Chronic Adaptions in Quadriceps Fascicle Mechanics Are Related to Altered Knee Biomechanics After Anterior Cruciate Ligament Reconstruction.

Following anterior cruciate ligament reconstruction (ACLR), patients exhibit abnormal walking mechanics and quadriceps dysfunction. Quadriceps dysfunction has been largely attributed to muscle atrophy and weakness. While important, these factors do not capture intrinsic properties of muscle that govern its ability to generate force and withstand load. While fascicle abnormalities after ACLR have been documented in early stages of recovery (<12 mo), long-term effects of ACLR on fascicle mechanics remain unexplored. We evaluated quadriceps fascicle mechanics during walking 3 years post-ACLR and examined the relationship with knee mechanics. Participants included 24 individuals with ACLR and 24 Controls. Linear mixed models compared the ACLR, Contralateral, and Controls limbs for (1) quadriceps strength, (2) fascicle architecture and mechanics, and (3) knee mechanics. No difference in strength or overall fascicle length excursions was found between limbs. The ACLR limb exhibited longer fascicles at heel strike and peak knee extension moment (P < .001-.004), and smaller fascicle angles at heel strike, peak knee extension moment, and overall suppressed fascicle angle excursions (P < .001-.049) relative to the Contralateral and/or Control limb. This indicates an abnormality in fascicle architecture and mechanics following ACLR and suggests abnormalities in contractile function that cannot be explained by muscle weakness and may contribute to long-term gait irregularities.

Beyond weakness: Exploring intramuscular fat and quadriceps atrophy in ACLR recovery.

Muscle weakness following anterior cruciate ligament reconstruction (ACLR) increases the risk of posttraumatic osteoarthritis (OA). However, focusing solely on muscle weakness overlooks other aspects like muscle composition, which could hinder strength recovery. Intramuscular fat is a non-contractile element linked to joint degeneration in idiopathic OA, but its role post-ACLR has not been thoroughly investigated. To bridge this gap, we aimed to characterize quadriceps volume and intramuscular fat in participants with ACLR (male/female = 15/9, age = 22.8 ± 3.6 years, body mass index [BMI] = 23.2 ± 1.9, time since surgery = 3.3 ± 0.9 years) and in controls (male/female = 14/10, age = 22.0 ± 3.1 years, BMI = 23.3 ± 2.6) while also exploring the associations between intramuscular fat and muscle volume with isometric strength. Linear mixed effects models assessed (I) muscle volume, (II) intramuscular fat, and (III) strength between limbs (ACLR vs. contralateral vs. control). Regression analyses were run to determine if intramuscular fat or volume were associated with quadriceps strength. The ACLR limb was 8%-11% smaller than the contralateral limb (p < 0.05). No between-limb differences in intramuscular fat were observed (p 0.091-0.997). Muscle volume but not intramuscular fat was associated with strength in the ACLR and control limbs (p < 0.001-0.002). We demonstrate that intramuscular fat does not appear to be an additional source of quadriceps dysfunction following ACLR and that muscle size only explains some of the variance in muscle strength.

Conditioning of Motor Evoked Responses After Anterior Cruciate Ligament Reconstruction: Effects of Stimulus Intensity.

