Physical Factors Differentiate Pain-free Return To Play And Return With Knee Symptoms 9 Months After ACL Reconstruction

Abstract

PURPOSE: The aim of this study was to identify strength, power and biomechanical differences between male athletes who made a pain free return to play (RTP) and those that did not at 9 month post ACL reconstruction. METHODS: Nine months after ACLR 158 males athletes who had returned to pre-injury sport participation (64 reporting knee symptoms/94 reporting none) carried out strength testing using isokinetic dynamometry on quadriceps and hamstrings and 3D biomechanical analysis of single countermovement jump, single leg drop jump and planned and unplanned 90° change of direction (CoD) as well as an IKDC questionnaire. Differences in IKDC, strength and jump height measures on the ACLR side and in limb symmetry index (LSI) between groups were analysed with statistical parametric mapping (SPM, 0D unpaired t-test). The odds ratio for making a pain free RTP if LSI >90% was also calculated for the strength and jump variables independently and collectively. Biomechanical differences in the jump and CoD tests on the ACLR side and in symmetry between groups was analysed with SPM (1d, unpaired t-test). Effect size was calculated using Cohen’s D for all analyses. RESULTS: There was a large effect size (ES) difference in IKDC score between groups (89 +/- 6 with no pain; 80 +/- 8 with pain; ES 1.1). There were medium effect size differences in quadriceps strength on ACLR side (ES 0.42) and LSI (0.45) with an odds ratio of 2.7. There were similar differences in SLDJ height on ACLR side (ES 0.3) and LSI (0.37) with an odds ratio of 3.5. The odds of making a pain free RTP when LSI >90% on all tests was 6.8. There were no biomechanical differences between groups on the jump tests. There were biomechanical differences on the more demanding CoD tests with differences on the on the ACLR side and symmetry in foot rotation angle, knee extension moment and hip rotation angle (ES 0.51 to 0.61) in the unplanned CoD and in symmetry of posterior and vertical ground reaction force and COM velocity at initial contact (ES 0.5 to 0.58) in the unplanned CoD with greater asymmetry in the painful group. CONCLUSION: This study demonstrates strength, power and biomechanical differences in those that RTP with knee symptoms after ACLR with those achieving >90% LSI in all 4 strength and jump tests almost 7 times more likely to make a pain free RTP.