Criteria Used to Determine Unrestricted Return to Activity After ACL Reconstruction in Pediatric and Adolescent Patients: A Systematic Review.

Background: The rates of anterior cruciate ligament (ACL) graft failure or contralateral ACL rupture range from 17% to 30% in pediatric patients after ACL reconstruction (ACLR). A contributing factor to the high reinjury rate in this population may be the limited evidence regarding appropriate criteria for allowing unrestricted return to activity (RTA) postoperatively. Purpose: To review the literature and identify the most commonly used criteria when determining unrestricted RTA after ACLR in pediatric patients. Study Design: Systematic review; Level of evidence, 4. Methods: A search was performed of the Medline/PubMed, Cochrane Central Register of Controlled Trials, Embase, CINAHL, and SPORTDiscus databases using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The authors identified studies that included pediatric patients (<19 years of age) and specified the criteria used to determine RTA after ACLR. Results: A total of 27 articles met all criteria for review, of which 13 studies only used 1 criterion when determining RTA. Objective criteria were the most common type of criteria for RTA (17 studies). Strength tests (15 studies) and hop tests (10 studies) were the most commonly used tasks when deriving RTA criteria. Only 2 studies used validated questionnaires to assess the patient's physiological readiness for RTA, and only 2 studies used an objective assessment of movement quality before RTA. Conclusion: Only 14 of the 27 reviewed studies reported using >1 criterion when determining RTA. Furthermore, few studies used patient-reported outcome measures or lower limb kinematics as RTA criteria, indicating that more research is needed to validate these metrics in the pediatric population.

Altered movement strategy during functional movement after an ACL injury, despite ACL reconstruction.

Knee joint functional deficits are common after anterior cruciate ligament (ACL) injury, but different assessment methods of joint function seem to provide contradicting information complicating recovery monitoring. We previously reported improved perceived knee function and functional performance (forward lunge ground contact time) in patients with an ACL injury from pre to 10 months post ACL reconstruction without improvement in knee-specific biomechanics. To further investigate this discrepancy, we additionally analyzed knee extensor and flexor muscle strength, and movement quality in the forward lunge (subjective and objective evaluations) and performed a full lower limb biomechanical analysis of the forward lunge movement. We included 12 patients with an ACL injury (tested before and after ACL reconstructive surgery) and 15 healthy controls from the previous study to the current investigation. Outcome measures were obtained pre and ~11 months post ACL reconstruction for the patients and at a single time point for the controls. Objective movement quality in the patients with an ACL injury showed an improvement from their pre reconstruction surgery visit to the post reconstruction visit but this was not observable in the subjective evaluation. Knee extensor muscle strength declined after the ACL reconstruction by 29% (p = 0.002) and both knee extensors (p < 0.001) and flexors (p = 0.027) were weaker in the patients post ACL reconstruction compared to healthy controls. ACL injured patients had an altered movement strategy in the forward lunge with reduced knee extensors contribution and increased hip extensor contribution compared to the controls both before and after the reconstruction. The altered movement strategy was associated with knee extensor muscle strength. This explorative study with a limited sample size found that clinicians should be aware that significant functional deficits in the knee extensor muscles, both in isolated muscle strength testing and during a functional movement, may be present although patients perceive an improvement in their knee function and present good functional performance without obvious movement quality issues.

Females with knee osteoarthritis use a detrimental knee loading strategy when squatting.

BACKGROUND: The purpose of this study was to identify sex differences in lower limb kinematics, kinetics, and muscle activation patterns between individuals with osteoarthritis and healthy controls during a two-legged squat. METHOD: Thirty OA (15 females) and 30 healthy (15 females) participants performed three 2-legged squats. Sagittal and frontal plane hip, knee, and ankle kinematics and kinetics were calculated. Two-way ANOVAs (Sex X OA Status) were used to characterize differences in squatting strategies between sexes and between those with and without knee OA. RESULTS: A greater decrease in sagittal hip, knee, and ankle range of motion and knee joint power was observed in the OA participants compared to the healthy controls. Females with OA had significantly reduced hip and knee adduction angles compared to the healthy females and males with OA. Females also had decreased hip power, hip flexion, and hip adduction moments and knee adduction moments compared to their male counterparts, with the greatest deficits observed in the females with OA. Females with OA also had the highest magnitude of muscle activation for the quadriceps, hamstrings, and gastrocnemius throughout the squat, while males with OA showed increased activation of the vastus lateralis and medial gastrocnemius compared to the healthy males. CONCLUSIONS: OA significantly altered biomechanics and neuromuscular control during the squat, with males employing a hip-dominant strategy, allowing them to achieve a greater lower limb range of motion.

