Persistent neuromuscular and corticomotor quadriceps asymmetry after anterior cruciate ligament reconstruction

Athletes after anterior cruciate ligament reconstruction demonstrate asymmetric intracortical facilitation early after surgery

Quadriceps dysfunction persists after anterior cruciate ligament reconstruction (ACLR), yet the etiology remains elusive. Inhibitory and facilitatory intracortical networks (ie, intracortical excitability) may be involved in quadriceps dysfunction, yet the investigation of these networks early after ACLR is sparse. The purposes of this study were to examine (a) changes in intracortical excitability in athletes after ACLR compared to uninjured athletes during the course of postoperative rehabilitation, (b) the association between intracortical excitability and quadriceps strength in athletes after ACLR. Eighteen level I/II athletes after ACLR between the ages of 18 to 30 years and eighteen healthy sex, age, and activity matched athletes were tested at three-time points: (a) 2 weeks after surgery, (b) achievement of a "quiet knee" defined as full range of motion and minimal effusion, (c) return to running time point defined as achievement of a quadriceps index ≥80% and at least 12 weeks post-ACLR. Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), measured via transcranial magnetic stimulation and isometric quadriceps strength were examined bilaterally at each time point. There was a significant group × limb interaction (P = .017) for ICF. The ACLR group demonstrated asymmetric ICF (greater in the nonsurgical limb) compared to controls and a significant relationship between SICI and quadriceps strength of the surgical limb at the quiet knee time point (P = .018). ACLR individuals demonstrate differential effects on ICF between limbs. Also, SICI is associated with isometric quadriceps strength after ACLR, suggesting increased inhibition of the motor cortex may contribute to impaired quadriceps strength following ACLR.

Concussion Is Associated With Increased Odds of Acute Lower-Extremity Musculoskeletal Injury Among National Basketball Association Players

Purpose

To determine the odds of sustaining an acute lower-extremity (LE) musculoskeletal injury during the 90-day period after return-to-play (RTP) from concussion in National Basketball Association (NBA) athletes.

Methods

Concussion data for NBA players were collected from the 1999-2000 to 2017-2018 seasons, from publicly available sources. Age, position, injury, time to RTP, and demographic factors were collected. The 90-day period after each case of concussion was reviewed for acute noncontact LE musculoskeletal injury. Control athletes without a documented history of concussion were matched to concussed athletes by age, body mass index, position, and experience. Conditional logistic regression with a calculated odds ratio and a 95% confidence interval were used to assess the association between concussion and subsequent risk of LE injury.

Results

In total, 189 concussions were documented in 153 athletes. Of these, 140 cases were the first recorded instance of concussion in players with publicly available data. Thirty-six (25.7%) athletes sustained a LE injury within 90 days of concussion; 26 (20.2%) were non–season-ending and included in RTP analysis. The odds of sustaining an acute LE musculoskeletal injury within the 90-day period after concussion was 4.69 times greater in concussed players compared with controls (95% confidence interval 1.96-11.23, P < .001). There was no significant difference in games (4.2 ± 5.0 vs 4.7 ± 4.7 games, P = .566) or days (18.5 ± 39.1 days vs 10.9 ± 10.6 days, P = .912) missed between concussed players with LE injury and nonconcussed controls. The most common LE injuries in concussed athletes were ligament sprains/tears (65%).

Conclusions

Concussed NBA athletes have increased odds for sustaining an acute LE musculoskeletal injury within 90 days of RTP compared with nonconcussed controls. The most common injuries were ligament strains or tears. Changes in neuromotor control and proprioception following a concussion should be evaluated in high-level basketball players returning to sport.

Level of Evidence

Level III, Case-Control Study.

Examination of Corticospinal and Spinal Reflexive Excitability During the Course of Postoperative Rehabilitation After Anterior Cruciate Ligament Reconstruction

OBJECTIVE

To investigate corticospinal and spinal reflexive excitability and quadriceps strength in healthy athletes and athletes after anterior cruciate ligament reconstruction (ACLR) over the course of rehabilitation.

DESIGN

Prospective cohort study.

METHODS

Eighteen athletes with ACLR and 18 healthy athletes, matched by sex, age, and activity, were tested at (1) 2 weeks after surgery, (2) the "quiet knee" time point, defined as full range of motion and minimal effusion, and (3) return to running, defined as achieving a quadriceps index of 80% or greater. We measured (1) corticospinal excitability, using resting motor threshold (RMT) and motor-evoked potential amplitude at a stimulator intensity of 120% of RMT (MEP₁₂₀) to the vastus medialis, (2) spinal reflexive excitability, calculating the ratio of the maximal Hoffmann reflex to the maximal M-wave to the vastus medialis, and (3) isometric quadriceps strength.

RESULTS

The ACLR group had higher RMTs in the nonsurgical limb and higher MEP₁₂₀ in the surgical limb at all time points. The healthy-athlete group did not have interlimb differences. The RMT was positively associated with quadriceps strength 2 weeks after surgery; MEP₁₂₀ was associated with quadriceps strength at all time points.

CONCLUSION

Compared to healthy athletes, athletes after ACLR had altered corticospinal excitability that did not change from 2 weeks after surgery to the time of return to running. J Orthop Sports Phys Ther 2020;50(9):516-522. Epub 1 Aug 2020. doi:10.2519/jospt.2020.9329.

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.

Type of measurement used influences central and peripheral contributions to quadriceps weakness after anterior cruciate ligament (ACL) reconstruction

OBJECTIVE

The relative contribution of muscle size and voluntary activation (VA) on quadriceps strength after anterior cruciate ligament (ACL) reconstruction remains inconclusive. Here, we aimed to determine the contributions of muscle size and VA on quadriceps strength in ACL-reconstructed patients and determine if contributions were similar if unilateral outcomes (i.e. ACL-reconstructed limb) or the LSI was used.

DESIGN

A cross-sectional study.

SETTING

A university research laboratory.

PARTICIPANTS

Sixteen individuals 6-12 months after ACL reconstruction (Age: 22.3 ± 6.0yr, Height: 1.7 ± 0.1 m, Mass: 68.7 ± 11.5 kg) were recruited.

MAIN OUTCOME MEASURES

Quadriceps isometric strength and VA, via the interpolated triplet technique, were assessed bilaterally. Ultrasound images were acquired of the vastus lateralis to calculate cross-sectional area (CSA) in both legs. LSI's were computed for all variables by expressing values of the reconstructed leg as a percent of the non-reconstructed leg. Separate stepwise linear regressions were performed to examine the contribution of VA and CSA on quadriceps strength. Model 1 used LSI for all outcomes and model 2 used outcomes from the reconstructed leg.

RESULTS

We observed between limb deficits of 27.78% in quadriceps strength, 13.61% in vastus lateralis CSA, and 13.18% in VA (P < 0.05). Strength LSI was significantly predicted by VA LSI (R² = 0.45, P < 0.01), but not by CSA LSI (R² = 0.01, P =0.87). Reconstructed leg strength was significantly predicted by VL CSA (R² = 0.50, P < 0.01) but not quadriceps VA (R² = 0.08, P =0.11).

CONCLUSIONS

The contributions of VA and CSA on quadriceps PT differed greatly if LSI or reconstructed leg outcomes were used. Evaluation of VA and CSA in unison may be provide a more holistic understanding of the sources of muscle weakness after ACL reconstruction.

Anterior cruciate ligament reconstruction with the use of adductor canal block can achieve similar pain control as femoral nerve block

PURPOSE

Moderate-to-severe postoperative pain remains a challenge for both patients and surgeons after anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to systematically review the current evidence in the literature to compare adductor canal block (ACB) with femoral nerve block (FNB) in the treatment of ACLR.

METHODS

A comprehensive search of the published literature in PubMed, Scopus, EMBASE, and Cochrane Library databases was performed. Only English randomized clinical trials (RCTs) were included in this study. The primary outcome was pain score. Secondary outcome measures included opioid consumption, postoperative adverse events, patient satisfaction, and quadriceps strength.

RESULTS

Eight RCTs with a total of 587 patients were included. No statistically significant difference was observed between the ACB and FNB groups in pain scores at 6 h, 12 h, 24 h, or 48 h; cumulative opioid consumption at 24 h or 48 h; patient satisfaction at 24 or 48 h; and postoperative adverse event. However, ACB showed superior quadriceps strength in the early postoperative period.

CONCLUSIONS

Both treatments provided similar overall pain relief after ACLR. The potential benefits of quadriceps preservation with ACB are worthy of future study. Therefore, ACB is recommended as an attractive alternative to FNB as the peripheral nerve block of choice for ACLR.

LEVEL OF EVIDENCE

Meta-analysis of Level 1 was performed in this study.

Assessing Step Count-Dependent Changes in Femoral Articular Cartilage Using Ultrasound

OBJECTIVES

To evaluate changes in the femoral cartilage cross-sectional area (CSA) measured with ultrasound (US) between baseline and 1000, 2000, 3000, 4000, and 5000 steps of walking on a treadmill.

METHODS

Forty-one healthy individuals completed a single testing session. Participants rested with their knees extended on a plinth for 45 minutes to unload the femoral cartilage. Ultrasound was used to acquire images of the femoral cartilage before the treadmill-walking protocol. After the baseline US acquisition, participants walked on a treadmill at their preferred overground walking speed for 1000 steps, after which additional US images of the femoral cartilage were acquired. This process was repeated after 2000, 3000, 4000, and 5000 steps. A 1-way repeated-measures analysis of variance compared the CSA across the 6 step counts. An analysis of variance with repeated measures on time and Bonferroni corrected planned comparisons (.05/5) were used to evaluate differences in the femoral cartilage at each step count compared to baseline.