BACKGROUND: Operant conditioning of motor evoked torque (MEPTORQUE) can directly target the corticospinal pathway in patients with anterior cruciate ligament (ACL) reconstruction. However, it remains unclear whether operant conditioning can elicit short-term improvements in corticospinal excitability and whether these improvements are influenced by stimulus intensity. HYPOTHESIS: Quadriceps MEPTORQUE responses can be upconditioned in a single session and will elicit short-term adaptations in corticospinal excitability, with higher stimulus intensities eliciting greater effects. STUDY DESIGN: Randomized controlled laboratory study. LEVEL OF EVIDENCE: Level 2. METHODS: Thirty-six participants were assessed during a single session of an operant conditioning protocol. Participants were randomized into 1 of 3 groups for stimulus intensity used during operant conditioning based on the participant's active motor threshold (AMT: 100%, 120%, and 140%). Quadriceps MEPTORQUE amplitude was evaluated during a block of control transcranial magnetic stimulation trials (CTRL) to establish baseline corticospinal excitability, and 3 blocks of conditioning trials (COND) during which participants trained to upcondition their MEPTORQUE. MEPTORQUE recruitment curves were collected to evaluate the effect of operant conditioning on acute corticospinal adaptations. RESULTS: Participants with ACL reconstruction could upcondition their MEPTORQUE in a single session (P < 0.01; CTRL, 17.27 ± 1.28; COND, 21.35 ± 1.28 [mean ± standard error [SE] in N·m]), but this ability was not influenced by the stimulus intensity used during training (P = 0.84). Furthermore, significant improvements in corticospinal excitability were observed (P = 0.05; PRE, 687.91 ± 50.15; POST, 761.08 ± 50.15 [mean ± SE in N·m %AMT]), but stimulus intensity did not influence corticospinal adaptations (P = 0.67). CONCLUSION: Operant conditioning can elicit short-term neural adaptations in ACL-reconstructed patients. Future operant conditioning paradigms may effectively use any of the 3 stimulus intensities studied herein. CLINICAL RELEVANCE: Operant conditioning may be a feasible approach to improve corticospinal excitability after ACL reconstruction.

Associations between Body Mass Index, Gait Mechanics and Trochlear Cartilage Thickness in those with ACL Reconstruction.

PURPOSE: High body mass index (BMI) is a strong predictor of post-traumatic osteoarthritis (OA) after anterior cruciate ligament reconstruction (ACLR). Altered gait mechanics are independently affected by BMI and ACLR, and influence OA risk. Yet, evidence directly assessing the impact of high BMI on gait or cartilage characteristics after ACLR are limited. Here, we evaluated if high BMI moderates associations between gait and trochlear cartilage structure in individuals with ACLR. METHODS: Treadmill walking biomechanics were evaluated in forty normal BMI and twenty-four high BMI participants with ACLR at self-selected speeds. Normalized and absolute peak and cumulative loads (i.e., impulse) were extracted for peak knee flexion and adduction moments (KFM, KAM) and vertical ground reaction force (GRF). Medial and lateral femoral cartilage thickness and medial: lateral thickness ratios were assessed via ultrasound. RESULTS: Those with ACLR and high BMI walked with reduced normalized peak vertical GRFs, and greater absolute peak and cumulative loads compared to normal BMI individuals with ACLR. Those with ACLR and high BMI also exhibited thinner cartilage and greater medial: lateral ratios in ACLR limbs compared to contralateral limbs whereas normal BMI individuals with ACLR exhibited thicker ACLR limb cartilage. Lastly, greater peak KAM and KAM cumulative load were associated with thicker lateral cartilage and lesser medial: lateral thickness ratios, but only in the high BMI group. CONCLUSIONS: We observed those with high BMI after ACLR exhibited trochlear cartilage structural alterations not observed in normal BMI patients, while differential associations between loading outcomes and cartilage thickness in ACLR knees were observed between groups. Those with high BMI after ACLR may require different therapeutic strategies to optimize joint health in this subset of patients.

Open-sourced semi-automatic program for ultrasound assessments of femoral trochlea cartilage health.

We developed an open-sourced program that accounts for the current limitations of B-mode ultrasound and extends the clinical utility of ultrasound for assessing femoral trochlear cartilage thickness. Images were collected on 18 patients with a history of knee surgery. By failing to account for ultrasound acoustics and beam refraction, cartilage thickness was underestimated by 26% and overestimated by 0-4%, respectively (p < 0.001). Comprehensive thickness measurements achieved by measuring the Euclidean distance between every point were significantly different than traditional single-location measurements or by using the area/length (p = 0.004-0.006). Sub-regions were significantly different than all whole regions of interest (p = 0.001-0.012).

Biomechanical Effects of Manipulating Preferred Cadence During Treadmill Walking in Patients With ACL Reconstruction.