Protocol for the systematic review of return-to-activity criteria in adolescent patients following an anterior cruciate ligament reconstruction.

BACKGROUND: Anterior cruciate ligament (ACL) rupture is a debilitating knee injury associated with sequela such as joint instability and progressive degeneration. Unfortunately, following surgical ACL reconstruction in adolescents, the rates of ACL graft failure range from 17 to 19%. A contributing factor to the high reinjury rate in this population may be the limited evidence regarding appropriate criteria for allowing unrestricted return-to-activities (RTA) postoperatively. Several systematic reviews have already sought to develop a consensus on what criteria should be utilized for releasing patients to unrestricted sports activities; however, these reviews have focused on adult populations, a group at much lower risk for reinjury. Our objective is to systematically examine the literature and identify the criteria used when determining unrestricted RTA following an ACL reconstruction in an adolescent population. METHODS: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a systematic search will be performed of the MEDLINE/PubMed, Cochrane, Embase, CINAHL, and SPORTDiscus electronic databases. Searches will be conducted from January 1, 2000, until submission of the final review. Studies will be identified that include adolescent patients (10-18 years old) undergoing a primary ACL reconstruction and which have specified the criteria used to determine RTA. Each article will be independently screened by two reviewers. To supplement the electronic database search, citations within all included studies will be manually reviewed. Reviewers will record the RTA assessment utilized and the rates of ACL reinjury through a standardized data extraction sheet. Reviewers will resolve full-text screening and data extraction disagreements through discussion. Synthesis of the collected data will focus on compiling and mapping the most commonly used types of RTA criteria. DISCUSSION: This systematic review will determine the most commonly used RTA criteria in adolescent patients post-ACL reconstruction. This will help future interventions build more effective adolescent-specific RTA assessments through the validation of current RTA criteria as well as the implementation of new criteria according to the identified literature gaps.

Sex differences in muscle activation patterns associated with anterior cruciate ligament injury during landing and cutting tasks: A systematic review.

Neuromuscular control is critical for maintaining dynamic joint stability and mitigating the risk of anterior cruciate ligament (ACL) injury. Given the increased risk of ACL injury in females, sex-based differential muscle activation strategies are often associated with this risk. For example, the quadriceps-dominant muscle activation strategy sometimes observed in females has been discussed as a cause of their increased risk of ACL injury. However, there has been no synthesised knowledge on sex differences in muscle activation patterns associated with ACL injuries. Therefore, the purpose of this review was to synthesise sex differences in muscle activation patterns in movements associated with ACL injuries in both adult and adolescent populations. A systematic electronic database search was conducted. Thirty studies were included in the review. Females demonstrated higher pre- and post-landing activation of the quadriceps and lower activation of the hamstrings in 15 studies. Females also had higher quadriceps-to-hamstring co-contraction ratios during pre- and post-landing phases compared to their male counterparts in 4 of 9 studies that considered co-contraction. While some studies supported the quadriceps-dominant activation strategies in females, no consensus can be drawn due to methodological inconsistencies and limitations. Also, despite the importance of ACL injury prevention in children and adolescents, the evidence on sex difference in muscle activation patterns in this population is insufficient to draw meaningful conclusions.

Functional muscle synergies to support the knee against moment specific loads while weight bearing.

