Upright Magnetic Resonance Imaging Tasks in the Knee Osteoarthritis Population: Relationships Between Knee Flexion Angle, Self-Reported Pain, and Performance.

OBJECTIVE: To characterize the ability of patients with symptomatic knee osteoarthritis (OA) to perform a weight-bearing activity compatible with upright magnetic resonance imaging (MRI) scanning and how this ability is affected by knee pain symptoms and flexion angles. DESIGN: Cross-sectional observational study assessing effects of knee flexion angle, pain level, and study sequence on accuracy and duration of performing a task used in weight-bearing MRI evaluation. Visual feedback of knee position from an MRI compatible sensor was provided. Pain levels were self-reported on a standardized scale. SETTING: Simulated MRI setup in a research laboratory. PARTICIPANTS: Convenience sample of individuals (N=14; 9 women, 5 men; mean, 69±14y) with symptomatic knee OA. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Averaged absolute and signed angle error from target knee flexion for each minute of trial and duration tolerance (the duration that subjects maintained position within a prescribed error threshold). RESULTS: Absolute targeting error increased at longer trial durations (P<.001). Duration tolerance decreased with increasing pain (mean ± SE, no pain: 3min 19s±11s; severe pain: 1min 49s±23s; P=.008). Study sequence affected duration tolerance (first knee: 3min 5s±9.1s; second knee: 2min 19s±9.7s; P=.015). CONCLUSIONS: The study provided evidence that weight-bearing MRI evaluations based on imaging protocols in the range of 2 to 3 minutes are compatible with patients reporting mild to moderate knee OA-related pain.

Using Inertial Measurement Unit Sensor Single Axis Rotation Angles for Knee and Hip Flexion Angle Calculations During Gait.

BACKGROUND: Hip and knee flexion joint motions are frequently examined in clinical practice using camera based motion capture (CBMC) systems; however, these systems require elaborate setups and dedicated space. Inertial measurement unit (IMU) based systems avoid these disadvantages but require validation before widespread adoption. Moreover, it is important for clinical practice to determine the stability of these systems for prolonged evaluation periods. The purpose of this study was to assess the validity of a three-sensor inertial measurement unit system for calculating hip and knee flexion angles during gait by comparing with a gold standard CBMC system. Validity was also examined before and after a treadmill walking session. METHODS: Twenty healthy participants were tested. Twenty seconds of gait at preferred walking speed were analyzed before and after thirty-two minutes of treadmill walking using previously validated CBMC methods and with a custom IMU model. Measurement validity for the IMU system was evaluated using Bland & Altman 95 percent limits of agreement, linear regression, mean absolute error and root mean square error. The effects of a measurement zeroing calibration strategy were also investigated. RESULTS: Strong measurement agreement was observed for both hip and knee flexion angles, although overall agreement for the hip exceeded that for the knee. Linear regressions between the datasets for each participant illustrated strong (> 0.94) relationships between IMU and CBMC measurements. More significant changes between timepoints were observed for the knee than for the hip. Error values were generally reduced when zeroing calibration was implemented. CONCLUSION: The IMU system presented in this study is a convenient and accessible technique to measure joint angles. The protocol described in the current study can be easily applied in the clinical setting for evaluation of clinical populations. Additional development work on sensor placement and calibration methods may further increase the accuracy of such methods. Clinical translation statement: The IMU system presented in this study is a convenient and accessible technique to measure joint angles. Additional developmentwork on sensor placement and calibration methods may further increase the accuracy of such methods.

A pilot study testing an Achilles tendinopathy human cadaver model using intratendinous injection of collagenase.

