Concurrent Force Feedback on Load Symmetry in Total Knee Arthroplasty Patients.

Background and Purpose: Load asymmetry can be present before and after total knee arthroplasty (TKA), which may affect progress during knee rehabilitation in an outpatient sports medicine setting. Current rehabilitation primarily focuses on strength, pain, and range of motion deficits; however, recent evidence suggests the use of movement retraining strategies such as load feedback to address load asymmetry. Therefore, the purpose of this study was to examine how a single session of concurrent force feedback influences load symmetry during the leg-press and body-weight squat exercises in individuals following TKA. Additionally, a secondary purpose was to examine the retention of any changes over the course of a week. Study design: Case-series study. Methods: This observational, repeated-measures study design examined the effect of concurrent force feedback training on the mean and standard deviation of load symmetry index during the leg press and squat exercises in 26 patients with TKA in an outpatient sports medicine clinic.The load asymmetry was measured with loadpad sensors placed underneath the each extremity during leg press and squat (baseline), after one training session consisting of concurrent force feedback during these exercises within a single physical therapy session (post feedback), and after seven to ten days of a washout period (post retention). Separate 2 x 3 repeated measures analysis of variance was used to compare the mean and standard deviation of load symmetry across exercise (leg press and squat) and across time (baseline, post feedback and post retention). Results: There was a time effect for the mean load symmetry index (p=0.027) but not for the standard deviation (p=0.441) during these exercises. The leg press showed a greater mean symmetry index compared to the squat regardless of time (p=0.001). Conclusions: A reduction in the mean load symmetry index following concurrent feedback training suggests improved use of the surgical limb during both leg press and squat exercises during the same therapy session but the more symmetric loading pattern was not retained one week later. Overall, the leg press showed greater mean asymmetry than the squat. Standard deviation in the load symmetry index did not change across time or by exercise. Level of Evidence: 3©The Author(s).

Alterations in Achilles tendon stress and strain across a range of running velocities.

Running has a high incidence of overuse injuries. Achilles tendon (AT) injuries may occur due to high forces and repetitive loading during running. Foot strike pattern and cadence have been linked to the magnitude of AT loading. The effect of running speed on AT stress and strain, muscle forces, gait parameters and running kinematics is not well addressed in recreational runners with lower pace of running. Twenty-two female participants ran on an instrumented treadmill between 2.0 and 5.0 m/s. Kinetic and kinematic data were obtained. AT cross-sectional area data were collected using ultrasound imaging. Inverse dynamics with static optimization was used to calculate muscle forces and AT loading. AT stress, strain and cadence increased with greater running speed. Foot inclination angle indicated a rearfoot strike pattern among all participants, which increased as running speed increased but the latter plateaued after 4.0 m/s. The soleus contributed more force in running compared to the gastrocnemius throughout all speeds. Highest running speeds had the most stress on the AT, with changes to foot inclination angle and cadence. Understanding the relation of AT loading variables with running speed may aid in understanding how applied load may influence injury.

Effects of Body Weight Support in Running on Achilles Tendon Loading.

Achilles tendon (AT) tendinopathy is common in runners. Repetitive AT loading may play a role in etiology. Interventions such as body weight support (BWS) may reduce loading on the AT in running. Examine how ground reaction force, AT loading, foot strike, and cadence variables change in running with BWS. Twenty-four healthy female runners free from injury were examined. Participants ran on an instrumented treadmill with and without BWS using a harness-based system at a standardized speed. The system has 4 elastic cords affixed to a harness that is attached to a frame-like structure. Kinematic data and kinetic data were used in a musculoskeletal model (18 segments and 16 degrees of freedom) to determine AT loading variables, foot strike angle, and cadence. Paired t-tests were used to compare each variable between conditions. Ground reaction force was 9.0% lower with BWS (p<.05). Peak AT stress, force, and impulse were 9.4, 11.7%, and 14.8% lower when using BWS in running compared to no support (p<.05). Foot strike angle was similar (p<.05) despite cadence being reduced (p<.05). BWS may reduce AT loading and impulse variables during running. This may be important in rehabilitation efforts.

Dynamic postural control in injured collegiate cross-country runners is not associated with running-related injury.