OBJECTIVE: Externally applied abduction and rotational loads are major contributors to the knee joint injury mechanism; yet, how muscles work together to stabilize the knee against these loads remains unclear. Our study sought to evaluate lower limb functional muscle synergies in healthy young adults such that muscle activation can be directly related to internal knee joint moments. METHODS: Concatenated non-negative matrix factorization extracted muscle and moment synergies of 22 participants from electromyographic signals and joint moments elicited during a weight-bearing force matching protocol. RESULTS: Two synergy sets were extracted: Set 1 included four synergies, each corresponding to a general anterior, posterior, medial, or lateral force direction. Frontal and transverse moments were coupled during medial and lateral force directions. Set 2 included six synergies, each corresponding to a moment type (extension/flexion, ab/adduction, internal/external rotation). Hamstrings and quadriceps dominated synergies associated with respective flexion and extension moments while quadriceps-hamstring co-activation was associated with knee abduction. Rotation moments were associated with notable contributions from hamstrings, quadriceps, gastrocnemius, and hip ab/adductors, corresponding to a general co-activation muscle synergy. CONCLUSION: Our results highlight the importance of muscular co-activation of all muscles crossing the knee to support it during injury-inducing loading conditions such as externally applied knee abduction and rotation. Functional muscle synergies can provide new insight into the relationship between neuromuscular control and knee joint stability by directly associating biomechanical variables to muscle activation.

Sex-specific landing biomechanics and energy absorption during unanticipated single-leg drop-jumps in adolescents: implications for knee injury mechanics.

Females aged between 13 and 17 years old possess the highest non-contact ACL injury incidence of any sex-age strata. Considering that energy absorption strategies have been associated with a reduced risk for sustaining an ACL injury, evaluating landing performance in youth athletes requires investigations beyond the kinematic level. The purpose of this study was to identify sex-specific energy absorption strategies in adolescent males and females, including the relationship between strength and the observed strategies. Thirty-one healthy adolescent athletes completed unanticipated single-leg drop-jump landings on their dominant limb. Sex-specific kinematics and lower-limb contributions to energy absorption were then compared over the landing phase for each jump. Pearson and Spearman correlation coefficients determined the relationship between isometric joint strength and the observed kinematics and energy absorption. Female participants absorbed a larger proportion of the landing energy at the ankle (p = 0.046, d = 0.75) and smaller proportion at the hip (p = 0.028, d = 0.85) compared to males. Females also reached larger peak negative joint power in their knee (p = 0.001, d = 1.1) and ankle (p = 0.04, d = 0.79). Hip extension strength was positively correlated with trunk flexion (r = 0.559, p = 0.001) and negatively correlated with forward pelvic tilt (r = -0.513, p = 0.003). Females adopted an energy absorption strategy which utilized the distal joints to absorb a larger portion of the landing forces and tended to absorb the forces later in the landing phase relative to males. The greater reliance on distal joints is correlated to reduced hip strength and may increase the risk for sustaining an ACL injury.

Decision Tree Learning Algorithm for Classifying Knee Injury Status Using Return-to-Activity Criteria.

Anterior cruciate ligament (ACL) injury rates in female adolescents are increasing. Irrespective of treatment options, approximately 1/3 will suffer secondary ACL injuries following their return to activity (RTA). Despite this, there are no evidence-informed RTA guidelines to aid clinicians in deciding when this should occur. The first step towards these guidelines is to identify relevant and feasible measures to assess the functional status of these patients. The purpose of this study was therefore to evaluate tests frequently used to assess functional capacity following surgery using a Reduced Error Pruning Tree (REPT). Thirty-six healthy and forty-two ACLinjured adolescent females performed a series of functional tasks. Motion analysis along with spatiotemporal measures were used to extract thirty clinically relevant variables. The REPT reduced these variables down to two limb symmetry measures (maximum anterior hop and maximum lateral hop), capable of classifying injury status between the healthy and ACL injured participants with a 69% sensitivity, 78% specificity and kappa statistic of 0.464. We, therefore, conclude that the REPT model was able to evaluate functional capacity as it relates to injury status in adolescent females. We also recommend considering these variables when developing RTA assessments and guidelines.Clinical Relevance- Our results indicate that spatiotemporal measures may differentiate ACL-injured and healthy female adolescents with moderate confidence using a REPT. The identified tests may reasonably be added to the clinical evaluation process when evaluating functional capacity and readiness to return to activity.

