Fall Prevention Training for Service Members With an Amputation or Limb Salvage Following Lower Extremity Trauma

INTRODUCTION

Recent military conflicts have resulted in a significant number of lower extremity injuries to U.S. service members that result in amputation or limb preservation (LP) procedures. Service members receiving these procedures report a high prevalence and deleterious consequences of falls. Very little research exists to improve balance and reduce falls, especially among young active populations such as service members with LP or limb loss. To address this research gap, we evaluated the success of a fall prevention training program for service members with lower extremity trauma by (1) measuring fall rates, (2) quantifying improvements in trunk control, and (3) determining skill retention at 3 and 6 months after training.

MATERIALS AND METHODS

Forty-five participants (40 males, mean [±SD] age, 34 ± 8 years) with lower extremity trauma (20 with unilateral transtibial amputation, 6 with unilateral transfemoral amputation, 5 with bilateral transtibial amputation, and 14 with unilateral LP procedures) were enrolled. A microprocessor-controlled treadmill was used to produce task-specific postural perturbations which simulated a trip. The training was conducted over a 2-week period and consisted of six 30-minute sessions. The task difficulty was increased as the participant's ability progressed. The effectiveness of the training program was assessed by collecting data before training (baseline; repeated twice), immediately after training (0 month), and at 3 and 6 months post-training. Training effectiveness was quantified by participant-reported falls in the free-living environment before and after training. Perturbation-induced recovery step trunk flexion angle and velocity was also collected.

RESULTS

Participants reported reduced falls and improved balance confidence in the free-living environment following the training. Repeated testing before training revealed that there were no pre-training differences in trunk control. The training program improved trunk control following training, and these skills were retained at 3 and 6 months after training.

CONCLUSION

This study showed that task-specific fall prevention training reduced falls across a cohort of service members with diverse types of amputations and LP procedures following lower extremity trauma. Importantly, the clinical outcome of this effort (i.e., reduced falls and improved balance confidence) can lead to increased participation in occupational, recreational, and social activities and thus improved quality of life.

Upper extremity asymmetry due to nerve injuries or central neurologic conditions: a scoping review

BACKGROUND

Peripheral nerve injuries and central neurologic conditions can result in extensive disabilities. In cases with unilateral impairment, assessing the asymmetry between the upper extremity has been used to assess outcomes of treatment and severity of injury. A wide variety of validated and novel tests and sensors have been utilized to determine the upper extremity asymmetry. The purpose of this article is to review the literature and define the current state of the art for describing upper extremity asymmetry in patients with peripheral nerve injuries or central neurologic conditions.

METHOD

An electronic literature search of PubMed, Scopus, Web of Science, OVID was performed for publications between 2000 to 2022. Eligibility criteria were subjects with neurological conditions/injuries who were analyzed for dissimilarities in use between the upper extremities. Data related to study population, target condition/injury, types of tests performed, sensors used, real-world data collection, outcome measures of interest, and results of the study were extracted. Sackett's Level of Evidence was used to judge the quality of the articles.

RESULTS

Of the 7281 unique articles, 112 articles met the inclusion criteria for the review. Eight target conditions/injuries were identified (Brachial Plexus Injury, Cerebral Palsy, Multiple Sclerosis, Parkinson's Disease, Peripheral Nerve Injury, Spinal Cord Injury, Schizophrenia, and stroke). The tests performed were classified into thirteen categories based on the nature of the test and data collected. The general results related to upper extremity asymmetry were listed for all the reviewed articles. Stroke was the most studied condition, followed by cerebral palsy, with kinematics and strength measurement tests being the most frequently used tests. Studies with a level of evidence level II and III increased between 2000 and 2021. The use of real-world evidence-based data, and objective data collection tests also increased in the same period.

CONCLUSION

Adequately powered randomized controlled trials should be used to study upper extremity asymmetry. Neurological conditions other than stroke should be studied further. Upper extremity asymmetry should be measured using objective outcome measures like motion tracking and activity monitoring in the patient's daily living environment.

Outcome of bracing vs. surgical treatment in adolescents with idiopathic scoliosis based on device measured daily physical activity: a prospective pilot study

Adolescent idiopathic scoliosis (AIS) can be treated with bracing or surgery, which may affect patient's physical activity (PA). However, there are limited objective assessments of PA in patients with AIS. This study aims to compare the outcome of spinal bracing vs. surgery in patients with AIS based on a device that measured daily PA. In total 24 patients with AIS participated, including 12 patients treated with bracing and 12 with spinal surgery. Daily PA was measured throughout 4 consecutive days using four tri-axial accelerometers and patient-reported functional status was reported using the SRS-22 questionnaire. The participants were assessed both before the treatment and after treatment at a 12-month follow-up. Patients with AIS had no significant change in their PA levels at the 12-month follow-up after surgical correction. On the contrary, patients with AIS following a year-long bracing treatment had significantly reduced time spent active ( P  = 0.04) with an average reduction in walking steps by 2137 steps/day ( P  = 0.005). There was no significant difference in function, pain, self-image and mental health domains following both treatments, as reported by the SRS-22. There was a significant improvement in satisfaction for both treatment groups ( P  ≤ 0.02). Significantly reduced PA and increased sedentary time are reported in patients with AIS following bracing treatment. An objective PA assessment is recommended to track the effect of scoliosis treatment on PA. Patients with AIS should be actively encouraged to achieve and maintain their recommended daily PA levels irrespective of the type of treatment. Level of evidence: Level II.

American Society of Biomechanics Journal of Biomechanics Award 2022: Computer models do not accurately predict human muscle passive muscle force and fiber length: Evaluating subject-specific modeling impact on musculoskeletal model predictions

Musculoskeletal models are valuable for studying and understanding the human body in a variety of clinical applications that include surgical planning, injury prevention, and prosthetic design. Subject-specific models have proven to be more accurate and useful compared to generic models. Nevertheless, it is important to validate all models when possible. To this end, gracilis muscle-tendon parameters were directly measured intraoperatively and used to test model predictions. The aim of this study was to evaluate the benefits and limitations of systematically incorporating subject-specific variables into muscle models used to predict passive force and fiber length. The results showed that incorporating subject-specific values generally reduced errors, although significant errors still existed. Optimization of the modeling parameter "tendon slack length" was explored in two cases: minimizing fiber length error and minimizing passive force error. The results showed that using all subject-specific values yielded the most favorable outcome in both models and optimization cases. However, the trade-off between fiber length error and passive force error will depend on the specific circumstances and research objectives due to significant individual errors. Notably, individual fiber length and passive force errors were as high as 20% and 37% respectively. Finally, the modeling parameter "tendon slack length" did not correlate with any real-world anatomical length.

Optimal Distal Tendon Insertion Point for Elbow Flexion in Free-Functioning Gracilis Muscle Transfer for Panbrachial Plexus Injuries: A Cadaveric Study

PURPOSE

Following pan-brachial plexus injuries, restoration of elbow flexion is widely accepted as the reconstructive priority. A gracilis free functioning muscle transfer (FFMT) can be used to restore elbow flexion alone with insertion into the biceps brachii (BIC) or brachioradialis (BRD) tendons or restore combined elbow and finger flexion with a more distal insertion into the flexor digitorum profundus (FDP) tendons. Using cadaveric experiments, we determined the peak instantaneous moment arm for each insertion option.

METHODS

Six simulated gracilis transfer surgeries were performed using both arms of three fresh-frozen full body cadaveric specimens (age: 79 + 10 years. 2 female). The gracilis muscles from both legs were harvested and transferred to the contralateral upper extremity. The elbow was manually moved through three flexion-extension cycles while the instantaneous moment arm was calculated from measurements of gracilis excursion and elbow joint angle for the three distal insertion sites.

RESULTS

Peak instantaneous moment arm for all three insertions occurred at an elbow angle between 83° to 92° with a magnitude ranging from 33 mm to 54 mm. The more distal (FDP/BRD) insertions produced a significantly greater (∼1.5 times) peak elbow flexion instantaneous moment arm compared to the BIC insertion.

CONCLUSIONS

Based on the instantaneous moment arm, the gracilis FFMT distal insertion locations could result in greater reconstructed elbow flexion strength. In addition, direct measurement of the shape and magnitude of the moment arm curve for differing insertion sites allows high resolution surgical planning and model testing.

CLINICAL RELEVANCE

This study presents the first direct experimental quantification of the gracilis FFMT instantaneous moment arm. The experimental evidence supports the use of FDP/BRD insertion locations by providing a quantitative explanation for the increased elbow flexion torque observed clinically in patients with a gracilis FFMT and distal FDP insertion.

Are 4D Motion Sensors Valid and Reliable for Studying Baseball Pitching?

BACKGROUND

Baseball pitching injuries are on the rise. Inertial measurement units (IMUs) provide immediate feedback to players and coaches, allowing for collection outside of the traditional laboratory setting with real-world application. The 4D Motion system provides kinematics throughout the pitching motion and may be beneficial for individualized programs in the throwing athlete. A systematic analysis of these sensors has not been completed.

PURPOSE

To evaluate the validity of the 4D Motion IMU system for analyzing the baseball pitching motion compared with marker-based motion capture, and evaluate the internal reliability and consistency of the device.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten high school pitchers participated in this study (10 male; 9 right-hand dominant; mean age, 16.6 ± 1.3 years; mean body mass index, 24.1 ± 3.9). Participants were simultaneously outfitted with six 4D Motion IMU sensors and retroreflective markers. The pitchers threw fastballs at maximum effort off a mound at the standard height and distance. A comparison was made between the IMUs and corresponding motion capture values for shoulder external rotation, elbow flexion, chest extension, pelvis and chest rotation velocity, and rotation acceleration.

RESULTS

Significant differences were found for 5 of 7 metrics analyzed. The IMU overreported most metrics, except for elbow flexion and pelvis rotation angular acceleration, where both positive and negative errors were observed. The root mean square error and percentage errors indicated smaller discrepancies for chest extension (4°± 5°) and pelvis (38 ± 19 deg/s) and chest (96 ± 42 deg/s) rotation velocity, with elbow flexion having the largest variance (21°± 9°).