RESULTS

The study included 20 male and 21 female participants (mean age ± SD, 21.5 ± 2.8 years; mean body mass index, 24.3 ± 3.4 kg/m ² ). The CSAs were significantly greater at the 2000-step (1.27 ± 1.75 mm ² ; P < .001), 4000-step (0.89 ± 1.17 mm2; P < .001), and 5000-step (2.10 ± 1.73 mm ² ; P < .001) points compared to baseline. The CSA was significantly less at the 3000-step point (1.05 ± 1.29 mm ² ; P < .001) compared to baseline.

CONCLUSIONS

Changes in the CSA after walking may be dependent on the number of steps. The participants had a significant decrease in the CSA after 3000 steps of normal walking and a significant increase in the CSA after 2000, 4000, and 5000 steps of normal walking.

The Warrior Athlete Part 2-Return to Duty in the US Military: Advancing ACL Rehabilitation in the Tactical Athlete

Rehabilitation following an anterior cruciate ligament reconstruction is a crucial component of the healing and recovery process and full return to duty/play in the tactical modern-day warfighter. The burden of anterior cruciate ligament injuries and subsequent loss of readiness in these military warfighters highlights one of the most significant gaps in musculoskeletal injury care today. Emphasis must be placed on early weight-bearing and range of motion (ROM), namely in this athlete population, to best facilitate a timely care and recovery process. Preoperative rehabilitation should commence immediately following the diagnosis of an anterior cruciate ligament tear, because one of the best predictors of postoperative ROM is preoperative ROM. Recent advances in rehabilitation technology such as Alter-G treadmills, inertial measurement units, and blood flow restriction therapy systems, have demonstrated success in the early rehabilitation of tactical athletes. Alter-G treadmills allow for early weight-bearing with reduced impact and progression in ROM following operative management, while inertial measurement units have been applied to tailoring rehabilitation protocols specifically to an athlete's unique functional deficits. When used in conjunction with a fined tune rehabilitation protocol, implemented by a well versed clinical team, these treatment techniques can greatly expedite the return to duty process and limit long-term complications.

Knee Joint and Quadriceps Dysfunction in Individuals With Anterior Knee Pain, Anterior Cruciate Ligament Reconstruction, and Meniscus Surgery: A Cross-Sectional Study

CONTEXT

While arthrogenous muscle inhibition associated with knee injuries is evident, the relative magnitude of functional deficiency related to each individual knee pathology is unclear.

OBJECTIVE

To compare the knee joint and quadriceps dysfunction among patients with anterior knee pain (AKP) without surgical history and those with surgical history (anterior cruciate ligament reconstruction [ACLR]; meniscus surgery) without current AKP, with matched healthy controls.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PARTICIPANTS

A total of 66 patients with knee pathologies and 30 controls.

MAIN OUTCOME MEASURES

Pain perception and lower-extremity functional outcomes were assessed. Knee joint function was measured by replication tests. Quadriceps function was measured by strength, voluntary activation, and torque-generating capacity.

RESULTS

Patients with AKP reported greater pain perception compared with the other knee conditions (4.3 vs 0.1 of 10 in Numeric Pain Rating Scale, P < .0001). Compared with the controls: (1) patients with AKP showed a greater error on knee-flexion replications at 75° (2.9° vs 5.4°, P = .002), (2) patients with AKP and ACLR showed less quadriceps strength (AKP: 3.3 vs 2.6 N·m/kg, P = .002; ACLR: 3.3 vs 2.7 N·m/kg, P = .02) and voluntary activation (AKP: 0.982 vs 0.928, P < .0001; ACLR: 0.982 vs 0.946, P = .003), and (3) all knee pathologies reported lower scores on functional outcomes (79 vs 65 of 80 points in Lower-Extremity Functional Scale, P < .0001) and showed less quadriceps torque-generating capacity (10.7 vs 7.8 N·m/s/kg, P < .0001). Among the knee pathologies, patients with AKP showed less quadriceps voluntary activation compared with the patients with meniscus surgery (0.928 vs 0.964, P = .03).

CONCLUSION

As patients with AKP had an additional impairment in knee joint flexion replications and reported a less score in functional outcomes, knee pain may produce a greater impact on functional deficiency.

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.

Corticomotor function is associated with quadriceps rate of torque development in individuals with ACL surgery

Impaired corticomotor function arising from altered intracortical and corticospinal pathways are theorized to impede muscle recovery following anterior cruciate ligament (ACL) surgery, yet functional implications of centrally driven adaptations remain unclear. We aimed to assess relationships between quadriceps corticomotor and neuromechanical function after ACL surgery, and to compare with contralateral and control limbs. 16 individuals after primary, unilateral ACL surgery and 16 sex- and age-matched controls participated. Corticomotor function was assessed using transcranial magnetic stimulation, and quantified via active motor thresholds (AMT), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Neuromechanical function was quantified via electromechanical delay, early and late-phase rate of torque development (RTD_0-50, RTD_100-200), coefficient of variation, maximal voluntary isometric contraction (MVIC) torque, and central activation ratio. We observed significant correlations in the ACL limbs between: AMT and RTD_0-50 (r = - 0.513, p = 0.031), SICI and RTD_100-200 (r = 0.501, p = 0.048), AMT and SICI (r = - 0.659, p = 0.010), AMT and ICF (r = 0.579, p = 0.031), RTD_0-50 and MVIC (r = 0.504, p = 0.023), and RTD_100-200 and MVIC (r = 0.680, p = 0.002). The ACL limbs demonstrated higher AMT compared to controls (44.9 ± 8.4 vs. 30.1 ± 8.2%, p < 0.001), and lesser MVIC torque (2.37 ± 0.52 vs. 2.80 ± 0.59 Nm/kg, p = 0.005) and RTD_100-200 (6.79 ± 1.72 vs. 7.90 ± 1.98 Nm/kg/s, p = 0.006) compared to the contralateral limbs. Our findings indicate that lesser corticospinal excitability is associated with lesser early-phase RTD, and greater intracortical inhibition is associated with lesser late-phase RTD. These findings provide evidence of implications of altered intracortical and corticospinal pathways relative to the ability to rapidly generate quadriceps torque following ACL surgery.

Functional Brain Plasticity Associated with ACL Injury: A Scoping Review of Current Evidence

Anterior cruciate ligament (ACL) injury is a common problem with consequences ranging from chronic joint instability to early development of osteoarthritis. Recent studies suggest that changes in brain activity (i.e., functional neuroplasticity) may be related to ACL injury. The purpose of this article is to summarize the available evidence of functional brain plasticity after an ACL injury. A scoping review was conducted following the guidelines of the Joanna Briggs Institute and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. The terms "brain," "activity," "neuroplasticity," "ACL," "injury," and "reconstruction" were used in an electronic search of articles in PubMed, PEDro, CINAHL, and SPORTDiscus databases. Eligible studies included the following criteria: (a) population with ACL injury, (b) a measure of brain activity, and (c) a comparison to the ACL-injured limb (contralateral leg or healthy controls). The search yielded 184 articles from which 24 were included in this review. The effect size of differences in brain activity ranged from small (0.05, ACL-injured vs. noninjured limbs) to large (4.07, ACL-injured vs. healthy control). Moreover, heterogeneity was observed in the methods used to measure brain activity and in the characteristics of the participants included. In conclusion, the evidence summarized in this scoping review supports the notion of functional neuroplastic changes in people with ACL injury. The techniques used to measure brain activity and the presence of possible confounders, as identified and reported in this review, should be considered in future research to increase the level of evidence for functional neuroplasticity following ACL injury.

Associations between isometric quadriceps strength characteristics, knee flexion angles, and knee extension moments during single leg step down and landing tasks after anterior cruciate ligament reconstruction

BACKGROUND

It is unclear of how peak knee extension torque and early rate of torque development outcomes are related to lower extremity loading and sagittal plane movement in activities of daily living and landing tasks despite consistent deficits after anterior cruciate ligament reconstruction. The purpose of this cross-section study is to assess the ability of quadriceps strength characteristics to predict movement patterns during a step down and single leg drop crossover hopping tasks.

METHODS

Fifty-two individuals with a unilateral history of anterior cruciate ligament reconstruction completed three trials of the step down and crossover hopping tasks on their involved limb. Participants completed three isometric knee extension contractions at 90° knee flexion with visual feedback to assess peak knee extension torque and rate of torque development during the first 0-100 ms and 100-200 ms of the contraction.

FINDINGS

Peak knee extension torque explained the greatest variance in peak knee extension moment (R² = 40.4%, p < 0.001) and knee flexion angle (R² = 46.7%, p < 0.001) during the crossover hop landing. Rate of torque development (0-100 ms) was the only predictor of knee flexion angle (R² = 19.8%, p = 0.01) at initial contact during the crossover hopping landing. Rate of torque development (100-200 ms) explained 17.6% of the variance in peak knee extension moment during the step down (p = .03).

INTERPRETATION

Peak knee extension torque and early rate of torque development outcomes demonstrate limited relationships between movement of activities of daily living and sport-specific tasks. These limitations should be considered when interpreting the results of isometric strength testing in a clinical setting.