Divergence analysis of failed and successful unanticipated single-leg landings reveals the importance of the flight phase and upper body biomechanics.

The purpose of this study was to describe neuromuscular and kinematic differences during failed and successful drop-vertical jumps in a pediatric population. Healthy young athletes (n = 32) completed single-leg drop vertical jump landings where the required landing leg was unanticipated. Trials were categorized as failed if the participant shifted their base of support during the landing. Joint kinematics and muscle activation amplitudes were time normalized over the flight and landing phases. Statistical parametric mapping (SPM) was used to compare landings and a moving average convergence divergence oscillator was then calculated to determine where failed and successful waveforms began to diverge prior to reaching statistical significance. SPM determined that participants performed the failed trials with reduced pelvic tilt towards the landing limb during 41-69% of the flight phase, greater trunk flexion angle during 31-100% of the landing phase and greater trunk tilt away from the landing limb during 3-13% and 21-90% of the landing phase. Greater rectus femoris activation during the failed trials was identified during 88-100% of the flight phase, as well as 1-4% and 71-97% of the landing phase. Greater gluteus medius and biceps femoris activation was also identified in the failed trials during 54-72% and 76-89% of the landing phase respectively. These findings indicate that the control of proximal joints has an important role in determining if a participant will fail a landing; and that how athletes prepare for a landing may be more relevant than the kinematics following ground contact.

Forward lunge before and after anterior cruciate ligament reconstruction: Faster movement but unchanged knee joint biomechanics.

The forward lunge (FL) may be a promising movement to assess functional outcome after ACL reconstruction. Thus, we aimed to investigate the FL movement pattern before and after ACL reconstruction with a comparison to healthy controls to determine if differences were present. Twenty-eight ACL injured participants and 28 matched healthy controls were included. They performed FL movements while sagittal plane biomechanics of the knee and electromyography (EMG) of nine leg muscles was assessed. The ACL injured group was tested before and 10 months after surgery. The perceived knee function and activity level was assessed by questionnaires. The ACL injured group performed the FL significantly slower than the controls before surgery (mean difference: 0.41 s [95%CI: 0.04-0.79 s; p<0.05]) while they performed the FL as fast as the controls after surgery (~28% movement time reduction post-surgery). Perceived knee function and activity level improved significantly post-surgery. The knee joint flexion angle, extensor moment, power, angular velocity in the ACL injured group did not differ from pre to post-surgery. For the ACL injured group, the peak knee extensor moment observed both pre and post-surgery was significantly lower when compared to the controls. The EMG results showed minimal differences. In conclusion, at 10 months post-surgery, the FL was performed significantly faster and the movement time was comparable to that of the controls. While the perceived knee function and activity level improved post-surgery, the knee joint biomechanics were unchanged. This may reflect that knee joint function was not fully restored.

Relationship of Knee Forces to Subjective Function Pre- and Post-ACL Reconstruction.

PURPOSE: Although basic objective measures (e.g., knee laxity, strength, and hop tests) have been related to subjective measures of function, associations between knee-specific objective and subjective measures have yet to be completed. The objective was to determine if knee joint contact and ligament forces differ between pre- and post-anterior cruciate ligament (ACL) reconstructed states and if these forces relate to their patient's respective subjective functional ability scores. METHODS: Twelve patients performed a hopping task before and after reconstruction. Magnetic resonance images and OpenSim were used to develop patient-specific models in static optimization and joint reaction analyses. Questionnaires concerning each patient's subjective functional ability were also collected and correlated with knee joint contact and ligament forces. RESULTS: No significant differences were observed between deficient and reconstructed groups with respect to knee joint contact or ligament forces. Nevertheless, there were several significant (P < 0.05) moderate to strong correlations between subjective and objective measures including Tegner activity level to contact force in both states (r = 0.67-0.76) and International Knee Documentation Committee to compressive and anterior shear forces (r = 0.64-0.66). CONCLUSION: Knee-specific objective measures of a patient's functional capacity can represent their subjective ability, which explains this relationship to a greater extent than past anatomical and gross objective measures of function. This consolidation is imperative for improving the current rehabilitation schema as it allows for external validation of objective and subjective functional measures. With poor validation of subjective function against objective measures of function, the reinjury rate is unlikely to diminish, continuing the heavy financial burden on health care systems.