CONCLUSION

The values of the 4D Motion IMU system should not be considered equivalent when compared with marker-based motion capture studies. The system lacked internal consistency and reliability, with angular velocities being the most consistent. Caution should be used when using the metrics provided by an IMU-based system for individualized monitoring.

CLINICAL RELEVANCE

If found valid and reliable, IMUs could be used for longitudinal workload monitoring, individualized throwing and rehabilitation programs, and ultimately injury prevention. This study demonstrates that the data obtained from a 4D Motion system using Gen 3 sensors are not equivalent to the data obtained from a marker-based motion capture system.

Characterization of elbow flexion torque after nerve reconstruction of patients with traumatic brachial plexus injury

BACKGROUND

The modified British Medical Research Council muscle grading system remains the primary method for assessing outcomes following surgical intervention despite its subjectivity and numerous inherent flaws. A new objective outcome measure of elbow function in patients with a brachial plexus injury is proposed.

METHODS

11 patients with a reconstructed brachial plexus (nerve reconstruction) and 10 unimpaired control subjects were evaluated. A custom apparatus measuring elbow flexion torque was developed. The subjects were asked to match their elbow flexion torque to a predefined torque. Time taken to achieve this predefined elbow flexion torque (latency) and duration of steady torque output were used as outcome measures.

RESULTS

Healthy individuals were better at maintaining and regulating elbow torque. The patients with a brachial plexus injury showed similar latency while increasing their elbow torque (normalized to maximum elbow torque) but lacked the ability to modulate the latency with demand as the healthy subjects.

INTERPRETATION

This novel measure provides objective information regarding the patient's ability to control elbow torque after nerve reconstruction.

Objective assessment of patients with idiopathic normal pressure hydrocephalus following ventriculoperitoneal shunt placement using activity-monitoring data: pilot study

OBJECTIVE

Idiopathic normal pressure hydrocephalus (iNPH) results in significant morbidity in the elderly with symptoms of dementia, gait instability, and urinary incontinence. In well-selected patients, ventriculoperitoneal shunt (VPS) placement often results in clinical improvement. Most postshunt assessments of patients rely on subjective scales. The goal of this study was to assess the utility of remote activity monitoring to provide objective evidence of gait improvement following VPS placement for iNPH.

METHODS

Patients with iNPH were prospectively enrolled and fitted with 5 activity monitors (on the hip and bilateral thighs and ankles) that they wore for 4 days preoperatively within 30 days of surgery and for 4 days within 30 days postoperatively. Monitors collected continuous data for number of steps, cadence, body position (upright, prone, supine, and lateral decubitus), gait entropy, and the proportion of each day spent active or static. Data were retrieved from the devices and a comparison of pre- and postoperative movement assessment was performed. The gait data were also correlated with formal clinical gait assessments before and after lumbar puncture and with motion analysis laboratory testing at baseline and 1 month and 1 year after VPS placement.

RESULTS

Twenty patients fulfilled the inclusion and exclusion criteria (median age 76 years). The baseline median number of daily steps was 1929, the median percentage of the day spent inactive was 70%, the median percentage of the day with a static posture was 95%, the median gait velocity was 0.49 m/sec, and the median number of steps required to turn was 8. There was objective improvement in median entropy from pre- to postoperatively, increasing from 0.6 to 0.8 (p = 0.002). There were no statistically significant differences for any of the remaining variables measured by the activity monitors when comparing the preoperative to the 1-month postoperative time point. All variables from motion analysis testing showed statistically significant differences or a trend toward significance at 1 year after VPS placement. Among the significantly correlated variables at baseline, cadence was inversely correlated with percentage of gait cycle spent in the support phase (contact with ground vs swing phase).

CONCLUSIONS

This pilot study suggests that activity monitoring provides an early objective measure of improvement in gait entropy after VPS placement among patients with iNPH, although a more significant improvement was noted on the detailed clinical gait assessments. Further long-term studies are needed to determine the utility of remote monitoring for assessing gait improvement following VPS placement.

Direct intraoperative measurement of isometric contractile properties in living human muscle

Skeletal muscle's isometric contractile properties are one of the classic structure-function relationships in all of biology allowing for extrapolation of single fibre mechanical properties to whole muscle properties based on the muscle's optimal fibre length and physiological cross-sectional area (PCSA). However, this relationship has only been validated in small animals and then extrapolated to human muscles which are much larger in terms of length and PCSA. The purpose of this study was to measure directly the in situ properties and function of the human gracilis muscle to validate this relationship. We leveraged a unique surgical technique in which a human gracilis muscle is transferred from the thigh to the arm, restoring elbow flexion after brachial plexus injury. During this surgery we directly measured subject specific gracilis muscle force-length relationship in situ and properties ex vivo. Each subject's optimal fiber length was calculated from their muscle's length-tension properties. Each subject's PCSA was calculated from their muscle volume and optimal fiber length. From these experimental data we established a human muscle fibre-specific tension of 171 kPa. We also determined that average gracilis optimal fiber length is 12.9 cm. Using this subject-specific fibre length we observed an excellent fit between experimental and theorical active length-tension curves. However, these fibre lengths were about half of the previously reported optimal fascicle lengths of 23 cm. Thus, the long gracilis muscle appears to be composed of relatively short fibres acting in parallel that may not have been appreciated based on traditional anatomical methods. KEY POINTS: Skeletal muscle's isometric contractile properties represent one of the classic structure-function relationships in all of biology and allow scaling single fibre mechanical properties to whole muscle properties based on the muscle's architecture. This physiologic relationship has only been validated in small animals but is often extrapolated to human muscles which are orders of magnitude larger. We leverage a unique surgical technique in which a human gracilis muscle is transplanted from the thigh to the arm to restore elbow flexion after brachial plexus injury, to directly measure muscles properties in situ and test directly, the architectural scaling predictions. Using these direct measurements, we establish human muscle fibre-specific tension of ∼170 kPa. Further, we show that the gracilis muscle actually functions as a muscle with relatively short fibres acting in parallel, verses long fibers as previously thought based on traditional anatomical models. Abstract figure legend Schematic of a unique surgical procedure in which the gracilis muscle is removed from the medial thigh and transplanted into the bed of the biceps brachii muscle to restore elbow flexion after brachial plexus injury as a free functioning muscle transfer (top panel). During this surgery and prior to removal of the gracilis from the lower limb we have the unique opportunity to measure the subject specific gracilis muscle force-length relationship directly. The muscle's nerve was stimulated to produce an isometric contraction while gracilis force was measured at the distal insertion tendon using a buckle force transducer (bottom left). By moving the lower limb into four positions we can recreate the normalized muscle force-length relationship (bottom right) and, using subject-specific fibre lengths (solid grey line) we can accurately predict the muscle properties. In contrast, literature anatomical fascicle length values (dashed grey line) do not accurately predict the muscle's properties. The long gracilis muscle appears to be composed of relatively short fibres that may not have been appreciated based on traditional anatomical methods. This article is protected by copyright. All rights reserved.

Changes in Elbow Stress and Ball Velocity During Reduced Effort Pitching: A Marker-Based Motion Capture Analysis

BACKGROUND

Baseball pitchers often participate in throwing programs that involve throwing at reduced effort levels to gradually increase the amount of stress experienced across the elbow. It is currently unknown how reduced effort pitching compares with maximum effort with respect to elbow stress and ball velocity.

PURPOSE/HYPOTHESIS

The purpose was to determine the correlation between elbow stress and ball velocity with reduced effort pitching. We hypothesized that decreased perceived effort would disproportionately correlate with elbow stress and ball velocity.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Ten healthy male high school baseball pitchers threw 5 pitches from a regulation pitching mound at 3 effort levels: maximum effort, 75% effort, and 50% effort. Elbow stress, specifically elbow varus torque, was calculated for all pitches using a validated marker-based 3-dimensional motion capture system. Ball velocity was measured using a Doppler radar gun. Intrathrower variability was calculated for each effort level.

RESULTS

Elbow stress and ball velocity decreased with reduced effort throws (P < .001 and P = .003, respectively). However, the reductions in elbow stress and ball velocity were not proportional. At 75% effort throws, elbow stress measured 81% (intraclass correlation coefficient [ICC], 0.95), and ball velocity measured 90% (ICC, 0.80) of maximum, respectively. At 50% effort throws, elbow stress measured 75% (ICC, 0.93), and ball velocity measured 85% (ICC, 0.87) of maximum. Intrathrower reliability was excellent for elbow stress and ball velocity, with all ICCs ≥0.80.

CONCLUSION

Pitching at a reduced effort level resulted in decreased elbow stress and ball velocity. However, for every 25% reduction in perceived effort, elbow stress decreased by a mean 13%, and ball velocity decreased 7.5%. When baseball pitchers attempt to throw at a reduced effort of maximum, throwing metrics do not decrease proportionately.

CLINICAL RELEVANCE

While pitching at a reduced effort of maximum decreases elbow stress and ball velocity, the decrease is not proportional, subjecting the elbow to more stress than intended. This has significant clinical importance to pitchers, coaches, and medical professionals in the setting of injury prevention and return to sports.

Muscle activation for targeted elbow force production following surgical reconstruction in adults with brachial plexus injury

Nerve transfer or grafting surgery to restore elbow flexion in peripheral nerve injuries has been an effective technique, but alters neuromuscular control compared with healthy individuals. This study compared neuromuscular control in the elbow flexors of 11 unimpaired control subjects and 11 adult patients with traumatic brachial plexus injury who underwent a nerve transfer or grafting procedure to the biceps motor branch to restore elbow flexion. The subjects performed a series of trials to generate a specific percentage of their maximum elbow torque. Each trial had an increasing and decreasing stairstep torque pattern that the subjects were asked to match. The amount of time that the subject's elbow torque was maintained within 5% of the target torque was calculated. The hypothesis was that there was a significant difference in the neuromuscular control between the two groups during elbow isometric torque generation. A secondary hypothesis was that a relationship existed between the neuromuscular control and the torque level for each group. The results demonstrated that neuromuscular control was different between the groups and there were significant differences in how torque levels are generated. The control group more easily modulated their myoelectric activation and achieved greater neuromuscular control variability with varying torque demand. The nerve transfer or grafting group could not modulate their myoelectric activation with changing torque demands. Further studies focusing on the improvement of neuromuscular control are needed to optimize functional outcomes in nerve injury patients.