BACKGROUND: Abnormal gait is common after anterior cruciate ligament reconstruction (ACLR) which may influence osteoarthritis risk in this population. Yet few gait retraining options currently exist in ACLR rehabilitation. Cueing cadence changes is a simple, low-cost method that can alter walking mechanics in healthy adults, but few studies have tested its effectiveness in an ACLR population. Here, we evaluated the acute effects of altering cadence on knee mechanics in patients 9 to 12 months post ACLR. HYPOTHESIS: Cueing larger steps will facilitate larger knee angles and moments, while cueing smaller steps would induce smaller knee angles and moments. STUDY DESIGN: Randomized cross-sectional design. LEVEL OF EVIDENCE: Level 3. METHODS: Twenty-eight patients with unilateral ACLR underwent gait assessments on a treadmill at preferred pace. Preferred walking gait was assessed first to obtain preferred cadence. Participants then completed trials while matching an audible beat set to 90% and 110% of preferred cadence in a randomized order. Three-dimensional sagittal and frontal plane biomechanics were evaluated bilaterally. RESULTS: Compared with preferred cadence, cueing larger steps induced larger peak knee flexion moments (KFMs) and knee extension excursions bilaterally (P < 0.01), whereas cueing smaller steps only reduced knee flexion excursions (P < 0.01). Knee adduction moments remain unchanged across conditions and were similar between limbs (P > 0.05). Peak KFMs and excursions were smaller in the injured compared with uninjured limb (P < 0.01). CONCLUSION: Frontal plane gait outcomes were unchanged across conditions suggesting acute cadence manipulations result in mainly sagittal plane adaptations. Follow-up studies using a longitudinal cadence biofeedback paradigm may be warranted to elucidate the utility of this gait retraining strategy after ACLR. CLINICAL RELEVANCE: Cueing changes in walking cadence can target sagittal plane knee loading and joint range of motion in ACLR participants. This strategy may offer high clinical translatability given it requires relatively minimal equipment (ie, free metronome app) outside of a treadmill.

Quadriceps torque complexity before and after anterior cruciate ligament reconstruction.

OBJECTIVES: The purpose of this project was to longitudinally examine quadriceps torque complexity in a group of individuals who tore their ACL and underwent ACL reconstruction. DESIGN: Cohort analysis. METHODS: Thirty-four individuals completed maximal effort bilateral isometric strength testing after ACL injury but pre-surgery, five months' post-surgery (mid-point of rehabilitation), and when cleared to return to activity. Sample entropy, a nonlinear analysis of quadriceps torque control (complexity), was calculated from maximal isometric contractions. Two 3 × 2 repeated measures analysis of variance were used to examine changes over time and between limbs for quadriceps torque complexity and peak torque. RESULTS: Quadriceps peak torque was lower in the involved limb when compared to the uninvolved limb at every time point (p < 0.001). Peak torque of the involved limb was decreased at mid-point of rehabilitation compared to before surgery (p = 0.023) and at mid-point compared to return to activity (p = 0.041). Quadriceps sample entropy was higher in the involved limb compared to the uninvolved limb at the mid-point of rehabilitation (p < 0.001) and return to activity (p < 0.001), indicating greater complexity. The involved limb also demonstrated increased torque sample entropy from pre-surgery to mid-point of rehabilitation (p = 0.023), but not from pre-surgery to return to activity (p = 0.169) or from mid-point to return to activity (p = 0.541). CONCLUSIONS: Not only does quadriceps strength decline with ACL reconstruction, but quality of the quadriceps muscle contraction is also compromised. Increased torque complexity experienced in the ACL limb after reconstruction may contribute to impaired physical function in individuals following ACL reconstruction.

Walking speed differentially affects lower extremity biomechanics in individuals with anterior cruciate ligament reconstruction compared to uninjured controls.

BACKGROUND: Walking biomechanics are commonly affected after anterior cruciate ligament reconstruction and differ compared to uninjured controls. Manipulating task difficulty has been shown to affect the magnitude of walking impairments in those early after knee surgery but it is unclear if patients in later phases post-op are similarly affected by differing task demands. Here, we evaluated the effects of manipulating walking speed on between-limb differences in ground reaction force and knee biomechanics in those with and without anterior cruciate ligament reconstruction. METHODS: We recruited 28 individuals with anterior cruciate ligament reconstruction and 20 uninjured control participants to undergo walking assessments at three speeds (self-selected, 120%, and 80% self-selected speed). Main outcomes included sagittal plane knee moments, angles, excursions, and ground reaction forces (vertical and anterior-posterior). FINDINGS: We observed walking speed differentially impacted force and knee-outcomes in those with anterior cruciate ligament reconstruction. Between-limb differences increased at fast and decreased at slow speeds in those with anterior cruciate ligament reconstruction while uninjured participants maintained between-limb differences regardless of speed (partial η2 = 0.13-0.33, p < 0.05). Anterior cruciate ligament reconstruction patients underloaded the surgical limb relative to both the contralateral, and uninjured controls in GRFs and sagittal plane knee moments (partial η2 range = 0.13-0.25, p < 0.05). INTERPRETATION: Overall, our findings highlight the persistence of walking impairments in those with anterior cruciate ligament reconstruction despite completing formal rehabilitation. Further research should consider determining if those displaying larger changes in gait asymmetries in response to fast walking also exhibit poorer strength and/or joint health outcomes.