Translation and Validation of the Hospital for Special Surgery Pediatric Functional Activity Brief Scale for French Paediatric Populations.

Purpose: Physical activity level is a prognostic variable for patients with injuries. Self-report questionnaires exist to obtain these measures; however, they are not accessible to all populations because of language barriers. Therefore, the purpose of this study was to translate and validate the Hospital for Special Surgery Pediatric Functional Activity Brief Scale (HSS Pedi-FABS) for francophones. Method: We translated the HSS Pedi-FABS using the forward-reverse translation approach and validated it among bilingual adults and an expert panel before administering it to a paediatric population. A repeated-measures crossover design was used: forty-three middle school students, aged 13.1 (SD 0.75) years, were randomly administered either the English or the French questionnaire. Two days later, all participants completed the other version. The translated questionnaire was assessed for its convergent validity (Spearman's r correlation coefficients [rs ]), internal consistency (Cronbach's α), and reliability (standard error of measurement [SEM]). Results: All assessments had a significance level of p < 0.001 with an excellent Spearman's r correlation coefficient between the participants' total scores on the translated questionnaires (rs  = 0.911). The overall scores for the questionnaire and the individual items of the questionnaire revealed excellent internal consistency (α = 0.868) and reliability (SEM = 0.334). Conclusions: The validated and reliable translated questionnaire can be used by researchers and clinicians to assess physical activity levels in French paediatric populations.

Objectif : le niveau d'activité physique est un pronostic variable pour les patients qui présentent des blessures. Il existe des questionnaires d'autoévaluation pour obtenir ces mesures, mais ils ne sont pas accessibles à toutes les populations à cause de la barrière de la langue. La présente étude visait à traduire et à valider le Hospital for Special Surgery Pediatric Functional Activity Brief Scale (HSS Pedi-FABS) pour les francophones. Méthodologie : les chercheurs ont traduit le HSS Pedi-FABS au moyen du processus de rétrotraduction et l'ont validé auprès d'adultes bilingues et d'un groupe d'experts avant de l'utiliser auprès d'une population pédiatrique. Ils ont utilisé une méthodologie transversale par mesures répétées : 43 élèves du début du secondaire de 13,1 ans (ÉT 0,75) ont répondu au hasard au questionnaire anglais ou français. Deux jours plus tard, tous les participants ont rempli l'autre version. Les questionnaires traduits ont été évalués pour leur validité convergente (coefficients de corrélation Rho de Spearman [rs ]), leur cohérence interne (coefficient alpha [α] de Cronbach) et leur fiabilité (erreur type de mesure). Résultats : toutes les évaluations présentaient un seuil de signification de p < 0,001 et un excellent coefficient de corrélation Rho de Spearman entre les scores totaux des participants dans les questionnaires traduits (rs  = 0,911). Les scores totaux du questionnaire et de chacun de ses éléments ont révélé une excellente cohérence interne (α = 0,868) et une excellente fiabilité (erreur type de mesure = 0,334). Conclusion : le questionnaire validé et traduit avec fiabilité peut être utilisé par les chercheurs et les cliniciens pour évaluer les niveaux d'activité physique de populations pédiatriques francophones.

Predicting post-operative functional ability from pre-operative measures in ACL-injured individuals.

