Reconstructive surgery is done to re-establish dynamic knee stability after anterior cruciate ligament (ACL) rupture. Clinical results show that only 50% of patients return to their previous competative level and 33% suffer a contralateral ACL rupture or re-rupture. Literature shows increased risk of rupture near the end of a competition, yet no research has been done on combined neuromuscular and kinematic changes following sport-specific fatigue in ACL reconstructed (ACLr) knees. Research has been restricted to laboratories, though advances in sensor technology now allow for outside, sport-specific measurements.
PURPOSE: Objectifying effects of sport-specific fatigue on joint angles and neuromuscular activation of the ACLr knee.
METHODS: 8 patients (5 male, 3 female, 21.6 ± 3.7 yrs, 179.5 ± 9.2 cm. 70 ± 27.6 kg) 1 year post ACLr (Hamstring tendon graft) ran 4x15 minutes on a 20m course, interspersed with hop-tests (HT) (drop-vertical jump (DVJ) and hop for distance (HfD)). Bilateral surface electromyography (EMG) of the m. vastus lateralis (VL) and m. biceps femoris (BF) was combined with wireless inertial magnetic units (IMU’s) at the sacrum, upper and lower legs to measure kinematics. A repeated measures ANOVA (P < .05) was used to compare EMG (VL:BF activation ratio) and IMU data (3D knee ROM) during landing phases of 5 HT series and each running block.
RESULTS: VL:BF ratio increased during the 2nd running block (0.83 ± 0.14 → 1.07 ± 0.08). Changes in knee flexion angles were seen (F4,28 = 40.96, P < .001). Post hoc Tukey analysis showed significant changes between the unfatigued 1st and slightly fatigued 3rd HT (DVJ: 18.3 ± 5.10 → 15.9 ± 5.70. HfD: 22.3 ± 5.50 → 19.4 ± 6.10). Non-significant decreases are seen in the last HT (DVJ: 9.9 ± 5.80. HfD: 19.0 ± 6.10). Max knee valgus angles during the DVJ HT increased with fatigue (F4,28 = 18.18, P < .001. 2.7 ± 3.60 → 4.9 ± 3.00). Strikingly, ACLr knees showed significant (Wilcoxon, P<0.031) lower valgus angles (4.0 ± 1.50) compared to the healthy side (5.6 ± 2.40) in fatigued HT.
CONCLUSIONS: This was the first study to combine neuromuscular and kinematic measurements in a sport-specific setting to objectify effects of fatigue. In line with the notion of increasing ACL ruptures towards the end of competition, sport-specific fatigue affected muscle activation and kinematics of the ACLr knee.