Joint and Limb Loading during Gait in Adults with ACL Reconstruction: Comparison between Single-Step and Cumulative Load Metrics.

PURPOSE: Individuals with anterior cruciate ligament reconstruction (ACLR) generally exhibit limb underloading behaviors during walking, but most research focuses on per-step comparisons. Cumulative loading metrics offer unique insight into joint loading as magnitude, duration, and total steps are considered, but few studies have evaluated if cumulative loads are altered post-ACLR. Here, we evaluated if underloading behaviors are apparent in ACLR limbs when using cumulative load metrics and how load metrics change in response to walking speed modifications. METHODS: Treadmill walking biomechanics were evaluated in 21 participants with ACLR at three speeds (self-selected (SS); 120% SS and 80% SS). Cumulative loads per step and per kilometer were calculated using knee flexion and adduction moment (KFM and KAM) and vertical ground reaction force (GRF) impulses. Traditional magnitude metrics for KFM, KAM, and GRF were also calculated. RESULTS: The ACLR limb displayed smaller KFM and GRF in early and late stances, but larger KFM and GRF during midstance compared with the contralateral limb ( P < 0.01). Only GRF cumulative loads (per step and per kilometer) were reduced in the ACLR limb ( P < 0.01). In response to speed modifications, load magnitudes generally increased with speed. Conversely, cumulative load metrics (per step and per kilometer) decreased at faster speeds and increased at slow speeds ( P < 0.01). CONCLUSIONS: Patients with ACLR underload their knee in the sagittal plane per step, but cumulatively over the course of many steps/distance, this underloading phenomenon was not apparent. Furthermore, cumulative load increased at slower speeds, opposite to what is identified with traditional single-step metrics. Assessing cumulative load metrics may offer additional insight into how load outcomes may be impacted in injured populations or in response to gait modifications.

Functional Resistance Training Differentially Alters Gait Kinetics After Anterior Cruciate Ligament Reconstruction: A Pilot Study.

BACKGROUND: Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction and can alter gait mechanics. Functional resistance training (FRT) is a novel approach to retraining strength after injury, but it is unclear how it alters gait mechanics. Therefore, we tested how 3 different types of FRT devices: a knee brace resisting extension (unidirectional brace), a knee brace resisting extension and flexion (bidirectional brace), and an elastic band pulling backwards on the ankle (elastic band)-acutely alter gait kinetics in this population. HYPOTHESIS: The type of FRT device will affect ground-reaction forces (GRFs) during and after the training. Specifically, the uni- and bidirectional braces will increase GRFs when compared with the elastic band. STUDY DESIGN: Crossover study. LEVEL OF EVIDENCE: Level 2. METHODS: A total of 15 individuals with ACL reconstruction received FRT with each device over 3 separate randomized sessions. During training, participants walked on a treadmill while performing a tracking task with visual feedback. Sessions contained 5 training trials (180 seconds each) with rest between. Vertical and anterior-posterior GRFs were assessed on the ACL-reconstructed leg before, during, and after training. Changes in GRFs were compared across devices using 1-dimensional statistical parametric mapping. RESULTS: Resistance applied via bidirectional brace acutely increased gait kinetics during terminal stance/pre-swing (ie, push-off), while resistance applied via elastic band acutely increased gait kinetics during initial contact/loading (ie, braking). Both braces behaved similarly, but the unidirectional brace was less effective for increasing push-off GRFs. CONCLUSION: FRT after ACL reconstruction can acutely alter gait kinetics during training. Devices can be applied to selectively alter gait kinetics. However, the long-term effects of FRT after ACL reconstruction with these devices are still unknown. CLINICAL RELEVANCE: FRT may be applied to alter gait kinetics of the involved limb after ACL reconstruction, depending on the device used.