PURPOSE: This study aimed to quantify the relationship between objective and subjective measures of functional ability and determine if measures in the deficient (ACLd) state were correlated to, and capable of predicting a patient's objective and subjective measures in the reconstructed (ACLr) state. METHODS: Twenty ACL-injured participants completed hop and side cut movements prior to and 10 months post-reconstruction. Their subjective measures (Tegner, Lysholm, IKDC, KOOS, and KNEEs) were related to objective measures of functional ability (peak knee flexion, peak knee extensor moment, stiffness, knee joint center excursion (KJCE), and knee joint center boundary). Correlations were used to determine relationships between variables whereas regressions were used to identify ACLd score's predictive ability of an ACLr score. RESULTS: Relationships between objective and subjective measures were task and ACL status dependent with KJCE and stiffness most commonly being related to subjective scores. The greatest correlation was between knee stiffness and Tegner in the ACLr group during the side cut (r = 0.69). Peak knee flexion angle (adj. R2  = 0.4-0.66) was the best objective predictor between ACLd and ACLr states while KOOS-ADL had the strongest correlations (r = 0.70-0.77) and Tegner had the greatest predictive power (odds ratio: 1.46-1.86) between states in both tasks. CONCLUSION: Objective measures show a wide range of correlation to subjective measures with some being quite strong. Furthermore, objective measures in the ACLd state are more correlated and more often capable of predicting ACLr scores than the subjective measures of functional ability.

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

BACKGROUND: Voluntary activation deficit of the quadriceps muscle group is a common symptom in populations with knee joint injury. Musculoskeletal modeling and simulations can improve our understanding of pathological conditions; however, they are mathematically complex which can limit their clinical application. A practical subject-specific modeling framework is introduced to evaluate knee extensor inhibition and muscle force contributions to isometric knee joint torques in healthy adults with and without experimentally induced quadriceps muscle pain. METHODS: A randomized cross-over placebo controlled study design was used. Subject-specific maximum knee joint extension torque and quadriceps electromyographic data from 13 uninjured young adults were combined in a modeling framework to determine optimal muscle strength scaling parameters and ideal torque. Strength deficit ratios (experimental torque/ideal torque) and individual muscle contribution to experimental torque was computed before and after intramuscular hypertonic (pain inducing) and isotonic (sham) saline was injected to the vastus medialis. FINDINGS: Decreased experimental knee extension torque (-8%) and vastus medialis electromyography (-26%) amplitude pre- to post- hypertonic injection was observed. Correspondingly, significant decreases in the knee extensor strength deficit ratio (-18%) and percent contribution of vastus medialis to experimental torque (-24%) was observed pre- to post- hypertonic injection. No differences were observed with isotonic injections, confirming the validity of the model. INTERPRETATION: Our practical method to estimate strength ratios can be easily implemented within a musculoskeletal modeling framework to improve the validity of model estimates. This, in turn, can increase our understanding of the relationship between neuromuscular deficits and functional outcomes in patient populations.

Assessment of objective dynamic knee joint control in anterior cruciate ligament deficient and reconstructed individuals.

BACKGROUND: There is a lack of objective dynamic knee joint control measures that can be related to the status of the anterior cruciate ligament (ACL). The purpose of this study was to introduce two novel measures and apply a third to determine how dynamic knee joint control changes in relation to ACL status during dynamic movements. METHODS: Twenty patients (13 male) were tested pre- (ACLd) and 10-months post- (ACLr) ACL reconstructive surgery and matched to an uninjured participant (CON). Kinetic and kinematic data were synchronously recorded with a force platform and motion capture system. Three objective control measures including dynamic angular stiffness, knee joint center excursion (KJCE), and knee joint center boundary (KJCB) were assessed for each participant when completing the side cut and hop tasks. RESULTS: During the side cut, stiffness was found to be significantly lower in ACLd (0.06 ±â€¯0.01 Nm/kg/°) and ACLr (0.07 ±â€¯0.02 Nm/kg/°) compared to CON (0.08 ±â€¯0.02 Nm/kg/°), while there were no differences in stiffness during the hop. No significant differences were observed in the KJCE during the side cut, while KJCE was significantly greater (p = 0.006) during the hop in CON compared to the ACLd. There were no differences in KJCB. CONCLUSIONS: These high-functioning ACL injured in both ACLd and ACLr phases, aside from reduced stiffness, were able to complete both tasks with similar dynamic control as the CON. Although improvements in self-perceived control between ACLd and ACLr have been observed, this lack of improvement in objective control demonstrates a gap between a patient's self-efficacy and the level of control.