Reactive Strength Index and Knee Extension Strength Characteristics Are Predictive of Single-Leg Hop Performance After Anterior Cruciate Ligament Reconstruction

Birchmeier, T, Lisee, C, Geers, B, and Kuenze, C. Reactive strength index and knee extension strength characteristics are predictive of single-leg hop performance after anterior cruciate ligament reconstruction. J Strength Cond Res 33(5): 1201-1207, 2019-Single-leg hop distance is incorporated into return to sport criteria after anterior cruciate ligament reconstruction (ACLR) because of its relationship with knee extension strength; however, it may be related to other strength and plyometric characteristics. The purpose of this study was to assess the association between isometric knee extension strength and plyometric characteristics, including amortization and reactive strength index (RSI), measured during a single-leg drop vertical jump and single-leg hop performance in individuals with unilateral ACLR. Participants attended 2 testing sessions. During the first session, a biomechanical analysis using a 3D motion capture system was performed to measure RSI and amortization during a single-leg drop vertical jump for maximal height. Participants completed a single hop and a triple hop for maximal distance. During the second session, isometric knee extension strength was measured during a maximal voluntary isometric contraction. Strength characteristics included peak torque, rate of torque development (RTD), RTD 0-100 ms (RTD 100), and RTD 100-200 ms (RTD 200). Fifty-two individuals (17 men/35 women) participated. Multivariable regression models revealed jump height, peak torque, and RTD 200 explained 60.9% of the variance in normalized single-leg hop distance (p < 0.001). Reactive strength index, peak torque, RTD 200, and RTD 100 significantly explained 61.8% of the variance in normalized triple hop distance (p < 0.001). Single hop distance may indicate improved knee extension strength, whereas triple hop distance may indicate improvement in reactive strength. Training to improve RSI may improve triple hop performance and clinical outcomes in this population.

Impact of a Carbohydrate Mouth Rinse on Quadriceps Muscle Function and Corticomotor Excitability

PURPOSE

The purpose of this investigation is to determine the effects of different forms of a CHO MR on quadriceps muscle performance and corticospinal motor excitability.

METHODS

Ten subjects (5 females, 5 males; 25±1 years; 1.71±0.03 m 73±5 kg) completed 4 trials. A different MR condition was applied during each trial (Placebo (PLA), 6.4% glucose (GLU), 6.4% maltose (MAL), 6.4% maltodextrin (MDX)). Maximal voluntary contraction (MVIC) of the right quadriceps and motor-evoked potential (MEP) of the right rectus femoris was determined pre (10 min), immediately after, and post (10 min) MR. MEP was precipitated by transcranial magnetic stimulation (TMS) during muscle contraction (50% of MVIC). MR was held in the mouth for 20 s and treatments were applied using a Latin square design. The relative change in MEP from pre-measures was different across treatments (p=0.025) but was not different across time (p=0.357).

RESULTS

Relative change in MEP was greater for all CHO conditions immediately after (GLU=2.58±5.33%; MAL=3.92±3.90%; MDX=18.28±5.57%) and 10 min after (GLU=14.09±13.96%; MAL=8.64±8.67%; MDX=31.54±12.77%) MR compared to PLA (Immediately after=-2.19±4.25%, 10 min=-13.41±7.46%). The relative change in MVC was greater for CHO conditions immediately (GLU=3.98±2.49%; MAL=5.89±2.29.90%; MDX=7.66±1.93%) and 10 min after (GLU=7.22±2.77%; MAL=10.26±4.22%; MDX=10.18±1.50%) MR compared to PLA (Immediately after=-3.24±1.50%, 10 min=-6.46±2.22%).

CONCLUSIONS

CHO MR increased corticospinal motor excitability and quadriceps muscle performance immediately and 10 min after application; however, the form of CHO used did not influence this response.

Anterior Cruciate Ligament Reconstruction Rehabilitation Clinical Practice Patterns: A Survey of the PRiSM Society

Background:

Recovery after anterior cruciate ligament (ACL) reconstruction (ACLR) requires extensive postoperative rehabilitation. Although no ideal rehabilitation procedure exists, most experts recommend a fusion of time and strength and functional measures to guide decision making for activity progression during rehabilitation. This process is often directed by surgeon protocols; however, the adoption of contemporary rehabilitation recommendations among surgeons is unknown.

Purpose:

To understand the current landscape of surgeon practice as it relates to ACLR rehabilitation recommendations in adolescent athletes.

Study Design:

Cross-sectional study.

Methods:

An online survey was distributed among members of the Pediatric Research in Sports Medicine (PRiSM) Society in January 2017. The survey was designed to identify clinical practice patterns during 3 key transitional points of rehabilitation after ACLR: progression to jogging, modified sports activity, and unrestricted return to sports.

Results:

Responses from 60 orthopaedic surgeons were analyzed. While 80% of surgeons agreed upon initiating jogging within a 1-month range (3-4 months postoperatively), similar levels of agreement were only captured when including a wider 4-month (4-8 months) and 6-month range (6-12 months) for modified sports activity and unrestricted return to sports, respectively. All respondents (100%) reported using knee strength as a determinant to progress to modified sports activity; however, the mode of testing varied, with most using manual muscle testing (60%), followed by isokinetic (28%) or isometric (12%) testing. Most surgeons (68%) reported using some form of functional testing to return to modified sports activity, but the mode of testing and required progression criteria varied considerably among all reported testing procedures. The use of patient-reported outcome measures was limited to 20% of the sample, and no respondents reported using fear or self-efficacy questionnaires. Upon completion of rehabilitation, 73% recommended injury prevention programs, and 50% recommended the use of a functional ACL brace.

Conclusion:

Rehabilitation progression practices in adolescent athletes are variable and become more inconsistent as the time from surgery increases. While the majority of the sample considered strength and functional testing important, the mode of testing and criteria thresholds for activity advancement varied considerably.

Deficits in Quadriceps Force Control After Anterior Cruciate Ligament Injury: Potential Central Mechanisms

CONTEXT

Poor quadriceps force control has been observed after anterior cruciate ligament (ACL) reconstruction but has not been examined after ACL injury. Whether adaptations within the central nervous system are contributing to these impairments is unknown.

OBJECTIVE

To examine quadriceps force control in individuals who had sustained a recent ACL injury and determine the associations between cortical excitability and quadriceps force control in these individuals.

DESIGN

Cross-sectional study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Eighteen individuals with a recent unilateral ACL injury (6 women, 12 men; age = 29.6 ± 8.4 years, height = 1.74 ± 0.07 m, mass = 76.0 ± 10.4 kg, time postinjury = 69.5 ± 42.5 days) and 18 uninjured individuals (6 women, 12 men; age = 29.2 ± 6.8 years, height = 1.79 ± 0.07 m, mass = 79.0 ± 8.4 kg) serving as controls participated.

MAIN OUTCOME MEASURE(S)

Quadriceps force control was quantified as the root mean square error between the quadriceps force and target force during a cyclical force-matching task. Cortical excitability was measured as the active motor threshold and cortical silent period. Outcome measures were determined bilaterally in a single testing session. Group and limb differences in quadriceps force control were assessed using mixed analyses of variance (2 × 2). Pearson product moment correlations were performed between quadriceps force control and cortical excitability in individuals with an ACL injury.

RESULTS

Individuals with an ACL injury exhibited greater total force-matching error with their involved (standardized mean difference [SMD] = 0.8) and uninvolved (SMD = 0.9) limbs than did controls (F_1,27 = 11.347, P = .03). During the period of descending force, individuals with an ACL injury demonstrated greater error using their involved (SMD = 0.8) and uninvolved (SMD = 0.8) limbs than uninjured individuals (F_1,27 = 4.941, P = .04). Greater force-matching error was not associated with any cortical excitability measures (P > .05).

CONCLUSIONS

Quadriceps force control was impaired bilaterally after recent ACL injury but was not associated with selected measures of cortical excitability. The findings highlight a need to incorporate submaximal-force control tasks into rehabilitation and "prehabilitation," as the deficits were present before surgery.

Adductor Canal Nerve Versus Femoral Nerve Blockade for Pain Control and Quadriceps Function Following Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autograft: A Prospective Randomized Trial

PURPOSE

To compare femoral nerve blockade (FNB) versus adductor canal nerve blockade (ACB) for postoperative pain control and quadriceps muscle function in patients undergoing anterior cruciate ligament (ACL) reconstruction with patellar tendon autograft.

METHODS

A randomized therapeutic trial of 90 patients undergoing ACL reconstruction with patellar tendon autograft was conducted comparing ACB versus FNB at 24 hours, 2 and 4 weeks, and 6 months postsurgery. Early outcome measures included average pain score and morphine equivalent units (milligrams) consumed, quadriceps surface electromyography, straight leg raise, and ability to ambulate without assistive devices. The 6-month outcome measures included knee range of motion (ROM), isokinetic knee extension peak torque, single-leg squat, and single-leg hop performance. Complications were recorded throughout the study for the development of anterior knee pain, knee extension ROM loss, deep vein thrombosis, and graft failure. Mixed-model analysis of variance and Mann-Whitney U tests were performed using an alpha of .05.

RESULTS

Quadriceps surface electromyography deficits were higher for FNB at 24 hours (P < .001) and 2 weeks (P < .001) when compared with the ACB group. There were no between-groups difference for subjective pain (P = .793) or morphine consumption (P = .358) within the first 24 hours of surgery. A higher percentage of patients in the ACB group met the full ambulation criteria at 4 weeks compared with the FNB group (100% vs 84.2%, P < .001). No between-group differences were observed at 6 months; however, the rate of knee extension ROM loss was higher for the FNB group versus the ACB group (21.1% vs 5.0%, P = .026), respectively.

CONCLUSIONS

ACB was as effective as FNB at providing pain control while eliciting fewer quadriceps muscle activation deficits and fewer postoperative complications. Based on previous evidence and the results of this study, we recommend the use of ACB over FNB for the analgesic management of patients undergoing ACL reconstruction with patellar tendon autograft.

LEVEL OF EVIDENCE

Level I, prospective randomized controlled trial.

Demographic and surgical factors affect quadriceps strength after ACL reconstruction

PURPOSE

To investigate the effects of graft source, time since surgery, age, and sex on unilateral and symmetry-based measures of knee extension strength among individuals with ACL reconstruction (ACLR).

METHODS

Three hundred and eight individuals aged 13-40 years old with primary, unilateral ACLR in the last 60 months were enrolled in this multi-site clinical measurement study. Participants completed bilateral knee extension maximal voluntary isometric contraction (MVIC) torque assessments which were normalized to body mass (Nm/kg) and limb symmetry indices (LSI) were calculated. The effects of graft source (patellar tendon autograft; hamstring tendon autograft), time since surgery (≤ 12 months; >12 mo.), age (≤ 18 years; >18 years), and sex were evaluated using separate ANCOVAs.

