Neural drive and motor unit characteristics after anterior cruciate ligament reconstruction: implications for quadriceps weakness

Purpose

The purpose of this investigation was to compare the quality of neural drive and recruited quadriceps motor units' (MU) action potential amplitude (MUAPAMP) and discharge rate (mean firing rate (MFR)) relative to recruitment threshold (RT) between individuals with anterior cruciate ligament reconstruction (ACLR) and controls.

Methods

Fourteen individuals with ACLR and 13 matched controls performed trapezoidal knee extensor contractions at 30%, 50%, 70%, and 100% of their maximal voluntary isometric contraction (MVIC). Decomposition electromyography (dEMG) and torque were recorded concurrently. The Hoffmann reflex (H-reflex) and central activation ratio (CAR) were acquired bilaterally to detail the proportion of MU pool available and volitionally activated. We examined MUAPAMP-RT and MFR-RT relationships with linear regression and extracted the regression line slope, y-intercept, and RT range for each contraction. Linear mixed effect modelling used to analyze the effect of group and limb on regression line slope and RT range.

Results

Individuals with ACLR demonstrated lower MVIC torque in the involved limb compared to uninvolved limb. There were no differences in H-reflex or CAR between groups or limbs. The ACLR involved limb demonstrated smaller mass-normalized RT range and slower MU firing rates at high contraction intensities (70% and 100% MVIC) compared to uninvolved and control limbs. The ACLR involved limb also demonstrated larger MU action potentials in the VM compared to the contralateral limb. These differences were largely attenuated with relative RT normalization.

Conclusions

These results suggest that persistent strength deficits following ACLR may be attributable to a diminished quadriceps motor neuron pool and inability to upregulate the firing rate of recruited MUs.

Effects of n-3 polyunsaturated fatty acid supplementation on quadriceps weakness immediately after total knee arthroplasty: a pilot, randomized, open-label clinical trial

[Purpose] Severe quadriceps weakness immediately after total knee arthroplasty can be problematic. The n-3 long-chain polyunsaturated fatty acids have antioxidant and anti-inflammatory effects against ischemia-reperfusion injury, whereas n-6 long-chain polyunsaturated fatty acids exert pro-inflammatory effects, thereby promoting ischemia-reperfusion injury. [Participants and Methods] We explored the efficacy of preoperative n-3 long-chain polyunsaturated fatty acid supplementation against early quadriceps weakness among 20 patients scheduled for total knee arthroplasty (intervention group, n=10; control group, n=10). The intervention group received 645 mg of eicosapentaenoic acid) and 215 mg of docosahexaenoic acid daily for 30 days preoperatively. Serum eicosapentaenoic acid, docosahexaenoic acid, and arachidonic acid levels were measured preoperatively. We compared serum derivatives of reactive oxygen metabolites as oxidative stress biomarkers, knee circumference, thigh volume, knee pain during the quadriceps strength test, and quadriceps strength preoperatively and 4 days postoperatively to quantify the change. [Results] Preoperative n-3 long-chain polyunsaturated fatty acid supplementation significantly increased the (eicosapentaenoic acid+docosahexaenoic acid)/arachidonic acid ratio in the intervention group. A significantly lower increase in quadriceps weakness was exhibited in the intervention group than in the control group. However, changes in oxidative stress, knee/thigh swelling, and knee pain during strength testing did not significantly differ between the two groups. [Conclusion] Preoperative n-3 long-chain polyunsaturated fatty acid supplementation exhibited beneficial effects on quadriceps weakness immediately after total knee arthroplasty.

Magnetic twitch assessment of diaphragm and quadriceps weakness in critically ill mechanically ventilated patients

Critically ill mechanically ventilated (MV) patients develop significant muscle weakness, which has major clinical consequences. There remains uncertainty, however, regarding the severity of leg weakness, the precise relationship between muscle strength and thickness, and the risk factors for weakness in MV patients. We therefore measured both diaphragm (PdiTw) and quadriceps (QuadTw) strength in MV patients using magnetic stimulation and compared strength to muscle thickness. Both PdiTw and QuadTw were profoundly reduced for MV patients, with PdiTw 19 % of normal and QuadTw 6% of normal values. There was a poor correlation between strength and thickness for both muscles, with thickness often remaining in the normal range when strength was severely reduced. Regression analysis revealed reductions in PdiTw correlated with presence of infection (p = 0.006) and age (p = 0.007). QuadTw best correlated with duration of MV (p = 0.036). Limb muscles are profoundly weak in critically ill patients, with a severity that mirrors the level of weakness observed in the diaphragm.

