Torque complexity of maximal knee extensor isometric contraction in individuals following anterior cruciate ligament reconstruction.

BACKGROUND: Current rehabilitation goals following anterior cruciate ligament reconstruction are structured around the maximal force generating capabilities of the muscle. Force fluctuations, an index of force control, have been observed to alter post- anterior cruciate ligament reconstruction. The temporal structure, or "complexity" of force fluctuations may provide important insight into the post-operative muscular recovery. The aims of this study were 1) to compare quadriceps torque complexity in anterior cruciate ligament reconstructed patients to the contralateral limb and to healthy, controls and 2) to assess the relationships between torque complexity to patient outcomes. METHODS: Data from 120 anterior cruciate ligament reconstructed participants (65 Females, 21.0 ± 8.3 years, 5.96 ± 0.48-months post-surgery) and 95 healthy controls (50 Females, 21.5 ± 2.9 years) were collected. A 30-s knee extensor maximal isometric contraction was completed to calculate approximate entropy, a measure of torque complexity. FINDINGS: Approximate entropy was found to decrease throughout the 30-s trial (P < .001, Cohen's d = 1.87 [1.64,2.10]). The anterior cruciate ligament reconstructed limb demonstrated greater approximate entropy compared to the contralateral limb or to healthy controls (P < .001, Cohen's d = 0.64 [0.38,0.90]). approximate entropy at the end of the trial demonstrated weak, negatively relationships with peak torque, patient reported outcome measures, and knee extensor fatigue (r = -0.21 to -0.32, P < .05). INTERPRETATION: A greater torque complexity in individuals following anterior cruciate ligament reconstruction was weakly related to lower quadriceps strength, lower subjective function, and quadriceps fatigue resistance. The complexity of force fluctuations during a sustained maximal task may draw clinical insight into the recovery of motor function following anterior cruciate ligament reconstruction.

Patient function in serial assessments throughout the post-ACL reconstruction progression.

OBJECTIVE: To assess the changes in patient strength and function from 4- to 6-month assessments following ACLR, determine relationships between changes in strength to changes in subjective function, and identify factors that predict patients that fail to increase in strength. DESIGN: Prospective, Cohort Study. SETTING: Controlled Laboratory. PARTICIPANTS: Forty-seven patients(27 female, 24.3 ± 11.1 years) completed a battery of performance assessments at approximately 4- and 6-months following primary ACLR (4.03 ±0 .49 and 6.46 ±0 .68 months). MAIN OUTCOME MEASURES: Subjective scores and isokinetic knee flexor and extensor strength were compared across visits. Patients were categorized per their ability to increase in strength beyond a previously defined threshold(0.22 Nm/kg). Binary logistic regression models were used to determine predictors of patients that failed to meet strength changes. RESULTS: Patients demonstrated improvements in patient-reported outcomes and strength measures between visits(P's < 0.05). Higher age (B = -0.073, P = .039), lower pre-injury activity levels (B = 0.61, P = .022), and higher limb symmetry indexes (B = -0.044, P = .05) at 4-months were predictors of patients that did not achieve improvements in quadriceps strength between assessments. CONCLUSIONS: From 4- to 6-months post-ACLR, increases in subjective function, strength and symmetry were observed. High quadriceps symmetry at interim assessments without consideration of the magnitude of strength values could overestimate recovery of quadriceps function.