Corticomuscular cross-recurrence analysis reveals between-limb differences in motor control among individuals with ACL reconstruction

Surgical reconstruction of the anterior cruciate ligament (ACL) and subsequent physical therapy can help athletes return to competition; however, re-injury rates remain disproportionately high due, in part, to lingering biomechanical and neurological factors that are not fully addressed during rehabilitation. Prior reports indicate that individuals exhibit altered electrical activity in both brain and muscle after ACL reconstruction (ACLR). In this investigation, we aimed to extend existing approaches by introducing a novel non-linear analysis of corticomuscular dynamics, which does not assume oscillatory coupling between brain and muscle: Corticomuscular cross-recurrence analysis (CM-cRQA). Our findings indicate that corticomuscular dynamics vary significantly between involved (injured) and uninvolved legs of participants with ACLR during voluntary isometric contractions between the brain and both the vastus medialis and lateralis. This finding points to a potential lingering neural deficit underlying re-injury for athletes after surgical reconstruction, namely the dynamical structure of neuromuscular (brain to quad muscle) coordination, which is significantly asymmetric, between limbs, in those who have ACLR.

Athlete Muscular Phenotypes Identified and Compared with High-Dimensional Clustering of Lower Limb Muscle Volume Measurements

INTRODUCTION

Athletes use their skeletal muscles to demonstrate performance. Muscle force generating capacity is correlated with volume, meaning that variations in sizes of different muscles may be indicative of how athletes meet different demands in their sports. Medical imaging enables in vivo quantification of muscle volumes; however, muscle volume distribution has not been compared across athletes of different sports.

PURPOSE

The goal of this work was to define "muscular phenotypes" in athletes of different sports and compare these using hierarchical clustering.

METHODS

Muscle volumes normalized by body mass of athletes (football, baseball, basketball, or track) were compared with control participants to quantify size differences using z -scores. z -Scores of 35 muscles described the pattern of volume deviation within each athlete's lower limb, characterizing their muscular phenotype. Data-driven high-dimensional clustering analysis was used to group athletes presenting similar phenotypes. Efficacy of clustering to identify similar phenotypes was demonstrated by grouping athletes' contralateral limbs before other athletes' limbs.

RESULTS

Analyses revealed that athletes did not tend to cluster with others competing in the same sport. Basketball players with similar phenotypes grouped by clustering also demonstrated similarities in performance. Clustering also identified muscles with similar volume variation patterns across athletes, and principal component analysis revealed specific muscles that accounted for most of the variance (gluteus maximus, sartorius, semitendinosus, vastus medialis, vastus lateralis, and rectus femoris).

CONCLUSIONS

Athletes exhibit heterogeneous lower limb muscle volumes that can be characterized and compared as individual muscular phenotypes. Clustering revealed that athletes with the most similar phenotypes do not always play the same sport such that patterns of muscular heterogeneity across a group of athletes reflect factors beyond their specific sports.

In vivo imaging of skeletal muscle form and function: 50 years of insight

Skeletal muscle form and function has fascinated scientists for centuries. Our understanding of muscle function has long been driven by advancements in imaging techniques. For example, the sliding filament theory of muscle, which is now widely leveraged in biomechanics research, stemmed from observations made possible by scanning electron microscopy. Over the last 50 years, advancing in medical imaging, combined with ingenuity and creativity of biomechanists, have provide a wealth of new and important insights into in vivo human muscle function. Incorporation of in vivo imaging has also advanced computational modeling and allowed our research to have an impact in many clinical populations. While this review does not provide a comprehensive or meta-analysis of the all the in vivo muscle imaging work over the last five decades, it provides a narrative about the past, present, and future of in vivo muscle imaging.

Quadriceps Dysfunction Following Joint Preservation Surgery: A Review of the Pathophysiologic Basis and Mitigation Strategies

PURPOSE OF REVIEW

To characterize quadriceps muscle dysfunction associated with knee joint preservation surgery, with a focus on its pathophysiology and promising approaches to mitigate its impact on clinical outcomes.

RECENT FINDINGS

Quadriceps dysfunction (QD) associated with knee joint preservation surgery results from a complex interplay of signaling, related to changes within the joint and from those involving the overlying muscular envelope. Despite intensive rehabilitation regimens, QD may persist for many months postoperatively and negatively impact clinical outcomes associated with various surgical procedures. These facts underscore the need for continued investigation into the potential detrimental effects of regional anesthetic and intraoperative tourniquet use on postoperative quadriceps function, with an outward focus on innovation within the field of postoperative rehabilitation. Neuromuscular stimulation, nutritional supplementation, cryotherapy, blood flow restriction (BFR), and open-chain exercises are all potential additions to postoperative regimens. There is compelling literature to suggest that these modalities are efficacious and may diminish the magnitude and duration of postoperative QD. A clear understanding of QD, with respect to its pathophysiology, should guide perioperative treatment and rehabilitation strategies and influence ongoing rehabilitation-based research and innovation. Moreover, clinicians must appreciate the magnitude of QD's effect on diminished clinical outcomes, risk for re-injury and patients' ability (or inability) to return to pre-injury level of activity following knee joint preservation procedures.

Evaluation of raw segmental bioelectrical impedance variables throughout anterior cruciate ligament reconstruction rehabilitation

Background.Raw bioelectrical impedance analysis (BIA) variables are related to physical function in healthy and diseased populations. Therefore, BIA may be an insightful, noninvasive method of assessment to track following anterior cruciate ligament reconstruction (ACLR).Objectives.Evaluate phase angle, reactance and impedance at 50 kHz (PhA₅₀, Xc₅₀, andZ₅₀, respectively) in the operative (OP) and non-operative (NOP) limbs during ACLR rehabilitation.Approach.Seventeen patient (12 M, 5 F; 18.8 ± 4.8 years) clinic reports were evaluated prior to ACLR (PRE), two- (2 W), six- (6 W), and twelve-weeks (12 W) post-ACLR and at return to sport testing (RTS).Setting.All observations occurred during the participant's physical therapy visits.Measurements.A multi-frequency BIA device measured segmental PhA, Xc, andZ. Linear mixed effects models were used to assess any leg and time interaction and changes over leg and time, independently. Any interactions or main effects were considered significant atp< 0.05.Main results.Significant legxtime interactions were observed for each variable. PhA₅₀and Xc₅₀of NOP were higher (p< 0.001) than OP at each time point by an average of by 0.9° and 4.9 Ω, respectively. In OP, PhA₅₀and Xc₅₀decreased from PRE to 2 W and increased from 6 to 12 W and 12 W to RTS (p< 0.01, for all). At RTS, PhA₅₀and Xc₅₀were similar to PRE in OP (p> 0.05). ForZ₅₀, the OP leg did not change over time (p> 0.05).Z₅₀was greater in NOP at 2 and 6 W (p< 0.01, for both). There were differences in PhA₅₀in NOP between PRE and 6 W and from 6 W to RTS (p< 0.05 for both). Xc₅₀did not change (p> 0.05), andZ₅₀PRE was lower than at 2 W (p< 0.05).Significance.A multi-frequency BIA device can detect changes in segmental BIA variables following ACLR.

Factors Influencing Treatment Outcome and Proprioception after Electrocoagulation of the Femoral Insertion of the Anterior Cruciate Ligament

(1) Background: Studies have established that exercises shaping the sense of deep sensation are an important element of medical rehabilitation of patients after vaporization of the femoral insertion of the anterior cruciate ligament and affect the restoration of correct movement patterns, thus reducing the risk of injuries. The aim of this study was to determine the factors influencing the treatment outcome and deep-feeling function after applying a specific rehabilitation scheme 12 weeks after anterior cruciate ligament electrocoagulation surgery. (2) Methods: The study group consisted of 41 patients after partial rupture of the anterior cruciate ligament, who underwent electrocoagulation of the femoral cruciate ligament attachment and microfracture of the femoral attachment area. All patients were operated on by the same surgeon and then rehabilitated according to the same medical rehabilitation protocol. The anthropometric and clinical data were collected through an anterior drawer test, Lachman test, assessment of the range of movements in the knee joint, muscle strength test, Unterberger test and Lysholm questionnaire. The assessment was performed before the surgery, and then on days 7-10, after 6 and 12 weeks of rehabilitation treatment. (3) Results: Statistical improvement of the parameters was demonstrated by strength of the quadriceps and hamstrings muscle, the Unterberger test, and the Lysholm scale after surgery. A negative correlation was found between the Unterberger test and Lysholm scale at the end of the research period and it differed depending on the gender and the dominant limb. The Lysholm scale and muscle strength were independent of sex, dominant extremity and associated damage of the meniscus and cartilage. The Lysholm scale 6 weeks after surgery negatively correlated with BMI. (4) Conclusions: Stability of the knee joint and improvement of proprioception were demonstrated 12 weeks after treatment with an ACL electrocoagulation and rehabilitation regimen. The factors contributing to a better treatment outcome were greater muscle strength, less thigh asymmetry, better sense of depth, younger age and lower body weight.