Military training alters the fractal behavior of step width

Non-linear analyses have been successfully applied to gait with evidence that fractal behavior of gait-related variables provide insights into function. Specifically, shifts in the fractal behavior of step width from pink toward white noise reflects a loss of complexity and diminished adaptive capacity and functionality. We previously reported an apparent difference in the fractal behavior of step width during treadmill walking between Service members with transtibial amputations and able-bodied civilian. We now combine recently collected data and data from two previous studies to further explore the relationship between lower limb injury, military service, and step width fractal behavior. Service member, regardless of the presence or type of injury, demonstrate step width fractal behavior walked in a way that the fractal behavior of their gait was significantly closer to white noise (-0.5 dB/Hz²) than uninjured civilians (-0.82 dB/Hz²). This data suggests that military training/service leads to a change in step width fractal behavior. Further studies are needed to explore what may cause this difference and any implications this may have on stability or performance.

Common fall-risk indicators are not associated with fall prevalence in a high-functioning military population with lower limb trauma

BACKGROUND

Persons with lower limb trauma are at high risk for falls. Although there is a wide range of measures used to assess stability and fall-risk that include performance measures, temporal-spatial gait parameters, and nonlinear dynamic stability calculations, these measures are typically derived from fall-prone populations, such as older adults. Thus, it is unclear if these commonly used fall-risk indicators are effective at evaluating fall-risk in a younger, higher-functioning population of Service members with lower limb trauma.

METHODS

Twenty-one Service members with lower limb trauma completed a battery of fall-risk assessments that included performance measures (e.g., four-square-step-test), and gait parameters (e.g., step width, step length, step time) and dynamic stability measures (e.g., local divergence exponents) during 10 min of treadmill walking. Participants also reported the number of stumbles and falls over the previous 4 weeks. Negative Binomial and Quasibinomial Regressions were used to evaluate the strength of associations between fall-risk indicators and self-reported falls.

FINDING

Participants reported on average stumbling 6(4) times and falling 2(3) times in the previous 4 weeks. At least one fall was reported by 62% of the participants. None of the fall-risk indicators were significantly associated with fall prevalence in this population of Service members with lower limb trauma (p > 0.1).

INTERPRETATION

Despite the high number of reported falls in this young active population, none of the fall-risk indicators investigated effectively captured and quantified the fall-risk. Further research is needed to identify appropriate fall-risk assessments for young, high-functioning individuals with lower limb trauma.

Human Exposure to Hand-Arm Vibration from a Surgical Drill During Simulated Spine Surgery

OBJECTIVE

During spine surgery, surgeons are exposed to vibrations from surgical drills. Increased exposure to vibration can result in neurologic, vascular, and musculoskeletal impairments. To reduce these risks, occupational health standards have been implemented to limit exposure levels. The purpose of this study was to quantify human exposure to hand-arm vibration from a surgical drill during a simulation of a common spine procedure.

METHODS

Vibration measurements were collected during three 30-second surgical trials on a fresh frozen cadaver torso specimen using a standard surgical drill. The daily vibration exposure A(8) was evaluated on the basis of International Organization for Standardization 5349-1, and the occupational health standards, exposure action value, and exposure limit value were calculated.

RESULTS

On the basis of vibration exposure, surgeons in this study reached their exposure limits in 8 minutes to monitor tool usage and 32 minutes to terminate equipment usage.

CONCLUSIONS

The results demonstrate that a common surgical drill transmits hand-arm vibration levels approaching the exposure action value and exposure limit value over short periods of use. Further investigation is needed to determine the total vibration exposure over an entire workday, specifically in surgeons who perform multiple surgeries within a single day.

Ulnar Wrist Pain in a Tennis Player: Case Review and Discussion: A Team-Based Approach

»

Ulnar-sided wrist pain is a common cause of debilitating wrist pain in stick-handling athletes. Due to the complexity of surrounding anatomy, the evaluation and diagnosis can be challenging.

»

Injury of the triangular fibrocartilage complex (TFCC) is the most common cause of ulnar-sided wrist pain. Repetitive, unrestricted pronosupination, wrist deviation, and axial-loading activity, such as in tennis, place substantial stress on the TFCC.

»

The ulnotriquetral (UT) ligament is a palmar thickening of the ulnar capsule arising from the palmar radioulnar (PRU) ligament of the TFCC. When injured, the UT ligament can be a source of acute or chronic ulnar-sided wrist pain. The ligament can avulse off bone, can rupture completely, or can split longitudinally.

»

Arthroscopic-assisted repair is a safe, reliable, and effective treatment for UT ligament split tears and peripheral TFCC tears.

»

Although the benefit of a team-based approach may be realized by most patients, high-performing, stick-handling athletes are part of a unique population who execute repetitive, extraordinary wrist movements. The high demand and functional requirement expected of the wrists require a uniquely tailored approach to return them to the same level of competitive play.

Skeletal muscle mitochondrial dysfunction and muscle and whole body functional deficits in cancer patients with weight loss

Reductions in skeletal muscle mass and function are often reported in patients with cancer-associated weight loss and are associated with reduced quality of life, impaired treatment tolerance, and increased mortality. Although cellular changes, including altered mitochondrial function, have been reported in animals, such changes have been incompletely characterized in humans with cancer. Whole body and skeletal muscle physical function, skeletal muscle mitochondrial function, and whole body protein turnover were assessed in eight patients with cancer-associated weight loss (10.1 ± 4.2% body weight over 6-12 mo) and 19 age-, sex-, and body mass index (BMI)-matched healthy controls to characterize skeletal muscle changes at the whole body, muscle, and cellular level. Potential pathways involved in cancer-induced alterations in metabolism and mitochondrial function were explored by interrogating skeletal muscle and plasma metabolomes. Despite similar lean mass compared with control participants, patients with cancer exhibited reduced habitual physical activity (57% fewer daily steps), cardiorespiratory fitness [22% lower V̇o_2peak (mL/kg/min)] and leg strength (35% lower isokinetic knee extensor strength), and greater leg neuromuscular fatigue (36% greater decline in knee extensor torque). Concomitant with these functional declines, patients with cancer had lower mitochondrial oxidative capacity [25% lower State 3 O₂ flux (pmol/s/mg tissue)] and ATP production [23% lower State 3 ATP production (pmol/s/mg tissue)] and alterations in phospholipid metabolite profiles indicative of mitochondrial abnormalities. Whole body protein turnover was unchanged. These findings demonstrate mitochondrial abnormalities concomitant with whole body and skeletal muscle functional derangements associated with human cancer, supporting future work studying the role of mitochondria in the muscle deficits associated with cancer.NEW & NOTEWORTHY To our knowledge, this is the first study to suggest that skeletal muscle mitochondrial deficits are associated with cancer-associated weight loss in humans. Mitochondrial deficits were concurrent with reductions in whole body and skeletal muscle functional capacity. Whether mitochondrial deficits are causal or secondary to cancer-associated weight loss and functional deficits remains to be determined, but this study supports further exploration of mitochondria as a driver of cancer-associated losses in muscle mass and function.

Assessments of trunk postural control within a fall-prevention training program for service members with lower limb trauma and loss

BACKGROUND

Trunk postural control (TPC) is critical in maintaining balance following perturbations (i.e., avoiding falls), and impaired among persons with lower extremity trauma, contributing to elevated fall risk. Previously, a fall-prevention program improved TPC in individuals with unilateral transtibial amputation following trip-inducing perturbations. However, it is presently unclear if these improvements are task specific.

RESEARCH QUESTION

Do improvements to TPC gained from a fall-prevention program translate to another task which assesses TPC in isolation (i.e., unstable sitting)? Secondarily, can isolated TPC be used to identify who would benefit most from the fall-prevention program?

METHODS

Twenty-five individuals (21 male/4 female) with lower extremity trauma, who participated in a larger fall-prevention program, were included in this analysis. Trunk flexion and flexion velocity quantified TPC following perturbation; accelerometer-based sway parameters quantified TPC during unstable sitting. A generalized linear mixed-effects model assessed training-induced differences in TPC after perturbation; a generalized linear model assessed differences in sway parameters following training. Spearman's rho related training-induced changes to TPC following perturbation (i.e., the difference in TPC measures at pre- and post-training assessments) with pre- vs. post-training changes to sway parameters during unstable sitting (i.e., the difference in sway parameters at pre- and post-training assessments) as well as pre-training sway parameters with the pre- vs. post-training differences in TPC following perturbation.

RESULTS

Following training, trunk flexion angles decreased, indicating improved TPC; however, sway parameters did not differ pre- and post-training. In addition, pre- vs. post-training differences in TPC following perturbation were neither strongly nor significantly correlated with sway parameters. Moreover, pre-training sway parameters did not correlate with pre- vs. post-training differences in trunk flexion/flexion velocity.

SIGNIFICANCE

Overall, these results indicate that improvements to TPC gained from fall-prevention training are task-specific and do not translate to other activities. Moreover, isolated TPC measures are not able to identify individuals that benefit most from the fall-prevention program.

