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 cruciateligament reconstruction (ACLR). Given that bilateral deficits are present after ACLR, this may result in afalsely 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 ACLRdemonstrate decreased jump distance on the single hop for distance (SLH) and triple leg hop for dis-tance (TLH) and decreased number of hops for the side hop (SH) for both involved and uninvolved limbscompared 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 age21.7 ± 3.5 years) who had undergone an ACLR participated in this study. Patients performed the 3 hoptests at a mean time of 7 months after ACLR. Hop distance, number of side hops and LSI were comparedwith normative data of 188 healthy athletes.Results: The differences between the involved limb and the uninvolved limb were significant in all hoptests (SLH P = 0.003, TLH P = 0.003, SH P = 0.018). For females, only significant between limb differenceswere found in the SLH (P = 0.049). For both the SLH and the TLH, significant differences were foundbetween the involved limb and the normative data (males; SLH P < 0.001, TLH P < 0.001; females; SLHP < 0.001, TLH P = 0.006) and between the uninvolved limb and the normative data for both males andfemales (males; SLH P < 0.001, TLH P < 0.001; females; SLH P = 0.003, TLH P = 0.038). For the SH, only sig-nificant 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 com-parison to age and sex matched normative data of healthy controls. Using the LSI may underestimateperformance deficits and should therefore be analyzed with caution when used as a criterion for RTSafter ACL