Isometric Knee Muscle Strength and Patient-Reported Measures Five Years after Anterior Cruciate Ligament Reconstruction: Comparison of Single versus Dual Autograft Hamstring Tendon Harvesting

There is some controversy regarding the use of one or two hamstring tendons for anterior cruciate ligament reconstruction (ACLR). In this study, two cohorts of 22 male patients underwent an ACLR with hamstring tendon autografts. One cohort was reconstructed through an all-inside technique with the semitendinosus tendon (ST group) and the other with the semitendinosus and gracilis tendons (ST-G group). Anterior tibial translation (ATT), Lysholm, and IKDC scores were assessed preoperatively and five years postoperation. Additionally, isometric knee muscle strength was manually measured in both groups and in another cohort of 22 uninjured control male subjects five years after the operation. There were no significant differences in ATT and Lysholm scores between the operated groups. The IKDC score was lower in the ST-G group than in the ST group—9.57 (CI 14.89−4.25) (p < 0.001). No significant differences between injured and uninjured knees were detected in hamstring to quadriceps ratio strength and quadriceps limb symmetry index of the two operated groups, but the hamstring limb symmetry index was significantly lower in the ST-G group than in the ST and control groups. This study shows that using an ST-G autograft for ACLR yielded less flexor strength and worse results in some patient-reported outcome measures (PROM) than using an ST autograft five years after the operation. The observed results let us suggest that the use of one autograft hamstring tendon for ACLR is clinically preferable to the use of two hamstring tendons.

Effect of Lymphaticovenous Anastomosis on Muscle Edema, Limb, and Subfascial Volume in Lower Limb Lymphedema: MRI Studies

BACKGROUND

Although satisfactory volume reduction in secondary unilateral lower limb lymphedema after lymphaticovenous anastomosis (LVA) in the affected limb has been well reported, alleviation of muscle edema and the impact of LVA on the contralateral limb have not been investigated.

STUDY DESIGN

This retrospective cohort study enrolled patients who underwent supermicrosurgical LVA between November 2015 and January 2017. Pre- and post-LVA muscle edema were assessed using fractional anisotropy (FA) and apparent diffusion coefficient (ADC). The primary endpoint was changes in limb/subfascial volume assessed with magnetic resonance volumetry at least 6 months after LVA.

RESULTS

Twenty-one patients were enrolled in this study. Significant percentage reductions in post-LVA muscle edema were found in the affected thigh (83.6% [interquartile range = range of Q1 to Q3; 29.8-137.1] [FA], 53.3% [27.0-78.4] [ADC]) as well as limb (21.7% [4.4-26.5]) and subfascial (18.7% [10.7-39.1]) volumes. Similar findings were noted in the affected lower leg: 71.8% [44.0-100.1] (FA), 59.1% [45.8-91.2] (ADC), 21.2% [6.8-38.2], and 28.2% [8.5-44.8], respectively (all p < 0.001). Significant alleviation of muscle edema was also evident in the contralateral limbs (thigh: 25.1% [20.4-57.5] [FA]; 10.7% [6.6-17.7] [ADC]; lower leg: 47.1% [35.0-62.8] [FA]; 14.6% [6.5-22.1] [ADC]; both p < 0.001), despite no statistically significant difference in limb and subfascial volumes.

CONCLUSIONS

Our study found significant reductions in muscle edema and limb/subfascial volumes in the affected limb after LVA. Our findings regarding edema in the contralateral limb were consistent with possible lymphedema-associated systemic influence on the unaffected limb, which could be surgically relieved.

Bilateral muscle atrophy after anterior cruciate ligament reconstruction in rats: Protective effects of anti-inflammatory drug celecoxib

BACKGROUND

Muscle atrophy after anterior cruciate ligament (ACL) reconstruction occurs bilaterally and contributes to a decrease in muscle strength. However, effective treatment strategies for ACL reconstruction-induced muscle atrophy have not been established. We examined the effects of anti-inflammatory drug on muscle atrophy after ACL reconstruction.

MATERIALS AND METHODS

Rats were divided into groups according to treatment received: untreated control (n = 4), arthrotomy (n = 6), ACL transection (n = 7), ACL reconstruction (n = 8), and ACL reconstruction plus anti-inflammatory drug celecoxib (CBX; 50 mg/kg/day) administration (n = 8). At one-week post-surgery, the muscle fiber cross-sectional area (CSA) in the rectus femoris (RF) and semitendinosus (ST) was measured to assess muscle atrophy. In addition, we examined joint swelling and serum C‑reactive protein (CRP) levels to assess local and systemic inflammation, respectively.

RESULTS

Each additional procedure (i.e., arthrotomy, ACL transection, and ACL reconstruction) gradually decreased the muscle fiber CSAs in the RF and ST on both operated and contralateral sides. The degree of muscle fiber atrophy on the operated side was larger than that detected on the contralateral side. Moreover, ACL reconstruction induced joint swelling on the operated side and tended to increase serum CRP levels. CBX lessened the RF atrophy on both sides and was associated with less joint swelling and a smaller increase CRP level; however, it did not affect ST atrophy on either side.

CONCLUSIONS

Anti-inflammatory treatments after ACL reconstruction may be effective in lessening muscle atrophy in the quadriceps, but not in the hamstrings.

Arthrogenic Muscle Inhibition Following Anterior Cruciate Ligament Injury

Arthrogenic muscle inhibition (AMI) is a common impairment in individuals who sustain an anterior cruciate ligament (ACL) injury. The AMI causes decreased muscle activation, which impairs muscle strength, leading to aberrant movement biomechanics. The AMI is often resistant to traditional rehabilitation techniques, which leads to persistent neuromuscular deficits following ACL reconstruction. To better treat AMI following ACL injury and ACL reconstruction, it is important to understand the specific neural pathways involved in AMI pathogenesis, as well as the changes in muscle function that may impact movement biomechanics and long-term structural alterations to joint tissue. Overall, AMI is a critical factor that limits optimal rehabilitation outcomes following ACL injury and ACL reconstruction. This review discusses the current understanding of the: (1) neural pathways involved in the AMI pathogenesis following ACL injury; (2) consequence of AMI on muscle function, joint biomechanics, and patient function; and (3) development of posttraumatic osteoarthritis. Finally, the authors review the evidence for interventions specifically used to target AMI following ACL injury.

Effects of Blood Flow Restriction Training on Clinical Outcomes for Patients With ACL Reconstruction: A Systematic Review

CONTEXT

Knee muscle atrophy and weakness are common impairments after anterior cruciate ligament (ACL) reconstruction. Blood flow restriction (BFR) training represents a new approach to treat such impairments. However, limited evidence currently exists to support this intervention in related patients.

OBJECTIVE

To appraise literature comparing the effects of BFR training with conventional therapy on knee muscle morphological and strength properties in ACL-reconstructed patients.

DATA SOURCES

PubMed, SPORTDiscus, CINAHL, and Cochrane Central Register databases were searched for relevant articles from January 1991 through April 2021.

STUDY SELECTION

Articles were minimum Level 3 evidence focusing on knee muscle morphologic as well as extensor and flexor strength outcomes in ACL-reconstructed patients of all graft types.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 2.

DATA EXTRACTION

Critical appraisal instruments (Downs and Black checklist, Cochrane Collaboration tool, ROBINS-1 tool) were used to evaluate study quality. We independently calculated effect sizes (ESs) (Cohen d) between groups in each study. The Strength of Recommendation Taxonomy grading scale was used for clinical recommendations.

RESULTS

Six articles (4 randomized control studies, 1 nonrandomized study, and 1 case-control study) met inclusion criteria. Exercises paired with BFR training included open kinetic chain, closed kinetic chain, and passive applications. Diverse assessments and time of intervention were observed across studies. ESs ranged from trivial to large in favor of BFR training for muscle morphological (d = 0.06 to 0.81) and strength assessments (d = -0.12 to 1.24) with CIs spanning zero.

CONCLUSION

At this time, grade B or inconsistent and limited-quality patient-oriented evidence exists to support using BFR training to improve or maintain thigh muscle size as well as knee extensor and flexor strength in ACL-reconstructed patients. ESs indicated no consistent clinically meaningful differences when compared with conventional therapy. Subsequent analyses should be repeated as new evidence emerges to update practice guidelines.

Long-Lasting Impairments in Quadriceps Mitochondrial Health, Muscle Size, and Phenotypic Composition Are Present After Non-invasive Anterior Cruciate Ligament Injury

Introduction

Despite rigorous rehabilitation aimed at restoring muscle health, anterior cruciate ligament (ACL) injury is often hallmarked by significant long-term quadriceps muscle weakness. Derangements in mitochondrial function are a common feature of various atrophying conditions, yet it is unclear to what extent mitochondria are involved in the detrimental sequela of quadriceps dysfunction after ACL injury. Using a preclinical, non-invasive ACL injury rodent model, our objective was to explore the direct effect of an isolated ACL injury on mitochondrial function, muscle atrophy, and muscle phenotypic transitions.

Methods

A total of 40 male and female, Long Evans rats (16-week-old) were exposed to non-invasive ACL injury, while 8 additional rats served as controls. Rats were euthanized at 3, 7, 14, 28, and 56 days after ACL injury, and vastus lateralis muscles were extracted to measure the mitochondrial respiratory control ratio (RCR; state 3 respiration/state 4 respiration), mitochondrial reactive oxygen species (ROS) production, fiber cross sectional area (CSA), and fiber phenotyping. Alterations in mitochondrial function and ROS production were detected using two-way (sex:group) analyses of variance. To determine if mitochondrial characteristics were related to fiber atrophy, individual linear mixed effect models were run by sex.