Dynamic knee stiffness during walking is increased in individuals with anterior cruciate ligament reconstruction.

Individuals with anterior cruciate ligament (ACL) reconstruction often display abnormal gait mechanics reflective of a "stiff-knee" gait (i.e., reduced knee flexion angles and moments). However, dynamic knee stiffness, which is the dynamic relationship between the position of the knee and the moment acting on it, has not been directly examined during walking in individuals with ACL reconstruction. Here, we aimed to evaluate dynamic knee stiffness in the involved compared to the uninvolved limb during weight-acceptance and mid-stance phases of walking. Twenty-six individuals who underwent ACL reconstruction (Age: 20.2 ± 5.1 yrs., Time post-op: 7.2 ± 0.9 mo.) completed an overground walking assessment using a three-dimensional motion capture system and two force plates. Dynamic knee stiffness (Nm/°) was calculated as the slope of the regression line during weight-acceptance and midstance, obtained by plotting the sagittal plane knee angle versus knee moment. Paired t-tests with Bonferroni corrections were used to compare differences in dynamic stiffness, knee excursions, and moment ranges between limbs during both stance phases. Greater dynamic knee stiffness was found in the involved compared with the uninvolved limb during weight-acceptance and mid-stance (p < 0.01). Knee flexion and extension excursions were reduced in the involved limb during both weight-acceptance and mid-stance, respectively (p < 0.01). Sagittal plane knee moment ranges were not different between limbs during weight-acceptance (p = 0.1); however, the involved limb moment range was reduced relative to the uninvolved limb during mid-stance (p < 0.01). These results indicate that individuals with ACL reconstruction walk with a stiffer knee throughout stance, which may influence knee contact forces and could contribute to the high propensity for post-traumatic knee osteoarthritis development in this population.

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

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

Quadriceps motor evoked torque is a reliable measure of corticospinal excitability in individuals with anterior cruciate ligament reconstruction.

This study comprehensively evaluated the test-retest reliability of raw and normalized quadriceps motor evoked responses elicited by transcranial magnetic stimulation (TMS) in individuals with anterior cruciate ligament (ACL) reconstruction. Fifteen participants were tested on three different days that were separated at least by 24 h. Motor evoked responses were collected during a small background contraction on the reconstructed leg across a range of TMS intensities using torque (MEPTORQUE) and electromyographic (MEPEMG) responses. MEPTORQUE and MEPEMG were evaluated using different normalization procedures (raw, normalized to maximum voluntary isometric contraction [MVIC], peak MEP, and background contraction). MEPTORQUE was also normalized to the magnetically-evoked peripheral resting twitch torque. The area under the recruitment curve was computed for both raw and normalized MEPs. Intraclass correlation coefficients (ICCs) were determined to assess test-retest reliability. Results indicated that MEPTORQUE generally showed greater reliability than MEPEMG for all normalization procedures. Vastus medialis MEPEMG generally showed greater reliability than rectus femoris MEPEMG. Finally, both MEPTORQUE and MEPEMG exhibited good reliability, even when not normalized. These findings indicate that MEPTORQUE and MEPEMG offer reliable measures of corticospinal function and suggest that MEPTORQUE is a suitable alternative to MEPEMG for measuring quadriceps corticospinal excitability in individuals with ACL reconstruction.

Mechanical Factors Contributing to Altered Knee Extension Moment during Gait after ACL Reconstruction: A Longitudinal Analysis.