Suppressed quadriceps fascicle behavior is present in the surgical limbs of those with a history of ACL reconstruction

The balance of published data have largely focused on adaptations in muscle and fiber size after anterior cruciate ligament reconstruction (ACLR), failing to account for the dynamic changes in the behavior of the muscles' contractile elements that strongly contribute to force production. To better understand the sources of quadriceps dysfunction, the purpose of our research was to determine if alterations in fascicle behavior are present after ACLR. Unilateral ACLR individuals (9 m/9f; 21 ± 3 yrs; 1.74 ± 0.12 m;71.58 ± 13.31 kg; months from surgery:38 ± 36) and healthy controls (3 m/6f; 23 ± 2 yrs; 1.67 ± 0.10 m; 63.51 ± 10.11 kg) participated. In-vivo vastus lateralis fascicle behavior was recorded using ultrasonography during three maximal isokinetic knee extensions (60°·s^-1). Fascicle length, angle, and shortening velocity were calculated and analyzed from rest to peak torque. Peak knee extension torque was averaged between isokinetic trials (Nm·kg^-1). Group by limb interactions were assessed using separate two-way analyses of variance and were further evaluated by comparing 95% confidence intervals where appropriate. Significant interactions were present for fascicle angle at peak torque (P = 0.01), fascicle length excursion (P = 0.05), fascicle angle excursion (P < 0.01), fascicle shortening velocity (P = 0.05) and strength (P = 0.03). Upon post-hoc evaluation, the surgical limb displayed altered in-vivo fascicle behavior compared to all limbs (P < 0.05) and reduced strength compared to the contralateral and right control limbs (P < 0.05). No other significant interactions were present (P > 0.05). Our data show that those with a history of ACLR have fascicles that are slower, lengthen less and operate with lower angles relative to the axis of force production. Altered fascicle behavior after ACLR may be an important underlying factor to explaining the protracted quadriceps dysfunction.

Effects of preoperative low-intensity training with slow movement on early quadriceps weakness after total knee arthroplasty in patients with knee osteoarthritis: a retrospective propensity score-matched study

Background

Severe and early quadriceps weakness (QW) after total knee arthroplasty (TKA), which is caused by acute inflammation resulting from surgical trauma and tourniquet-induced ischemia-reperfusion (IR) injury, can be especially problematic. We focused on tourniquet-induced IR injury, because it has been shown to be preventable through ischemic and exercise preconditioning. Low-intensity resistance exercise with slow movement and tonic force generation (LST) share some similarities with ischemic and exercise preconditioning. The present study primarily aimed to clarify the efficacy of preoperative LST program as prehabilitation for early QW among patients with TKA using propensity score matching analysis.

Methods

This single-center retrospective observational study used data from patients with knee osteoarthritis (n = 277) who were scheduled to undergo unilateral TKA between August 2015 and January 2017. Those with missing outcome data due to their inability to perform tests were excluded. The LST group included participants who performed LST and aerobic exercise (LST session) more than seven times for three months prior to surgery. The control group included participants who performed less than eight LST sessions, a general and light exercise or had no exercise for three months prior to surgery. Knee circumference, thigh volume, knee pain during quadriceps strength test (QST) and timed up and go test (TUG), quadriceps strength, and TUG were measured before and 4 days after surgery. Knee swelling, thigh swelling, Δknee pain, QW, and ΔTUG were determined by comparing pre- and postoperative measurements.

Results

Propensity score matching generated 41 matched pairs who had nearly balanced characteristics. The LST group had a significantly lower knee and thigh swelling, QW, and ΔTUG compared to the control group (all, p < 0.05). No significant differences in Δknee pain during the QST and TUG were observed between both groups (both, p > 0.05).

Conclusions

The present study demonstrated the beneficial effects of preoperative LST program on knee swelling, thigh swelling, QW, and walking disability immediately after TKA.

Hop tests can result in higher limb symmetry index values than isokinetic strength and leg press tests in patients following ACL reconstruction

PURPOSE

Quadriceps weakness is a common clinical sign following anterior cruciate ligament injury and reconstruction surgery (ACLR). The aim of this study was to compare strength deficits and the limb symmetry index (LSI) from three different types of functional tests: isokinetic dynamometry, hop test, and leg press.

METHODS

A total of 26 subjects with ACLR (average 8.3 months post-operation) participated in the study. The peak knee extension torque was tested with isokinetic dynamometry at 60/180/300 °/s (ISO60/180/300). Hop distance was tested during single hop (SH) and triple hop (TH). Unilateral peak leg power (POWER) was tested during a bilateral leg press test. LSI was calculated as the ratio of the involved limb over the uninvolved limb values. Pearson correlation coefficients and paired t-tests were used to establish relationships among ISO60/180/300, SH/TH, and POWER values and compare these values between the limbs, respectively. Within-subject one-way analysis of variance (ANOVA) with post hoc analyses was used to compare LSI values among different tests.