BACKGROUND: Biomechanical factors have been associated with running-related injury, but associations are unclear. Dynamic postural stability may be a factor related to injury that has not been studied extensively. RESEARCH QUESTION: Does dynamic postural control differ in those with a history of running-related injury or those who go on to sustain a running-related injury? METHODS: Sixty-five (45 injured; 20 uninjured) and fifty-eight (13 injured; 45 uninjured) collegiate cross-country runners were available for our retrospective and prospective analyses. Time to stabilization and dynamic postural stability index were collected during two separate jump landing tasks (forward and lateral direction) for each leg. Retrospective injury was tabulated by a running history survey. Prospective injuries were recorded by a licensed athletic trainer during the competitive season. Differences in postural stability were compared between injured and uninjured groups and between limbs using two-way ANOVA's. An overall group by leg comparison was completed for each task. RESULTS: The non-dominant limb demonstrated better postural stability indices regardless of injury history. An interaction was observed between limbs and history of injury for the anterior-posterior time to stabilization for the lateral task. The non-dominant limb demonstrated better medio-lateral postural stability indices and time to stabilization during the lateral task, regardless of prospective injury. SIGNIFICANCE: Dynamic postural stability was reduced in the dominant limb, but no clear differences were seen between injured and uninjured runners. This suggests dynamic postural stability may be altered in individuals with a history of a running-related injury, but no relationship to subsequent injury was substantiated. Further work is needed to understand how dynamic postural stability may be related to running-related injury.

Kinematic and muscle force asymmetry in healthy runners: How do different methods measure up?

BACKGROUND: Comparing the performance of one leg to another is a common means of assessing running gait to help inform clinical management strategies. Various methods are employed to quantify asymmetries between limbs. However, limited data is available describing the amount of asymmetry that may be expected during running and no index has been identified as preferable for making a clinical determination of asymmetry. Therefore, this study aimed to describe amounts of asymmetry in collegiate cross-country runners and compare different methods of calculating asymmetry. RESEARCH QUESTION: What can be expected as a normal amount of asymmetry in biomechanical variables in healthy runners when using different indices to quantify limb symmetry? METHODS: Sixty-three (29 male and 34 female) runners participated. Running mechanics were assessed during overground running using 3D motion capture and a musculoskeletal model using static optimization to estimate muscle forces. Independent t-tests were utilized to determine statistical differences in variables between legs. Different methods of quantifying asymmetry were then compared to statistical differences between limbs to determine cut-off values and the sensitivity and specificity of each method. RESULTS: A large portion of runners demonstrated asymmetry during running. Kinematic variables can be expected to have small differences (2-3 degrees) between limbs while muscle forces may show greater amounts of asymmetry. The sensitivities and specificities for each method of calculating asymmetry were similar, however, different methods led to different cut-off values for each variable investigated. SIGNIFICANCE: Asymmetry can be expected between limbs during running. However, when assessing asymmetry, practitioners should consider the joint, variable, and method of calculating asymmetry when determining differences between limbs.

Added mass increases Achilles tendon stress in female runners.

CONTEXT: Achilles tendon (AT) injuries are common in female runners and military personnel where increased AT loading may be a contributing factor. Few studies have examined AT stress during running with added mass. The purpose was to examine the stress, strain, and force placed on the AT, kinematics and temporospatial variable in running with different amounts of added mass. DESIGN: Repeated measure design METHODS: Twenty-three female runners with a rear-foot strike pattern were participants. AT stress, strain, and force were measured during running using a musculoskeletal model that used kinematic (180 Hz) and kinetic data (1800 Hz) as input. Ultrasound data were used to measure AT cross sectional area. A repeated measures multivariate analysis of variance (α = 0.05) was used on AT loading variables, kinematics and temporospatial variables. RESULTS: Peak AT stress, strain, and force were greatest during the 9.0 kg added load running condition (p < .0001). There was a 4.3% and 8.8% increase in AT stress and strain during the 4.5 kg and 9.0 kg added load conditions, respectively, compared to baseline. Kinematics at the hip and knee changed with added load but not at the ankle. Small changes in temporospatial variables were seen. CONCLUSION: Added load increased stress on the AT during running. There may be an increased risk for AT injury with added load. Individuals may consider slowly progressing training with added load to allow for increased AT loading.

An Updated Model Does Not Reveal Sex Differences in Patellofemoral Joint Stress during Running.

Background: Structure-specific loading may have implications in understanding the mechanisms of running related injury. As females demonstrate a prevalence of patellofemoral pain twice that of males, this may indicate differences in patellofemoral loads between males and females. Previous works investigating differences in patellofemoral joint stress have shown conflicting results, but the models employed have not used estimates of muscle forces or sex specific contact areas. Hypothesis/Purpose: The aim of this study was to examine sex differences in patellofemoral joint stress using an updated model to include estimates of quadriceps muscle force and sex-specific patellofemoral contact area. Study Design: Descriptive Laboratory Study. Methods: Forty-five healthy recreational runners ran at a controlled speed down a 20-meter runway. Kinetic and kinematic data were utilized to estimate muscle forces using static optimization. Quadriceps muscle force was utilized with sex-specific patellofemoral joint contact area in a two-dimensional patellofemoral joint model to estimate patellofemoral joint stress. Multivariate tests were utilized to detect sex differences in patellofemoral loading and hip and knee kinematics. Results: No differences were found between sexes in measures of patellofemoral loading or quadriceps force. Females displayed a reduced knee extension moment and greater hip adduction and internal rotation than males. Conclusion: The inclusion of static optimization to estimate quadriceps muscle force and sex-specific contact area of the patellofemoral joint did not reveal sex differences in patellofemoral joint stress, but differences in non-sagittal plane hip motion were detected. Therefore, two-dimensional patellofemoral models may not fully characterize differences in patellofemoral joint stress between males and females. Three-dimensional patellofemoral models may be necessary to determine if sex differences in patellofemoral joint stress exist. Level of Evidence: 3b.

