Variability in Leg Muscle Power and Hop Performance After Anterior Cruciate Ligament Reconstruction

Thomee R, Neeter C, Gustavsson A, Thomee P, Augustsson J, Eriksson G, Karlsson J,  Knee Surg Sports Traumatol Arthrosc. 2012 Feb 8. [Epub ahead of print]

After anterior cruciate ligament reconstruction (ACLR) a battery of functional tests is often used to evaluate lower extremity function to determine return-to-sport eligibility and as well as long-term function. Muscle strength measures and single-leg hop performance are most commonly used to calculate a limb symmetry index (LSI). Different levels of limb symmetry (70-90%) have been reported in the literature as acceptable minimal values. The purpose of this study was to prospectively evaluate hop performance as well as leg muscle power up to 2 years after ACLR and determine an acceptable cut-off value for normal limb symmetry. Eighty-two subjects who underwent ACLR with either hamstring or patellar tendon graft were included in this study. All subjects underwent functional testing 3 months before surgery as well as 6, 12, and 24 months after ACLR.  Functional testing consisted of open-chain quadriceps and hamstring strength measures, closed-chain lower extremity power measures using a leg press machine and three single-leg hop tests; (1) vertical jump, (2) hop for distance, and (3) side hop. LSI was calculated as involved leg/ uninvolved leg x 100. Results showed that before surgery there was a significant difference between limbs for knee extension and leg press measures with the involved limb being weaker than the uninvolved limb. Regardless of time point, all hop measures were significantly better for the uninvolved limb. Significant improvements were seen in all strength and hop measures from pre-surgery to 24 months after surgery, except for knee flexion strength measures. All LSI values were ≥90% for individual muscle power at 12 and 24 months for all measures and individual hop performance values were ≥87% at 12 months and ≥90% at 24 months for all hops. It is believed that the goal of functional testing is for patients to achieve ≥90% on ALL measures to ensure limb symmetry with all tasks. This cut-off was used based on previous works with healthy controls [Risberg, 1995]. Therefore, the results of this study were evaluated based on success rate of ALL hop measures, ALL strength measures, as well as ALL strength AND hop measures combined. Individuals were grouped based on LSI of ≥ 80, ≥ 85, ≥ 90, ≥ 95 and ≥ 100%, with ≥90% considered normal knee function. For the strength test battery, the hop test battery, as well as the strength and hop test batteries combined, as the LSI value increased the number of individuals that achieved this criteria decreased. No individual achieved 100% on all strength and hop tests combined. Additionally, no differences were found based on graft type.

These results show that at 12 and 24 months after surgery patients begin to demonstrate greater limb symmetry with individual strength and hop test measures. But when all strength and hop measures are used to determine LSI, fewer patients demonstrated scores of ≥90%. It appears that this battery of tests, instead of one individual measure, is successful at detecting deficits in patients after ACLR. It is more importantly demonstrating that these individuals continue to have deficits 1 and 2 years after reconstruction. This is consistent with the current literature [Gustavsson, 2006; De Jong, 2007; Eitzen, 2009; Logerstedt, 2012]. These continued limb asymmetries may be related to high re-injury rates and one reason why individuals do not return to their previous levels of activity after ACLR.  A more critical battery of tests may be warranted. What criteria do you use to determine limb symmetry? Do you feel that it is sensitive enough to detect limb symmetry deficits? Do you think detecting these asymmetries through functional testing can decrease re-injury rates?

Written By: Kathleen White

Thomeé R, Neeter C, Gustavsson A, Thomeé P, Augustsson J, Eriksson B, & Karlsson J (2012). Variability in leg muscle power and hop performance after anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy PMID: 22314862