RESULTS

ISO60/180/300 values were significantly positively correlated with SH/TH and POWER (P < 0.05), while SH/TH and POWER values were not significantly correlated. Significant limb differences were found in all tests (P = 0.001-0.008). ANOVA revealed significant LSI differences among different tests. Specifically, post hoc analyses revealed that LSI during SH was significantly higher than LSI during ISO60. Similarly, LSI during TH was significantly higher than LSIs from ISO60, ISO180, and POWER tests.

CONCLUSIONS

Peak knee extension torque values were positively associated with hop distance and leg power during the leg press test. However, LSI values should be interpreted with caution as hop tests provided significantly higher LSI values than isokinetic testing. Both isokinetic dynamometry and unilateral leg press machine could be used to isolate and strengthen the quadriceps in the involved limb. The current "gold standard" isokinetic testing at slow speed (ISO60) provided the lowest LSI value among all functional tests; therefore, the current study supported a continued use of isokinetic testing when examining individual's readiness and return-to-sport.

LEVEL OF EVIDENCE

III.

Experimental muscle pain of the vastus medialis reduces knee joint extensor torque and alters quadriceps muscle contributions as revealed through musculoskeletal modeling

BACKGROUND

Voluntary activation deficit of the quadriceps muscle group is a common symptom in populations with knee joint injury. Musculoskeletal modeling and simulations can improve our understanding of pathological conditions; however, they are mathematically complex which can limit their clinical application. A practical subject-specific modeling framework is introduced to evaluate knee extensor inhibition and muscle force contributions to isometric knee joint torques in healthy adults with and without experimentally induced quadriceps muscle pain.

METHODS

A randomized cross-over placebo controlled study design was used. Subject-specific maximum knee joint extension torque and quadriceps electromyographic data from 13 uninjured young adults were combined in a modeling framework to determine optimal muscle strength scaling parameters and ideal torque. Strength deficit ratios (experimental torque/ideal torque) and individual muscle contribution to experimental torque was computed before and after intramuscular hypertonic (pain inducing) and isotonic (sham) saline was injected to the vastus medialis.

FINDINGS

Decreased experimental knee extension torque (-8%) and vastus medialis electromyography (-26%) amplitude pre- to post- hypertonic injection was observed. Correspondingly, significant decreases in the knee extensor strength deficit ratio (-18%) and percent contribution of vastus medialis to experimental torque (-24%) was observed pre- to post- hypertonic injection. No differences were observed with isotonic injections, confirming the validity of the model.

INTERPRETATION

Our practical method to estimate strength ratios can be easily implemented within a musculoskeletal modeling framework to improve the validity of model estimates. This, in turn, can increase our understanding of the relationship between neuromuscular deficits and functional outcomes in patient populations.

Alterations in quadriceps muscle cellular and molecular properties in adults with moderate knee osteoarthritis

OBJECTIVE

Quadriceps muscle weakness is common in knee osteoarthritis (OA). While pain, disuse, and atrophy are commonly cited causes for muscle weakness in OA, emerging evidence suggests changes in muscle quality also occur. Alterations in muscle quality are not well understood, but likely include both cellular and morphologic adaptions. The purpose of this study was to conduct the first cellular-level analysis of the vastus lateralis in adults with moderate knee OA.

METHODS

Vastus lateralis biopsies were obtained from 24 subjects with moderate knee OA and 15 healthy controls. Quadriceps strength, muscle fiber cross sectional area (CSA), fiber type distribution, extracellular matrix (ECM) content, satellite cell abundance, and profibrotic gene expression were assessed.

RESULTS

Relative to controls, quadriceps strength was significantly lower in OA subjects (OA 62.23, 50.67-73.8 Nm vs 91.46, 75.91-107.0 Nm, P = 0.003) despite no difference in fiber CSA. OA subjects had significantly fewer Type I fibers (OA 41.51, 35.56-47.47% vs 53.07, 44.86-61.29%, P = 0.022) and more hybrid IIa/x fibers (OA 24.61, 20.61-28.61% vs 16.4, 11.60-21.20%, P = 0.009). Significantly greater ECM content, lower satellite cell density, and higher profibrotic gene expression was observed with OA, and muscle collagen content was inversely correlated to strength and satellite cell (SC) density.

