Contribution of Neuromuscular Factors to Quadriceps Asymmetry After Anterior Cruciate Ligament Reconstruction

Context: To quantify quadriceps weakness after anterior cruciate ligament reconstruction (ACLR), researchers have often analyzed only peak torque. However, analyzing other characteristics of the waveform, such as the rate of torque development (RTD), time to peak torque (TTP), and central activation ratio (CAR), can lend insight into the underlying neuromuscular factors that regulate torque development. Objective: To determine if interlimb neuromuscular asymmetry was present in patients with ACLR at the time of clearance to return to activity. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: A total of 10 individuals serving as controls (6 men, 4 women; age = 23.50 ± 3.44 years, height = 1.73 ± 0.09 m, mass = 71.79 ± 9.91 kg) and 67 patients with ACLR (43 men, 24 women; age = 21.34 ± 5.73 years, height = 1.74 ± 0.11 m, mass = 77.85 ± 16.03 kg, time postsurgery = 7.52 ± 1.36 months) participated. Main Outcome Measure(s): Isokinetic (60°/s) and isometric quadriceps strength were measured. Peak torque, TTP, and RTD were calculated across isometric and isokinetic trials, and CAR was calculated from the isometric trials via the superimposed burst. Repeated-measures analyses of variance were used to compare limbs in the ACLR and control groups. Results: No between-limbs differences were detected in the control group (P > .05). In the ACLR group, the involved limb demonstrated a longer TTP for isokinetic strength (P = .04; Cohen d effect size [ES] = 0.18; 95% confidence interval [CI] = −0.16, 0.52), lower RTD for isometric (P < .001; Cohen d ES = 0.73; 95% CI = 0.38, 1.08) and isokinetic (P < .001; Cohen d ES = 0.84; 95% CI = 0.49, 1.19) strength, lower CAR (P < .001; Cohen d ES = 0.37; 95% CI = 0.03, 0.71), and lower peak torque for isometric (P < .001; Cohen d ES = 1.28; 95% CI = 0.91, 1.65) and isokinetic (P < .001; Cohen d ES = 1.15; 95% CI = 0.78, 1.52) strength. Conclusions: Interlimb asymmetries at return to activity after ACLR appeared to be regulated by several underlying neuromuscular factors. We theorize that interlimb asymmetries in isometric and isokinetic quadriceps strength were associated with changes in muscle architecture. Reduced CAR, TTP, and RTD were also present, indicating a loss of motor-unit recruitment or decrease in firing rate.

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STRONGER THAN EVER! ADOLESCENT ATHLETES SHOW STRENGTH GAINS WITHIN THE UNINJURED LEG AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967121s00050 ◽

2021 ◽

Vol 9 (7_suppl3) ◽

pp. 2325967121S0005

Author(s):

Elliot Greenberg ◽

Joshua Bram ◽

Theodore Ganley

Keyword(s):