Upper extremity function in the free living environment of adults with traumatic brachial plexus injuries

Transition of data acquisition out of the laboratory, into the real world offers a previously inaccessible perspective of physical function. This proves to be beneficial when assessing surgical intervention, especially after a traumatic brachial plexus injury (BPI) causing loss of motor function in an upper extremity (UE). Moving towards the use of real world data in clinical practice as an outcome measure, this study developed a method to report bilateral UE activity in patients with BPI. Three groups of ten subjects each participated in this study-healthy controls, subjects with traumatic BPI prior to surgical treatment (pre-), and subjects who had surgical reconstruction to treat BPI (post-). Subjects wore four activity monitors on bilateral forearms and upper arms for four days. Tri-axial acceleration data were used to calculate asymmetry indices for forearm and upper arm usage. Analysis revealed a bimodal distribution in the post- group, prompting division of this group into two subgroups based on injury type: pan-plexus and upper trunk. While median asymmetry indices at the forearm and upper arm were decreased in the post- group when compared to the pre- group, these differences were not significant. Compared to controls, the pre-surgery group (p < 0.0001, p < 0.0001) and post-surgery group with pan-plexus injuries (p = 0.0074, p = 0.0242) both exhibited statistically significant differences in forearm and upper arm asymmetry, respectively. Further investigation to establish clinically significant differences in asymmetry index is warranted. Importantly, analyzing the activity of UEs following treatment of a BPI provides objective real world evidence of function.

Application of myoelectric elbow flexion assist orthosis in adult traumatic brachial plexus injury: a retrospective clinical study

BACKGROUND

Adult traumatic brachial plexus injuries (BPIs) can result in severe impairment following penetrating wounds, falls, and motor vehicle accidents or other high-energy trauma.

OBJECTIVE

Quantify functional outcomes of adult patients with a BPI using a myoelectric orthosis to restore elbow flexion.

STUDY DESIGN

Retrospective review.

METHODS

A clinic specializing in the BPI treatment at a large academic medical center tested nineteen adult patients with BPI. These patients had failed to achieve antigravity elbow flexion following their injury and observation or surgical reconstruction. They were provided a myoelectric elbow orthosis (MEO) if they had detectable electromyography signals.

RESULTS

There was significant improvement in strength and significant reductions in function and pain when using an MEO. Following initiation of the MEO, 12 of the 19 patients had clinical improvements in muscle strength, 15 patients showed improvement in their DASH, and 13 patients reported improvements in their Visual Analog Scale.

CONCLUSION

The use of an MEO improves elbow flexion strength, increases function, and reduces pain in the majority of patients with BPI and inadequate elbow flexion following observation or surgical reconstruction.

Application of a myoelectric elbow flexion assist orthosis in adult traumatic brachial plexus injury: patient perspectives

BACKGROUND

Individuals with brachial plexus injuries (BPIs) can be prescribed assistive devices, including myoelectric elbow orthoses (MEOs), for rehabilitation or functional use after failed treatment for elbow flexion restoration. Although recent case studies indicate potential for clinical improvements after using an MEO after BPI, the patients' perspectives on such use are still unknown.

OBJECTIVE

To explore patient perspectives on the use of an MEO after surgical treatment for a traumatic BPI.

STUDY DESIGN

Qualitative using both a focus group and semistructured interviews.

METHODS

Patients with BPI that used an MEO were recruited. Five patients participated in an in-person focus group, whereas three patients participated in individual phone interviews. Themes that emerged from the focus group were compared against those that emerged from the personal interviews.

RESULTS

Feedback was grouped into three themes: device usage, hardware performance, and device design. Within each theme, positive elements, areas for improvement, and additional considerations emerged. Patients indicated a positive attitude toward using an MEO as a rehabilitation tool. They desired a streamlined, stronger device to support them and assist during activities of daily living.

CONCLUSIONS

For patients with BPI, a well-designed MEO that meets their needs could assist with rehabilitation and increase independence in daily activities. Continued patient engagement in the evaluation and development of both medical devices and treatment plans offers the best opportunity for improved outcomes that are important to the patient.

Developing and Establishing Biomechanical Variables as Risk Biomarkers for Preventable Gait-Related Falls and Assessment of Intervention Effectiveness

The purpose of this review is to position the emerging clinical promise of validating and implementing biomechanical biomarkers of falls in fall prevention interventions. The review is framed in the desirability of blunting the effects of the rapidly growing population of older adults with regard to the number of falls, their related injuries, and health care costs. We propose that biomechanical risk biomarkers may be derived from systematic study of the responses to treadmill-delivered perturbations to both identify individuals with a risk of specific types of falls, such as trips and slips as well as quantifying the effectiveness of interventions designed to reduce that risk. The review follows the evidence derived using a specific public health approach and the published biomedical literature that supports trunk kinematics as a biomarker as having met many of the criteria for a biomarker for trip-specific falls. Whereas, the efficacy of perturbation training to reduce slip-related falls by older adults appears to have been confirmed, its effectiveness presently remains an open and important question. There is a dearth of data related to the efficacy and effectiveness of perturbation training to reduce falls to the side falls by older adults. At present, efforts to characterize the extent to which perturbation training can reduce falls and translate the approaches to the clinic represents an important research opportunity.

In vivo human gracilis whole-muscle passive stress-sarcomere strain relationship

We measured the passive mechanical properties of intact, living human gracilis muscles (n=11 individuals, 10 male and 1 female, age: 33±12 years, mass: 89±23 kg, height: 177±8 cm). Measurements were performed in patients undergoing surgery for free-functioning myocutaneous tissue transfer of the gracilis muscle to restore elbow flexion after brachial plexus injury. Whole-muscle force of the gracilis tendon was measured in four joint configurations (JC1-JC4) with a buckle force transducer placed at the distal tendon. Sarcomere length was also measured by biopsy from the proximal gracilis muscle. After the muscle was removed, a three-dimensional volumetric reconstruction of the muscle was created via photogrammetry. Muscle length from JC1 to JC4 increased by 3.3±1.0, 7.7±1.2, 10.5±1.3 and 13.4±1.2 cm, respectively, corresponding to 15%, 34%, 46% and 59% muscle fiber strain, respectively. Muscle volume and an average optimal fiber length of 23.1±0.7 cm yielded an average muscle physiological cross-sectional area of 6.8±0.7 cm2 which is approximately 3 times that measured previously from cadaveric specimens. Absolute passive tension increased from 0.90±0.21 N in JC1 to 16.50±2.64 N in JC4. As expected, sarcomere length also increased from 3.24±0.08 µm at JC1 to 3.63±0.07 µm at JC4, which are on the descending limb of the human sarcomere length-tension curve. Peak passive muscle stress was 27.8±5.5 kPa in JC4 and muscle modulus ranged from 44.8 MPa in JC1 to 125.7 MPa in JC4. Comparison with other mammalian species indicates that human muscle passive mechanical properties are more similar to rodent muscle than to rabbit muscle. These data provide direct measurements of whole-human muscle passive mechanical properties that can be used in modeling studies and for understanding comparative passive mechanical properties among mammalian muscles.

Intramuscular pressure of human tibialis anterior muscle detects age-related changes in muscle performance

Intramuscular pressure (IMP) reflects forces produced by a muscle. Age is one of the determinants of skeletal muscle performance. The present study aimed to test whether IMP mirrors known age-related muscular changes. We simultaneously measured the tibialis anterior (TA) IMP, compound muscle action potential (CMAP), and ankle torque in thirteen older adults (60-80 years old) in vivo by applying different stimulation intensities and frequencies. We found significant positive correlations between the stimulation intensity and IMP and CMAP. Increasing stimulation frequency caused ankle torque and IMP to increase. The electromechanical delay (EMD) (36 ms) was longer than the onset of IMP (IMPD) (29 ms). Compared to the previously published data collected from young adults (21-40 years old) in identical conditions, the TA CMAP and IMP of older adults at maximum intensity of stimulation were 23.8% and 39.6% lower, respectively. For different stimulation frequencies, CMAP, IMP, as well as ankle torque of older adults were 20.5%, 24.2%, and 13.2% lower, respectively. Surprisingly, the EMD did not exhibit any difference between young and older adults and the IMPD was consistent with the EMD. Data supporting the hypotheses suggest that IMP measurement is an indicator of muscle performance in older adults.

Method for characterization of dynamic ankle stiffness in patients with spasticity

BACKGROUND

Dynamic ankle stiffness has been quantified as the slope of the ankle joint moment-angle curve over the gait interval of the second rocker, defined explicitly as the period of the gait cycle from the first relative maximum plantar flexion in early stance to maximum dorsiflexion in midstance. However, gastrocnemius spasticity may interfere with the second ankle rocker in patients with spasticity. This gait disruption results in stiffness calculations which are misleading. Current dynamic stiffness metrics need to be modified.

RESEARCH QUESTION

The main goal of this study was to develop and test a new method to better evaluate dynamic ankle stiffness in individuals with pathologic gait who lack a second rocker interval.

METHODS

Twenty unimpaired ambulators (10/20 female, 26.7 ± 5.0 years, BMI: 23.2 ± 2.2) and 9 individuals with cerebral palsy (5/9 female, 5.7 ± 1.7 years, BMI: 14.6 ± 2.1, GMFCS Levels: I - 2, II - 5, III - 2) participated in this study. Dynamic ankle stiffness was evaluated using the previous kinematic method, defined by the interval of maximum plantar flexion to maximum dorsiflexion angle in midstance, and the proposed kinetic method, defined by the interval from the maximum dorsiflexion moment to first peak plantar flexion moment. Stiffness was quantified as the linear slope between the sagittal plane ankle angle and moment. Method differences were explored using an equivalence test (α = 0.05).

RESULTS AND SIGNIFICANCE

There was equivalence between the methods for unimpaired ambulators (p = 0.000) and a lack of equivalence for patients with spasticity (p = 0.958). The new method was successfully applied to all 9 pediatric ambulators with CP and demonstrated increased stiffness in patients with spasticity as compared to the previous method. The ability to objectively calculate ankle stiffness in pathologic gait is critical for determining change associated with clinical intervention.