PURPOSE: This study aimed to comprehensively examine the extent to which knee flexion angle at initial contact, peak knee flexion angle, and vertical ground reaction force (vGRF) contribute to knee extension moments during gait in individuals with anterior cruciate ligament (ACL) reconstruction. METHODS: Overground gait biomechanics were evaluated in 26 participants with ACL reconstruction at three time points (about 2, 4, and 6 months after the surgery). Knee flexion angle at initial contact, peak knee flexion angle, peak vGRF, and peak knee extension moment were calculated for each limb during the early stance phase of gait for all three time points. A change score from baseline (time point 2 - time point 1 and time point 3 - time point 1) along with limb symmetry values (ACL - non-ACL limb values) was also calculated for these variables. Multiple linear regressions utilizing classical and Bayesian interference methods were used to determine the contribution of knee flexion angle and vGRF to knee extension moment during gait. RESULTS: Peak knee flexion angle and peak vGRF positively contributed to knee extension moment during gait in both the reconstructed ( R2 = 0.767, P < 0.001) and nonreconstructed limbs ( R2 = 0.815, P < 0.001). Similar results were observed for the symmetry values ( R2 = 0.673, P < 0.001) and change scores ( R2 = 0.731-0.883; all P < 0.001), except that the changes in knee flexion angle at initial contact also contributed to the model using the change scores in the nonreconstructed limb (time point 2 - time point 1: R2 = 0.844, P < 0.001; time point 3 - time point 1: R2 = 0.883, P < 0.001). Bayesian regression evaluating the likelihood of these prediction models showed that there was decisive evidence favoring the alternative model over the null model (all Bayes factors >1000). Standardized ß coefficients indicated that changes in knee flexion angle had a greater impact (>2×) on knee extension moments than vGRF at both time points in both limbs ( ßvGRF = 0.204-0.309; ßkneeflexion = 0.703-0.831). CONCLUSIONS: The findings indicate that both knee flexion angle and peak vGRF positively contribute to altered knee extension moments during gait, but the contribution of knee flexion angle is much greater than vGRF. Therefore, treatment strategies targeting these variables may improve knee loading after ACL reconstruction.

Functional Resistance Training After Anterior Cruciate Ligament Reconstruction Improves Knee Angle and Moment Symmetry During Gait: A Randomized Controlled Clinical Trial.

PURPOSE: The purpose of this study was to determine 1) whether progressive functional resistance training (FRT) during walking would improve knee biomechanical symmetry after anterior cruciate ligament (ACL) reconstruction and 2) whether the mode of delivery of FRT would have a differential effect on symmetry. METHODS: Thirty individuals who underwent primary ACL reconstruction at a single institution volunteered for this study. Participants were randomized into one of three groups: 1) BRACE, 2) BAND, or 3) CONTROL. The BRACE group received FRT with a novel robotic knee brace along with real-time kinematic feedback. The BAND group received FRT with a custom resistance band device along with real-time kinematic feedback. The CONTROL group received only real-time kinematic feedback. Participants in all groups received training (2-3/week for 8 weeks) while walking on a treadmill. Knee angle and moment symmetry were calculated immediately prior to beginning the intervention and within 1 week of completing the intervention. Statistical Parametric Mapping was used to assess differences in biomechanical symmetry between groups across time. RESULTS: There was a significant interaction in knee moment symmetry from 21 and 24% of the stance phase (P = .046), in which the BAND group had greater improvements following training compared with both BRACE (P = .043) and CONTROL groups (P = .002). There was also a significant time effect in knee angle symmetry from 68 to 79% of the stance phase (P = .028) and from 97 to 100% of the swing phase (P = .050) in which only the BRACE group showed significant improvements after the intervention (stance: P = .020 and swing: P < .001). CONCLUSION: The results of this randomized controlled clinical trial indicate that 8 weeks of progressive FRT during treadmill walking in individuals with ACL reconstruction improves knee angle and moment symmetry during gait. The findings suggest that FRT could serve as a potential therapeutic adjuvant to traditional rehabilitation after ACL reconstruction and can help restore knee joint biomechanical symmetry. LEVEL OF EVIDENCE: Level II, randomized controlled trial.

Functional Resistance Training Improves Thigh Muscle Strength after ACL Reconstruction: A Randomized Clinical Trial.