BACKGROUND: Achilles tendinopathy is one of the most frequently occurring soft-tissue injuries. Despite decades of research, there is still much that is unknown about the progression of tendinopathy. Animal models, such as collagenase injection, allow researchers to gain insight into disease progression and investigate clinical interventions, yet are limited in their direct application to humans. Establishment of a cadaver model of tendinopathy would provide another method of investigating clinical interventions in human tissues. The purpose of this study is to develop such a model and evaluate biomechanical changes in cadaveric Achilles tendons using ultrasound elastography. METHODS: Achilles tendons of five female foot/ankle cadavers were injected with two different concentrations (three with 10 mg/mL, two 20 mg/mL) of collagenase and incubated for 24 h. Ultrasound elastography images were collected at baseline, 16 and 24 h post-injection. Elasticity of tendons was calculated using a custom image analysis program. FINDINGS: Elasticity decreased over time in both dosage groups. In the 10 mg/mL group, mean elasticity decreased from 642 ± 246 kPa at baseline to 392 ± 38.3 kPa at 16 h and 263 ± 87.3 kPa at 24 h. In the 20 mg/mL group, mean elasticity decreased from 628 ± 206 kPa at baseline to 176 ± 152 kPa at 16 h and 188 ± 120 kPa at 24 h. INTERPRETATION: Injection of collagenase into cadaveric Achilles tendons resulted in decreases in elasticity. Decreases were observed in tendons that received injections with both 10 and 20 mg/mL collagenase dosages. Further biomechanical and histological testing is needed to evaluate this cadaveric tendinopathy.

Differences between adults and adolescents in responding to hip and knee pattern feedback during gait.

Visual feedback techniques have shown potential in interventions aiming to retrain deviated gait patterns. Understanding the abilities of different age groups to modify their gait is needed to optimize interventions. Twelve adults (6F, 6 M; 26.3 ± 5.9 yrs.) and twelve adolescents (4F, 8 M; 13.6 ± 2.3 yrs) without disabilities participated in one training session. During the session, the responses to a visual kinematic feedback task in which one hip or knee target pattern was modified while unmodified target patterns were maintained in the other hip and knee joints were investigated. Limb orientation and acceleration data were collected using Inertial Measurement Units (IMU) (Xsens Awinda, Enschede, The Netherlands) with a sampling frequency of 60 Hz. Adults tended to outperform adolescents in tracking modified target patterns and showed smaller errors in unmodified regions of modified patterns (p = 0.045); they also outperformed adolescents in unmodified joints (Contralateral Hip: p = 0.003; Contralateral Knee: p = 0.002; Ipsilateral Joint: p = 0.048). These findings suggest different levels of awareness of the need and/or ability to minimize errors across joints, in turn suggesting the need for specialization of training for these age groups.

Comparison of MRI-based estimates of articular cartilage contact area in the tibiofemoral joint.

Knee osteoarthritis (OA) detrimentally impacts the lives of millions of older Americans through pain and decreased functional ability. Unfortunately, the pathomechanics and associated deviations from joint homeostasis that OA patients experience are not well understood. Alterations in mechanical stress in the knee joint may play an essential role in OA; however, existing literature in this area is limited. The purpose of this study was to evaluate the ability of an existing magnetic resonance imaging (MRI)-based modeling method to estimate articular cartilage contact area in vivo. Imaging data of both knees were collected on a single subject with no history of knee pathology at three knee flexion angles. Intra-observer reliability and sensitivity studies were also performed to determine the role of operator-influenced elements of the data processing on the results. The method's articular cartilage contact area estimates were compared with existing contact area estimates in the literature. The method demonstrated an intra-observer reliability of 0.95 when assessed using Pearson's correlation coefficient and was found to be most sensitive to changes in the cartilage tracings on the peripheries of the compartment. The articular cartilage contact area estimates at full extension were similar to those reported in the literature. The relationships between tibiofemoral articular cartilage contact area and knee flexion were also qualitatively and quantitatively similar to those previously reported. The MRI-based knee modeling method was found to have high intra-observer reliability, sensitivity to peripheral articular cartilage tracings, and agreeability with previous investigations when using data from a single healthy adult. Future studies will implement this modeling method to investigate the role that mechanical stress may play in progression of knee OA through estimation of articular cartilage contact area.

