Disturbed multi-planar muscular support of the knee after anterior cruciate ligament reconstruction.

This study compared lower-limb muscle contributions to multi-planar knee loading between individuals with anterior cruciate ligament reconstruction (ACLR) and healthy controls during sidestep cutting. Eleven ACLR participants with quadrupled hamstring autografts and eleven matched healthy controls performed pre-planned sidestep cutting. Whole-body kinematics, ground reaction forces, and electromyograms (EMG) were recorded. An EMG-informed neuromusculoskeletal modelling approach was used to estimate muscle contributions to anteroposterior force (in bodyweights, BW), varus/valgus moment (BW*Height, BWH), and internal/external rotation moment (BWH) at the knee. Between-group differences in muscle contributions to knee loads were assessed comparing their means +/- standard deviation and their effect sizes (Cohen's d). Compared to controls, ACLR participants had smaller hamstring contributions to posterior knee force (-0.165 ± 0.08 vs -0.343 ± 0.05 BW; d = 2.66), greater quadriceps contributions to valgus moments (-0.080 ± 0.04 vs - 0.050 ± 0.02 BWH; d = 0.94), and greater quadriceps contribution to external rotation moments (-0.042 ± 0.01 vs - 0.025 ± 0.01 BWH; d = 1.7). In conclusion, participants with ACLR exhibited persistent multi-planar alterations in muscle contribution patterns during sidestep cutting, characterised by reduced hamstring contributions, which may be relevant to ACL graft loading and secondary ACL injury risk but require further investigation.