Results

Mitochondria-derived ROS increased from days 7 to 56 after ACL injury (30–100%, P &lt; 0.05), concomitant with a twofold reduction in RCR (P &lt; 0.05). Post-injury, male rats displayed decreases in fiber CSA (days 7, 14, 56; P &lt; 0.05), loss of IIa fibers (day 7; P &lt; 0.05), and an increase in IIb fibers (day 7; P &lt; 0.05), while females displayed no changes in CSA or phenotyping (P &gt; 0.05). Males displayed a positive relationship between state 3 respiration and CSA at days 14 and 56 (P &lt; 0.05), while females only displayed a similar trend at day 14 (P = 0.05).

Conclusion

Long-lasting impairments in quadriceps mitochondrial health are present after ACL injury and play a key role in the dysregulation of quadriceps muscle size and composition. Our preclinical data indicate that using mitoprotective therapies may be a potential therapeutic strategy to mitigate alterations in muscle size and characteristic after ACL injury.

Effect of High-Protein Diets on Integrated Myofibrillar Protein Synthesis before Anterior Cruciate Ligament Reconstruction: A Randomized Controlled Pilot Study

Increasing dietary protein intake during periods of muscle disuse may mitigate the resulting decline in muscle protein synthesis (MPS). The purpose of this randomized pilot study was to determine the effect of increased protein intake during periods of disuse before anterior cruciate ligament (ACL) reconstruction on myofibrillar protein synthesis (MyoPS), and proteolytic and myogenic gene expression. Six healthy, young males (30 ± 9 y) were randomized to consume a high-quality, optimal protein diet (OP; 1.9 g·kg−1·d−1) or adequate protein diet (AP; 1.2 g·kg−1·d−1) for two weeks before ACL reconstruction. Muscle biopsies collected during surgery were used to measure integrated MyoPS during the intervention (via daily deuterium oxide ingestion) and gene expression at the time of surgery. MyoPS tended to be higher, with a large effect size in OP compared to AP (0.71 ± 0.1 and 0.54 ± 0.1%·d−1; p = 0.076; g = 1.56). Markers of proteolysis and myogenesis were not different between groups (p > 0.05); however, participants with greater MyoPS exhibited lower levels of MuRF1 gene expression compared to those with lower MyoPS (r = −0.82, p = 0.047). The data from this pilot study reveal a potential stimulatory effect of increased daily protein intake on MyoPS during injury-mediated disuse conditions that warrants further investigation.

Estimates of voluntary activation in individuals with anterior cruciate ligament reconstruction: Effects of type of stimulator, number of stimuli, and quantification technique

BACKGROUND

Accurate quantification of voluntary activation is important for understanding the extent of quadriceps dysfunction in individuals with anterior cruciate ligament reconstruction (ACLR). Voluntary activation has been quantified using both percent activation derived from the interpolated twitch technique and central activation ratio (CAR) derived from the burst superimposition technique, as well as by using different types of electrical stimulators and pulse train conditions. However, it is unclear how these parameters affect voluntary activation estimates in individuals with ACLR. This study was performed to fill this important knowledge gap in the anterior cruciate ligament literature.

METHODS

Quadriceps strength and voluntary activation were examined in 18 ACLR participants (12 quadriceps/patellar tendon graft, 6 hamstring tendon graft; time since ACLR: 1.06 ± 0.82 years, mean ±  SD) at 90° of knee flexion using 2 stimulators (Digitimer and Grass) and pulse train conditions (3-pulse and 10-pulse). Voluntary activation was quantified by calculating both CAR and percent activation.

RESULTS

Results indicated that voluntary activation was significantly overestimated by CAR when compared with percent activation (p < 0.001). Voluntary activation estimates were not affected by pulse train conditions when using percent activation; however, 3-pulse stimuli resulted in greater overestimation than 10-pulse stimuli when using CAR (p = 0.003). Voluntary activation did not differ between stimulators (p > 0.05); however, the Digitimer evoked greater torque at rest than the Grass (p < 0.001).

CONCLUSION

These results indicate that percent activation derived from the interpolated twitch technique provides superior estimates of voluntary activation than CAR derived from burst superimposition and is less affected by pulse train conditions or stimulators in individuals with ACLR.

Correlation among Knee Muscle Strength and Self-Reported Outcomes Score, Anterior Tibial Displacement, and Time Post-Injury in Non-Coper Anterior Cruciate Ligament Deficient Patients: A Cross-Sectional Study

Little attention has been paid to knee muscle strength after ACL rupture and its effect on prognostic outcomes and treatment decisions. We studied hamstrings (H) and quadriceps (Q) strength correlation with a patient-reported outcome measures score (International Knee Documentation Committee, IKDC), anterior tibial translation (ATT), and time post-injury in 194 anterior cruciate ligament deficient patients (ACLD) who required surgery after a failed rehabilitation program (non-copers). The correlation between knee muscle strength and ATT was also studied in 53 non-injured controls. ACLD patients showed decreased knee muscle strength of both the injured and non-injured limbs. The median (interquartile range) values of the H/Q ratio were 0.61 (0.52-0.81) for patients' injured side and 0.65 (0.57-0.8) for the non-injured side (p = 0.010). The median H/Q ratio for the controls was 0.52 (0.45-0.66) on both knees (p < 0.001, compared with the non-injured side of patients). The H/Q, ATT, and time post-injury were not significantly correlated with the IKDC score. ATT was significantly correlated with the H/Q of the injured and non-injured knees of patients, but not in the knees of the controls. Quadriceps strength and H/Q ratio were significantly correlated with ATT for both limbs of the patients. IKDC score correlated significantly with the quadriceps and hamstrings strengths of the injured limb but not with the H/Q ratio, ATT or time passed after injury.

Arthrogenic Muscle Inhibition: Best Evidence, Mechanisms, and Theory for Treating the Unseen in Clinical Rehabilitation

CONTEXT

Arthrogenic muscle inhibition (AMI) impedes the recovery of muscle function following joint injury, and in a broader sense, acts as a limiting factor in rehabilitation if left untreated. Despite a call to treat the underlying pathophysiology of muscle dysfunction more than three decades ago, the continued widespread observations of post-traumatic muscular impairments are concerning, and suggest that interventions for AMI are not being successfully integrated into clinical practice.

OBJECTIVES

To highlight the clinical relevance of AMI, provide updated evidence for the use of clinically accessible therapeutic adjuncts to treat AMI, and discuss the known or theoretical mechanisms for these interventions.

EVIDENCE ACQUISITION

PubMed and Web of Science electronic databases were searched for articles that investigated the effectiveness or efficacy of interventions to treat outcomes relevant to AMI.

EVIDENCE SYNTHESIS

122 articles that investigated an intervention used to treat AMI among individuals with pathology or simulated pathology were retrieved from 1986 to 2021. Additional articles among uninjured individuals were considered when discussing mechanisms of effect.

CONCLUSION

AMI contributes to the characteristic muscular impairments observed in patients recovering from joint injuries. If left unresolved, AMI impedes short-term recovery and threatens patients' long-term joint health and well-being. Growing evidence supports the use of neuromodulatory strategies to facilitate muscle recovery over the course of rehabilitation. Interventions should be individualized to meet the needs of the patient through shared clinician-patient decision-making. At a minimum, we propose to keep the treatment approach simple by attempting to resolve inflammation, pain, and effusion early following injury.

Electrically Evoked Torque at Rest is Strongly Related to Quadriceps Muscle Size in Individuals with Anterior Cruciate Ligament Reconstruction

Electrically evoked torque at rest (i.e., the torque produced from supramaximal stimul applied to a resting muscle) has been shown to be related to muscle size in healthy adults, but this relationship has not been evaluated in pathological populations where atrophy is present. This study aimed to evaluate the relationship between the electrically evoked torque at rest and vastus lateralis cross-sectional area (CSA) in individuals with anterior cruciate ligament (ACL) reconstruction. Eighteen individuals with ACL reconstruction participated. Quadriceps electrically evoked torque at rest was elicited bilaterally via sex-specific, standardized supramaximal triplet stimulations. Vastus lateralis CSA was measured at 50% of thigh length using ultrasound. Pearson's r and partial correlations were used to evaluate associations between outcomes. Evoked torque at rest was positively associated with vastus lateralis CSA in the ACL reconstructed limb (r=0.865, partial r=0.816, P<0.01), non-reconstructed limb (r=0.628, partial r=0.575, P<0.05), and side-to-side ratios (r=0.670, partial r=0.659, P<0.01). These results indicate that electrically evoked torque at rest may indirectly assess side-to-side differences in quadriceps muscle size after ACL reconstruction.

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.