Feasibility of a real-time pattern-based kinematic feedback system for gait retraining in pediatric cerebral palsy.

INTRODUCTION: Visual biofeedback of lower extremity kinematics has the potential to enhance retraining of pathological gait patterns. We describe a system that uses wearable inertial measurement units to provide kinematic feedback on error measures generated during periods of gait in which the knee is predominantly extended ('extension period') and flexed ('flexion period'). METHODS: We describe the principles of operation of the system, a validation study on the inertial measurement unit derived knee flexion angle on which the system is based, and a feasibility study to assess the ability of a child with cerebral palsy to modify a gait deviation (decreased swing phase knee flexion) in response to the feedback. RESULTS: The validation study demonstrated strong convergent validity with an independent measurement of knee flexion angle. The gait pattern observed during training with the system exhibited increased flexion in the flexion period with maintenance of appropriate extension in the extension period. CONCLUSIONS: Inertial measurement units can provide robust feedback during gait training. A child with cerebral palsy was able to interpret the novel two phase visual feedback and respond with rapid gait adaptation in a single training session. With further development, the system has the potential to support clinical retraining of deviated gait patterns.

Dynamic Margins of Stability During Robot-Assisted Walking in Able-Bodied Individuals: A Preliminary Study.

Background: Gait analysis studies during robot-assisted walking have been predominantly focused on lower limb biomechanics. During robot-assisted walking, the users' interaction with the robot and their adaptations translate into altered gait mechanics. Hence, robust and objective metrics for quantifying walking performance during robot-assisted gait are especially relevant as it relates to dynamic stability. In this study, we assessed bi-planar dynamic stability margins for healthy adults during robot-assisted walking using EksoGT™, ReWalk™, and Indego® compared to independent overground walking at slow, self-selected, and fast speeds. Further, we examined the use of forearm crutches and its influence on dynamic gait stability margins. Methods: Kinematic data were collected at 60 Hz under several walking conditions with and without the robotic exoskeleton for six healthy controls. Outcome measures included (i) whole-body center of mass (CoM) and extrapolated CoM (XCoM), (ii) base of support (BoS), (iii) margin of stability (MoS) with respect to both feet and bilateral crutches. Results: Stability outcomes during exoskeleton-assisted walking at self-selected, comfortable walking speeds were significantly (p < 0.05) different compared to overground walking at self-selected speeds. Unlike overground walking, the control mechanisms for stability using these exoskeletons were not related to walking speed. MoSs were lower during the single support phase of gait, especially in the medial-lateral direction for all devices. MoSs relative to feet were significantly (p < 0.05) lower than those relative to crutches. The spatial location of crutches during exoskeleton-assisted walking pushed the whole-body CoM, during single support, beyond the lateral boundary of the lead foot, increasing the risk for falls if crutch slippage were to occur. Conclusion: Careful consideration of crutch placement is critical to ensuring that the margins of stability are always within the limits of the BoS to control stability and decrease fall risk.

Visual kinematic feedback enhances the execution of a novel knee flexion gait pattern in children and adolescents.

BACKGROUND: Altered knee motion is one of the most common gait deviations in pediatric populations with gait disorders. The potential for pediatric gait retraining using visual feedback based on knee kinematic patterns is under-explored. RESEARCH QUESTION: This study investigated whether pediatric participants could successfully modify knee flexion patterns in response to a visual kinematic feedback system (VKFS). METHODS: Knee flexion angles from twelve typically developing children and adolescents (6 M, 6 F; 11.9 ±â€¯2.7 years) were calculated using wearable inertial measurement units. Participants were tested while walking on a treadmill using pattern based visual feedback (FB). Four novel target patterns which amplified or attenuated swing phase peak knee flexion were tested. No feedback (NFB) tests assessed the participant's ability to independently reproduce the patterns. Mean absolute cycle error (MACE) and magnitude of peak knee flexion error (PK) were calculated during the last 10 strides of FB and NFB trials. Pre-exposure reference values (R) were also calculated. RESULTS AND SIGNIFICANCE: PK-FB was significantly smaller (p < 0.05) than PK-R for all targets. Average values for PK-NFB were higher than for PK-FB, although PK-NFB remained significantly lower than PK-R for two targets. Contrary to one of the study's hypotheses, MACE-FB and MACE-NFB were larger than MACE-R. The study provided evidence that pediatric participants were able to modify peak knee flexion during gait in the sense targeted by the VKFS. Analysis suggested that MACE increases were explained by increases in gait cycle deviation outside of the changed region.