PURPOSE: Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction, resulting in prolonged disability and increased risk for reinjury and osteoarthritis. Functional resistance training (FRT) combines resistance training with task-specific training and may prove beneficial in restoring quadriceps strength. The primary purpose of this study was to determine if a walking-specific FRT program (e.g., resisted walking) improves knee strength in individuals after ACL reconstruction. METHODS: Thirty participants were randomized into one of three groups: 1) FRT with a customized knee BRACE applied to the ACL leg, 2) FRT with elastic BAND tethered to the ankle of the ACL leg, or 3) a TARGET MATCH condition where no resistance was externally applied. Participants in all groups received training while walking on a treadmill 2-3 times per week for 8 wk. Isometric knee extension and flexion strength were measured before the start of the intervention, after the intervention (POST), and 8 wk after intervention completion (POST-2). RESULTS: The BRACE group had greater knee extensor strength compared with the TARGET MATCH group at POST and POST-2 ( P < 0.05). The BRACE group had greater knee flexor strength than the TARGET MATCH group at POST and POST-2 ( P < 0.05) and the BAND group at POST ( P < 0.05). CONCLUSIONS: FRT applied via a customized knee brace results in improvements in knee extensor and flexor strength after ACL reconstruction. FRT is a beneficial adjuvant to ACL rehabilitation and leads to better strength compared with standard of care.

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

BACKGROUND: Accurate quantification of voluntary activation is important for understanding the extent of quadriceps dysfunction in individuals with anterior cruciate ligament reconstruction (ACLR). Voluntary activation has been quantified using both percent activation derived from the interpolated twitch technique and central activation ratio (CAR) derived from the burst superimposition technique, as well as by using different types of electrical stimulators and pulse train conditions. However, it is unclear how these parameters affect voluntary activation estimates in individuals with ACLR. This study was performed to fill this important knowledge gap in the anterior cruciate ligament literature. METHODS: Quadriceps strength and voluntary activation were examined in 18 ACLR participants (12 quadriceps/patellar tendon graft, 6 hamstring tendon graft; time since ACLR: 1.06 ± 0.82 years, mean ±  SD) at 90° of knee flexion using 2 stimulators (Digitimer and Grass) and pulse train conditions (3-pulse and 10-pulse). Voluntary activation was quantified by calculating both CAR and percent activation. RESULTS: Results indicated that voluntary activation was significantly overestimated by CAR when compared with percent activation (p < 0.001). Voluntary activation estimates were not affected by pulse train conditions when using percent activation; however, 3-pulse stimuli resulted in greater overestimation than 10-pulse stimuli when using CAR (p = 0.003). Voluntary activation did not differ between stimulators (p > 0.05); however, the Digitimer evoked greater torque at rest than the Grass (p < 0.001). CONCLUSION: These results indicate that percent activation derived from the interpolated twitch technique provides superior estimates of voluntary activation than CAR derived from burst superimposition and is less affected by pulse train conditions or stimulators in individuals with ACLR.

Factors That Predict Sagittal Plane Knee Biomechanical Symmetry After Anterior Cruciate Ligament Reconstruction: A Decision Tree Analysis.

BACKGROUND: Biomechanical knee asymmetry is commonly present after anterior cruciate ligament (ACL) reconstruction. Factors that could assist in identification of asymmetrical biomechanics after ACL reconstruction could help clinicians in making return-to-play decisions. The purpose of this study is to determine factors that may contribute to knee biomechanical asymmetry present after ACL reconstruction. HYPOTHESIS: We hypothesized that quadriceps strength and activation and patient-reported function would allow for identification of patients with symmetrical knee biomechanics. STUDY DESIGN: Cross-sectional study. LEVEL OF EVIDENCE: Level 3. METHODS: Thirty-one subjects (18 women; time since ACL reconstruction = 284.4 ± 53.6 days) who underwent ACL reconstruction and were to return to activity were recruited. Participants completed bilateral assessments of isokinetic quadriceps strength, quadriceps activation using the superimposed burst technique, and biomechanical function testing during a single-leg forward hop. The International Knee Documentation Committee (IKDC) subjective knee form was also completed. Symmetry values were calculated for each variable. Decision trees were utilized to determine which input factors (quadriceps strength symmetry, quadriceps activation symmetry, IKDC score, age, sex, height, mass, graft type) were able to identify participants who had symmetrical knee flexion angles (KFAs) and extension moments. Angles and moments were considered symmetrical if symmetry values were ≥90%. RESULTS: Quadriceps strength and activation symmetry were able to predict whether a patient landed with symmetrical or asymmetrical KFAs, with thresholds of 77.2% strength symmetry and 91.3% activation symmetry being established. Patient-reported function and quadriceps strength were factors that allowed for classification of participants with symmetrical/asymmetrical knee extension moments, with thresholds of 89.1 for the IKDC and 80.0% for quadriceps strength symmetry. CONCLUSIONS: Quadriceps strength contributed to both models and appears to be a critical factor for achieving symmetrical knee biomechanics. High patient-reported function and quadriceps activation are also important for restoring knee biomechanical symmetry after ACL reconstruction. CLINICAL RELEVANCE: Quadriceps strength and activation and patient-reported function may be able to assist clinicians in identifying ACL patients with symmetrical/asymmetrical knee biomechanics.