CONCLUSION

Lower quadriceps function with moderate OA may not result from fiber size impairments, but is associated with ECM expansion. Impaired satellite cell density, high profibrotic gene expression, and a slow-to-fast fiber type transition may contribute to reduced muscle quality in OA. These findings can help guide therapeutic interventions to enhance muscle function with OA.

Muscle contributions to knee extension in the early stance phase in patients with knee osteoarthritis

The aim of this study was to analyze individual muscle contributions to knee angular acceleration using a musculoskeletal simulation analysis and evaluate knee extension mechanics in the early stance phase in patients with knee osteoarthritis (OA). The subjects comprised 15 patients with medial knee OA and 14 healthy elderly individuals. All participants underwent gait performance test using 8 infrared cameras and two force plates to measure the kinetic and kinematic data. The simulation was driven by 92 Hill-type muscle-tendon units of the lower extremities and a trunk with 23° of freedom. We analyzed each muscle contribution to knee angular acceleration in the 5%-15% and 15%-25% periods of the stance phase (% SP) using an induced acceleration analysis. We compared accelerations by individual muscles between the two groups using an analysis of covariance for controlling gait speed. Patients with knee OA had a significantly lesser knee extension acceleration by the vasti muscles and higher knee acceleration by hip adductors than those in controls in 5-15% SP. In addition, knee OA resulted in significantly lesser knee extension acceleration by the vasti muscles in 15-25% SP. These results indicate that patients with knee OA have decreased dependency on the vasti muscles to control knee movements during early stance phase. Hip adductor muscles, which mainly control mediolateral motion, partly compensate for the weak knee extension by the vasti muscles in patients with knee OA.

Contributions of neural excitability and voluntary activation to quadriceps muscle strength following anterior cruciate ligament reconstruction

BACKGROUND

Persistent quadriceps weakness is common following anterior cruciate ligament reconstruction (ACLr). Alterations in spinal-reflexive excitability, corticospinal excitability and voluntary activation have been hypothesized as underlying mechanisms contributing to quadriceps weakness. The aim of this study was to evaluate the predictive capabilities of spinal-reflexive excitability, corticospinal excitability and voluntary activation on quadriceps strength in healthy and ACLr participants.

METHODS

Quadriceps strength was measured using maximal voluntary isometric contractions (MVIC). Voluntary activation was quantified via the central activation ratio (CAR). Corticospinal and spinal-reflexive excitability were measured using active motor thresholds (AMT) and Hoffmann reflexes normalized to maximal muscle responses (H:M), respectively. ACLr individuals were also split into high and low strength subsets based on MVIC.

RESULTS

CAR was the only significant predictor in the healthy group. In the ACLr group, CAR and H:M significantly predicted 47% of the variance in MVIC. ACLr individuals in the high strength subset demonstrated significantly higher CAR and H:M than those in the low strength subset.

CONCLUSION

Increased quadriceps voluntary activation, spinal-reflexive excitability and corticospinal excitability relates to increased quadriceps strength in participants following ACLr.

CLINICAL RELEVANCE

Rehabilitation strategies used to target neural alterations may be beneficial for the restoration of muscle strength following ACLr.

The relationship between quadriceps muscle weakness and worsening of knee pain in the MOST cohort: a 5-year longitudinal study

OBJECTIVE

To determine whether quadriceps weakness is associated with elevated risk of worsening knee pain over 5 years.

METHODS

The Multicenter Osteoarthritis Study (MOST) is a longitudinal study of 50-79-year-old adults with knee osteoarthritis (OA) or known risk factors for knee OA. The predictor variable was baseline isokinetic quadriceps strength. Covariates included baseline body mass index (BMI), physical activity level, and history of knee surgery. The outcome was worsening pain reported on the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index pain subscale or knee replacement surgery between baseline and 5-year follow-up. Analyses were knee-based and used generalized estimating equations, stratified by sex to assess whether the lowest compared with the highest tertile of baseline quadriceps strength was associated with an increased risk of worsening knee pain at 5-year follow-up, controlling for age, BMI, history of knee surgery, and physical activity level as well as correlation between knees within participants.

RESULTS

Analyses of worsening knee pain included 4,648 knees from 2,404 participants (61% female). Men with lower quadriceps strength did not have a higher risk of worsening knee pain (RR {95% CI} = 1.01 {0.78-1.32}, P = 0.9183). However, women in the lowest compared with the highest strength tertile had a 28% increased risk of worsening knee pain (RR {95% CI} = 1.28 {1.08-1.52}, P = 0.0052).

CONCLUSION

Quadriceps weakness was associated with an increased risk of worsening of knee pain over 5 years in women, but not in men.