Kinematics and pushrim kinetics in adolescents propelling high-strength lightweight and ultra-lightweight manual wheelchairs.

PURPOSE: The purpose of this study is to describe and compare pushrim forces, propulsive work cost, and upper body kinematics in adolescents propelling (1) a standard high strength lightweight wheelchair, and (2) an ultra-lightweight wheelchair with adjustable main axle positioning, on a level tiled floor ("Tile"), ascending a ramp ("Ramp"), and across a foam mat ("Mat"). METHODS: A within-subjects repeated measures study design was used. Eight adolescent manual wheelchair users propelled the standard and ultra-lightweight wheelchairs across the three conditions. Average pushrim tangential force, propulsive power and work per unit distance travelled, as well as upper body kinematic angles, were analyzed. RESULTS: Average pushrim tangential force (1.80 ± 0.7 N, p = .042) and propulsive work per unit distance travelled (8.3 ± 1.7 J·m- 1, p = .002) were higher for the standard lightweight wheelchair, whereas average speed was lower (0.12 ± 0.03 m/s, p = .006). Maximum shoulder (9.2 ± 2.0°, p = .003) and elbow flexion (8.0 ± 2.2°, p = .009) were higher for the ultra-lightweight wheelchair. Compared with Tile, propulsion on Mat and Ramp was associated with higher average tangential force, work per unit distance, power, and maximum flexion of the neck and trunk, whereas shoulder extension and average speed were lower for Mat and Ramp. CONCLUSIONS: Compared with the standard lightweight wheelchair, ultra-lightweight wheelchair propulsion was associated with lower pushrim forces, lower energy costs, higher self-selected speeds, and increased shoulder and elbow flexion. These variables have been linked to injury risk and mobility efficiency, and the results provided evidence that differences in weight and configuration options are both contributors. Findings can inform decision-making in the prescription of manual wheelchairs for pre-adult populations. Implications for Rehabilitation A significant proportion of manual wheelchair users are children and adolescents, and due to the early onset of use they may be especially predisposed to the development of chronic overuse injuries. The study reports differences in energy costs, pushrim forces, and upper body kinematics measured when adolescents propelled standard and ultra-lightweight wheelchairs across three trial conditions. In the ultra-lightweight wheelchair, reduced energy cost is linked to more efficient mobility, and lower forces may be linked to lower risk of chronic injury. Significant differences in elbow and shoulder kinematics are also reported, and the findings support the importance of both weight and setup options in the selection of manual wheelchairs.

Mechanisms underlying quadriceps weakness in knee osteoarthritis.

PURPOSE: To identify determinants of quadriceps weakness among persons with end-stage knee osteoarthritis (OA). METHODS: One-hundred twenty-three individuals (mean age 64.9 +/- 8.5 yr) with Kellgren/Lawrence grade IV knee OA participated. Quadriceps strength (MVIC) and volitional muscle activation (CAR) were measured using a burst superimposition test. Muscle composition (lean muscle cross-sectional area (LMCSA) and fat CSA (FCSA)) were quantified using magnetic resonance imaging. Specific strength (MVIC/LMCSA) was computed. Interlimb differences were analyzed using paired-sample t-tests. Regression analysis was applied to identify determinants of MVIC. An alpha level of 0.05 was adopted. RESULTS: The OA limb was significantly weaker, had lower CAR, and had smaller LMCSA than the contralateral limb. CAR explained 17% of the variance in the contralateral limb's MVIC compared with 40% in the OA limb. LMCSA explained 41% of the variance in the contralateral limb's MVIC compared with 27% in the OA limb. CONCLUSION: Both reduced CAR and LMCSA contribute to muscle weakness in persons with knee OA. Similar to healthy elders, the best predictor of strength in the contralateral, nondiseased limb was largely determined by LMCSA, whereas CAR was found to be the primary determinant of strength in the OA limb. Deficits in CAR may undermine the effectiveness of volitional strengthening programs in targeting quadriceps weakness in the OA population.