Implementing Ultrasound Imaging for the Assessment of Muscle and Tendon Properties in Elite Sports: Practical Aspects, Methodological Considerations and Future Directions

Ultrasound (US) imaging has been widely used in both research and clinical settings to evaluate the morphological and mechanical properties of muscle and tendon. In elite sports scenarios, a regular assessment of such properties has great potential, namely for testing the response to training, detecting athletes at higher risks of injury, screening athletes for structural abnormalities related to current or future musculoskeletal complaints, and monitoring their return to sport after a musculoskeletal injury. However, several practical and methodological aspects of US techniques should be considered when applying this technology in the elite sports context. Therefore, this narrative review aims to (1) present the principal US measures and field of applications in the context of elite sports; (2) to discuss, from a methodological perspective, the strengths and shortcomings of US imaging for the assessment of muscle and tendon properties; and (3) to provide future directions for research and application.

Changes in gastrocnemii activation at mid-to-late stance markedly affects the intact and anterior cruciate ligament deficient knee biomechanics and stability in gait

INTRODUCTION

We aimed to quantify the sensitivity in biomechanical response and stability of the intact and anterior cruciate ligament deficient (ACL-D) joints at mid-to-late stance periods of gait to the alterations in activation of gastrocnemii (Gas) muscles.

METHODS

A validated kinematics-driven musculoskeletal finite-element model of the lower extremity is used to compute knee joint response and stability under reported kinetics-kinematics of healthy subjects. Activation in Gas is altered under prescribed gait data at the mid-to-late stance of gait and associated changes in remaining muscle forces/contact forces/areas/ACL force and joint stability are computed in both intact and ACL-D joints.

RESULTS

In the intact joint, the anterior-tibial-translation (ATT) as well as ACL and joint contact forces follow variations in Gas forces. Both the stability and ATT of an ACL-D joint are restored to the near-intact levels when the activity in Gas is reduced. Knee joint instability, excessive ATT as well as larger peak articular contact stresses with a posterior shift in contact areas are estimated under greater Gas forces.

CONCLUSIONS

ACL-D joint is unstable with ATT > 10 mm under larger activities in Gas. Gas is an ACL-antagonist while hamstrings and soleus are ACL-agonists. The near-intact joint stability and ATT of an ACL-D joint can be restored at a lower activation in Gas; or in other words, when activation in ACL-antagonist muscles drops compared with that in ACL-agonist muscles. Results could help analyze the gait of ACL-D copers and non-copers and provide better understanding towards improved preventive, diagnostic, and treatment approaches.

Hamstrings Muscle Morphology After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-Analysis

BACKGROUND

Hamstrings muscle morphology is determinant of muscle function (i.e. strength). Among individuals with ACL reconstruction (ACLR), less cross-sectional area (CSA) and volume in the ACLR-limb are associated with muscle weakness, and may contribute to lower rates of return to preinjury activity level and an increased risk for long-term sequelae.

OBJECTIVES

To effectively treat muscular impairments, an accurate understanding of differences in hamstrings morphology following ACLR is needed. A systematic review and meta-analysis were undertaken to describe the morphology of the hamstring muscle complex after ACLR.

METHODS

We searched five databases for studies evaluating the difference between hamstrings size and architecture in individuals with ACLR. Two independent reviewers assessed each paper for inclusion and quality. Means and standard deviations were extracted from each included study to allow fixed-effect size meta-analysis calculations for comparison of results.

RESULTS

Twenty-four studies were included for final review. Eight categories of morphological outcomes were identified, and studies were grouped accordingly: (1) volume, (2) cross-sectional area (CSA), (3) muscle length, (4) muscle thickness, (5) fascicle length, (6) pennation angle, (7) fiber area, and (8) fiber type. Meta-analysis demonstrated lower hamstrings volume in the ACLR-limb in both contralateral and control group comparisons, and lower CSA, length, and thickness in the ACLR-limb in contralateral comparisons. The semitendinosus and gracilis were most profoundly impacted. Limited moderate evidence demonstrated greater biceps femoris pennation angle in the ACLR-limb.

CONCLUSIONS

Individuals with ACLR demonstrated large deficits in semitendinosus and gracilis muscle CSA and volume in the ACLR-limb compared contralaterally, with no differences observed in the biceps femoris or semimembranosus. Clinical implications regarding assessment and treatment of individuals with ACLR are discussed.

Preoperative and postoperative assessment of temporal and masseter muscle size with magnetic resonance imaging in patients undergoing unilateral temporomandibular joint surgery

The aim of this study was to assess any change between the preoperative and postoperative sizes of temporal and masseter muscles with magnetic resonance imaging (MRI) in patients undergoing unilateral temporomandibular joint surgery. This study was designed and implemented retrospectively. For clinical evaluation, a visual analog scale (VAS) and maximum mouth opening (MMO) were used. In order to make a preoperative diagnosis and perform a 6-month control, muscle size was measured in millimeters (mm) on T1 axial sections in MRI. Statistical analyses were performed using the SPSS 23.0 software package. Numeric variables were compared between two dependent groups using the Wilcoxon signed rank test. Statistical significance was set at p < 0.05. Twelve patients who underwent unilateral discectomy plus dermis-fat grafting, with classical preauricular inverse L incision, were included in the study, and data for eleven female patients were evaluated. The difference in size between the operated and non-operated sides was found to be statistically insignificant at the preoperative stage for both masseter muscle (operated side m^M: 13.264 ± 1.822 mm; non-operated side m^M: 13.264 ± 2.315 mm; p^M = 0.929) and temporal muscle (operated side m^T: 20.345 ± 2.609 mm; non-operated side m^T: 20.582 ± 2.366 mm; p^T = 0.594). There was a significant size reduction in the masseter muscle on the operated side in the postoperative period (preop m^M: 13.264 ± 1.822 mm; postop m^M: 12.036 ± 1.728 mm; p^M = 0.018). Although there was also a size reduction in the operated side of the temporal muscle in the postoperative period, that difference did not reach statistical significance (preop m^T: 20.345 ± 2.609 mm; postop m^T: 19.445 ± 1.603 mm; p^T = 0.182). On the non-operated side, there were no significant postoperative changes in the sizes of either the masseter muscle (preop m^M: 13.264 ± 2.315 mm; postop m^M: 12.682 ± 2.059 mm; p^M = 0.248) or the temporal muscle (preop m^T: 20.582 ± 2.366; postop m^T: 19.891 ± 3.487 mm; p^T = 0.625). Considering the study findings as a whole, a size reduction was observed in the operated side of the masseter muscle after TMJ surgery. The etiology of this change may be surgical trauma to the temporal and masseter muscles, skeletal alteration resulting from condylar change secondary to discectomy, and patients restraining themselves from application of maximum bite force as a result of a self-protection mechanism due to postoperative pain.

Hamstrings Neuromuscular Function After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-Analysis

BACKGROUND

Hamstrings neuromuscular function is a crucial component of functional movement, and changes after anterior cruciate ligament (ACL) injury contribute to risk factors for secondary injury and long-term sequelae. To effectively treat muscular impairments, an accurate understanding of hamstrings neuromuscular function in patients with ACL reconstruction (ACLR) is needed.

OBJECTIVE

A systematic review and meta-analysis were undertaken to describe and quantify hamstrings neuromuscular function in individuals with ACLR compared to controls.

METHODS

We searched PubMed, Web of Science, SPORTDiscus, CINAHL, and EBSCOhost databases in October of 2020 for studies evaluating the difference between hamstrings electromyography (EMG) between individuals with ACLR and controls. Two independent reviewers assessed each paper for inclusion and quality. Means and standard deviations were extracted from each included study to allow random-effect size (ES) meta-analysis calculations for comparison of results.

RESULTS

Thirty-four studies were included for final review. From these, 5 categories of neuromuscular outcomes were identified, and studies were grouped accordingly: (1) muscle activation levels (EMG amplitude), (2) co-activation, (3) onset timing, (4) electromechanical delay, and (5) time-to-peak activity. Moderate to strong evidence indicates that individuals with ACLR demonstrate higher hamstrings EMG amplitude (normalized to % maximum voluntary isometric contraction) and hamstrings-to-quadriceps co-activation during gait and stair ambulation compared to controls. In addition, there was moderate evidence of longer electromechanical delay during knee flexion and greater hamstrings-to-quadriceps co-activation during knee extension compared to controls.

CONCLUSIONS

Greater hamstrings EMG amplitude and co-activation during gait and ambulation tasks and longer electromechanical delay of the hamstrings in individuals with ACLR align with clinical impairments following ACLR and have implications for re-injury risk and long-term joint health, thus warranting attention in rehabilitation.

Thigh-Muscle and Patient-Reported Function Early After Anterior Cruciate Ligament Reconstruction: Clinical Cutoffs Unique to Graft Type and Age

CONTEXT

Patient-reported function is an important outcome in anterior cruciate ligament rehabilitation. Identifying which metrics of thigh-muscle function are indicators of normal patient-reported function can help guide treatment.

OBJECTIVE

To identify which metrics of thigh-muscle function discriminate between patients who meet and patients who fail to meet age- and sex-matched normative values for patient-reported knee function in the first 9 months after anterior cruciate ligament reconstruction (ACLR) and establish cutoffs for these metrics by covariate subgroups.