Measuring and modeling in vivo human gracilis muscle-tendon unit length

Musculoskeletal models rely heavily on the use of an anatomical dataset and clearly defined assumptions to accurately model the subject being studied. Therefore, it is important to understand the limitations of using musculoskeletal models to study individuals. This paper describes a method of measuring in vivo gracilis muscle-tendon unit length and presents a comparison of experimental data versus predictions from four musculoskeletal models in OpenSim. The largest errors occurred when the knee was fully extended. At this position, the absolute average muscle-tendon unit length error was 7% and the absolute average fiber length error was between 15% and 32%. However, the variability of these errors was significant. Manual linear scaling based on an anthropometric database did not capture the variability observed in subjects. The fiber length errors observed are predicted to have a significant impact on muscle force production that may not represent true subject specific force-length relationship of the gracilis.

Functional performance differences between carbon fiber and fiberglass prosthetic feet

BACKGROUND

Persons with lower limb amputation require increased functionality. The largest category of feet for active individuals with a transtibial amputation is energy storage and return (ESR) feet. These feet are typically constructed of carbon fiber composite materials. Recently, a prosthetic foot composed of a fiberglass composite has emerged in the market. However, there are no comparative studies of these devices.

OBJECTIVES

Compare the biomechanical performance and prosthesis-related quality of life when using a fiberglass prosthetic foot design compared with traditional carbon fiber ESR designs.

STUDY DESIGN

This is a repeated-measures randomized cross-over trial.

METHODS

Gait analysis was performed on 10 experienced male subjects with unilateral transtibial amputations (K-level III) while walking on level ground and a ramp. Patient-reported outcomes were collected using the Prosthesis Evaluation Questionnaire.

RESULTS

Gait data demonstrated increased ankle dorsiflexion (P < .01), similar ankle moments (P = .07), and increased ankle power generation (P = .01) when using the fiberglass foot. The increased power generation occurred at the correct time in the gait cycle such that the timing and magnitude of peak knee flexion was unaffected (P > .19). The fiberglass foot had greater energy absorption during gait (P = .01) with no difference in energy return (P = .37). The subjects expressed improved prosthesis-related quality of life with the fiberglass foot (P = .01).

CONCLUSIONS

The findings of this study demonstrate that the new ESR foot comprising a fiberglass material had better performance than traditional designs using a carbon fiber material.

Agreement between the Skull Vibration-Induced Nystagmus Test and Semicircular Canal and Otolith Asymmetry

BACKGROUND

 How significant asymmetries in otolith organ function in the presence of symmetrical and asymmetrical semicircular canal function influence skull vibration-induced nystagmus testing (SVINT) has not been well described.

PURPOSE

 The aim of the study is to examine the agreement between SVINT and caloric testing, ocular vestibular-evoked myogenic potentials (oVEMP), and cervical vestibular-evoked myogenic potentials (cVEMP) for detecting asymmetric vestibular function.

RESEARCH DESIGN

 This is a retrospective study of patients presenting with the chief complaint of vertigo, dizziness, or imbalance.

STUDY SAMPLE

 A total of 812 patients were studied with a median age at testing of 59 years (interquartile range 46-70; range 18-93) and included 475 (59%) women.

INTERVENTION

 Either the monothermal warm caloric test or alternate binaural bithermal caloric test, oVEMP, and cVEMP tests were administered to all patients. All patients underwent the SVINT prior to vestibular laboratory testing.

DATA COLLECTION AND ANALYSIS

 Agreement between tests categorized as normal versus abnormal was summarized using percent concordance (PC). Sensitivity and specificity values were calculated for SVINT compared with other tests of vestibular function.

RESULTS

 There was higher agreement between ipsilateral and contralateral SVINT with the caloric test (PC = 80% and 81%, respectively) compared with oVEMP (PC = 63% and 64%, respectively) and cVEMP (PC = 76% and 78%, respectively). Ipsilateral and contralateral SVINT showed higher sensitivity for the caloric test (sensitivity = 47% and 36%, respectively) compared with oVEMP (sensitivity = 26% and 21%, respectively), or cVEMP (sensitivity = 33% vs. 27%, respectively). Specificity of SVINT was high (>80%) for all assessments of vestibular function.

CONCLUSION

 The presence of SVIN is a useful indicator of the asymmetry of vestibular function between the two ears when making judgments about semicircular canal asymmetry but is less sensitive to asymmetries in otolith organ function.

Sensor Anchoring Improves the Correlation Between Intramuscular Pressure and Muscle Tension in a Rabbit Model

Intramuscular pressure (IMP) shows promise for estimating individual muscle tension in vivo. However, previous pressure measurements show high variability during isometric contraction and poor correlation with tension during dynamic contraction. We hypothesized that enhanced sensor anchoring/orientation would improve tension estimation and thus developed a novel pressure sensor with a barbed housing. Sensors were inserted into the tibialis anterior (TA) of New Zealand White rabbits (N = 8) both parallel and perpendicular to the fiber orientation. We measured muscle stress and IMP during both isometric and dynamic contractions. Passive stress showed good agreement for both insertion directions across muscle lengths (ICC > 0.8). Active stress and IMP agreement were good (ICC = 0.87 ± 0.04) for perpendicular insertions but poor (ICC = 0.21 ± 0.22) for parallel insertions across both dynamic contractions and isometric contractions within the muscle's range of motion. These findings support use of IMP measurements to estimate muscle tension across a range of contraction conditions.

Effects of elbow immobilization on upper extremity activity

BACKGROUND

It has been dogma that handedness greatly impacts daily activities. Interruptions in the ability to utilize the dominant arm due to neuromusculoskeletal injuries could negatively impact performance of activities of daily living. Daily activity can be measured using activity monitors. This study aimed to examine how arm dominance impacts function by immobilizing the arms of healthy individuals.

METHODS

Ten individuals wore four upper extremity activity monitors for three days-one day without immobilization, one day with their dominant arm immobilized, and one day with their non-dominant arm immobilized. Triaxial acceleration data was used to calculate average daily activity and an asymmetry index. Between-condition differences were examined.

FINDINGS

During dominant arm immobilization, the dominant forearm had significantly less average daily activity when compared to the no immobilization day (p = .0001) and the non-dominant immobilized day (p < .0001). A similar trend was observed at the non-dominant forearm when the non-dominant arm was immobilized. Immobilization of an arm increased asymmetry index and reliance on the non-immobilized arm. Significant differences in asymmetry index were not observed between the two casted conditions.

INTERPRETATION

When an upper extremity was casted, immobilized forearm and upper arm average daily activity was comparable. Dominance did not have an effect on asymmetry index. Immobilization affected asymmetry index compared to no immobilization. This study has demonstrated that regardless of arm immobilized, there will be a reliance on the contralateral limb about twice as much as the immobilized limb. This could prove problematic if the contralateral limb is restricted or injured, limiting independent.

Posterior single-stepping thresholds are prospectively related to falls in older women

BACKGROUND

Falls are a leading cause of injury in older women. Stepping thresholds quantify balance-reaction capabilities. It is unclear how such evaluations predict falls in comparison to, or as a complement to, other objective measures of gait, standing postural control, strength, and balance confidence.

AIMS

The objective of this study was to determine if stepping thresholds are prospectively related to falls in older women.

METHODS

For this prospective cohort study, 125 ambulatory, community-dwelling women, age ≥ 65 years were recruited. Using a treadmill to deliver perturbations to standing participants, we determined anteroposterior single- and multiple-stepping thresholds. Here, thresholds represent the minimum perturbation magnitudes that consistently evoke one step or multiple steps. In addition, gait kinematics, obstacle-crossing kinematics, standing sway measures, unipedal stance time, the functional reach, lower extremity isometric strength, grip strength, balance confidence, and fall history were evaluated. Falls were prospectively recorded for one year.

RESULTS

Seventy-four participants (59%) fell at least once. Posterior single-stepping thresholds were the only outcome that predicted future fall status (OR = 1.50, 95% CI 1.01-2.28; AUC = .62). A multivariate approach added postural sway with eyes closed as a second predictive variable, although predictive abilities were not meaningfully improved.

DISCUSSION

These results align with the previous evidence that reactive balance is a prospective indicator of fall risk. Unlike previous studies, strength scaled to body size did not contribute to fall prediction.

CONCLUSION

Posterior single-stepping thresholds held a significant relationship with future fall status. This relationship was independent of, and superior to that of, other measures of standing balance, gait, strength, and balance confidence.

Interfaces with the peripheral nervous system for the control of a neuroprosthetic limb: a review

The field of prosthetics has been evolving and advancing over the past decade, as patients with missing extremities are expecting to control their prostheses in as normal a way as possible. Scientists have attempted to satisfy this expectation by designing a connection between the nervous system of the patient and the prosthetic limb, creating the field of neuroprosthetics. In this paper, we broadly review the techniques used to bridge the patient's peripheral nervous system to a prosthetic limb. First, we describe the electrical methods including myoelectric systems, surgical innovations and the role of nerve electrodes. We then describe non-electrical methods used alone or in combination with electrical methods. Design concerns from an engineering point of view are explored, and novel improvements to obtain a more stable interface are described. Finally, a critique of the methods with respect to their long-term impacts is provided. In this review, nerve electrodes are found to be one of the most promising interfaces in the future for intuitive user control. Clinical trials with larger patient populations, and for longer periods of time for certain interfaces, will help to evaluate the clinical application of nerve electrodes.