Mechanisms for improving walking speed after longitudinal powered robotic exoskeleton training for individuals with spinal cord injury.

The goal of this study was to establish strideparameter gait models correlated to speed on individuals with chronic SCI and able-bodied controls walking with a powered robotic exoskeleton (EksoGT $^{\mathrm{ TM}}$). Longitudinal exoskeleton training $( >100$ hours) across eight individuals with SCI resulted in a 30% increase in walking speed. A simple linear regression between step length, stride length for given speed were very tightly correlated along a line of best fit $( \mathrm {p}<$.001). The temporal parameters of stride time, stance time and double support time depicted a non-linear exponentially decaying relationship for given walking speed. The research findings indicate that although longitudinal exoskeleton training reduces the temporal parameters, increases in spatial parameters are only marginal.

Altered knee kinematics in ACL-deficient non-copers: a comparison using dynamic MRI.

Kinematics measured during a short arc quadriceps knee extension exercise were compared in the knees of functionally unstable ACL-deficient patients, these patients' uninjured knees, and uninjured control subjects' knees. Cine phase contrast dynamic magnetic resonance imaging, in combination with a model-based tracking algorithm developed by the authors, was used to measure tibiofemoral kinematics as the subjects performed the active, supine posture knee extension exercise in the terminal 30 degrees of motion. Two determinants of tibiofemoral motion were measured: anterior/posterior location of the tibia relative to the femur, and axial rotation of the tibia relative to the femur. We hypothesized that more anterior tibial positioning, as well as differences in axial tibial rotation patterns, would be observed in ACL-deficient (ACL-D) knees when compared to uninjured knees. Multifactor ANOVA analyses were used to determine the dependence of the kinematic variables on (i) side (injured vs. uninjured, matched by subject in the control group), (ii) flexion angle measured at five-degree increments, and (iii) subject group (ACL-injured vs. control). Statistically significant anterior translation and external tibial rotation (screw home motion) accompanying knee extension were found. The ACL-D knees of the injured group exhibited significantly more anterior tibial positioning than the uninjured knees of these subjects (average difference over extension range=3.4+/-2.8 mm, p<0.01 at all angles compared), as well as the matched knees of the control subjects. There was a significant effect of interaction between side and subject group on A/P tibial position. We did not find significant differences in external tibial rotation associated with ACL deficiency. The changes to active joint kinematics documented in this entirely noninvasive study may contribute to cartilage degradation in ACL-D knees, and encourage more extensive investigations using similar methodology in the future.

Lower extremity muscle morphology in young athletes: an MRI-based analysis.

PURPOSE: This study was conducted to describe lower extremity muscle morphology (volume and peak cross-sectional area (CSA)) in young athletes and compare these with previously reported values. A second aim was to determine if muscle morphological values differ significantly between sides, implying that unilateral measurements cannot represent both limbs accurately. METHODS: Axial spin-echo T1-weighted magnetic resonance (MR) images were obtained between the ankle mortise and iliac crest in 10 athletes (age 18.8 +/- 3.7 yr). Subsequently, each subject's three-dimensional anatomy was digitally reconstructed. Muscle volume, peak CSA, and length were calculated for 13 muscles. RESULTS: The mean volumes and CSA for the current sample of athletes were larger than previously reported values (primarily from cadaver studies of nonathletes). The ratio of total quadriceps volume to total hamstrings volume averaged nearly 3:1 (2.9 +/- 0.2), whereas previous reports have been closer to 2:1 (2.1 +/- 0.2). The relative contribution of each muscle to the muscle group (hamstrings or quadriceps) volume was also different for these athletes. Significant differences in side-to-side muscle morphology were observed in several knee muscles (P < 0.03). Vastus medialis muscle volume was larger in the dominant leg (difference between sides: 59 +/- 25 cm3, representing 15.9 +/- 6.7% of its average volume), whereas vastus lateralis muscle volume was larger in the nondominant leg (difference: 54 +/- 47 cm3 representing 9.6 +/- 8.3% of its average). Despite this, total quadriceps volumes were similar between sides. CONCLUSIONS: Findings suggest that the morphology data presented in this study should be used instead of data from cadavers when studying young athletic people. These data should improve the accuracy of biomechanical modeling in the athletic population.