A time-efficient multi-deviant paradigm to determine the effects of gap duration on the mismatch negativity.

The insertion of a silent period (or gap) in a frequently occurring standard stimulus elicits a negative-going event-related potential (ERP), called the Deviant-Related Negativity (DRN). This is often studied using a single-deviant paradigm. To study the effects of gaps with multiple durations, a different sequence would be required for each gap. A more time-efficient multi-deviant paradigm has been developed in which stimuli of various gap widths are included in a single sequence. In the present study, 14 young adults watched a silent video while ignoring an auditory sequence. A single run of a multi-deviant sequence was presented in which 6 different rare deviants alternated with a standard stimulus. The standard was a 200-ms white noise burst. The deviants were constructed by inserting a gap in the standard. The duration of the 6 gaps ranged from 2 to 40 ms. Participants were also presented with multiple runs of single-deviant sequences. Each of the 3 deviants was run in a separate sequence. The amplitude of the DRN elicited by the deviant increased as gap duration became longer, although it did plateau for the longer duration gaps. The amplitudes of the DRNs were larger in the single-deviant paradigm than in the multi-deviant paradigm. However, the difference was only significant when the mastoid reference was used. Behavioural data showed a mean d' of 2.1 for the 5-ms gap. None of the participants were able to detect the 2-ms gap. There was no correlation between d' and the DRN amplitude. Still, the effects of gap duration on the amplitude of the DRN were similar between the single and multi-deviant sequences. This makes the multi-deviant paradigm a possible time-saving alternative to the single-deviant paradigm.

Differences in EMG-moment relationships between ACL-injured and uninjured adults during a weight-bearing multidirectional force control task.

Anterior cruciate ligament injury (ACLi) reduces mechanical knee joint stability. Differences in muscle activation patterns are commonly identified between ACLi individuals and uninjured controls (CON); however, how and which of these differences are adaptations to protect the knee or adversely increase risk of joint instability remain unclear. Since the neuromuscular system integrates activity of all muscles crossing the knee to create a moment-of-force that opposes an external load, this study sought to quantify differences in individual muscle electromyography (EMG)-moment relationships between ACLi and CON. Participants isometrically modulated ground reaction forces during a standing force matching protocol to elicit combinations of sagittal, frontal and transverse plane moments. Partial least squares regressions determined which internal joint moment(s) predicted activation of 10 leg muscles for each group. Compared to CON, ACLi demonstrated greater contribution of rectus femoris to knee extension, semitendinosus and gastrocnemii to knee flexion, and lateral gastrocnemii to knee external rotation moments. ACLi also showed lower contributions of biceps femoris to knee flexion, medial gastrocnemius to internal rotation, and varied hip muscle contributions to frontal plane hip moments. Between group differences in EMG-moment relationships during static conditions suggest neuromuscular contributions to sagittal plane stability increases after ACL injury, while knee stability during knee abduction and external rotation is reduced. Clinical Significance: Clinical assessments of ACLi should account for deficits in frontal and rotational plane stability by including tasks that elicit such loads. Improving hamstring muscle balance, hip abductor and gastrocnemius function may benefit ACLi rehabilitation interventions and should be studied further. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Anterior cruciate ligament reconstruction improves subjective ability but not neuromuscular biomechanics during dynamic tasks.