Effects of Selective Dorsal Rhizotomy on Ankle Joint Function in Patients With Cerebral Palsy

Selective dorsal rhizotomy (SDR) is a neurosurgical technique performed to reduce muscle spasticity and improve motor functions in children with cerebral palsy (CP). In long term, muscle contractures were observed even after SDR. To better understand what is contributing to contracture formation, it is necessary to assess the effects of SDR on joint stiffness. We hypothesized that ankle passive range of motion (ROM) increases and the quasi-stiffness of the ankle joint decreases after SDR in children with CP. This retrospective study included 10 children with diplegic CP (median age 6 years 2 months) who had undergone SDR and for whom gait analysis data were collected 3 months before (Pre-SDR) and 13 months after (Post-SDR) surgery. Additional to clinical measures, ankle quasi-stiffness (the slope of the ankle moment vs. ankle angle plot) was analyzed from gait data. Passive ankle ROM at 0° (p < 0.0001) and 90° knee angles (p < 0.0001) increased after SDR. Dynamic EMG analysis showed improved phasic gastrocnemius activity (p < 0.0001). Equinus gait was improved with the reduction of peak plantar flexion (p < 0.0001), as well as an increase in peak dorsiflexion (p = 0.006) during walking was observed. Ankle joint quasi-stiffness (Pre- and post-SDR median = 0.056 Nm/kg/° and 0.051 Nm/kg/°, and interquartile range: 0.031 Nm/kg/° and 0.019 Nm/kg/°, respectively) decreased significantly (p = 0.0017) after SDR. Moreover, even though the total time of the gait cycle did not change (p = 0.99), the time interval from maximum dorsiflexion to maximum plantar flexion (Pre- and post-SDR median = 0.125 s and 0.156 s, and interquartile range: 0.153 and 0.253 s, respectively) increased significantly (p = 0.0068) after SDR. In conclusion, the decreased ankle quasi-stiffness and the enhanced time interval in the gait cycle due to SDR indicate better motor control and joint stability. Our findings suggest that the long-term contracture formation occurring even after surgical interventions may be related to the stiffening of non-contractile structures.

Kinematic profiles during activities of daily living in adults with traumatic brachial plexus injuries

BACKGROUND

Injuries to the brachial plexus leave individuals with lasting effects in upper extremity motor function, even with successful surgical restoration of elbow flexion. Quantitatively describing independent patient function during activities of daily living utilizing motion analysis could aid in prioritization of secondary surgical targets, as well as serve as an outcome measure. This study explored the upper extremity kinematic profiles during activities of daily living in adults with brachial plexus injury.

METHODS

Eight adult participants (4 subjects with brachial plexus injury, 4 healthy controls) completed activities of daily living during one motion capture setting. Trunk, shoulder, and elbow joint minima, maxima, and range of motion were calculated and compared between groups. Kinematic profiles over a motion cycle were compared between groups using statistical parametric mapping.

FINDINGS

Subjects with brachial plexus injuries had significantly greater trunk range of motion during feeding and dressing tasks compared to control subjects. This compensatory trunk motion was accompanied by limited shoulder external rotation demonstrated using conventional descriptors and statistical parametric mapping.

INTERPRETATION

Significant compensatory trunk motion is required to complete select activities of daily living in subjects with brachial plexus injury. Additionally, restoration of shoulder external rotation would be a beneficial secondary target of surgical restoration of motor function. These aspects should be considered in treatment planning, as they could impact patient outcomes. Combining conventional descriptors of patient motion (e.g. joint minima, maxima, and range of motion) with statistical parametric mapping can provide a rich description of patient compensations and limitations.

Modeling Skeletal Muscle Stress and Intramuscular Pressure: A Whole Muscle Active-Passive Approach

Clinical treatments of skeletal muscle weakness are hindered by a lack of an approach to evaluate individual muscle force. Intramuscular pressure (IMP) has shown a correlation to muscle force in vivo, but patient to patient and muscle to muscle variability results in difficulty of utilizing IMP to estimate muscle force. The goal of this work was to develop a finite element model of whole skeletal muscle that can predict IMP under passive and active conditions to further investigate the mechanisms of IMP variability. A previously validated hypervisco-poroelastic constitutive approach was modified to incorporate muscle activation through an inhomogeneous geometry. Model parameters were optimized to fit model stress to experimental data, and the resulting model fluid pressurization data were utilized for validation. Model fitting was excellent (root-mean-square error or RMSE <1.5 kPa for passive and active conditions), and IMP predictive capability was strong for both passive (RMSE 3.5 mmHg) and active (RMSE 10 mmHg at in vivo lengths) conditions. Additionally, model fluid pressure was affected by length under isometric conditions, as increases in stretch yielded decreases in fluid pressurization following a contraction, resulting from counteracting Poisson effects. Model pressure also varied spatially, with the highest gradients located near aponeuroses. These findings may explain variability of in vivo IMP measurements in the clinic, and thus help reduce this variability in future studies. Further development of this model to include isotonic contractions and muscle weakness would greatly benefit this work.

McArdle Sign: A Specific Sign of Multiple Sclerosis

OBJECTIVE

To measure McArdle sign (rapidly reversible weakness induced by neck flexion) both qualitatively and quantitatively and to evaluate its specificity and clinical utility for diagnosis of multiple sclerosis (MS).

PATIENTS AND METHODS

In this prospective study, McArdle sign was evaluated by a technician blinded to diagnosis by measuring changes in finger extensor strength in successive trials of neck extension and flexion, first clinically and then with a torque measurement device. We studied 25 healthy controls and 81 patients with finger extensor weakness. Patients were not selected for having McArdle sign. Fifty-two patients had MS, 24 had other myelopathies, and 5 had peripheral nerve lesions accounting for their weakness. The study was conducted between February 1, 2016, and June 30, 2017.

RESULTS

The median clinical McArdle sign and the 2 quantitative measures of neck flexion-induced strength reduction were greater in patients with MS than in the other groups (P<.001). Baseline strength did not confound the difference. The area under the receiver operating characteristic curve was 0.84 (95% CI, 0.75-0.93) comparing patients with MS vs healthy controls and 0.84 (95% CI, 0.75-0.93) comparing MS vs patients with other myelopathies. The 2 quantitative and 1 clinical measurement of McArdle sign by the technician who performed the quantitative testing were correlated (r=.57 and r=.58; P<.001), and in turn, the technician's and unblinded referring physician's clinical assessments were correlated (r=.58; P<.001). McArdle sign was evident in some patients who had minor disability and who were in early phases of MS.

CONCLUSION

McArdle sign, when defined as greater than 10% neck flexion-induced reduction in strength, is entirely specific and 65% sensitive for a diagnosis of MS when compared with other conditions that mimic MS-associated myelopathy. It may facilitate diagnosis in certain clinical situations.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT03122873.

Assessment of Upper Extremity Function

Assessment of upper extremity function either before or after surgical treatment has been a rapidly evolving field. A reproducible, accurate, and valid assessment tool provides the ability to compare surgical interventions, evaluate physical therapy regimens, and assess novel assistive and restorative technologies. The purpose of this article is to detail the various upper extremity assessment tools and introduce the concept of real-world data acquisition of upper extremity function.

Cross-sectional validation of inertial measurement units for estimating trunk flexion kinematics during treadmill disturbances

Postural perturbation training has been shown to reduce falls. The key outcome measures are trunk flexion kinematics, at recovery step. Motion capture is typically used, but requires space and trained staff. Small, inexpensive, portable inertial measurement units (IMU) are preferred for routine clinical care. IMUs have been validated for trunk motion during walking and running on a treadmill, however treadmill fall prevention training generates higher accelerations. The purpose of this study was to validate the IMU estimate of trunk kinematics against motion capture during treadmill disturbances. Ten healthy young adults had an IMU with a retro-reflective marker triad placed on their sternum to estimate trunk kinematics. Disturbances, increasing in magnitude, were delivered until the harness supported at least 50% of the subject's weight. Equivalence testing (α = 0.05) demonstrated the trunk angle (TA) and angular velocity (TAV) measured by the IMU and motion capture were equivalent. The 95% Confidence Intervals (TA: [-1, 1], TAV: [0, 17]) were within the equivalence interval (TA: [-2, 2], TAV: [-20, 20]) and the p-Values (TA: 0.005, TAV: 0.011) were less than alpha. This data confirms that IMUs provide a valid method for measuring trunk kinematics during treadmill perturbation training.

Patient-Reported and Objectively Measured Function Before and After Reverse Shoulder Arthroplasty

BACKGROUND AND PURPOSE

Documenting functional outcomes after reverse shoulder arthroplasty (RSA) is critical to advancing patient care. The interplay been self-reported and objectively measured outcome measures has not been widely described. The utilization of wearable devices to document upper extremity limb activity is a new approach for objectively measuring outcomes. Therefore, the purpose of this study was to evaluate changes in pain, and self-reported function and objectively measured limb activity after RSA. We also assessed the influence of pain on self-reported function and objectively measured limb activity to determine the impact of pain on outcomes after RSA.

MATERIALS

This study implemented a prospective, repeated-measures design. Fourteen patients undergoing RSA underwent testing before surgery, and 2 and 12 months after surgery. Patient-reported instruments included pain, Disabilities of Arm, Shoulder and hands (DASH), and physical component summary (PCS) of the 36-Item Short Form Health Survey. Objective limb activity (mean activity value, m/s/min epoch; inactive time, %; low activity, %; and high activity, %) was captured with triaxial accelerometers worn on the upper and lower arm. A repeated-measures ANOVA tested for differences across time. The Spearman rank-order correlation was calculated to evaluate the influence of pain on DASH, PCS scores, and mean limb activity.

RESULTS

Patient-reported measures improved after surgery (pain, P < .01; DASH, P < .01; PCS, P = .01). No change in limb activity was found at 1 year compared with preoperative values for mean (forearm, P = 1.00; arm, P = .36), inactivity (forearm, P = .33; arm, P = .22), low (forearm, P = .77; arm, P = .11) or high (forearm, P = 1.00; arm, P = .20) activity. There was a relationship between pain and DASH scores 1 year after surgery (P = .04) but not before surgery (P = .16), or 2 months after surgery (P = .30). There was no relationship between pain and PCS scores at any time point (preoperative, P = .97; 2 months, P = .21; 1 year, P = .08) nor pain and limb activity (forearm: preoperative, P = .36; 2 months, P = .67; 1 year, P = .16; arm: preoperative, P = .97; 2 months, P = .59; 1 year, P = .51).

CONCLUSIONS

RSA reduced pain and enhanced patient-perceived function. Objectively measured upper extremity limb activity is not different 1 year after surgery compared with preoperative levels.

LEVEL OF EVIDENCE

III.

Low Back Pain in Adults With Transfemoral Amputation: A Retrospective Population-Based Study

BACKGROUND

Low back pain (LBP) is common among individuals with transfemoral amputation (TFA) and has a negative impact on quality of life. Little is known about health care utilization for LBP in this population and whether utilization varies by amputation etiology.