Quadriceps femoris muscle morphology and function after ACL injury: a differential response in copers versus non-copers.

The morphology (volume and peak cross-sectional area) and voluntary muscle control of 27 athletic people were evaluated with magnetic resonance imaging (MRI) and an established method of testing neuromuscular control in order to explain why some people are able to cope with anterior cruciate ligament (ACL) injury (copers), whereas most cannot (non-copers). Axial spin-echo T1 weighted MRI images were acquired from the level of the ankle mortise to the iliac crest. The subjects' quadriceps, hamstrings, and gastrocnemius muscles were digitally reconstructed from the MRI images. The volume and peak cross-sectional area (CSA) of each muscle were then calculated. Voluntary muscle control was evaluated using an established target-matching protocol that requires subjects to produce and modulate force with control over a range of directions. Electromyographic signals were collected from seven muscles as the subjects performed the experiment. Circular statistics methods were used to calculate a specificity index that describes how focused the activity pattern of each muscle was with respect to its principal direction of action. The results of the non-copers, copers, and uninjured subjects were then compared. The non-copers displayed significantly greater quadriceps atrophy than the copers. The most profound differences were observed in the vastus lateralis muscle. The non-copers also displayed diminished vastus lateralis and lateral gastrocnemius muscle control. Little differences were observed in the results of the copers and uninjured subjects. In general, the copers' results fell between those of the non-copers and uninjured subjects. The results of this study suggest that quadriceps muscle function is a critical factor in the differential response to ACL injury.

Quadriceps weakness, atrophy, and activation failure in predicted noncopers after anterior cruciate ligament injury.

BACKGROUND: Quadriceps weakness is common after anterior cruciate ligament injury, especially in those who do not compensate well for the injury ("noncopers"). Both atrophy and activation failure have been demonstrated in this population but have not been directly related to quadriceps weakness. HYPOTHESES: (1) Quadriceps strength, volumes, and cross-sectional areas of the noncopers would be smaller than those of the contralateral muscles, whereas other muscles would not demonstrate atrophy. (2) Quadriceps muscle activation deficits would be observed. (3) Atrophy and activation failure would account for the quadriceps weakness in these patients. STUDY DESIGN: Cross-sectional study, Level of evidence, 3. METHODS: Seventeen noncopers with isolated anterior cruciate ligament injury underwent burst-superimposition strength and activation testing of the quadriceps and magnetic resonance imaging of 12 muscles an average of 2 months after injury. Morphological characteristics was described by digitally reconstructing each muscle from the axial images and calculating muscle volume and peak cross-sectional area. RESULTS: The quadriceps muscles of the anterior cruciate ligament-deficient limb were significantly weaker (average 25%) than those of the uninjured side; activation failure (8%-10%) was observed for the quadriceps muscles of both limbs. The total quadriceps, vastus lateralis, and vastus intermedius volume and cross-sectional area were significantly smaller in the anterior cruciate ligament-deficient limb. There was no significant atrophy of any other muscle or muscle group. Atrophy and activation failure explained more than 60% of the variance in quadriceps weakness (P = .004). CONCLUSION: The quadriceps femoris weakens soon after acute anterior cruciate ligament injury. Activation deficits and atrophy occur and affect quadriceps strength. Rehabilitation techniques that address activation deficits as well as atrophy may be necessary to restore quadriceps strength.