PURPOSE: The purpose of this study was to identify high-functioning anterior cruciate ligament-deficient patients and assess the effects of reconstruction on their self-reported functionality, muscle activations and biomechanical properties. METHODS: Twenty young and active patients participated pre- (11.5 ± 14.3 months post-injury) and again 10.5 ± 1.7 months post-reconstruction and were individually matched to 20 healthy controls. Participants completed hop and side cut movements while patient-related outcome measures, lower limb electromyography, kinetic, and whole body kinematic data were collected. One-dimensional statistical parametric mapping was used to test for group differences (healthy vs deficient; deficient vs reconstructed; reconstructed vs healthy). RESULTS: When comparing healthy to anterior cruciate ligament-deficient participants, all questionnaires indicated significant lower subjective function while the only substantial biomechanical difference between these participants was a decreased knee extensor moment in both the hop (peak difference: 0.63 Nm/kg, p < 0.001) and side cut (peak difference: 0.76 Nm/kg, p < 0.001). When comparing patients' pre- and post-reconstruction, no biomechanical differences were observed whereas only half of the questionnaires (Tegner, Lysholm, KNEES-ADL, KNEES-Slackness, KNEES-Looseness, KNEES-Sport Behaviour, IKDC, and KOOS-QoL) indicated higher function in the reconstructed state. When comparing the reconstructed patients to the healthy participants, all questionnaires were still significantly higher in the healthy controls. The reconstructed group also had a smaller flexion angle (peak difference: 14.5°, p = 0.007) and knee extensor moment (peak difference: 0.62 Nm/kg, p < 0.001) during the hop and a smaller knee extensor moment (peak difference: 0.90 Nm/kg, p < 0.001) during the side-cut task. CONCLUSION: At 10-months post-reconstruction, the current results indicate that in high-functioning anterior cruciate ligament-deficient patients, reconstruction had little impact on objective measures of functional ability during dynamic tasks although self-reported function was improved. LEVEL OF EVIDENCE: Therapeutic prospective cohort study, Level II.

Effect of implementing magnetic resonance imaging for patient-specific OpenSim models on lower-body kinematics and knee ligament lengths.

BACKGROUND: OpenSim models are typically based on cadaver findings that are generalized to represent a wide range of populations, which curbs their validity. Patient-specific modelling through incorporating magnetic resonance imaging (MRI) improves the model's biofidelity with respect to joint alignment and articulations, muscle wrapping, and ligament insertions. The purpose of this study was to determine if the inclusion of an MRI-based knee model would elicit differences in lower limb kinematics and resulting knee ligament lengths during a side cut task. METHODS: Eleven participants were analyzed with the popular Rajagopal OpenSim model, two variations of the same model to include three and six degrees of freedom knee (DOF), and a fourth version featuring a four DOF MRI-based knee model. These four models were used in an inverse kinematics analysis of a side cut task and the resulting lower limb kinematics and knee ligament lengths were analyzed. RESULTS: The MRI-based model was more responsive to the movement task than the original Rajagopal model while less susceptible to soft tissue artifact than the unconstrained six DOF model. Ligament isometry was greatest in the original Rajagopal model and smallest in the six DOF model. CONCLUSIONS: When using musculoskeletal modelling software, one must acutely consider the model choice as the resulting kinematics and ligament lengths are dependent on this decision. The MRI-based knee model is responsive to the kinematics and ligament lengths of highly dynamic tasks and may prove to be the most valid option for continuing with late-stage modelling operations such as static optimization.

A hierarchy in functional muscle roles at the knee is influenced by sex and anterior cruciate ligament deficiency.

BACKGROUND: Sex-related neuromuscular differences have been linked to greater risk of anterior cruciate ligament injuries in females. Despite this, it remains unclear if sex-related differences are present after injury. This study sought to determine if sex differences are present in the functional roles of knee joint muscles in an anterior cruciate ligament deficient population. METHODS: An isometric, weight-bearing, force-generation protocol required injured and healthy males and females to modulate ground reaction forces. Electromyography was used to classify the functional role of 10 lower limb muscles in their contribution to knee joint stability during various loading directions. These roles were compared between the four groups at 12 loading directions using a directional analysis. FINDINGS: Functional muscle roles were different between groups, except for injured males and healthy females. Healthy males had either joint actuators or specific joint stabilisers, but no general stabilisers; the vastus medialis and lateralis of injured males and healthy females were classified as general stabilisers while injured females added the gluteus medialis and medial gastrocnemius as general stabilisers. INTERPRETATION: A population-based hierarchy in functional muscle roles was discovered. Healthy males demonstrated the most specific muscle roles, which can be viewed as more adaptive to variable loading conditions. The more generalised stabilisation strategies seen in injured males and females would alter joint loading which may be detrimental to the knee joint health over time. In summary, (1) these injuries alter muscle roles; (2) these alterations are sex-specific; (3) rehabilitation might be optimised if sex-differences are considered.