RESULTS

A significant interaction was present between time since surgery and graft source for LSI (P = 0.01) as participants with patellar tendon autografts ≤ 12 months post-ACLR experienced the greatest asymmetry (LSI = 69.2 ± 24.5%). Significant interactions were present between time since surgery and sex for involved limb (P = 0.01) and uninvolved limb MVIC torque (P = 0.05) with females ≤ 12 months post-ACLR being weakest (involved MVIC = 1.81 ± 0.70 N m/kg; uninvolved MVIC = 2.40 ± 0.68 N m/kg). Participants ≤ 18-year-old displayed weaker involved limb (P < 0.001) and contralateral limb (P < 0.001) MVIC torque as compared to participants > 18-year-old during the first year after ACLR.

CONCLUSIONS

Graft source, sex, age, and time since surgery effect quadriceps strength and symmetry after ACLR. Surgical and demographic factors should be considered when developing treatment approaches to optimize quadriceps function prior to re-integration into pre-injury levels of physical activity.

LEVEL OF EVIDENCE

IV.

Corticospinal excitability can discriminate quadriceps strength indicative of knee function after ACL-reconstruction

PURPOSE

To investigate relationships between quadriceps strength and neural activity, and to establish a clinical threshold of corticospinal excitability able to discriminate between patients with quadriceps strength indicative of satisfactory and unsatisfactory knee function after ACLR.

METHODS

A total of 29 patients following primary, unilateral ACL-reconstruction (11 female, 23.2 ± 8.1 years of age, 7.3 ± 2.5 months since surgery) participated. Subjective knee function was quantified using the International Knee Documentation Committee (IKDC) subjective evaluation. Peak isokinetic knee extensor torque was assessed at 90°/s. Quadriceps corticospinal excitability was quantified via active motor threshold (AMT, %2-Tesla) using transcranial magnetic stimulation during a 5% maximal voluntary isometric contraction of the quadriceps. Pearson's r correlations were used to assess the relationship between peak knee extensor torque and AMT. Receiver operating characteristic (ROC) curves were used to establish a threshold of (a) mass-normalized peak knee extensor torque to discriminate satisfactory knee function (IKDC ≥ 75.9%), and (b) AMT to discriminate quadriceps strength indicative of satisfactory knee function. Likelihood ratios (LR) and the magnitude of change in pre-post-test probability were calculated for each threshold.

RESULTS

Active motor threshold was negatively correlated with mass-normalized peak knee extensor torque (r = -0.503, P = 0.005). Knee extensor torque ≥1.23 Nm/kg was an excellent discriminator of satisfactory knee function (AUC = 0.890, P = 0.002; (+)LR = 9.56). An AMT ≤50.5% was an excellent discriminator of quadriceps strength indicative of satisfactory knee function following ACLR (AUC = 0.839, P = 0.005; (+)LR = 23.75).

CONCLUSION

Lower corticospinal excitability was associated with lower quadriceps strength. An AMT above 50.5% was found to decrease the probability of having satisfactory knee strength by over 62%.

Muscle hypotrophy, not inhibition, is responsible for quadriceps weakness during rehabilitation after anterior cruciate ligament reconstruction

PURPOSE

Quadriceps weakness is common after anterior cruciate ligament reconstruction (ACLR). Limited neuromuscular activation may have a role in the weakness. The purpose of this study was to use peripheral magnetic stimulation to measure changes in quadriceps inhibition in patients during rehabilitation from ACLR.

METHODS

Ten patients (7M/3F; age 35 ± 8 years; BMI 26.0 ± 4.8 kg/m²) who had ACLR with patellar tendon autograft were recruited. At 3 and 6 months postoperatively, patients' knee extension peak torque was measured during maximum voluntary isometric contraction (MVIC), magnetic stimulation-evoked contraction, and MVIC augmented with superimposed burst magnetic stimulation to the femoral nerve. All tests were done bilaterally at 30° and 65° of knee flexion on a dynamometer. Central activation ratio was calculated by dividing the peak torque before stimulation by peak torque after stimulation.

RESULTS

Patients had marked deficits in MVIC, with improvement from 3 to 6 months that was more apparent at 65° versus 30° (P < 0.05). There was significant deficit in stimulation-evoked torque on the involved side that diminished over time, and this change occurred differently between the two angles (P < 0.05). Central activation ratio was lower on the involved side versus the noninvolved side and this effect was more prominent at 3 versus 6 months: combining the angles, mean central activation ratio on the involved and noninvolved sides, respectively, was 91.4 ± 7.6% and 97.5 ± 5.3% at 3 months, and 93.0 ± 7.8% and 95.8 ± 6.8% at 6 months.

CONCLUSIONS

At 3 and 6 months after ACLR, there were significant deficits in quadriceps strength and activation. Quadriceps activation levels were high (> 90%) for both sides at both time points. The substantial strength deficits at this postoperative period may be largely due to muscle atrophy with limited contribution from central inhibition. Rehabilitation interventions to normalize quadriceps strength should emphasize hypertrophic stimuli as opposed to neuromuscular activation strategies.

LEVEL OF EVIDENCE

II, prospective cohort study.

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.

Quadriceps and Patient-Reported Function in ACL-Reconstructed Patients: A Principal Component Analysis

Context: Assessment of physical function for individuals after anterior cruciate ligament reconstruction (ACL-R) is complex and warrants the use of diverse evaluation strategies. To maximize the efficiency of assessment, there is a need to identify tests that provide the most meaningful information about this population. Objective: To investigate underlying constructs of quadriceps muscle function that uniquely describe aspects of performance in patients after ACL-R and establish clinical thresholds for measures able to classify patients with and without ACL-R. Design: Cross-sectional. Setting: Research laboratory. Patients (or Other Participants): Seventy-two patients with a primary, unilateral ACL-R (32 males and 40 females, age = 26.0 [9.3] y, time since surgery = 46.5 [58.0] mo) and 30 healthy controls (12 males and 18 females, age = 22.7 [4.6] y). Intervention(s): Quadriceps function was assessed bilaterally during 1 study visit. Main Outcome Measures: Isokinetic strength (peak torque, total work, and average power) at 90° and 180°/s, maximal voluntary isometric contraction torque, fatigue index, central activation ratio, Hoffmann reflex, and active motor threshold. Principal component analyses were performed for the involved limb, contralateral limb, and limb symmetry. Receiver–operator characteristic curve analyses were conducted to determine the diagnostic utility of each variable. Binary logistic regression was used to predict group membership (ACL-R vs healthy). Results: Three components of peripheral, central, and combined (peripheral and central) muscle function were identified, explaining 70.7% to 80.5% of variance among measures of quadriceps function. Total knee-extensor work at 90°/s (≥18.4 J/kg), active motor threshold (≥39.5%), and central activation ratio (≥94.7%) of the involved limb were strong predictors of patient status and correctly classified 83.5% of patients with ACL-R (P < .001). Conclusions: Unique constructs of peripheral, central, and combined muscle function exist in patients with ACL-R. Total knee-extensor work at 90°/s, active motor threshold, and central activation ratio consistently explained a significant portion of variance in measures of quadriceps function, demonstrated acceptable to excellent diagnostic utility, and predicted group membership with 72.8% to 83.5% accuracy.

Corticospinal and intracortical excitability differ between athletes early after ACLR and matched controls

Neuromuscular impairments, such as quadriceps weakness and activation deficits, persist after anterior cruciate ligament reconstruction (ACLR). Recent research demonstrating changes in the function of the primary motor cortex after ACLR posits that quadriceps impairments may be influenced by reduced corticospinal excitability. The purpose of this study was to investigate whether the integrity of the neuromotor axis of the vastus medialis is altered in subjects 2 weeks post-ACLR compared to uninjured control subjects. Eighteen athletes 2 weeks post-ACLR and 18 age and sex matched uninjured control subjects participated in this cross-sectional study. We quantified corticospinal (resting motor threshold, RMT; motor evoked potential amplitudes at 120% RMT, MEP₁₂₀ ) and intracortical (inhibition and facilitation) excitability using single and paired pulse transcranial magnetic stimulation (TMS), respectively. We assessed spinal-reflex excitability (H-reflex amplitude normalized to maximal M-wave, H/M ratio) using peripheral stimulation. Subjects post-ACLR had higher RMTs (p = 0.001), greater MEP₁₂₀ amplitudes (p = 0.001), and more asymmetric facilitation (p = 0.041) than the uninjured control subjects. No significant group differences were found for intracortical inhibition (p = 0.289) and H/M ratio (p = 0.332). Our findings indicate that both intracortical and corticospinal excitability of vastus medialis are bilaterally altered in subjects 2 weeks after ACLR. Given persistent neuromuscular deficits seen after ACLR, rehabilitation strategies targeting intracortical and corticospinal deficits may potentially improve clinical outcomes. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2941-2948, 2018.

A comparative study of the neuromuscular response during a dynamic activity after anterior cruciate ligament reconstruction

BACKGROUND

Injury to the anterior cruciate ligament (ACL) not only causes mechanical instability but also produces proprioceptive deficit with an altered neuromuscular response. After ACL reconstruction, patients in general continue to complain of a feeling of knee instability. The objective of our study was to assess patient proprioception and its evolution over time by measuring the muscle latency time during a dynamic activity.

METHODS

Twenty-five patients with an ACL tear following sports injuries were included in a prospective, comparative, matched controlled study. The study group consisted of the injured knees in those patients, while the control group consisted of the contralateral non-injured knee in the same patients. The neuromuscular response in five leg muscles (vastus medialis, vastus lateralis, rectus femoris, semitendinosus and biceps femoris) was measured during a dynamic activity through the muscle latency time via the use of electromyography.