The Influence of Sex, Body Mass Index, and Age on Cartilage Metabolism Biomarkers in Patients After Anterior Cruciate Ligament Injury and Reconstruction.

CONTEXT: Serum biomarkers may allow for the early identification of posttraumatic osteoarthritis after anterior cruciate ligament (ACL) injury and reconstruction. Homeostasis of matrix-metalloproteinase-3 (MMP-3) and type II collagen turnover biomarkers (C2C:CPII ratio) is believed to be compromised in individuals with ACL injury, yet the influence of sex, body mass index (BMI), and age on these biomarkers before and after ACL reconstruction remains unknown. OBJECTIVE: To determine the relationship of sex, BMI, and age with serum levels of MMP-3 and C2C:CPII before and after ACL reconstruction. DESIGN: Descriptive laboratory study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-two (females = 18, males = 14) individuals with ACL injuries. MAIN OUTCOME MEASURE(S): Demographic variables and blood samples were collected before surgery and at return to activity. Serum was extracted from the blood and assays were used to quantify MMP-3 and C2C:CPII. Generalized linear mixed-effects regression models were used to assess the relationships between sex, BMI, age, time, and participant on the outcome variables. RESULTS: A significant time × sex interaction was identified for MMP-3 levels (P = .021), whereby MMP-3 levels were higher in males at return to activity (males, 2.71 ± 0.59 ng/mL; females, 1.92 ± 0.60 ng/mL; P = .017). Males also had higher MMP-3 levels at return to activity when compared with presurgery levels (P = .009). A main effect for age demonstrated that older age was associated with higher MMP-3 levels. No significant main or interaction effects were noted for C2C:CPII levels. CONCLUSIONS: Upregulation of MMP-3 serum levels may occur after ACL reconstruction, particularly in males, which may have deleterious consequences for the cartilage matrix. Sex, BMI, and time did not influence C2C:CPII ratios, but further research with larger sample sizes is needed to confirm these findings.

Gait asymmetries are exacerbated at faster walking speeds in individuals with acute anterior cruciate ligament reconstruction.

Previous research suggests more biomechanically demanding tasks (e.g., stair descent, hopping) magnify biomechanical asymmetries compared with walking after anterior cruciate ligament (ACL) reconstruction. However, it is unclear if modifying task-specific constraints, like walking speed also elicits greater biomechanical asymmetries in this population. We examined the effects of manipulating walking speed on ground reaction force (GRF) asymmetries in individuals with ACL reconstruction and uninjured controls. Thirty individuals with ACL reconstruction (age = 20.6 ± 5.4 years, body mass index [BMI] = 23.9 ± 3.3 kg/m2 ) and 15 controls (age = 23.1 ± 4.5 years, BMI = 23.6 ± 2.7 kg/m2 ) were tested on an instrumented treadmill at three speeds (100%, 120%, and 80% self-selected speed). Bilateral vertical and posterior-anterior GRFs were recorded at each speed. GRF asymmetries were calculated by subtracting the uninjured from the injured limb at each percent of stance. Statistical parametric mapping was used to evaluate the effects of speed on GRF asymmetries across stance. We found vertical and posterior GRF asymmetries were exacerbated at faster speeds and reduced at slower speeds in ACL individuals but not controls (p < .05). No differences in anterior GRF asymmetries were observed between speeds in either group (p > .05). Our results suggest increasing walking speed magnifies GRF asymmetries in individuals with ACL reconstruction. Statement of Clinical Significance: Evaluating both preferred and fast walking speeds may aid in characterizing biomechanical asymmetries in individuals with ACL reconstruction which may be valuable in earlier rehabilitative time points when more difficult tasks like hopping and running are not feasible.