OBJECTIVE

To determine if individuals with TFA have an increased likelihood of seeking care or reporting symptoms of acute or chronic LBP during physician visits after amputation compared with matched individuals without amputation.

DESIGN

Retrospective cohort.

SETTING

Olmsted County, Minnesota (2010 population: 144 248).

PARTICIPANTS

All individuals with incident TFA (N = 96), knee disarticulation, and transfemoral amputation residing in Olmsted County between 1987 and 2014. Each was matched (1:10 ratio) with non-TFA adults on age, sex, and duration of residency. Individuals were divided by etiology of amputation: dysvascular and trauma/cancer.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASUREMENTS

Death and presentation for evaluation of LBP (LBP event) while residing in Olmsted County. LBP events were identified using validated International Classification of Diseases, Ninth Revision (ICD-9) codes and corresponding Berkson, Hospital International Classification of Diseases Adapted (HICDA), and ICD-10 diagnostic codes. Hurdle and competing-risk Cox proportional hazard models were used.

RESULTS

Having a TFA of either etiology did appear to correlate with increased frequency of LBP events, although this association was only statistically significant within the dysvascular TFA cohort (dysvascular TFA cohort: relative risk [RR] 1.80, 95% confidence interval [CI] 1.07-3.03, median follow-up 0.78 years; trauma/cancer TFA cohort: RR 1.14, 95% CI 0.58-2.22, median follow-up 7.95 years). In time to event analysis, dysvascular TFA had an increased risk of death and event. Obesity did not significantly correlate with increased frequency of LBP events or time to event for either cohort. At any given point in time, individuals with TFA of either etiology who had phantom limb pain were 90% more likely to have an LBP event (hazard ratio [HR] 1.91, 95% CI 1.11-3.31). Conditional on not dying and no LBP event within the first 2.5 years, individuals with prosthesis had a decreased risk of LBP events in subsequent years.

CONCLUSIONS

Risk of LBP events appears to vary by TFA etiology. Obesity did not correlate significantly with increased frequency of LBP event or time to event. Phantom limb pain correlated with decreased time to LBP event after amputation. The association between prosthesis receipt and LBP events is ambiguous.

LEVEL OF EVIDENCE

III.

Intramuscular Pressure of Human Tibialis Anterior Muscle Reflects in vivo Muscular Activity

Intramuscular pressure (IMP) is the fluid hydrostatic pressure generated within a muscle and reflects the mechanical forces produced by a muscle. By providing accurate quantification of interstitial fluid pressure, the measurement of IMP may be useful to detect changes in skeletal muscle function not identified with established techniques. However, the relationship between IMP and muscle activity has never been studied in vivo in healthy human muscles. To determine if IMP is able to evaluate electromechanical performance of muscles in vivo, we tested the following hypotheses on the human tibialis anterior (TA) muscle: (i) IMP increases in proportion to muscle activity as measured by electrical [Compound Muscle Action Potential (CMAP)] and mechanical (ankle torque) responses to activation by nerve stimulation and (ii) the onset delay of IMP (IMPD) is shorter than the ankle torque electromechanical delay (EMD). Twelve healthy adults [six females; mean (SD) = 28.1 (5.0) years old] were recruited. Ankle torque, TA IMP, and CMAP responses were collected during maximal stimulation of the fibular nerve at different intensity levels of electrical stimulation, and at different frequencies of supramaximal stimulation, i.e., at 2, 5, 10, and 20 Hz. The IMP response at different stimulation intensities was correlated with the CMAP amplitude (r² = 0.94). The area of the IMP response at different stimulation intensities was also significantly correlated with the area of the CMAP (r² = 0.93). Increasing stimulation intensity resulted in an increase of the IMP response (P < 0.001). Increasing stimulation frequency caused torque (P < 0.001) as well as the IMP (P < 0.001) to increase. The ankle torque EMD [median (interquartile range) = 41.8 (14.4) ms] was later than the IMPD [33.0 (23.6) ms]. These findings support the hypotheses and suggest that IMP captures active mechanical properties of muscle in vivo and can be used to detect muscular changes due to drugs, diseases, or aging.

Assessment of gait kinetics in post-menopausal women using tri-axial ankle accelerometers during barefoot walking

BACKGROUND

Physical activity (PA) interventions, designed to increase exposure to ground reaction force (GRF) loading, are a common target for reducing fracture risk in post-menopausal women with low bone mineral density (BMD). Unfortunately, accurate tracking of PA in free-living environments and the ability to translate this activity into evaluations of bone health is currently limited.

RESEARCH QUESTION

This study evaluates the effectiveness of ankle-worn accelerometers to estimate the vertical GRFs responsible for bone and joint loading in post-menopausal women at a range of self-selected walking speeds during barefoot walking.

METHODS

Seventy women, at least one year post-menopause, wore Actigraph GT3X + on both ankles and completed walking trials at self-selected speeds (a minimum of five each at fast, normal and slow walking) along a 30 m instrumented walkway with force plates and photocells to measure loading and estimate gait velocity. Repeated measures correlation analysis and step-wise mixed-effects modelling were performed to evaluate significant predictors of peak vertical GRFs normalized to body weight (pVGRFbw), including peak vertical ankle accelerations (pVacc), walking velocity (Vel_w) and age.

RESULTS

A strong repeated measures correlation of r = 0.75 (95%CI [0.71-0.76] via 1000 bootstrap passes) between pVacc and pVGRFbw was observed. Five-fold cross-validation of mixed-model predictions yielded an average mean-absolute-error (MAE[95%CI]) and root-mean-square-error (RMSE) rate of 5.98%[5.61-6.42] and 0.076 [0.069-0.082] with a more complex model (including Vel_w,) and 6.80%[6.37-7.54] and 0.087BW[0.081-0.095] with a simpler model (including only pVacc), when comparing accelerometer-based estimations of pVGRFbw to force plate measures of pVGRFbw. Age was not found to be significant.

SIGNIFICANCE

This study is the first to show a strong relationship among ankle accelerometry data and high fidelity lower-limb loading approximations in post-menopausal women. The results provide the first steps necessary for estimation of real-world limb and joint loading supporting the goals of accurate PA tracking and improved individualization of clinical interventions.

Comparison of overhead harness configurations for measuring trunk kinematics during treadmill disturbances

BACKGROUND

Research has shown that postural perturbation training reduces falls. Trunk kinematics, at recovery step, are key outcome measures. Fall prevention training programs are being developed for routine clinical care. In these programs, the subject is positioned on a treadmill and subjected to forward and backward disturbances which simulate trips and slips. The patient wears a safety vest attached to an overhead harness to create a secure environment. Motion capture is used to measure trunk kinematics.

RESEARCH QUESTION

It is important to verify that trunk kinematics are independent of harness configuration. The purpose of this study was to compare the trunk flexion angle and angular velocity at recovery step after forward and backward disturbances on a treadmill measured by motion capture with the harness in both a fixed and free position.

METHODS

Ten healthy young adults (5/10 female, age: 29.2 ± 6.3 years, BMI: 24.2 ± 2.4) participated in this study. The subjects had retro-reflective markers placed on key anatomical landmarks to measure trunk kinematics. The participants experienced forward and backward disturbances, which incrementally increased in intensity until the harness clearly supported the subjects for three disturbances in both directions. The order of harness configurations was randomized across subjects and each subject participated in two consecutive rounds of disturbances, one round for each harness configuration. Equivalence testing was performed to demonstrate that the harness configurations were equivalent (α = 0.05).

RESULTS AND SIGNIFICANCE

The Equivalence Test demonstrated that the trunk angle (TA) and angular velocity (TAV) were equivalent for the different harness configurations. The 95% Confidence Intervals (TA: [-2, 1], TAV: [-18, 16]) were within the equivalence interval (TA: [-3, 3], TAV: [-20, 20]) and the p-Values (TA: 0.008, TAV: 0.034) were less than alpha. Trunk kinematics are independent of overheard harness configurations during treadmill induced disturbances for clinical postural perturbation training.

The accuracy of rapid treadmill-belt movements as a means to deliver standing postural perturbations

Treadmill-induced postural perturbations are a promising tool in assessing and reducing the risk of falls. We evaluated the accuracy with which two treadmills (Simbex ActiveStep^® and an AMTI instrumented treadmill) achieved commanded displacements, peak velocities, and average initial accelerations. To do so, we included a range of perturbation magnitudes (20, 30, and 40 cm displacements) applied in unweighted and weighted (body mass = 46-84 kg) conditions. Across treadmills and perturbation magnitudes, absolute errors in displacement (< 0.5 cm) and peak velocity (< 4 cm/s) were small (relative error < 5%). Between-treadmill differences in displacement and peak velocity were marginal (< 3%), regardless of the perturbation magnitude and participant body mass. Observed accelerations were more than 5% smaller than commanded values. The front, but not back, AMTI belt demonstrated less acceleration accuracy than the ActiveStep^® (≈ 5% difference). In summary, both treadmills demonstrated a reasonable, consistent level of accuracy in delivering postural perturbations.

The risk of major cardiovascular events for adults with transfemoral amputation

BACKGROUND

It is well-known that the risk of cardiac disease is increased for those with lower-limb amputations, likely as a result of the etiology of the amputation. Using a longitudinal population-based dataset, we examined the association between transfemoral amputation (TFA) status and the risk of experiencing a major cardiac event for those undergoing either dysvascular or traumatic amputations. The association of receiving a prosthesis with the risk of experiencing a major cardiac event was also examined.

METHODS

Study Population: All individuals with TFA (N 162), i.e. knee disarticulation and transfemoral amputation, residing in Olmsted County, MN, between 1987 and 2014. Each was matched (1:10 ratio) with non-TFA adults on age, sex, and duration of residency.

DATA ANALYSIS

A competing risk Cox proportional hazard model was used to estimate the relative likelihood of an individual with a TFA experiencing a major cardiac event in a given time period as compared to the matched controls. The cohort was divided by amputation etiology: dysvascular vs trauma/cancer. Additional analysis was performed by combining all individuals with a TFA to look at the relationship between prosthesis receipt and major cardiac events.