RESULTS

The comparison of the reaction time in the vastus medialis showed that time in the injured knee was longer at pre-op, but it reduced over time reaching a value at 6 months post-op that was close to the reaction time in the non-injured knee group. In the rectus femoris, biceps femoris and semitendinosus muscles, the reaction times in the injured knee group were similar to those in the non-injured knee group at pre-op and post-op visits.

CONCLUSION

Before ACL surgery, the muscle latency time of the vastus medialis was significantly longer in the injured knee group than in the non-injured knee group. 'Muscle reflex reaction' as a response during a dynamic task improved in the ACL reconstructed patients at 6 months post-op.

LEVEL OF EVIDENCE

Prospective, comparative, matched controlled study.

Eccentric cross-exercise after anterior cruciate ligament reconstruction: Novel case series to enhance neuroplasticity

OBJECTIVES

Substantial changes in neural function are historically present after anterior cruciate ligament reconstruction (ACLR), and are not rectified with traditional rehabilitation. Cross-exercise is a potential means to enhance neural excitability and improve recovery after ACLR. Hence our purpose, was to detail changes in brain activation, neural excitability and patient-reported outcomes in a cohort that completed an 8-week quadriceps-focused eccentric cross-exercise training program immediately following ACLR.

DESIGN

Case series.

SETTING

University.

PARTICPANTS

Five patients participated in an 8-week (24-session) eccentric cross-exercise intervention after ACLR.

MAIN OUTCOME MEASURES

Brain activation, neural activity and patient-reported outcomes were evaluated within 2 weeks post-ACLR and again at 10-weeks post-ACLR after the intervention. Each cross-exercise session consisted of 4 sets of 10 isokinetic eccentric contractions at 60 deg/sec with the noninvolved limb.

RESULTS

Following the intervention, patients demonstrated a facilitated spinal reflexive and muscle activity response from the motor cortex during a time when these measures are known to be depressed. Patients also demonstrated a reduce dependence on frontal cortex activity to generate quadriceps contractions. Further patients reported significant reductions in pain and symptoms and greater knee function.

CONCLUSIONS

Eccentric cross-exercise after ACLR helps to facilitate positive adaptations in neural function and patient reported outcomes.

Concussion May Increase the Risk of Subsequent Lower Extremity Musculoskeletal Injury in Collegiate Athletes

BACKGROUND

Laboratory-based studies on neuromuscular control after concussion and epidemiological studies suggest that concussion may increase the risk of subsequent musculoskeletal injury.

OBJECTIVE

The purpose of this study was to determine if athletes have an increased risk of lower extremity musculoskeletal injury after return to play from a concussion.

METHODS

Injury data were collected from 2006 to 2013 for men's football and for women's basketball, soccer and lacrosse at a National Collegiate Athletic Association Division I university. Ninety cases of in-season concussion in 73 athletes (52 male, 21 female) with return to play at least 30 days prior to the end of the season were identified. A period of up to 90 days of in-season competition following return to play was reviewed for time-loss injury. The same period was studied in up to two control athletes who had no concussion within the prior year and were matched for sport, starting status and position.

RESULTS

Lower extremity musculoskeletal injuries occurred at a higher rate in the concussed athletes (45/90 or 50 %) than in the non-concussed athletes (30/148 or 20 %; P < 0.01). The odds of sustaining a musculoskeletal injury were 3.39 times higher in the concussed athletes (95 % confidence interval 1.90-6.05; P < 0.01). Overall, the number of days lost because of injury was similar between concussed and non-concussed athletes (median 9 versus 15; P = 0.41).

CONCLUSIONS

The results of this study demonstrate a relationship between concussion and an increased risk of lower extremity musculoskeletal injury after return to play, and may have implications for current medical practice standards regarding evaluation and management of concussion injuries.

Quadriceps Neuromuscular Function in Patients With Anterior Cruciate Ligament Reconstruction With or Without Knee Osteoarthritis: A Cross-Sectional Study

CONTEXT

  Central and peripheral neural adaptations have been identified after anterior cruciate ligament (ACL) injury and reconstruction (ACLR) and are hypothesized to contribute to posttraumatic muscle dysfunction. Limited evidence exists about the temporal nature of neuromuscular adaptations during early and late-term phases of recovery after ACLR, and no researchers have studied patients with posttraumatic osteoarthritis.

OBJECTIVE

  To compare quadriceps neuromuscular function less than 2 years ( early) and more than 2 years ( late) after ACLR, including in patients who experienced posttraumatic knee osteoarthritis.

DESIGN

  Cross-sectional study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 72 patients after ACLR, consisting of 34 early (9.0 ± 4.3 months postsurgery), 30 late (70.5 ± 41.6 months postsurgery), and 8 with osteoarthritis (115.9 ± 110.0 months postsurgery), and 30 healthy control volunteers.

MAIN OUTCOME MEASURE(S)

  Quadriceps function was measured bilaterally during a single visit to determine normalized Hoffmann reflex (H : M ratio), knee-extension maximal voluntary isometric contraction torque (Nm/kg), central activation ratio (%), fatigue index (% decline), and active motor threshold (%). Comparisons were made using 2-way analyses of variance to identify the effect of limb and group on each outcome measure. We calculated Cohen d effect sizes to assess the magnitude of difference between ACLR and matched control limbs for each group.

RESULTS

  Compared with healthy control limbs, involved-limb maximal voluntary isometric contraction was lower among all patients after ACLR ( P < .001, Cohen d values = -1.00 to -1.75). The central activation ratio ( P < .001, Cohen d = -1.74) and fatigue index ( P = .003, Cohen d = -0.95) were lower among patients only early after ACLR. The active motor threshold was higher among all patients after ACLR ( P < .001, Cohen d values = -0.42 to -1.56).

CONCLUSIONS

  Neuromuscular impairments were present in patients early and late after ACLR, regardless of osteoarthritis status. Quadriceps strength and corticospinal excitability were impaired at each time point compared with values in healthy control individuals, suggesting the need to address cortical function early after ACLR.

Progressive Changes in Walking Kinematics and Kinetics After Anterior Cruciate Ligament Injury and Reconstruction: A Review and Meta-Analysis

CONTEXT

  Anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) result in persistent alterations in lower extremity movement patterns. The progression of lower extremity biomechanics from the time of injury has not been described.

OBJECTIVE

  To compare the 3-dimensional (3D) lower extremity kinematics and kinetics of walking among individuals with ACL deficiency (ACLD), individuals with ACLR, and healthy control participants from 3 to 64 months after ACLR.

DATA SOURCES

  We searched PubMed and Web of Science from 1970 through 2013.

STUDY SELECTION AND DATA EXTRACTION

  We selected only articles that provided peak kinematic and kinetic values during walking in individuals with ACLD or ACLR and comparison with a healthy control group or the contralateral uninjured limb.

DATA SYNTHESIS

  A total of 27 of 511 identified studies were included. Weighted means, pooled standard deviations, and 95% confidence intervals were calculated for the healthy control, ACLD, and ACLR groups at each reported time since surgery. The magnitude of between-groups (ACLR versus ACLD, control, or contralateral limb) differences at each time point was evaluated using Cohen d effect sizes and associated 95% confidence intervals. Peak knee-flexion angle (Cohen d = -0.41) and external knee-extensor moment (Cohen d = -0.68) were smaller in the ACLD than in the healthy control group. Peak knee-flexion angle (Cohen d range = -0.78 to -1.23) and external knee-extensor moment (Cohen d range = -1.39 to -2.16) were smaller in the ACLR group from 10 to 40 months after ACLR. Reductions in external knee-adduction moment (Cohen d range = -0.50 to -1.23) were present from 9 to 42 months after ACLR.

CONCLUSIONS

  Reductions in peak knee-flexion angle, external knee-flexion moment, and external knee-adduction moment were present in the ACLD and ACLR groups. This movement profile during the loading phase of gait has been linked to knee-cartilage degeneration and may contribute to the development of osteoarthritis after ACLR.

Quadriceps Neuromuscular Function and Jump-Landing Sagittal-Plane Knee Biomechanics After Anterior Cruciate Ligament Reconstruction

CONTEXT

  Aberrant biomechanics may affect force attenuation at the knee during dynamic activities, potentially increasing the risk of sustaining a knee injury or hastening the development of osteoarthritis after anterior cruciate ligament reconstruction (ACLR). Impaired quadriceps neuromuscular function has been hypothesized to influence the development of aberrant biomechanics.

OBJECTIVE

  To determine the association between quadriceps neuromuscular function (strength, voluntary activation, and spinal-reflex and corticomotor excitability) and sagittal-plane knee biomechanics during jump landings in individuals with ACLR.

DESIGN

  Cross-sectional study.

SETTING

  Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Twenty-eight individuals with unilateral ACLR (7 men, 21 women; age = 22.4 ± 3.7 years, height = 1.69 ± 0.10 m, mass = 69.4 ± 10.1 kg, time postsurgery = 52 ± 42 months).

MAIN OUTCOME MEASURE(S)

  We quantified quadriceps spinal-reflex excitability via the Hoffmann reflex normalized to maximal muscle response (H : M ratio), corticomotor excitability via active motor threshold, strength as knee-extension maximal voluntary isometric contraction (MVIC), and voluntary activation using the central activation ratio (CAR). In a separate session, sagittal-plane kinetics (peak vertical ground reaction force [vGRF] and peak internal knee-extension moment) and kinematics (knee-flexion angle at initial contact, peak knee-flexion angle, and knee-flexion excursion) were collected during the loading phase of a jump-landing task. Separate bivariate associations were performed between the neuromuscular and biomechanical variables.