Neuromuscular function after anterior cruciate ligament reconstruction with autologous semitendinosus-gracilis graft.

BACKGROUND: The quadrupled autologous semitendinosus-gracilis graft is the first choice of many orthopaedic surgeons when reconstructing the anterior cruciate ligament. The effect that this procedure has on voluntary muscle control remains unclear. The purpose of this study was to evaluate the effect that anterior cruciate ligament reconstruction with autologous semitendinosus-gracilis graft has on voluntary muscle control by assessing subjects' specificity of muscle action. METHODS: The voluntary muscle control of 10 people (seven males, three females) with acute, isolated ACL ruptures was assessed in the days prior to when they underwent anterior cruciate ligament reconstruction with quadrupled autologous semitendinosus-gracilis grafts and after they had returned to play in sports requiring quick changes of direction and jumping (approximately 6 months later). The experimental protocol included the use of an established target-matching protocol that requires subjects to produce and modulate force with fine control, electromyographic recordings from 11 muscles about the knee, and the use of circular statistics to calculate specificity indices that describe the degree of focus (specificity) associated with the activity pattern of each muscle. Data were analyzed by performing pre-surgery and post-return to sports side-to-side comparisons, as well as, pre-surgery to post-surgery ipsilateral comparisons. RESULTS: Diminished specificity of muscle action was observed in the activity patterns of most of the muscles of the subjects' anterior cruciate ligament deficient knees prior to surgery. The quadriceps muscles were particularly affected. Post-return to sports results indicated that voluntary muscle control had improved in most muscles. There was no significant difference in pre-surgery and post-return to sports semitendinosus and gracilis muscle control. The semimembranosus muscle displayed less specific muscle activity patterns following surgery, which may represent a compensation strategy for minor changes in neuromuscular function. CONCLUSIONS: Voluntary muscle control improved in most muscles following ACL reconstruction with semitendinosus-gracilis autografts. Semitendinosus and gracilis muscle control did not appear to be altered significantly by the procedure.

Specificity of muscle action after anterior cruciate ligament injury.

Neuromuscular control is believed to be a critical factor in dynamic knee stability. The purpose of this study was to evaluate voluntary muscle control in anterior cruciate ligament deficient (ACL-D) and uninjured people. Twenty athletes of similar age participated in this study. Subjects performed a target-matching protocol that required them to produce isometric moments about the knee with fine control in flexion, extension, varus, and valgus (i.e., loads were generated in the plane perpendicular to the long axis of the shank). Electromyographic data were collected from 10 muscles that span the knee. A specificity index was calculated for each muscle to describe how fine-tuned (specific) its muscle activity pattern was with respect to its principal direction of action in the load plane. Diminished specificity of muscle action was observed in 8 of 10 muscles in the ACL-D subjects' involved knees when compared with the activity patterns from their uninvolved knees and those from the uninjured subjects' knees. The vastus lateralis muscle was especially affected. Increased and more global co-contraction was also observed in the ACL-D limbs. The alterations in muscle firing patterns observed in this study are consistent with diminished neuromuscular control.

Altered quadriceps control in people with anterior cruciate ligament deficiency.