DESIGN

Cross-sectional retrospective study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 256 patients (129 females, 128 males; age = 17.1 ± 3.0 years, height = 1.7 ± 0.1 m, mass = 74.1 ± 17.9 kg, months since surgery = 6.4 ± 1.4), 3 to 9 months after primary unilateral ACLR.

MAIN OUTCOME MEASURE(S)

We stratified the sample into dichotomous groups by the International Knee Documentation Committee (IKDC) score (IKDCMET, IKDCNOT MET) using sex- and age-matched normative values. We measured quadriceps and hamstrings isokinetic (60°/s) torque and power bilaterally. Normalized quadriceps and hamstrings peak torque (Nm/kg) and power (W/kg), limb symmetry indices (LSI, %), and hamstrings : quadriceps ratios were calculated. Logistic regression indicated which of these metrics could predict IKDC classification while controlling for age, graft type, and sex. Receiver operating characteristic curves established cutoffs for explanatory variables for both total cohort and covariate subgroups. Odds ratios (OR) determined the utility of each cutoff to discriminate IKDC status.

RESULTS

Quadriceps torque LSI (≥69.4%, OR = 3.6), hamstrings torque (≥1.11 Nm/kg, OR = 2.1), and quadriceps power LSI (≥71.4%, OR = 2.0) discriminated between IKDC classification in the total cohort. Quadriceps torque LSI discriminated between IKDC classification in the patellar-tendon graft (≥61.6%, OR = 5.3), hamstrings-tendon graft (≥71.8%, OR = 10.5), and age <18 years (≥74.3%, OR = 5.2) subgroups. Hamstrings torque discriminated between IKDC classifications in the age <18 years (≥1.10 Nm/kg, OR = 2.6) subgroup.

CONCLUSIONS

Quadriceps torque LSI, hamstrings torque, and quadriceps power LSI were the most useful metrics for predicting normal patient-reported knee function early after ACLR. Further, cutoff values that best predicted normal patient-reported function differed by graft type and age.

Functional evaluation of triceps surae during heel rise test: from EMG frequency analysis to machine learning approach

Soleus muscle flap as coverage tissue is a possible surgical solution adopted to cover the wounds due to open fractures. Despite this procedure presents many clinical advantages, relatively poor information is available about the loss of functionality of triceps surae of the treated leg. In this study, a group of patients who underwent a soleus muscle flap surgical procedure has been analyzed through the heel rise test (HRT), in order to explore the triceps surae residual functionalities. A frequency band analysis was performed in order to assess whether the residual heads of triceps surae exhibit different characteristics with respect to both the non-treated lower limb and an age-matched control group. Then, an in-depth analysis based on a machine learning approach was proposed for discriminating between groups by generalizing across new unseen subjects. Experimental results showed the reliability of the proposed analyses for discriminating between-group at a specific time epoch and the high interpretability of the proposed machine learning algorithm allowed the temporal localization of the most discriminative frequency bands. Findings of this study highlighted that significant differences can be recognized in the myoelectric spectral characteristics between the treated and contralateral leg in patients who underwent soleus flap surgery. These experimental results may support the clinical decision-making for assessing triceps surae performance and for supporting the choice of treatment in plastic and reconstructive surgery. Graphical Abstract The Graphical abstract presents the scope of the proposed analysis of myoelectric signals of soleus and gastrocnemius muscles of patiens groups during Hell Rise Test, highlighting the applied methods and the obtained results.

Muscle Atrophy After ACL Injury: Implications for Clinical Practice

CONTEXT

Distinct from the muscle atrophy that develops from inactivity or disuse, atrophy that occurs after traumatic joint injury continues despite the patient being actively engaged in exercise. Recognizing the multitude of factors and cascade of events that are present and negatively influence the regulation of muscle mass after traumatic joint injury will likely enable clinicians to design more effective treatment strategies. To provide sports medicine practitioners with the best strategies to optimize muscle mass, the purpose of this clinical review is to discuss the predominant mechanisms that control muscle atrophy for disuse and posttraumatic scenarios, and to highlight how they differ.

EVIDENCE ACQUISITION

Articles that reported on disuse atrophy and muscle atrophy after traumatic joint injury were collected from peer-reviewed sources available on PubMed (2000 through December 2019). Search terms included the following: disuse muscle atrophy OR disuse muscle mass OR anterior cruciate ligament OR ACL AND mechanism OR muscle loss OR atrophy OR neurological disruption OR rehabilitation OR exercise.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 5.

RESULTS

We highlight that (1) muscle atrophy after traumatic joint injury is due to a broad range of atrophy-inducing factors that are resistant to standard resistance exercises and need to be effectively targeted with treatments and (2) neurological disruptions after traumatic joint injury uncouple the nervous system from muscle tissue, contributing to a more complex manifestation of muscle loss as well as degraded tissue quality.

CONCLUSION

Atrophy occurring after traumatic joint injury is distinctly different from the muscle atrophy that develops from disuse and is likely due to the broad range of atrophy-inducing factors that are present after injury. Clinicians must challenge the standard prescriptive approach to combating muscle atrophy from simply prescribing physical activity to targeting the neurophysiological origins of muscle atrophy after traumatic joint injury.

Panoramic ultrasound vs. MRI for the assessment of hamstrings cross-sectional area and volume in a large athletic cohort

We investigated the validity of panoramic ultrasound (US) compared to magnetic resonance imaging (MRI) for the assessment of hamstrings cross-sectional area (CSA) and volume. Hamstrings CSA were acquired with US (by an expert operator) at four different sites of femur length (FL) in 85 youth competitive alpine skiers (14.8 ± 0.5 years), and successively compared to corresponding scans obtained by MRI, analyzed by a trained vs. a novice rater. The agreement between techniques was assessed by Bland–Altman analyses. Statistical analysis was carried out using Pearson’s product moment correlation coefficient (r). US-derived CSA showed a very good agreement compared to MRI-based ones. The best sites were 40% FL (0 = mid patellar point) for biceps femoris long head (r = 0.9), 50% for semitendinosus (r = 0.9), and 30% for semimembranosus (r = 0.86) and biceps femoris short head (BFsh, r = 0.8). US-based vs. MRI-based hamstrings volume showed an r of 0.96. Poorer r values were observed for the novice compared to the trained rater, with the biggest difference observed for BFsh at 50% (r = 0.001 vs. r = 0.50, respectively) and semimembranosus at 60% (r = 0.23 vs. r = 0.42, respectively). Panoramic US provides valid CSA values and volume estimations compared to MRI. To ensure optimal US-vs.-MRI agreement, raters should preferably possess previous experience in imaging-based analyses.

Bilateral Comparisons of Quadriceps Thickness after Anterior Cruciate Ligament Reconstruction

Background and objectives: Anterior cruciate ligament reconstruction (ACLR) often results in quadricep atrophy. The purpose of this study was to compare the bilateral thickness of each quadricep component before and after ACLR. Materials and Methods: Cross-sectional study design. In 14 patients who underwent ACLR, bilateral quadricep muscle thicknesses were measured using a portable ultrasound device, 1 h before and 48–72 h after ACLR. Two-way analysis of variance (ANOVA) was used to compare muscle thickness pre- and post-ACLR between the limbs. Results: The primary finding was that the vastus intermedius (VI) muscle was significantly smaller in the reconstructed limb after ACLR compared to that in the healthy limb (Reconstructed limb; RCL = Pre-operated (PRE): 19.89 ± 6.91 mm, Post-operated(POST): 16.04 ± 6.13 mm, Healthy limb; HL = PRE: 22.88 ± 6.07, POST: 20.90 ± 5.78 mm, F = 9.325, p = 0.009, η²p = 0.418). Conclusions: The results represent a selective surgical influence on the quadricep muscle thickness. These findings highlight the need of advanced strengthening exercises in order to restore VI thickness after ACLR.

Quadriceps Muscle Size Following ACL Injury and Reconstruction: A Systematic Review

Image-based assessments of quadriceps muscle size facilitate examination of structural changes after anterior cruciate ligament (ACL) injury and reconstruction (ACLR). Understanding the effects of ACLR on muscle size measures may aid in clarifying the contribution of quadriceps atrophy toward quadriceps strength. The purpose of this study was to systematically review the literature examining the effects of ACLR on quadriceps muscle volume and cross-sectional area (CSA). An online database search was conducted using Web of Science, SportDISCUS, PubMed (Medline), CINHAL (EBSCO), and Cochrane Library limited to articles published after January 1, 1980. Means and standard deviations were extracted for the ACLR limb and the contralateral limb, and sample characteristics from relevant articles. Magnitude of between limb differences were assessed using pooled effect sizes (Hedge's g) and 95% confidence intervals. Eleven articles (five CSA, six muscle volume) were included in this systematic review. Included studies reported negative effective sizes, indicating that the ACLR limb was smaller in CSA or muscle volume compared with the contralateral limb; however, 36% of the included articles reported meaningful difference between the limbs. Quadriceps atrophy may occur following ACL injury and persist after rehabilitation, however, the magnitude of these reductions may not be clinically meaningful and may only partially explain the persistent quadriceps weakness that is ubiquitous among this patient population. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:598-608, 2020.