Transfer of post-trial feedback on impacts during drop landings in female athletes.

Increased vertical ground reaction force (vGRF) and dynamic knee valgus contribute to non-contact anterior cruciate ligament (ACL) injuries. We examined feedback's influence during landing and transfer to a game-specific drill, measured by deceleration. Thirty-one female athletes performed 30 drop landings with augmented feedback and dual-task conditions, with a game-specific drill before and after. Differences were shown across time (baseline, feedback, post-feedback) and between conditions (with or without dual-task) in peak vGRF and knee to ankle ratio (K:A ratio). K:A ratio is the ratio of the frontal plane distance between the knees relative to the frontal plane distance between the ankles. This measure serves as a surrogate for knee valgus where a ratio closer to 1 indicates less knee valgus. There were reductions in peak vGRF (p < 0.05) and improvements in K:A ratio (p < 0.05) across time, improvements in K:A ratio across time and by condition (p < 0.05), and reduction in deceleration during landing in a game-specific drill (p < 0.05). Feedback may improve landing mechanics and transfer to a game-specific drill that can influence ACL injury in sport.

Offloading Effects on Impact Forces and Patellofemoral Joint Loading During Running in Females.

BACKGROUND: Structure-specific loading is being increasingly recognized as playing a role in running related injuries. The use of interventions targeted at reducing patellofemoral joint loads have shown effectiveness in reducing symptoms of patellofemoral pain. Use of bodyweight support (BWS) has the potential to reduce loading on the patellofemoral joint during running to augment rehabilitation efforts. RESEARCH QUESTION: How is patellofemoral joint loading different when using a harness-based BWS system during running? METHODS: Twenty-five healthy females free from lower extremity injury were included. Participants completed four running trials on an instrumented treadmill with varying amounts of BWS using a commercially available harness system. Kinematic data from a 3D motion capture system and kinetic data from the treadmill were combined in a computer model to estimate measures of patellofemoral joint loading, knee kinematics, ground reaction force, and stride frequency. RESULTS: Peak patellofemoral joint stress and time-integral were reduced when running under BWS conditions compared to control conditions. Incremental decreases in patellofemoral loading were not observed with incremental increases in BWS. Peak knee flexion angle was reduced in all BWS conditions compared to control but was not different between BWS conditions. Knee flexion excursion was reduced in only the high BWS condition. Peak ground reaction force and stride frequency incrementally decreased with increased amounts of BWS. SIGNIFICANCE: Harness-based BWS systems may provide a simple means to reduce patellofemoral joint loading to assist in rehabilitation efforts, such as addressing patellofemoral pain.

Two-dimensional versus three-dimensional measurement of infant cervical active motion.

INTRODUCTION: Upright infant active cervical motion (ACM) is difficult to measure accurately by a single examiner. Clinically, physical therapists use visual estimation, which has limited reliability and concurrent validity with gold standards. Consistent, reliable, and valid active motion measurements are needed to document infant status and response to intervention. PURPOSE: Two-dimensional (2D) photo digitization measurements were compared to three-dimensional (3D) motion analysis measures of infant active neck rotation and lateral flexion. METHODS: Typically-developing infants participated (five boys, nine girls; 3-7.5 months). An experienced pediatric physical therapist and six novice raters marked photographs and used two different 2D methods to measure cervical rotation and three different 2D methods to measure cervical lateral flexion in photographs. To determine the intra- and interrater reliability of the 2D measurement methods and their concurrent validity with the 3D measures, a subset of lateral flexion photos was marked and measured by 14 experienced pediatric physical therapists. RESULTS: Novice and experienced examiner measurements of 2D ACM exhibited moderate to excellent intra- and inter-rater reliability. The results of the 2D lateral flexion ACM measurements completed by novice and experienced raters consistently differed from those obtained using the 3D measurement methods. CONCLUSION: The 2D rotation ACM measurement methods were reliable and demonstrated concurrent validity with the gold standard 3D measure. Infants' lateral flexion ACM examined using 2D measures did not correlate with the results of 3D measurements. This indicated that 2D measurements of active infant cervical lateral flexion could not be used as a valid indicators of 3D motion.