Abstract
This study is intended to find more effective and robust clinical diagnostic indices to characterize muscle strength and coordination alternation following anterior cruciate ligament (ACL) rupture. To evaluate angle-specific moments and hamstring (H)/quadriceps (Q) ratios, 46 male subjects with unilateral chronic ACL-rupture performed isokinetic concentric (c), eccentric (e) quadriceps and hamstring muscle tests respectively at 60°/s. Normalized moments and H/Q ratios were calculated for peak moment (PM) and 30°, 40°, 50°, 60°, 70°, 80° knee flexion angles. Furthermore, we introduced single-to-arithmetic-mean (SAM) and single-to-root-mean-square (SRMS) muscle co-contraction ratios, calculating them for specific angles and different contraction repetitions. Normalized PM and 40° specific concentric quadriceps, concentric hamstring strength in the ACL-deficient knee were reduced significantly (P ≤ 0.05). Concentric angle-specific moments together with Qe/Qc ratios at 40° (d = 0.766 vs. d = 0.654) identify more obvious differences than peak values in ACL ruptured limbs. Furthermore, we found SRMS-QeQc deficits at 40° showed stronger effect than Qe/Qc ratios (d = 0.918 vs. d = 0.766), albeit other ratio differences remained basically the same effect size as the original H/Q ratios. All the newly defined SAM and SRMS indices could decrease variance. Overall, 40° knee moments and SAM/SRMS ratios might be new potential diagnosis indices for ACL rupture detection.
Highlights
Muscle strength is important to the health of an individual, critical for optimal performance in sports and for preventing certain serious sport-related injuries
The Hamstring concentric/Quadriceps concentric (Hc/Qc) ratios and the Hamstring eccentric/Quadriceps eccentric (He/Qe) ratios of peak moments have been studied in ACLD subjects[14]
Hiemstra et al stated that the largest Hc/Qc ratio variations could be found at around 40° knee angle between normal and anterior cruciate ligament (ACL) reconstructed subjects[18], yet no concentration was paid on ACLD patients
Summary
Muscle strength is important to the health of an individual, critical for optimal performance in sports and for preventing certain serious sport-related injuries. Most studies of muscle strength related to the ACL injury have used the peak moment as main outcome measure[3,4,5]. Quadriceps peak moment represents the value during knee extension where the individual could produce the highest force[6]. ACLD patients have shown about 14–25% quadriceps[5, 7] and hamstring strength[7, 8] deficits on the injured limb. Compared to the commonly used peak moment values, angle of less than 40° specific thigh muscle moment values provided more information on the strength deficits after ACL injury[11]. Hiemstra et al stated that the largest Hc/Qc ratio variations could be found at around 40° knee angle between normal and ACL reconstructed subjects[18], yet no concentration was paid on ACLD patients. The optimal joint angle of the H/Q ratio which demonstrates the most obvious disparities between the healthy and ACLD limb needs to be clarified
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