RESULTS

  In the ACLR limb, greater MVIC was associated with greater peak knee-flexion angle ( r = 0.38, P = .045) and less peak vGRF ( r = -0.41, P = .03). Greater CAR was associated with greater peak internal knee-extension moment (ρ = -0.38, P = .045), and greater H : M ratios were associated with greater peak vGRF ( r = 0.45, P = .02).

CONCLUSIONS

  Greater quadriceps MVIC and CAR may provide better energy attenuation during a jump-landing task. Individuals with greater peak vGRF in the ACLR limb possibly require greater spinal-reflex excitability to attenuate greater loading during dynamic movements.

Unilateral Quadriceps Strengthening With Disinhibitory Cryotherapy and Quadriceps Symmetry After Anterior Cruciate Ligament Reconstruction

CONTEXT

  The effect of unilateral cryotherapy-facilitated rehabilitation exercise on involved-limb quadriceps function and limb symmetry in individuals with quadriceps dysfunction after anterior cruciate ligament reconstruction (ACLR) remains unclear.

OBJECTIVE

  To measure the effect of a 2-week unilateral cryotherapy-facilitated quadriceps-strengthening program on knee-extension strength and quadriceps central activation ratio (CAR) in participants with ACLR.

DESIGN

  Controlled laboratory study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 10 volunteers with unilateral ACLR (1 man, 9 women; age = 21.0 ± 2.8 years, height = 164.6 ± 5.0 cm, mass = 64.0 ± 6.1 kg, body mass index = 23.7 ± 2.7 kg/m²) and 10 healthy volunteers serving as control participants (1 man, 9 women; age = 20.8 ± 2.5 years, height = 169.1 ± 6.2 cm, mass = 61.1 ± 6.4 kg, body mass index = 21.4 ± 2.3 kg/m²) participated.

INTERVENTION(S)

  Participants with ACLR completed a 2-week unilateral cryotherapy-facilitated quadriceps-strengthening intervention.

MAIN OUTCOME MEASURE(S)

  Bilateral normalized knee-extension maximal voluntary isometric contraction (MVIC) torque (Nm/kg) and quadriceps CAR (%) were assessed preintervention and postintervention. Limb symmetry index (LSI) was calculated at preintervention and postintervention testing. Preintervention between-groups differences in unilateral quadriceps function and LSI were evaluated using independent-samples t tests. Preintervention-to-postintervention differences in quadriceps function were evaluated using paired-samples t tests. Cohen d effect sizes (95% confidence interval [CI]) were calculated for each comparison.

RESULTS

  Preintervention between-groups comparisons revealed less knee-extension MVIC torque and quadriceps CAR for the ACLR limb (MVIC: P = .01, Cohen d = -1.31 [95% CI = -2.28, -0.34]; CAR: P = .004, Cohen d = -1.48 [95% CI = -2.47, -0.49]) and uninvolved limb (MVIC: P = .03, Cohen d = -1.05 [95% CI = -1.99, -0.11]; CAR: P = .01, Cohen d = -1.27 [95% CI = -2.23, -0.31]) but not for the LSI (MVIC: P = .46, Cohen d = -0.34 [95% CI = -1.22, 0.54]; CAR: P = .60, Cohen d = 0.24 [95% CI = -0.64, 1.12]). In the ACLR group, participants had improved knee-extension MVIC torque in the involved limb ( P = .04, Cohen d = 0.32 [95% CI = -0.56, 1.20]) and uninvolved limb ( P = .03, Cohen d = 0.29 [95% CI = -0.59, 1.17]); however, the improvement in quadriceps CAR was limited to the involved limb ( P = .02, Cohen d = 1.16 [95% CI = 0.21, 2.11]). We observed no change in the LSI with the intervention for knee-extension MVIC torque ( P = .74, Cohen d = 0.09 [95% CI = -0.79, 0.97]) or quadriceps CAR ( P = .61, Cohen d = 0.26 [95% CI = -0.62, 1.14]).

CONCLUSIONS

  Two weeks of cryotherapy-facilitated exercise may improve involved-limb quadriceps function while preserving between-limbs symmetry in patients with a history of ACLR.

Persistent Muscle Inhibition after Anterior Cruciate Ligament Reconstruction: Role of Reflex Excitability

PURPOSE

Persistent voluntary quadriceps activation deficits are common after anterior cruciate ligament reconstruction (ACLR), but the direct causes are unclear. The primary purpose of this study was to determine whether spinal reflex excitability deficits are present in individuals with a history of ACLR, and secondarily to determine whether spinal reflex excitability predicts which individuals possess full voluntary quadriceps activation.

METHODS

One hundred and forty-seven individuals (74 healthy and 73 ACLR) participated in this cross-sectional case-control study. Quadriceps spinal reflex excitability was quantified using the Hoffmann reflex normalized to the maximal muscle response (H:M ratio). Voluntary quadriceps activation was evaluated with the burst superimposition technique and calculated via the central activation ratio (CAR). Separate 2 × 2 ANCOVA tests were used to compare between-limb and between-group differences for H:M ratio and CAR. A receiver operating characteristic curve was used to determine the accuracy of H:M ratio to predict if ACLR participants present with full voluntary activation (CAR ≥ 0.95).

RESULTS

The ACLR H:M ratio was not different between limbs or compared with the healthy group (P > 0.05). Although ACLR CAR was lower bilaterally compared with the healthy group (P < 0.001), it did not differ between limbs. The H:M ratio has poor accuracy for predicting which individuals exhibit full voluntary activation (receiver operating characteristic area under the curve = 0.52, 95% CI = 0.37,0.66; odds ratio = 2.2, 95% CI = 0.8, 5.9).

CONCLUSIONS

Spinal reflex excitability did not differ between limbs in individuals with ACLR or compared with healthy participants. The level of quadriceps spinal reflex excitability has poor accuracy at predicting which ACLR individuals would demonstrate full voluntary quadriceps activation.

Relationships of Muscle Function and Subjective Knee Function in Patients After ACL Reconstruction

BACKGROUND

After anterior cruciate ligament reconstruction (ACLR), relationships between objective measures of muscle function and patient-reported outcomes may change over time. Examining these measures at different time frames after surgery may help develop individualized approaches to improve post-ALCR analysis.

PURPOSE

To examine the associations between subjective knee function and lower-extremity muscle function in individual patients at various time points after ACLR.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Fifty-one participants who underwent primary, unilateral ACLR (15 males, 36 females; mean age, 22.9 ± 4.5 years; mean height, 172.4 ± 10.1 cm; mean weight, 68.7 ± 13.1 kg) were separated into 3 groups depending on time since surgery (early, <2 years; middle, 2-5 years; late, >5 years). Subjective knee function was quantified using the International Knee Documentation Committee (IKDC) subjective knee form and the Knee injury and Osteoarthritis Outcome Score (KOOS). Isometric knee extension and flexion strength were collected at 90 deg/s. Single-leg hop performance was measured using the single hop, triple hop, cross-over hop, and 6-m timed hop. Coefficient correlations were calculated between subjective knee function and objective measures of muscle function for each group.

RESULTS

The early group demonstrated moderate correlations between the KOOS and unilateral measures of flexion peak torque (r = 0.514, P = .035) and flexion power (r = 0.54, P = .027). The middle group demonstrated the strongest correlations between the KOOS and symmetry measures of the single hop (r = 0.69, P = .002) and extension work (r = 0.71, P = .002) as well as unilateral measures of the triple hop (r = 0.52, P = .034) and extension work (r = 0.66, P = .004). The late group demonstrated strong correlations between the 6-m timed hop symmetry and the IKDC (r = 0.716, P = .001) and KOOS (r = 0.71, P = .001).

CONCLUSION

Patients with a post-ACLR status of less than 2 years exhibited stronger relationships with unilateral strength measures to subjective function; graft type was found to change these relationships. Patients at 2 to 5 years postsurgery demonstrated relationships with both unilateral and symmetry measures of muscle function to subjective function. Patients who were more than 5 years after ACLR exhibited strong associations between hopping symmetry and subjective function.

CLINICAL RELEVANCE

Future clinical guidelines for patients after ACLR may need to consider time since surgery as a potential factor.

Eccentric Exercise to Enhance Neuromuscular Control

Context:

Neuromuscular alterations are a major causal factor of primary and secondary injuries. Though injury prevention programs have experienced some success, rates of injuries have not declined, and after injury, individuals often return to activity with functionality below clinical recommendations. Considering alternative therapies to the conventional concentric exercise approach, such as one that can target neuromuscular injury risk and postinjury alterations, may provide for more effective injury prevention and rehabilitation protocols.

Evidence Acquisition:

Peer-reviewed sources available on the Web of Science and MEDLINE databases from 2000 through 2016 were gathered using searches associated with the keywords eccentric exercise, injury prevention, and neuromuscular control.

Hypothesis:

Eccentric exercise will reduce injury risk by targeting specific neural and morphologic alterations that precipitate neuromuscular dysfunction.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Results:

Neuromuscular control is influenced by alterations in muscle morphology and neural activity. Eccentric exercise beneficially modifies several underlying factors of muscle morphology (fiber typing, cross-sectional area, working range, and pennation angle), and emerging evidence indicates that eccentric exercise is also beneficial to peripheral and central neural activity (alpha motorneuron recruitment/firing, sarcolemma activity, corticospinal excitability, and brain activation).

Conclusion:

There is mounting evidence that eccentric exercise is not only a therapeutic intervention influencing muscle morphology but also targets unique alterations in neuromuscular control, influencing injury risk.

Ultrasonographic assessment of medial femoral cartilage deformation acutely following walking and running

OBJECTIVE

To determine the magnitude of medial femoral cartilage deformation using ultrasonography (US) following walking and running in healthy individuals.