Longitudinal Assessment of Quadriceps Muscle Morphology Before and After Anterior Cruciate Ligament Reconstruction and Its Associations With Patient-Reported Outcomes

BACKGROUND

Reductions in muscle size are common after anterior cruciate ligament reconstruction (ACLR) and may contribute to suboptimal patient outcomes. However, few studies have quantified postoperative alterations in muscle quality and evaluated its associations with patient-reported function.

HYPOTHESES

Rectus femoris cross-sectional area (CSA) will decrease postoperatively but improve at return to activity (RTA), rectus femoris muscle quality (percentage fat [PF]) will increase postoperatively and be greater at RTA compared with preoperative values, and rectus femoris CSA and PF will be associated with International Knee Documentation Committee (IKDC) scores at both postoperative time points.

STUDY DESIGN

Case series.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 26 individuals who sustained an ACL injury and underwent reconstructive surgery were evaluated preoperatively (T₀), 9 weeks post-ACLR (T₁), and at RTA. Rectus femoris CSA and PF were evaluated bilaterally via ultrasound imaging, and patient-reported function was assessed using the IKDC score.

RESULTS

Bilateral reductions in rectus femoris CSA were noted from T₀ to T₁ (P < 0.01). Only the uninvolved limb returned to preoperative CSA (P = 0.80), as the involved limb failed to return to preoperative levels at RTA (P = 0.04). No significant changes in rectus femoris PF were observed across time points (P > 0.05). Lesser PF (P < 0.01) but not CSA (P = 0.75) was associated with higher IKDC score at T₁. Lesser PF (P = 0.04) and greater CSA (P = 0.05) was associated with higher IKDC score at RTA.

CONCLUSION

Substantial atrophy occurs bilaterally after ACLR, and the involved limb does not return to preoperative muscle size despite the patient completing rehabilitation. Quadriceps muscle morphology is associated with patient-reported function and may be an important rehabilitation target after ACLR.

CLINICAL RELEVANCE

Quadriceps atrophy and poor muscle quality may contribute to suboptimal patient functioning and quadriceps dysfunction and may be important in RTA decision making. Assessing muscle morphology using ultrasound may be a feasible and clinically beneficial tool in patients after ACLR.

Quadriceps Neuromuscular and Physical Function After Anterior Cruciate Ligament Reconstruction

CONTEXT

Persistent neuromuscular deficits in the surgical limb after anterior cruciate ligament reconstruction (ACLR) have been repeatedly described in the literature, yet little is known regarding their association with physical performance and patient-reported function.

OBJECTIVE

To describe (1) interlimb differences in neuromuscular and functional outcomes and (2) the associations of neuromuscular outcomes with measures of physical and knee-related patient-reported function.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty individuals after primary, unilateral ACLR (19 males; age = 21.5 years [range, 14-41 years]; 8 months [range = 6-23 months] postsurgery).

MAIN OUTCOME MEASURE(S)

Knee-extensor isometric and isokinetic peak torque was measured with an isokinetic dynamometer. Cross-sectional area (CSA) was measured bilaterally for each of the quadriceps muscles via magnetic resonance imaging. We measured quadriceps central activation bilaterally via the superimposed-burst technique. Physical performance (single-legged hop tests, step length via spatiotemporal gait analysis) and patient-reported outcomes (International Knee Documentation Committee questionnaire and Knee Injury and Osteoarthritis Outcome Score Sport and Recreation subscale) were also recorded. We conducted Wilcoxon signed rank tests to identify interlimb differences. Spearman ρ correlation analyses revealed associations between limb symmetry and neuromuscular and functional outcomes, as well as with patient-reported function.

RESULTS

Deficits in the surgical limb as compared with the nonsurgical limb were present for all outcomes (P values < .05). Greater single-legged hop-test symmetry (83%) was significantly correlated with greater symmetry in knee-extensor isometric (63%; r_s = 0.567, P = .002) and isokinetic (68%; r_s = 0.540, P = .003) strength, as well as greater cross-sectional area of the vastus medialis (78%; r_s = 0.519, P = .006) and vastus lateralis (82%; r_s = 0.752, P < .001). A higher International Knee Documentation Committee questionnaire score (82.2) was significantly correlated with greater symmetry in knee-extensor isokinetic strength (r_s = 0.379, P = .039).

CONCLUSIONS

Although deficits were observed in the surgical limb for all neuromuscular measures, greater symmetry in the size and strength of the quadriceps, rather than activation, was more strongly associated with physical performance after ACLR. Greater symmetry in strength was also more strongly associated with patient-reported function.

Quadriceps Muscle Size, Quality, and Strength and Self-Reported Function in Individuals With Anterior Cruciate Ligament Reconstruction

CONTEXT

Ultrasound imaging provides a cost-effective method of measuring quadriceps morphology, which may be related to self-reported function after anterior cruciate ligament reconstruction (ACLR).

OBJECTIVE

To compare quadriceps morphology and strength between limbs in individuals with ACLR and matched control limbs and determine their associations with self-reported function.

DESIGN

Cross-sectional study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Forty-two individuals with ACLR (females = 66%; age = 21.8 ± 2.6 years; time since ACLR = 50.5 ± 29.4 months) and 37 controls (females = 73%; age = 21.7 ± 1.2 years).

MAIN OUTCOME MEASURE(S)

Quadriceps peak torque (PT) and rate of torque development were assessed bilaterally. Ultrasonography was used to measure the cross-sectional area (CSA) and echo intensity (EI) of the rectus femoris, vastus lateralis (VL), and vastus medialis. Self-reported function was assessed via the International Knee Documentation Committee (IKDC) score and Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales. Paired-samples t tests were calculated to compare involved and uninvolved limbs. Independent t tests were conducted to compare groups (α = .05). Linear regression was performed to analyze associations between quadriceps function and self-reported function after accounting for time since ACLR, activity level, and sex, and models for EI added subcutaneous fat as a covariate.

RESULTS

Isometric PT did not differ between limbs or groups. Involved limbs had a lower rate of torque development compared with the control (P = .01) but not the uninvolved limbs (P = .08). Vastus lateralis CSA was smaller in the involved than in the uninvolved (P < .01) but not the control limbs (P = .10). Larger VL CSA (ΔR² = 0.103) and lower VL EI (ΔR² = 0.076) were associated with a higher IKDC score (P < .05). Larger VL CSA was associated with greater KOOS Symptoms (ΔR² = 0.09, P = .043) and Sport and Recreation (ΔR² = 0.125, P = .014) scores. Lower VL EI was associated with higher KOOS Symptoms (ΔR² = 0.104, P = .03) and Quality of Life (ΔR² = 0.113, P = .01) scores. Quadriceps PT and rate of torque development were not associated with IKDC or KOOS subscale scores.

CONCLUSIONS

Quadriceps morphology was associated with self-reported function in individuals with ACLR and may provide unique assessments of quadriceps function.

How Much Time Is Needed Between Serial "Return to Play" Assessments to Achieve Clinically Important Strength Gains in Patients Recovering From Anterior Cruciate Ligament Reconstruction?

BACKGROUND

Pass rates for return-to-play evaluations are alarmingly low for patients after anterior cruciate ligament reconstruction (ACLR). Since timing of return to play is a complicated decision, it is important that patients be given optimal time to realize meaningful improvements in strength that warrant additional testing.

PURPOSE

To (1) compare outcomes among patients assessed at different time points after ACLR, (2) determine strength gains indicative of improvements in subjective function, and (3) determine the amount of time necessary to achieve meaningful strength gains.

STUDY DESIGN

Cross-sectional/case-control study; Level of evidence, 3.

METHODS

A total of 293 patients participated in the study after ACLR (mean ± SD, 23.2 ± 10.1 years old; n = 142 female participants; 6.4 ± 0.9 months after ACLR). Participants were stratified on the month of their evaluation after ACLR: 5 to 6 months (n = 122), 6 to 7 months (n = 102), 7 to 8 months (n = 43), and 8 to 9 months (n = 26). The International Knee Documentation Committee (IKDC) subjective form and knee extensor and flexor torque and symmetry, as assessed through an isokinetic dynamometer, were compared among groups. Forty patients (20 female participants, 20.4 ± 7.1 years old) were referred for subsequent testing (2.14 ± 0.78 months after initial visit). Subjective improvement between visits was defined as a ≥9-point change of the IKDC score. Thresholds of knee extensor torque and symmetry indicative of subjective improvement and the time between assessments needed to achieve these strength improvements were determined.

RESULTS

Patients between 5 and 6 months (IKDC, 79.7; interquartile range [IQR], 70.1-88.5) had lower subjective function compared to patients between 6 and 7 months (IKDC, 83.9; IQR, 74.5-92.0; P = .019) and 8 and 9 months after ACLR (IKDC, 89.1; IQR 75.8-92.3; P = .026). Patients between 5 and 6 months (1.41 N·m/kg; IQR, 1.16-1.73 N·m/kg]) had lower knee extensor torque compared to patients 6 and 7 months (1.59 N·m/kg; IQR, 1.23-1.95 N·m/kg; P = .013) and 7 and 8 months after ACLR (1.62 N·m/kg; IQR, 1.30-1.86 N·m/kg; P = .046). Patients between 5 and 6 months (66.4%; IQR, 54.2-78.6) had lower symmetry compared to patients between 6 and 7 months (71.8%; IQR,61.1-82.9; P = .019) and 8 and 9 months afterACLR (75.2%; IQR, 66.6-87.7; P = .014). Of the 40 patients that completed follow-up assessments, an increase in knee extensor torque of 0.22 N·m/kg and symmetry of 5.75% discriminated patients that achieved subjective improvement. A period of 1.97 months between assessments discriminated those that achieved the established symmetry threshold.

