) and in same-family sibling pairs (p = .019). Significant (or close) differences were found between siblings for knee hyperextension (p < .001), knee valgus (p = .01), and foot pronation (p = .002) and for sibling pairs sharing knee hyperextension (p < .001), knee valgus (p = .06), and foot pronation (p = .06). Generalized hypermobility correlated with knee hyperextension (r = .722; p < .001), knee valgus (r = .385; p = .007), and foot pronation (r = .328; p = .023).

Conclusions: Generalized hypermobility and faulty limb alignment occur significantly more frequently in injured than uninjured families. Screening for both features would assist in identifying at-risk siblings. Prevention programmes reduce ACL injuries by 50-70% and should target hypermobile siblings of the ACL injured.