DESIGN

Twenty-five healthy participants with no history of osteoarthritis or knee injury volunteered for this study. Medial femoral cartilage thickness was assessed using US before and after three separate 30-min loading conditions: (1) walking at a self-selected speed, (2) running at a self-selected speed, and (3) sitting on a treatment table (i.e., control). Cartilage deformation was calculated as the percent change score from pre to post loading in each loading condition. The magnitude of cartilage deformation was compared between the three loading conditions.

RESULTS

There was no difference in baseline cartilage thickness between the three sessions (F_1,24 = 0.18, P = 0.68). Cartilage deformation was different between the loading conditions (F_1,24 = 47.54, P < 0.001). The walking (%Δ = -6.7, t₂₄ = 6.90, P < 0.001, d = -1.92) and running (%Δ = -8.9, t₂₄ = 8.14, P < 0.001, d = -1.85) conditions resulted in greater cartilage deformation when compared to the control condition (%Δ = +3.4). There was no difference in cartilage deformation between the running and walking conditions (t₂₄ = 1.10, P = 0.28, d = 0.33). US measured medial femoral cartilage thickness demonstrated reliability and precision within a single session (ICC_2,k = 0.966, SEM = 0.07 mm) and between additional sessions separated by seven (ICC_2,k = 0.964, SEM = 0.08 mm) and 16 days (ICC_2,k = 0.919, SEM = 0.11 mm).

CONCLUSIONS

US demonstrated to be a reliable and sensitive imaging modality at quantifying medial femoral cartilage deformation in healthy individuals. Both walking and running conditions created greater cartilage deformation when compared to the control conditions, but no difference was observed between the walking and running conditions.

Relationships Between Knee Extension Moments During Weighted and Unweighted Gait and Strength Measures That Predict Knee Moments After ACL Reconstruction

Background:

Weighted gait increases internal knee extension moment impulses (KEMI) in the anterior cruciate ligament–reconstructed (ACLR) limb; however, limb differences persist.

Hypotheses:

(1) KEMI during normal gait will influence KEMI during weighted gait and (2) peak knee extension (PKE) torque and time to reach PKE torque will predict KEMI during gait tasks.

Study Design:

Descriptive laboratory study.

Methods:

Twenty-four women and 14 men completed 3 gait tasks (unweighted, vest, sled) and strength testing after discharge from rehabilitation and clearance to return to sports. KEMI were calculated during the first 25% of stance. PKE torque and time to reach PKE torque were obtained using a dynamometer. Data on the ACLR limb and symmetry indices (SIs) were analyzed for each sex.

Results:

Women presented with asymmetrical PKE torques and KEMI across tasks. There were three correlations noted for KEMI: between the walk and vest, walk and sled, and vest and sled tasks. Slower time to PKE torque predicted limb asymmetries across tasks and KEMI in the ACLR limb during the sled task. Men presented with asymmetrical PKE torques and KEMI during the sled task. There was a correlation noted for KEMI between walk and vest tasks only. During the sled task, ACLR limb time to PKE torque predicted KEMI in the ACLR limb and PKE torque SI predicted KEMI SI.

Conclusion:

Women use asymmetrical KEMI profiles during all gait tasks, and those with worse KEMI during walking have worse KEMI during weighted gait. Men have asymmetrical KEMI when sled towing, and these KEMIs do not correlate with KEMI during walking or vest tasks.

Clinical Relevance:

PKE torque deficits persist when attempting to return to sports. Only men use gains in PKE torque to improve KEMI profiles. Although quicker PKE torque generation will increase KEMI in women, normalization of KEMI profiles will not occur by increasing rate of force development only. Gait retraining is recommended to correct asymmetrical KEMI profiles used across gait tasks in women.

Permanent knee sensorimotor system changes following ACL injury and surgery

The cruciate ligaments are components of the knee capsuloligamentous system providing vital neurosensory and biomechanical function. Since most historical primary ACL repair attempts were unsuccessful, reconstruction has become the preferred surgery. However, an increased understanding of the efficacy of lesion-site scaffolding, innovative suturing methods and materials, and evolving use of biological healing mediators such as platelet-rich plasma and stem cells has prompted reconsideration of what was once believed to be impossible. A growing number of in vivo animal studies and prospective clinical studies are providing increasing support for this intervention. The significance of ACL repair rather than reconstruction is that it more likely preserves the native neurosensory system, entheses, and ACL footprints. Tissue preservation combined with restored biomechanical function increases the likelihood for premorbid neuromuscular control system and dynamic knee stability recovery. This recovery should increase the potential for more patients to safely return to sports at their desired intensity and frequency. This current concepts paper revisits cruciate ligament neurosensory and neurovascular anatomy from the perspective of knee capsuloligamentous system function. Peripheral and central nerve pathways and central cortical representation mapping are also discussed. Surgical restoration of a more physiologically sound knee joint may be essential to solving the osteoarthritis dilemma. Innovative rehabilitative strategies and outcome measurement methodologies using more holistic and clinically relevant measurements that closely link biomechanical and neurosensory characteristics of physiological ACL function are discussed. Greater consideration of task-specific patient physical function and psychobehavioral links should better delineate the true efficacy of all ACL surgical and non-surgical interventions. Level of evidence IV.

Improving ACL Reconstruction Outcomes

Anterior cruciate ligament (ACL) reconstruction is a common and predominantly successful surgical intervention. But are there specific preoperative patient characteristics or intraoperative surgeon decisions that lead to better or worse outcomes? And can understanding brain function changes of patients after ACL reconstruction reveal insights into the ways that postsurgical rehabilitation can be improved to further enhance outcomes? These intriguing and clinically applicable questions are addressed in this webinar titled "Improving ACL Reconstruction Outcomes," hosted jointly by JOSPT and JBJS. The webinar is based on 2 published research articles-one from JBJS and the other from JOSPT. Participants in this continuing education activity are asked to read both articles carefully before watching the webinar. JBJS co-author Kurt Spindler, MD, discusses findings from a longitudinal analysis that identified certain baseline patient characteristics and intraoperative choices that predicted higher and lower SF-36 Physical Component scores after ACL reconstruction. JOSPT co-author Dustin Grooms, PhD, ATC, shares recently published results of a controlled laboratory study that employed functional MRI to investigate brain-activation differences between patients who did and did not undergo ACL reconstruction. Moderated by Kevin Wilk, PT, DPT, FAPTA, a leading authority on rehabilitation of sports injuries, the webinar includes additional insights from expert commentators Eric McCarty, MD, and Karin Grävare Silbernagel, PT, PhD, ATC.

Neuroplasticity Associated With Anterior Cruciate Ligament Reconstruction

Study Design Controlled laboratory study. Background Anterior cruciate ligament (ACL) injury may result in neuroplastic changes due to lost mechanoreceptors of the ACL and compensations in neuromuscular control. These alterations are not completely understood. Assessing brain function after ACL injury and anterior cruciate ligament reconstruction (ACLR) with functional magnetic resonance imaging provides a means to address this gap in knowledge. Objective To compare differences in brain activation during knee flexion/extension in persons who have undergone ACLR and in matched controls. Methods Fifteen participants who had undergone left ACLR (38.13 ± 27.16 months postsurgery) and 15 healthy controls matched on age, sex, height, mass, extremity dominance, education level, sport participation, and physical activity level participated. Functional magnetic resonance imaging data were obtained during a unilateral knee motor task consisting of repeated cycles of knee flexion and extension. Results Participants who had undergone ACLR had increased activation in the contralateral motor cortex, lingual gyrus, and ipsilateral secondary somatosensory area and diminished activation in the ipsilateral motor cortex and cerebellum when compared to healthy matched controls. Conclusion Brain activation for knee flexion/extension motion may be altered following ACLR. The ACLR brain activation profile may indicate a shift toward a visual-motor strategy as opposed to a sensory-motor strategy to engage in knee movement. Level of Evidence Cohort, level 3. J Orthop Sports Phys Ther 2017;47(3):180-189. Epub 5 Nov 2016. doi:10.2519/jospt.2017.7003.

Knee function among elite handball and football players 1-6 years after anterior cruciate ligament injury

The aim of the study was to describe objective and self-reported knee function for athletes who have returned to elite handball and football play after an ACL injury, comparing these to non-injured players at the same level. A total of 414 handball and 444 football players completed baseline tests from 2007 through 2014, examining lower extremity strength, dynamic balance, knee laxity, and knee function (KOOS questionnaire). Measures were compared between injured and non-injured legs and between injured legs and legs of controls. Eighty (9.3%) of the 858 players reported a previous ACL injury, 1-6 years post-injury (3.5±2.5 years), 49 handball (61.3%) and 31 football players (38.7%). We found no difference in strength or dynamic balance between previously ACL-injured (N=80) and non-injured players legs (N=1556). However, lower quadriceps (6.3%, 95% CI: 3.2-9.2) and hamstrings muscle strength (6.1%, 95% CI: 3.3-8.1) were observed in previously ACL-injured legs compared to the non-injured contralateral side (N=80). ACL-injured knees displayed greater joint laxity than the contralateral knee (N=80, 17%, 95% CI: 8-26) and healthy knees (N=1556, 23%, 95% CI: 14-33). KOOS scores were significantly lower for injured knees compared to knees of non-injured players. ACL-injured players who have successfully returned to elite sport have comparable strength and balance measures as their non-injured teammates. Subjective perception of knee function is strongly affected by injury history, with clinically relevant lower scores for the KOOS subscores Pain, Function, Sport, and Quality Of Life.