CONCLUSION

Patients demonstrate increasing subjective and quadriceps function when tested at later time points from surgery; however, the observed values are low, suggesting that at 9 months patients are demonstrating deficits that may be improving. Approximately 2 months is needed to observe clinically meaningful improvements.

Diagnostic Validity of an Isokinetic Testing to Identify Partial Anterior Cruciate Ligament Injuries

OBJECTIVE

To assess the diagnostic validity of an isokinetic testing to detect partial injuries on the anterior cruciate ligament (ACL).

DESIGN

Prospective diagnostic study.

SETTINGS

Orthopedic clinic, physiotherapy clinic, orthopedic hospital, and diagnostic/image clinic.

PARTICIPANTS

Consecutive patients (n = 29) with unilateral knee complaint submitted to physical examination, magnetic resonance images (MRIs), and isokinetic testing prior to surgery of ACL reconstruction.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The isokinetic torque curves data from extensor and flexor muscles were converted to frequency domain by fast Fourier transformation and compared with healthy contralateral limb. Differences were categorized as unstable knees and these conclusions were compared with patient's physical examinations (doctor's conclusion on ACL integrity) and MRIs (as the radiologist conclusions on ACL integrity). After surgery, all intraoperatively confirmed partial injured patient's data were collected. The diagnostic accuracy measures to compare the conclusions of all 3 professionals included sensitivity, specificity, positive predictive value, negative predictive value, disease prevalence, positive likelihood ratio, and accuracy-all using a confidence interval of 95%.

RESULTS

Compared with MRI, the sensitivity of isokinetic test for an ACL partial injury was 90.00%, specificity 83.33%, positive predictive value 52.94%, negative predictive value 97.56%, and accuracy 84.48%. Compared with physical examination, the sensitivity of isokinetic test for an ACL partial injury was 85.71%, specificity 78.43%, positive predictive value 35.29%, negative predictive value 97.56%, and accuracy 79.31%.

CONCLUSIONS

This method of isokinetic data analysis through fast Fourier transformation can be used to improve diagnostic accuracy of a difficult detection injury. Even present, a partial ACL injury can produce a stable knee during isokinetic testing and could be used to detect candidates for conservative treatment based on strengthening exercises, reducing surgery risks, and financial and social impact on patient's life.

The Effects of Anterior Cruciate Ligament Reconstruction on Individual Quadriceps Muscle Thickness and Circulating Biomarkers

Anterior cruciate ligament reconstruction (ACLR) frequently results in quadriceps atrophy. The present study investigated the effect of ACLR on the muscle thickness of the different constituent muscles of the quadriceps and circulating biomarkers related to muscle atrophy and hypertrophy. Fourteen subjects underwent anterior cruciate ligament reconstruction following injury. Quadriceps muscle thicknesses were measured using ultrasound, and circulating biomarkers in the blood were measured using enzyme-linked immunosorbent assays (ELISAs) at the preoperative visit (PRE) and at two postoperative visits (PO1, PO2) in the early stages post-surgery. Differences between time points were analyzed using one-way repeated measures analysis of variance (ANOVA) tests. The most important finding was that severe muscle atrophy occurred in the vastus intermedius (VI) after ACLR (PRE: 20.45 ± 6.82 mm, PO1: 16.05 ± 6.13 mm, PO2: 13.18 ± 4.7 mm, F = 59.0, p < 0.001). Furthermore, the myostatin level was slightly increased, and IGF-1 was significantly reduced throughout the entire period. Therefore, we suggest that inducing selective hypertrophy in the vastus intermedius during the process of rehabilitation would be important for athletes and individuals who engage in explosive sports. Moreover, inhibiting myostatin level increases and maintaining IGF-1 levels in the early phase of recovery after ACLR to prevent muscle atrophy may provide a pharmaceutical option for rehabilitation after anterior cruciate ligament injury.

The relationship between quadriceps strength asymmetry and knee biomechanics asymmetry during walking in individuals with anterior cruciate ligament reconstruction

BACKGROUND

Lower extremity movement asymmetries may lead to re-injury and knee osteoarthritis after anterior cruciate ligament (ACL) reconstruction surgery. However, there is no consensus regarding the effect of quadriceps strength asymmetry on lower extremity movement asymmetry after ACL reconstruction.

RESEARCH QUESTION

What is the relationship between quadriceps strength asymmetry and asymmetries in lower extremity kinematics and kinetics during walking in individuals who underwent ACL reconstruction surgery?.

METHODS

Isometric quadriceps strength, kinematic, and kinetic data during walking were collected from 24 men with unilateral ACL reconstruction. Knee joint angles and moments were reduced. Pearson correlation coefficients between asymmetry in selected knee biomechanics and isometric quadriceps strength asymmetry were determined.

RESULTS

The isometric quadriceps strength of the injured leg was significantly lower than that of the uninjured leg (P < 0.001). Knee flexion angles and knee extension moments were smaller in the injured leg than that in the uninjured leg during both loading response (P = 0.007, P = 0.047) and mid-stance phases (P = 0.005, P = 0.028). Isometric quadriceps strength asymmetry was significantly correlated with asymmetry in the peak knee flexion angle during loading response and mid-stance phases (r = -0.48, P = 0.017, r = -0.48, P = 0.017). Isometric quadriceps strength asymmetry was also significantly correlated with asymmetry in the peak knee extension moment during the mid-stance phase (r = -0.44, P = 0.033).

SIGNIFICANCE

Individuals with ACL reconstruction demonstrate knee movement asymmetry in the sagittal plane. Isometric quadriceps strength asymmetry is significantly correlated with asymmetry in knee flexion angles during the early stance phase and knee extension moments during the mid-stance phase. Rehabilitation programs should emphasise eccentric exercise to beneficially modify quadriceps neuromuscular control.

Quadriceps Recovery After Anterior Cruciate Ligament Reconstruction With Quadriceps Tendon Versus Patellar Tendon Autografts

Background

Quadriceps tendon (QT) autografts are being increasingly used for anterior cruciate ligament reconstruction (ACLR). A paucity of studies exist that compare QT autografts with alternative graft options. Additionally, concerns exist regarding quadriceps recovery after graft harvest insult to the quadriceps muscle-tendon unit.

Purpose/Hypothesis

The purpose of this study was to compare quadriceps recovery and functional outcomes in patients with QT versus bone-patellar tendon-bone (BPTB) autografts. The hypothesis was that those with QT autografts would demonstrate superior outcomes.

Study Design

Cohort study; Level of evidence, 3.

Methods

Active patients with a history of primary, unilateral ACLR with soft tissue QT or BPTB autografts participated. Quadriceps recovery was quantified using variables of strength, muscle size, and activation. Knee extensor isometric and isokinetic strength was measured bilaterally with an isokinetic dynamometer and normalized to body weight. Quadriceps activation was measured with the superimposed burst technique. The maximal cross-sectional area of each quadriceps muscle was measured bilaterally using magnetic resonance imaging. Assessors of muscle size were blinded to the graft type and side of ACLR. Functional tests included hop tests and step length symmetry during walking, measured via spatiotemporal gait analysis. Self-reported function was determined with the International Knee Documentation Committee (IKDC) questionnaire. Neuromuscular and functional outcomes were expressed as limb symmetry indices (LSIs: [surgical limb/nonsurgical limb]*100%). Wilcoxon rank-sum tests were used to compare the LSIs and IKDC scores between groups.

Results

There were 30 study participants (19 male, 11 female; median age, 22 years [range, 14-41 years]; median time since surgery, 8 months [range, 6-23 months]), with 15 patients in each group. There were no significant between-group differences in demographic variables or outcomes. LSIs were not significantly different between the QT versus BPTB group, respectively: knee extensor isokinetic strength at 60 deg/s (median, 70 [range, 41-120] vs 68 [range, 37-83]; P = .285), activation (median, 95 [range, 85-111] vs 92 [range, 82-105]; P = .148), cross-sectional area of the vastus medialis (median, 79 [range, 62-104] vs 77 [range, 62-95]; P = .425), single-leg hop test (median, 88 [range, 35-114] vs 77 [range, 49-100]; P = .156), and step length symmetry (median, 99 [range, 93-104] vs 98 [range, 92-103]; P = .653). The median IKDC scores between the QT and BPTB groups were also not significantly different: 82 (range, 67-94) versus 83 (range, 54-94); respectively (P = .683).

Conclusion

Patients with QT autografts demonstrated similar short-term quadriceps recovery and postsurgical outcomes compared with patients with BPTB autografts.

Quadriceps Strength and Volitional Activation After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis

Context:

Quadriceps function is a significant contributor to knee joint health that is influenced by central and peripheral factors, especially after anterior cruciate ligament reconstruction (ACLR).

