Limb symmetry on a battery of functional tests is becoming more common as a clinical rehabilitation tool serving as a proxy assessment for readiness to return to sport following anterior cruciate ligament reconstruction (ACLR). The predictive capability of each included test for determining the likelihood of a second ACL injury is not well known. This study combines 14 established functional tests into a comprehensive return-to-sport assessment (RTSA). Study purpose: to determine if any of the functional tests were independently related to a second ACL injury occurring after the patient was cleared for return to sport.

The RTSA was administered to 226 individuals after primary, unilateral ACLR who were followed for at least 24 months (51% female; mean ± SD age, 18.9 ± 4.0 years at RTSA, 9.4 ± 2.4 months post-surgery). The RTSA included 14 tests that involved calculation of Limb Symmetry Indices (LSI): leg press [LP], eccentric hamstring strength [HS], hip adductor strength [HA], Y Balance Test (anterior [YANT], posteromedial [YPM], posterolateral [YPL]), single hop [SH], triple hop [TH], crossover hop [CH], 6 meter timed hop [TiH], lateral hop [LH], medial hop [MH], vertical jump [VJ], single leg squat [SLS]. LSI averaged values of three trials for each leg for LP, HS, HA, SH, TH, CH, TiH, LH, MH, VJ, and SLS. The lowest bilateral difference across three trials was used for YANT, YPM, and YPL. Logistic regression using backward elimination was used to predict the odds of a second non-contact ACL injury using the RTSA, sex, age, and months post-surgery at RTSA as the independent variables.

Twenty-five (11%) patients returned to have a subsequent ACL surgery. Twenty of the 25 experienced a second non-contact ACL injury (70% female; 10 ipsilateral, 10 contralateral). Of the 14 female athletes, there were eight contralateral and six ipsilateral tears. In males, there were two contralateral and four ipsilateral tears. The mean time from surgery to injury was 20.5 ± 9.8 months. Age (OR; 95%CI: 0.75; 0.58, 0.92), LP (0.97; 0.93, 0.99), YANT (1.21; 1.02, 1.43), and TiH (1.10; 1.01, 1.20) were found to be significantly associated with the odds of re-injury.

Age, YANT, and the LSI of LP and TiH have a statistically significant impact on the odds of a second ACL injury after ACL reconstruction. YANT has an OR of 1.21, indicating that a 1cm increase in asymmetry will increase the likelihood of re-injury by 21%, holding all else constant. A 1% increase in the TiH LSI results in a 10% increase in the odds of re-injury. The risk of re-injury decreases as age increases. The OR for LP symmetry was near 1.0 and therefore may not have a clinically relevant effect on re-injury risk. Although LSI is a straightforward, quantitative measure, clinicians should not solely rely on it as a proxy for recovery of knee function. Many tests are available for clinical assessments, but this study found only a few of the tests to have significant associations with a subsequent ACL injury following return to play after ACL reconstruction.