PURPOSE: The purpose of this study was to determine whether similar patterns of quadriceps dysfunction are observed when people with anterior cruciate ligament (ACL) deficiency perform static and dynamic tasks. METHODS: EMG data were collected from 15 subjects with an ACL deficient knee and 15 uninjured subjects as they performed static and dynamic tasks that were isolated to the knee and presented no threat to joint stability. The dynamic task was cyclic flexion and extension in the terminal 30 degrees of knee extension; the static task was an established isometric target-matching protocol. The muscle activity patterns observed during the tasks were evaluated and compared. RESULTS: The subjects with ACL deficiency exhibited quadriceps muscle control strategies that were significantly different from those of the uninjured subjects. This was true in both the dynamic and the static tasks. The findings were most noteworthy in the vastus lateralis muscle. Good agreement (r = -0.73 to -0.75) was observed in subjects' static and dynamic VL results; more moderate agreement was observed in results of the other quadriceps muscles. CONCLUSION: Diminished quadriceps control was observed when people with ACL deficiency performed static and dynamic tasks. The most striking feature of this impaired control was failure to turn the quadriceps "off" when performing flexion tasks in which the knee extensors are usually "silent." Our findings suggest that quadriceps dyskinesia after ACL injury is relatively global. Changes in neural function and muscle physiology after ACL injury are put forth as the most likely source of the observed dyskinesia.

Muscle and tendon morphology after reconstruction of the anterior cruciate ligament with autologous semitendinosus-gracilis graft.

BACKGROUND: The autologous semitendinosus-gracilis graft is the first choice of many orthopaedic surgeons when reconstructing the anterior cruciate ligament. The effect that graft harvest has on muscle and tendon morphology remains unclear. The purpose of this study was to describe these effects more completely. METHODS: Magnetic resonance images were acquired from eight patients before the anterior cruciate ligament reconstruction with semitendinosus-gracilis autograft and then again postoperatively after they had returned to sports. Muscle and tendon morphology was described by determining the volume and peak cross-sectional area of each structure on digitally reconstructed images. The effects that the procedure had on muscle and tendon length were evaluated separately and then together as a muscle-tendon complex. RESULTS: Anterior cruciate ligament reconstruction with semitendinosus-gracilis autograft resulted in a marked decrease in volume, cross-sectional area, and length of the semitendinosus and gracilis muscles. Tendon regeneration occurred in varying degrees in nearly all subjects. The morphology of the biceps femoris and semimembranosus muscles suggested that they had been compensating for the reduced semitendinosus and gracilis muscle function. Although semitendinosus and gracilis muscle retraction occurred following tendon stripping, nearly all of the subjects displayed evidence of at least partial tendon regeneration. CONCLUSIONS: Anterior cruciate ligament reconstruction with semitendinosus-gracilis autograft had a marked impact on semitendinosus and gracilis muscle morphology. However, this altered muscle morphology did not appear to have a clinically important impact on short-term outcomes. The biceps femoris and semimembranosus muscles appear to compensate for reduced semitendinosus and gracilis function. Tendon regeneration is observed in most people, but it is often incomplete at six months.

American Society of Biomechanics Clinical Biomechanics Award 2013: tibiofemoral contact location changes associated with lateral heel wedging--a weight bearing MRI study.

BACKGROUND: Vertically open magnetic resonance imaging permits study of knee joint contact during weight bearing. Lateral wedging is a low cost intervention for knee osteoarthritis that may influence load distribution and contact. This study assessed the ability of feedback-assisted weight bearing magnetic resonance imaging to detect changes in tibiofemoral contact associated with lateral wedging. METHODS: One knee in each of fourteen subjects with symptomatic knee osteoarthritis was studied, without specification of compartmental involvement. Knees were imaged during upright standing and at 20° knee flexion. Bilateral external heel wedges were used to provide non-wedged and 5° lateral wedging conditions. Computer modeling was used to measure the medial and lateral compartment contact patch center coordinates on the tibial plateau and the respective contact areas. FINDINGS: Lateral heel wedging in flexion was associated with a significant anterior shift of the contact patch of the lateral femoral condyle. Changes with knee flexion were similar to previous reports: both medial and lateral contact centers moved posteriorly with flexion, and lateral condyle contact also moved laterally. Lateral condyle contact area significantly reduced with flexion, while lateral wedging did not significantly affect contact areas. INTERPRETATION: In symptomatic knee osteoarthritis patients standing in knee flexion, weight bearing magnetic resonance imaging recorded an anterior shift of lateral condyle contact in response to lateral heel wedging. Future studies may investigate lateral wedging effects more specifically in candidates for this clinical intervention.