A critical analysis of limb symmetry indices of hop tests in athletes after anterior cruciate ligament reconstruction:A case control study

Background: Hop tests are frequently used to determine return to sports (RTS) after anterior cruciate ligament reconstruction (ACLR). Given that bilateral deficits are present after ACLR, this may result in a falsely high limb symmetry index (LSI), since LSI is calculated as a ratio between the values of the limbs. Hypothesis: Athletes after ACLR would achieve LSI > 90% for the hop test. Secondly, athletes after ACLR demonstrate decreased jump distance on the single hop for distance (SLH) and triple leg hop for distance (TLH) and decreased number of hops for the side hop (SH) for both involved and uninvolved limbs compared to normative data of sex, age and type of sports matched healthy athletes.Materials and methods: Fifty-two patients (38 males mean age 23.9 +/- 3.5 years; 14 females mean age 21.7 +/- 3.5 years) who had undergone an ACLR participated in this study. Patients performed the 3 hop tests at a mean time of 7 months after ACLR. Hop distance, number of side hops and LSI were compared with normative data of 188 healthy athletes.Results: The differences between the involved limb and the uninvolved limb were significant in all hop tests (SLH P = 0.003, TLH P = 0.003, SH P = 0.018). For females, only significant between limb differences were found in the SLH (P = 0.049). For both the SLH and the TLH, significant differences were found between the involved limb and the normative data (males; SLH P <0.001, TLH P <0.001; females; SLH P <0.001, TLH P = 0.006) and between the uninvolved limb and the normative data for both males and females (males; SLH P <0.001, TLH P <0.001; females; SLH P = 0.003, TLH P = 0.038). For the SH, only significant differences were found between the involved limb and the normative values in males (P = 0.033).Conclusion: Athletes who have undergone an ACLR demonstrate bilateral deficits on hop tests in comparison to age and sex matched normative data of healthy controls. Using the LSI may underestimate performance deficits and should therefore be analyzed with caution when used as a criterion for RTS after ACLR.