Quadriceps function relates to muscle size following ACL reconstruction

It remains unclear what role reduced volume and cross-section area (CSA) of individual quadriceps muscles may play in persistent quadriceps weakness and more global dysfunction following ACL reconstruction (ACLR). The purpose of this investigation was to establish the relationship between cross-sectional area of the quadriceps muscle group and measures of knee related and quadriceps function following ACLR. Thirty participants with a history of primary, unilateral ACLR experiencing persistent quadriceps activation failure participated in this cohort study. Clinical factors including International Knee Documentation Committee (IKDC) score, normalized knee extension MVIC torque (Nm/kg) and quadriceps central activation ratio (CAR, %) were assessed in addition to CSA. Quadriceps CSA was measured via magnetic resonance imaging (MRI; Siemens Avanto 1.5T). Quadriceps CSA (cm(2) ) and quadriceps volume (cm(3) ) as well as individual muscle estimates were identified within a 10 cm mid-thigh capture area. Pearson's product-moment correlation coefficients (r) established relationships between CSA and all other variables. Stepwise linear regression established which CSA factors were able to successfully predict clinical factors. Knee extension MVIC torque was strongly correlated with Vastus Intermedius (VI; r =  0.857, p < 0.001) CSA as well as partial VI (r = 0.849, p < 0.001) and quadriceps (r = 0.830, p < 0.001) volume. Partial VI (r = 0.365, p = 0.047) volume was weakly correlated with IKDC score. Knee extension MVIC torque was strongly predicted using VI CSA alone (R(2)  = 0.725) or in combination with Vastus Medialis CSA (VM; R(2)  = 0.756). Statement of Clinical Significance: Atrophy of the VI and VM muscles negatively impacts knee extension strength following ACLR. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1656-1662, 2016.

Quadriceps cortical adaptations in individuals with an anterior cruciate ligament injury

BACKGROUND

Altered quadriceps corticomotor excitability has been demonstrated following anterior cruciate ligament (ACL) injury and reconstruction, however only the single joint vasti muscles have been assessed. There is no current data on rectus femoris corticomotor excitability following ACL injury, the biarticular quadriceps muscle also critical for force attenuation and locomotion. The purpose of this study was to examine rectus femoris corticomotor excitability, intracortical inhibition and cortical motor representation in individuals with and without an ACL injury.

METHODS

A cross-sectional design was used to evaluate corticomotor excitability bilaterally in individuals with a physician confirmed ACL injury (12 males, six females; mean±SD age: 29.6±8.4years; BMI: 24.8±2.3kg·m(2); 69.5±42.5days post-injury) compared to a healthy control group (12 males, six females; age: 29.2±6.8years; BMI: 24.6±2.3kg·m(2)). Single-pulse transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability and cortical motor representation, and paired-pulse TMS used to assess intracortical inhibition for rectus femoris while participants maintained a knee extension force at 10% of body weight.

RESULTS

The cortical silent period (cSP) duration was longer in the injured limb of the ACL group compared to the uninjured limb (P=0.004). No significant differences were found for corticomotor excitability, intracortical inhibition or cortical motor representation center position and size (P>0.05).

CONCLUSIONS

There is preliminary evidence that the cSP is longer, but changes in rectus femoris corticomotor excitability and cortical motor representation are not present following ACL injury.

Impact of quadriceps strengthening on response to fatiguing exercise following ACL reconstruction

OBJECTIVES

Patients commonly experience altered response to fatiguing exercise after ACL reconstruction (ACLR). The objective of this study was to assess the impact of quadriceps strengthening on response to exercise after ACLR.

DESIGN

Clinical trial.

METHODS

Ten participants with a history of primary, unilateral ACLR (sex=9F/1M, age=21.0±2.8 years, BMI=23.7±2.7kg/m²) and 10 healthy participants (sex=9F/1M, age=22.2±3.2 years, BMI=23.8±3.9kg/m²) participated. ACLR participants completed a 2-week quadriceps strengthening intervention including 14 progressive strengthening exercise sessions. Normalized knee extension maximum voluntary isometric contraction (MVIC) torque (Nm/kg) and quadriceps central activation ratio (%, CAR) were measured before and after a 30-minute fatiguing exercise protocol. ACLR participants completed testing before and after the 2-week intervention while control participants completed a single testing session.

RESULTS

The intervention significantly improved normalized knee extension MVIC torque (pre-intervention=1.85±0.67Nm/kg, post-intervention=2.09±0.81Nm/kg, p=0.04) and quadriceps CAR in the ACLR involved limb (pre-intervention=86.51±5.03%, post-intervention=92.94±5.99%, p=0.02). Quadriceps CAR (pre-intervention=1.13±9.04%, post-intervention=-3.97±4.59%, p=0.16) and normalized knee extension MVIC torque (pre-intervention=0.26±20.90%, post-intervention=-8.02±12.82%, p=0.30) response to exercise did not significantly change from pre-intervention to post-intervention conditions.

CONCLUSIONS

Two weeks of quadriceps strengthening reduced this between group difference in the involved limb which may indicate restoration of more optimal quadriceps neuromuscular function and increased demand on the quadriceps during physical activity.

Knee kinematics during stair descent 20 years following anterior cruciate ligament rupture with and without reconstruction

BACKGROUND

Changes and asymmetries for walking gait have been explored extensively following injuries of anterior cruciate ligaments within ten years of injury or reconstruction. We examined longer term knee joint kinematics of reconstructed and non-reconstructed knees during stair descent compared to controls.

METHODS

Three-dimensional knee kinematics during stair descent were registered for 33 subjects with ACL reconstruction, 36 subjects with ACL rupture managed with physiotherapy only and 31 uninjured controls. Injured subjects were 23.5 (2.1) years following injury. Linear mixed models were used to compare temporal variables and knee kinematics during stance phase between groups and contralateral sides.

FINDINGS

Walking speed was slower for the both ACL-injured groups compared to controls and stance duration was longer for the injured than the uninjured sides of the physiotherapy-only group. Compared to controls, the physiotherapy-only group had significantly less adduction at initial foot contact of the injured and uninjured knees. The uninjured side of the physiotherapy-only group also had less flexion than controls at initial foot contact and during weight acceptance. Compared to the surgically-managed group, the injured sides of the physiotherapy-only groups had significantly less adduction at initial contact, peak adduction during weight acceptance, and peak flexion during propulsion.

INTERPRETATION

Independent of treatment, altered knee kinematics exist more than 20 years following ACL injury during stair descent. We suggest that future studies investigating short and long-term kinematic outcomes of ACL injury could evaluate stair descent with particular emphasis on weight acceptance of stance, and potential associations to perceived knee function.

Knee-Extension Torque Variability and Subjective Knee Function in Patients with a History of Anterior Cruciate Ligament Reconstruction

CONTEXT

When returning to physical activity, patients with a history of anterior cruciate ligament reconstruction (ACL-R) often experience limitations in knee-joint function that may be due to chronic impairments in quadriceps motor control. Assessment of knee-extension torque variability may demonstrate underlying impairments in quadriceps motor control in patients with a history of ACL-R.

OBJECTIVE

To identify differences in maximal isometric knee-extension torque variability between knees that have undergone ACL-R and healthy knees and to determine the relationship between knee-extension torque variability and self-reported knee function in patients with a history of ACL-R.

DESIGN

Descriptive laboratory study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 53 individuals with primary, unilateral ACL-R (age = 23.4 ± 4.9 years, height = 1.7 ± 0.1 m, mass = 74.6 ± 14.8 kg) and 50 individuals with no history of substantial lower extremity injury or surgery who served as controls (age = 23.3 ± 4.4 years, height = 1.7 ± 0.1 m, mass = 67.4 ± 13.2 kg).

MAIN OUTCOME MEASURE(S)

Torque variability, strength, and central activation ratio (CAR) were calculated from 3-second maximal knee-extension contraction trials (90° of flexion) with a superimposed electrical stimulus. All participants completed the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, and we determined the number of months after surgery. Group differences were assessed using independent-samples t tests. Correlation coefficients were calculated among torque variability, strength, CAR, months after surgery, and IKDC scores. Torque variability, strength, CAR, and months after surgery were regressed on IKDC scores using stepwise, multiple linear regression.

RESULTS

Torque variability was greater and strength, CAR, and IKDC scores were lower in the ACL-R group than in the control group (P < .05). Torque variability and strength were correlated with IKDC scores (P < .05). Torque variability, strength, and CAR were correlated with each other (P < .05). Torque variability alone accounted for 14.3% of the variance in IKDC scores. The combination of torque variability and number of months after surgery accounted for 21% of the variance in IKDC scores. Strength and CAR were excluded from the regression model.

CONCLUSIONS

Knee-extension torque variability was moderately associated with IKDC scores in patients with a history of ACL-R. Torque variability combined with months after surgery predicted 21% of the variance in IKDC scores in these patients.

Considerations for late stage acl rehabilitation and return to sport to limit re-injury risk and maximize athletic performance

PURPOSE/BACKGROUND

Despite recent advances in anterior cruciate ligament reconstruction (ACL) surgical techniques, an improved understanding of the ACL's biomechanical role, and expanding research on optimal rehabilitation practices in ACL-reconstructed (ACLR) patients, the re-tear rate remains alarmingly high and athletic performance deficits persist after completion of the rehabilitation course in a large percentage of patients. Significant deficits may persist in strength, muscular activation, power, postural stability, lower extremity mechanics, and psychological preparedness. Many patients may continue to demonstrate altered movement mechanics associated with increased injury risk. The purpose of this clinical commentary and literature review is to provide a summary of current evidence to assist the rehabilitation professional in recognizing, assessing, and addressing factors which may have been previously underappreciated or unrecognized as having significant influence on ACLR rehabilitation outcomes.

METHODS

A literature review was completed using PubMed, Medline, and Cochrane Database with results limited to peer-reviewed articles published in English. 136 articles were reviewed and included in this commentary.

CONCLUSIONS

Barriers to successful return to previous level of activity following ACLR are multifactorial.Recent research suggests that changes to the neuromuscular system, movement mechanics, psychological preparedness, and motor learning deficits may be important considerations during late stage rehabilitation.

LEVEL OF EVIDENCE

Level 5- Clinical Commentary.