RESULTS

Individuals with a dysvascular TFA had an approximately four-fold increased risk of a cardiac event after undergoing an amputation (HR 3.78, 95%CI: 3.07-4.49). These individuals also had an increased risk for non-cardiac mortality (HR 6.27, 95%CI: 6.11-6.58). The risk of a cardiac event was no higher for those with a trauma/cancer TFA relative to the able-bodied controls (HR 1.30, 95%CI: 0.30-5.85). Finally, there was no difference in risk of experiencing a cardiac event for those with or without prosthesis (HR 1.20, 95%CI: 0.55-2.62).

CONCLUSION

The high risk of initial mortality stemming from an amputation event may preclude many amputees from cardiovascular disease progression. Amputation etiology is also an important factor: cardiac events appear to be more likely among patients with a dysvascular TFA. Providing a prosthesis does not appear to be associated with a reduced risk of a major cardiac event following amputation.

The relationships between compensatory stepping thresholds and measures of gait, standing postural control, strength, and balance confidence in older women

BACKGROUND

Compensatory stepping thresholds evaluate the response to postural disturbances. Although such fall-recovery measures are a promising indicator of fall risk, the relationships between stepping thresholds and other measures used to predict falls are not well established.

RESEARCH QUESTION

We sought to quantify the relationships between stepping thresholds and other measurements used to assess fall risk in older women, a population at high risk for falls and related injuries, including fractures.

METHODS

We studied 112 ambulatory, community-dwelling women, age 65 years or older. Using a treadmill to deliver standing postural disturbances, we determined anterior and posterior single-stepping and multiple-stepping thresholds. These thresholds represented the magnitude of the disturbance that elicited one step or more than one step, respectively. We also assessed balance confidence, functional reach, unipedal stance time, isometric strength, obstacle crossing, postural sway, and gait kinematics. Outcomes were normalized to body size.

RESULTS

After accounting for age, stepping thresholds were, at most, moderately correlated (Pearson partial correlation coefficients r = 0.20 to 0.40 and r = -0.21 to -0.31) to several assessments of gait, postural control, and strength. Approximately 24-52% of the variance in stepping thresholds was explained by a combination of age and other fall risk assessments, which frequently consisted of balance confidence, unipedal stance time, obstacle crossing, the Romberg ratio of postural sway, and/or strength.

SIGNIFICANCE

Our results suggest that anteroposterior fall-recovery ability, as assessed by stepping thresholds, can only be partially inferred from age and a combination of assessments of sway, strength, unipedal tasks, and balance confidence. Compensatory stepping thresholds may provide information on stability maintenance unique from other assessments of fall risk. Further investigation would be necessary to determine whether stepping thresholds are better predictors of falls in older women.

Evaluating skeletal muscle electromechanical delay with intramuscular pressure

INTRODUCTION

Intramuscular pressure (IMP) is the fluid pressure generated within skeletal muscle and directly reflects individual muscle tension. The purpose of this study was to assess the development of force, IMP, and electromyography (EMG) in the tibialis anterior (TA) muscle during ramped isometric contractions and evaluate electromechanical delay (EMD).

METHODS

Force, EMG, and IMP were simultaneously measured during ramped isometric contractions in eight young, healthy human subjects. The EMD between the onset of force and EMG activity (Δt-EMG force) and the onset of IMP and EMG activity (Δt EMG-IMP) were calculated.

RESULTS

A statistically significant difference (p < 0.05) was found between the mean force-EMG EMD (36 ± 31 ms) and the mean IMP-EMG EMD (3 ± 21 ms).

CONCLUSIONS

IMP reflects changes in muscle tension due to the contractile muscle elements.

Performance of an attention-demanding task during treadmill walking shifts the noise qualities of step-to-step variation in step width

BACKGROUND

The fractal scaling evident in the step-to-step fluctuations of stepping-related time series reflects, to some degree, neuromotor noise.

RESEARCH QUESTION

The primary purpose of this study was to determine the extent to which the fractal scaling of step width, step width and step width variability are affected by performance of an attention-demanding task. We hypothesized that the attention-demanding task would shift the structure of the step width time series toward white, uncorrelated noise.

METHODS

Subjects performed two 10-min treadmill walking trials, a control trial of undisturbed walking and a trial during which they performed a mental arithmetic/texting task. Motion capture data was converted to step width time series, the fractal scaling of which were determined from their power spectra.

RESULTS

Fractal scaling decreased by 22% during the texting condition (p < 0.001) supporting the hypothesized shift toward white uncorrelated noise. Step width and step width variability increased 19% and five percent, respectively (p < 0.001). However, a stepwise discriminant analysis to which all three variables were input revealed that the control and dual task conditions were discriminated only by step width fractal scaling.

SIGNIFICANCE

The change of the fractal scaling of step width is consistent with increased cognitive demand and suggests a transition in the characteristics of the signal noise. This may reflect an important advance toward the understanding of the manner in which neuromotor noise contributes to some types of falls. However, further investigation of the repeatability of the results, the sensitivity of the results to progressive increases in cognitive load imposed by attention-demanding tasks, and the extent to which the results can be generalized to the gait of older adults seems warranted.

Net ankle quasi-stiffness is influenced by walking speed but not age for older adult women

BACKGROUND

Insufficient plantar flexor resistance due to plantar flexor weakness, an impairment common in patient populations, causes substantial gait deficits. The bending stiffness of passive-dynamic ankle-foot orthoses (PD-AFOs) has the capacity to replace lost plantar flexor resistance. Many patients who are prescribed PD-AFOs are older adults. While PD-AFO bending stiffness should be customized for patients, a method to objectively prescribe this stiffness does not exist. Quantifying natural plantar flexor resistance during non-pathological gait could provide a reference value for objectively prescribing PD-AFO bending stiffness.

RESEARCH QUESTION

This study investigated the effect of age on plantar flexor resistance in 113 participants above the age of 65 years. We did so while also considering the confounding influence of gait speed, an aspect known to be reduced with old age.

METHODS

Ambulatory, community-dwelling older adult women (ages 65-91 years) with no current or recent lower-extremity injuries or surgeries underwent an instrumented gait analysis at a self-selected speed. Plantar flexor resistance was quantified via net ankle quasi-stiffness (NAS) defined as the slope of ankle joint moment-angle curve during late stance.

RESULTS

showed that NAS was not significantly influenced by age (r = -0.11, p = 0.12), and that the confounding factor of walking speed had a significant, positive relationship with NAS (r = 0.59, p < 0.001).

SIGNIFICANCE

By determining that gait speed, not age, is related to NAS in older adults, this study represents the initial step towards objectively prescribing PD-AFO bending stiffness to achieve a targeted gait speed for older adults with plantar flexor weakness.

Intramuscular Pressure of Tibialis Anterior Reflects Ankle Torque but Does Not Follow Joint Angle-Torque Relationship

Intramuscular pressure (IMP) is the hydrostatic fluid pressure that is directly related to muscle force production. Electromechanical delay (EMD) provides a link between mechanical and electrophysiological quantities and IMP has potential to detect local electromechanical changes. The goal of this study was to assess the relationship of IMP with the mechanical and electrical characteristics of the tibialis anterior muscle (TA) activity at different ankle positions. We hypothesized that (1) the TA IMP and the surface EMG (sEMG) and fine-wire EMG (fwEMG) correlate to ankle joint torque, (2) the isometric force of TA increases at increased muscle lengths, which were imposed by a change in ankle angle and IMP follows the length-tension relationship characteristics, and (3) the electromechanical delay (EMD) is greater than the EMD of IMP during isometric contractions. Fourteen healthy adults [7 female; mean (SD) age = 26.9 (4.2) years old with 25.9 (5.5) kg/m² body mass index] performed (i) three isometric dorsiflexion (DF) maximum voluntary contraction (MVC) and (ii) three isometric DF ramp contractions from 0 to 80% MVC at rate of 15% MVC/second at DF, Neutral, and plantarflexion (PF) positions. Ankle torque, IMP, TA fwEMG, and TA sEMG were measured simultaneously. The IMP, fwEMG, and sEMG were significantly correlated to the ankle torque during ramp contractions at each ankle position tested. This suggests that IMP captures in vivo mechanical properties of active muscles. The ankle torque changed significantly at different ankle positions however, the IMP did not reflect the change. This is explained with the opposing effects of higher compartmental pressure at DF in contrast to the increased force at PF position. Additionally, the onset of IMP activity is found to be significantly earlier than the onset of force which indicates that IMP can be designed to detect muscular changes in the course of neuromuscular diseases impairing electromechanical transmission.

Verification of an improved hip joint center prediction method

In motion analysis, the hip joint center (HJC) is used to define the proximal location of the thigh segment and is also the point about which hip moments are calculated. The HJC cannot be palpated; its location must be calculated. Functional methods have been proposed but are difficult to perform by some clinical populations. Therefore, regression methods are utilized, but yield large errors in estimating the HJC location. These prediction methods typically utilize the anterior and posterior superior iliac spines, where excessive adipose tissue makes correctly locating difficult. A new regression method (Hara) utilizes leg length and has been shown to improve HJC location in cadavers and less error than previous pelvic based regression methods, such as those proposed by Harrington et al. This study compared the accuracy of the HJC location calculated with both of the Harrington methods and the Hara method. The coronal knee angle was calculated for each method using a static motion analysis trial, and compared to the tibiofemoral angle measured on a gold standard digital full-leg coronal radiograph. This study demonstrated that the Hara method was more accurate than either of the Harrington methods. The mean error between the gold standard x-ray measurement and the motion analysis calculation for the Harrington (stepwise and LOOCV), the Harrington (linear regression), and Hara regression methods, respectively were 6.0°, 4.0°, and 1.8°. Accurately modeling the HJC is critical for data interpretation and patient care. This study confirmed that the Hara HJC regression method is valid in an in-vivo setting.