Anterior Cruciate Ligament ◽

Anterior Cruciate Ligament Reconstruction ◽

Ligament Reconstruction ◽

Cruciate Ligament ◽

Cohort Analysis ◽

Peak Torque ◽

Quadriceps Strength ◽

Strength Assessment ◽

Cruciate Ligament Reconstruction ◽

Anterior Cruciate

Background: The restoration of quadriceps strength after anterior cruciate ligament reconstruction (ACLR) is critical to restore optimal patient function and reduce the incidence of secondary ACL injury. Strength is typically quantified during return to sport assessments, by comparing the strength in the involved limb to that of the uninvolved limb. A limb symmetry index (LSI) is calculated and used to determine if any residual strength deficits persist. Recent evidence demonstrates that the uninvolved limb may lose strength during ACLR recovery and suggests that pre-operative uninvolved limb strength values may offer a better representation and more stringent indicator of strength recovery after ACLR. However, this body of literature is limited and no studies have specifically evaluated this occurrence within youth athletes. Purpose: To evaluate the change in strength in the uninvolved limb from pre-operative to 6 months post-ACLR, and assess the effect of pre-operative strength comparison on 6-month post-op LSI. Methods: A retrospective cohort analysis of pediatric patients (≤18 years) undergoing primary ACLR from 1/2018-1/2020 without concomitant multi-ligamentous reconstruction was conducted. Isokinetic peak torque values for the uninvolved and involved quadriceps were extracted at pre-operative (uninvolved only) and 6 months post-operative. Strength changes were analyzed using paired-samples t-test. Results: Complete data was available for a total of 17 subjects (mean age 15.1±1.7, 53% female). Pre-operative strength assessment was performed a mean of 11.5 days (range 1-26) prior to surgery. The mean 6-month post-operative assessment occurred at 177 days (range 127-246). The uninvolved limb was significantly stronger (p<0.001) at 6 months compared to preoperatively, with a mean improvement of 12.1ft/lbs (95%CI 18.3 – 7.2) with a change from 82.4ft/lbs to 95.1 ft/lbs. The LSI was calculated using both pre-operative and 6-month post-operative uninvolved limb values and demonstrated substantially lower LSI values when using concurrent 6-month data (LSIpre 91.3% vs LSI6M 76.9%). Conclusions: Among this sample, the uninvolved limb got stronger during post-ACLR recovery and comparison to concurrently assessed strength values led to a more stringent determination of LSI. Differences in rehabilitation programming, adolescent physiology, and pre-injury training patterns may explain why these results differ than those found in older cohorts.

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Quadriceps Function, Knee Pain, and Self-Reported Outcomes in Patients With Anterior Cruciate Ligament Reconstruction

Journal of Athletic Training ◽

10.4085/1062-6050-245-16 ◽

2018 ◽

Vol 53 (4) ◽

pp. 337-346 ◽

Cited By ~ 20

Author(s):

Adam S. Lepley ◽

Brian Pietrosimone ◽

Marc L. Cormier

Keyword(s):

Anterior Cruciate Ligament ◽

Anterior Cruciate Ligament Reconstruction ◽

Ligament Reconstruction ◽

Cruciate Ligament ◽

Quadriceps Strength ◽

Knee Function ◽

Cruciate Ligament Reconstruction ◽

Anterior Cruciate ◽

Quadriceps Function ◽

Return To Activity

Context: Interactions among muscle strength, pain, and self-reported outcomes in patients with anterior cruciate ligament reconstruction (ACLR) are not well understood. Clarifying these interactions is of clinical importance because improving physical and psychological function is thought to optimize outcomes after ACLR. Objective: To examine the relationships among neuromuscular quadriceps function, pain, self-reported knee function, readiness to return to activity, and emotional response to injury both before and after ACLR. Design: Descriptive laboratory study. Patients or Other Participants: Twenty patients (11 females and 9 males; age = 20.9 ± 4.4 years, height = 172.4 ± 7.5 cm, weight = 76.2 ± 11.8 kg) who were scheduled to undergo unilateral ACLR. Main Outcome Measure(s): Quadriceps strength, voluntary activation, and pain were measured at presurgery and return to activity, quantified using maximal voluntary isometric contractions (MVICs), central activation ratio, and the Knee Injury and Osteoarthritis Outcome Score pain subscale, respectively. Self-reported knee function, readiness to return to activity, and emotional responses to injury were evaluated at return to activity using the International Knee Documentation Committee questionnaire (IKDC), ACL Return to Sport After Injury scale (ACL-RSI), and Psychological Response to Sport Injury Inventory (PRSII), respectively. Pearson product moment correlations and linear regressions were performed using raw values and percentage change scores. Results: Presurgical levels of pain significantly predicted 31% of the variance in the ACL-RSI and 29% in the PRSII scores at return to activity. The MVIC and pain collected at return to activity significantly predicted 74% of the variance in the IKDC, whereas only MVIC significantly predicted 36% of the variance in the ACL-RSI and 39% in the PRSII scores. Greater increases in MVIC from presurgery to return to activity significantly predicted 49% of the variance in the ACL-RSI and 59% of the variance in the IKDC scores. Conclusion: Decreased quadriceps strength and higher levels of pain were associated with psychological responses in patients with ACLR. A comprehensive approach using traditional rehabilitation that includes attention to psychological barriers may be an effective strategy to improve outcomes in ACLR patients.

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