This study aimed to evaluate ACL-R patients at RTS with concurrent isokinetic tests and surface electromyography (sEMG) of the lateral Vs medial HS compared to healthy controls to identify abnormal HS activation patterns.
Mean lateral Vs medial HS sEMG amplitude and timing were measured during isokinetic tests at 60-180-300°/s in 92 subjects divided between 46 primary HS grafted ACL-Rs and 46 healthy controls matched per age (18-45 yrs), sex, and level of physical activity (Tegner 4-9). After the 8th post-operative month, ACL-R patients were evaluated with an isokinetic test with concurrent sEMG evaluation of the lateral and medial HS. The controls were tested with the same procedure. The subjects had to pass the minimum criteria to be cleared for RTS (HS/quadriceps ratio >=60% and quadriceps & HS interlimb peak torque difference at 60-180-300°/s =10%).
The isokinetic peak torque normalized to body weight was significantly lower for ACL-R subjects at all the angular velocities (p=0.01 at 60-180°/s, p=0.02 at 300°/s). Mean sEMG amplitude for the lateral HS of ACL-R Vs control groups resulted n.s. at 60°/s, but significantly lower at 180°/s (p=0.005) and 300°/s (p=0.01). The same sEMG data for the medial HS of ACL-R Vs control groups emerged n.s. in all tests. The medial/lateral HS ratio in ACL-R Vs control groups was found n.s. at 60-300°/s whereas was higher at 180°/s (p=0.01). Moreover, the sEMG mean time-to-peak of the lateral HS of ACL-R Vs control groups resulted n.s. in all tests whereas the medial HS of ACL-R Vs control groups was significantly faster at 60-180-300°/s (p=0.006, p=0.002, p=0.02).
ACL-R subjects presented lower strength than controls. The mean sEMG amplitude of the medial HS showed no between-group difference at any angular velocity. However, the medial HS showed a consistently faster sEMG time-to-peak across all the tests in the ACL-Rs. The simultaneous significantly lower mean sEMG amplitude of the lateral HS at 180-300°/s in the ACL-Rs proves an altered latero-medial HS muscular activation pattern at angular velocities closer to sports-specific tasks. These findings highlight a higher neuromuscular demand on the grafted medial HS in ACL-R subjects at RTS.
This study's findings showed a newly discovered impairment for ACL-R patients that clinicians should be aware of to avoid erroneous clearance at RTS.
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