Objective:

To assess differences of unilateral quadriceps isometric strength and activation between the involved limb and contralateral limb of individuals with ACLR and healthy controls.

Data Sources:

Web of Science, SportDISCUS, PubMed, CINAHL, and the Cochrane Database were all used during the search.

Study Selection:

A total of 2024 studies were reviewed. Twenty-eight studies including individuals with a unilateral history of ACLR, isometric knee extension strength normalized to body mass, and quadriceps activation measured by central activation ratios (CARs) through a superimposed burst technique were identified for meta-analysis. The methodological quality of relevant articles was assessed using a modified Downs and Black scale. Results of methodological quality assessment ranged from low to high quality (low, n = 10; moderate, n = 8; high, n = 10).

Study Design:

Meta-analysis.

Level of Evidence:

Level 2.

Data Extraction:

Means, standard deviations, and sample sizes were extracted from articles, and magnitude of between-limb and between-group differences were evaluated using a random-effects model meta-analysis approach to calculate combined pooled effect sizes (ESs) and 95% CIs. ESs were classified as weak (d < 0.19), small (d = 0.20-0.49), moderate (d = 0.50-0.79), or large (d > 0.80).

Results:

The involved limb of individuals with ACLR displayed lower knee extension strength compared with the contralateral limb (ES, –0.78; lower bound [LB], –0.99; upper bound [UB], –0.58) and healthy controls (ES, –0.76; LB, –0.98; UB, –0.53). The involved limb displayed a lower CAR compared with healthy controls (ES, –0.84; LB, –1.18; UB, –0.50) but not compared with the contralateral limb (ES, –0.15; LB, –0.37; UB, 0.07). The ACLR contralateral limb displayed a lower CAR (ES, –0.73; LB, –1.39; UB, –0.07) compared with healthy control limbs but similar knee extension strength (ES, –0.24; LB, –0.68; UB, –0.19).

Conclusion:

Individuals with ACLR have bilateral CAR deficits and involved limb strength deficits that persist years after surgery. Deficits in quadriceps function may have meaningful implications for patient-reported and objective outcomes, risk of reinjury, and long-term joint health after ACLR.

Angle-specific analysis of isokinetic quadriceps and hamstring torques and ratios in patients after ACL-reconstruction

Background

Strength deficits, muscle imbalances, and quadriceps inhibition are common after the surgical reconstruction of the anterior cruciate ligament (ACL), even after the patient’s returned-to-sport. Typically, asymmetries between the operated and non-operated leg as well as the hamstring/quadriceps (HQ) ratio are calculated using maximum isokinetic torque values. Moreover, the knee flexion angles, which correspond to the measured torque values, were not considered. Therefore, the aim of the study was to evaluate the usage of an angle-specific approach for the analysis of isokinetic data in patients after an ACL-reconstruction.

Methods

A cross-sectional laboratory study design was used to investigate the influence of leg (operated vs. non-operated) and two velocities on angle-specific isokinetic data. Concentric quadriceps and hamstring torques and ratios of 38 patients were assessed 6.6 months after ACL-reconstruction with a hamstring tendon graft. At a velocity of 60°/s and 180°/s, angle-specific torques and HQ-ratios were analyzed with conventional discrete parameters and a Statistical Parametric Mapping procedure, which evaluates continuous data. The relationship between angle-specific and conventional HQ-ratios was evaluated with Pearson correlation coefficients.

Results

Angle-specific torques and HQ-ratios were different between the operated and non-operated leg and between velocities. In the operated leg, the quadriceps deficit was higher at 60°/s in knee flexion angles > 50°. The HQ-ratios decreased with greater knee flexion at both velocities, but with a different magnitude. Around 30°, the HQ-ratios reached 1.0 and did not differ between the velocities, while leg differences were present from 40 to 60°. At the higher testing velocity, the maximum flexion torque occurred at greater knee flexion, whereas the maximum extension torque were present at a similar joint angle. The correlation coefficients between conventional and angle-specific HQ-ratios were low in knee angles < 35° and > 65° and varied according to leg and velocity.

Conclusions

The angle specific approach is recommended for future ACL-research, as it reveals strength deficits and imbalances, which were not captured by conventional parameters. The results provide a rationale for more specific joint angle and/or velocity based training and may help for return-to-sport decisions.

Effect of Impairment-Based Rehabilitation on Lower Leg Muscle Volumes and Strength in Patients With Chronic Ankle Instability: A Preliminary Study

Context: Patients with chronic ankle instability (CAI) have demonstrated atrophy of foot and ankle musculature and deficits in ankle strength. The effect of rehabilitation on muscle morphology and ankle strength has not previously been investigated in patients with CAI. Objective: Our objective was to analyze the effect of impairment-based rehabilitation on intrinsic and extrinsic foot and ankle muscle volumes and strength in patients with CAI. Design: Controlled laboratory study. Setting: Laboratory. Patients: Five young adults with CAI. Intervention: Twelve sessions of supervised impairment-based rehabilitation that included range of motion, strength, balance, and functional exercises. Main Outcome Measures: Measures of extrinsic and intrinsic foot muscle volume and ankle strength measured before and after 4 weeks of supervised rehabilitation. Novel fast-acquisition magnetic resonance imaging was used to scan from above the femoral condyles through the entire foot. The perimeter of each muscle was outlined on each axial slice and then the 2-dimensional area was multiplied by the slice thickness (5 mm) to calculate muscle volume. Plantar flexion, dorsiflexion, inversion, and eversion isometric strength were measured using a hand-held dynamometer. Results: Rehabilitation resulted in hypertrophy of all extrinsic foot muscles except for the flexor hallucis longus and peroneals. Large improvements were seen in inversion, eversion, and plantar flexion strength following rehabilitation. Effect sizes for significant differences following rehabilitation were all large and ranged from 1.54 to 3.35. No significant differences were identified for intrinsic foot muscle volumes. Conclusion: Preliminary results suggest that impairment-based rehabilitation for CAI can induce hypertrophy of extrinsic foot and ankle musculature with corresponding increases in ankle strength.

Quadriceps Function and Patient-Reported Outcomes After Anterior Cruciate Ligament Reconstruction in Patients With or Without Knee Osteoarthritis

CONTEXT

Relationships between quadriceps function and patient-reported outcomes after anterior cruciate ligament reconstruction (ACLR) are variable and may be confounded by including patients at widely different time points after surgery. Understanding these relationships during the clinically relevant phases of recovery may improve our knowledge of specific factors that influence clinical outcomes.

OBJECTIVE

To identify the relationships between quadriceps function and patient-reported outcomes in patients <2 years (early) and >2 years (late) after ACLR, including those with posttraumatic knee osteoarthritis.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 72 patients after ACLR: early (n = 34, time from surgery = 9.0 ± 4.3 months), late (n = 30, time from surgery = 70.5 ± 41.6 months), or osteoarthritis (n = 8, time from surgery = 115.9 ± 110.0 months).

MAIN OUTCOME MEASURE(S)

The total Knee Injury and Osteoarthritis Outcome Score (KOOS) and Veterans RAND 12-Item Health Survey (VR-12) were used to quantify knee function and global health. Predictors of patient-reported outcomes were involved-limb and symmetry indices of quadriceps function (isokinetic strength [peak torque, total work, average power], maximum voluntary isometric contraction torque, fatigue index, central activation ratio, Hoffmann reflex, active motor threshold) and demographics (age, activity level, pain, kinesiophobia, time since surgery). Multiple linear regression analyses were used to predict KOOS and VR-12 scores in each group.

RESULTS

In the early patients, knee-extensor work, active motor threshold symmetry, pain, and activity level explained 67.8% of the variance in the KOOS score ( P < .001); knee-extensor work, activity level, and pain explained 53.0% of the variance in the VR-12 score ( P < .001). In the late patients, age and isokinetic torque symmetry explained 28.9% of the variance in the KOOS score ( P = .004). In the osteoarthritis patients, kinesiophobia and isokinetic torque explained 77.8% of the variance in the KOOS score ( P = .010); activity level explained 86.4% of the variance in the VR-12 score ( P = .001).

CONCLUSIONS

Factors of muscle function and demographics that explain patient-reported outcomes were different in patients early and late after ACLR and in those with knee osteoarthritis.

Advanced MRI Techniques for Muscle Imaging

Advanced magnetic resonance imaging (MRI) techniques can evaluate a wide array of muscle pathologies including acute or chronic muscle injury, musculotendinous response to injury, intramuscular collections and soft tissue masses, and others. In recent years, MRI has played a more important role in muscle disease diagnosis and monitoring. MRI provides excellent spatial and contrast resolution and helps direct optimal sites for muscle biopsy. Whole-body MRI now helps identify signature patterns of muscular involvement in large anatomical regions with relative ease. Quantitative MRI has advanced the evaluation and disease tracking of muscle atrophy and fatty infiltration in entities such as muscular dystrophies. Multivoxel magnetic resonance spectroscopy (MRS) now allows a more thorough, complete evaluation of a muscle of interest without the inherent sampling bias of single-voxel MRS or biopsy. Diffusion MRI allows quantification of muscle inflammation and capillary perfusion as well as muscle fiber tracking.