Sensory integration and segmental control of posture during pregnancy.

BACKGROUND: Approximately 25% of pregnant people fall, yet the underlying mechanisms of this increased fall-risk remain unclear. Prior studies examining pregnancy and balance have utilized center of pressure analyses and reported mixed results. The purpose of this study was to examine sensory and segmental contributions to postural control throughout pregnancy using accelerometer-based measures of sway. METHODS: Thirty pregnant people (first trimester: n = 10, second trimester: n = 10, third trimester: n = 10) and 10 healthy, nonpregnant control people stood quietly for one minute in four conditions: eyes open on a firm surface, eyes closed on a firm surface, eyes open on a foam pad, and eyes closed on foam. Postural sway was quantified using the root mean square accelerations in the anterior-posterior and medial-lateral directions from an inertial sensor at the lumbar region. Sensory sway ratios, segmental coherence and co-phase, were calculated to assess sensory contributions and segmental control, respectively. FINDINGS: Pregnant people did not display greater sway compared to healthy, nonpregnant controls. There were no group differences in vestibular, visual, or somatosensory sway ratios, and no significant differences in balance control strategies between pregnant and nonpregnant participants across sensory conditions. INTERPRETATION: The small effects observed here contrast prior studies and suggest larger, definitive studies are needed to assess the effect of pregnancy on postural control. This study serves as a preliminary exploration of pregnant sensory and segmental postural control and highlights the need for future to hone the role of balance in fall risk during pregnancy.

Transhumeral prosthesis use affects upper body kinematics and kinetics.

BACKGROUND: Transhumeral (TH) limb loss leads to loss of body mass and reduced shoulder range of motion. Despite most owning a prosthesis, prosthesis abandonment is common. The consequence of TH limb loss and prosthesis use and disuse during gait may be compensation in the upper body, contributing to back pain or injury. Understanding the impact of not wearing a TH prosthesis on upper body asymmetries and spatial-temporal aspects of gait will inform how TH prosthesis use and disuse affects the body. RESEARCH QUESTION: Does TH limb loss alter upper body asymmetries and spatial-temporal parameters during gait when wearing and not wearing a prosthesis compared to able-bodied controls? METHODS: Eight male TH limb loss participants and eight male control participants completed three gait trials at self-selected speeds. The TH limb loss group performed trials with and without their prosthesis. Arm swing, trunk angular displacement, trunk-pelvis moment, and spatial-temporal aspects were compared using non-parametric statistical analyses. RESULTS: Both TH walking conditions showed greater arm swing in the intact limb compared to the residual (p≤0.001), resulting in increased asymmetry compared to the control group (p≤0.001). Without the prosthesis, there was less trunk flexion and lateral flexion compared to the control group (p≤0.001). Maximum moments between the trunk and pelvis were higher in the TH group than the control group (p≤0.05). Spatial-temporal parameters of gait did not differ between the control group and either TH limb loss condition. SIGNIFICANCE: Prosthesis use affects upper body kinematics and kinetics, but does not significantly impact spatial-temporal aspects of gait, suggesting these are compensatory actions. Wearing a prosthesis helps achieve more normative upper body kinematics and kinetics than not wearing a prosthesis, which may help limit back pain. These findings emphasize the importance of encouraging at least passive use of prostheses for individuals with TH limb loss.

The effect of amplitude normalization technique, walking speed, and reporting metric on whole-body angular momentum and its interpretation during normal gait.

Whole-body angular momentum (WBAM) represents the cancellations of angular momenta that are produced during a reciprocal gait pattern. WBAM is sensitive to small changes and is used to compare dynamic gait patterns under different walking conditions. Study designs and the normalization techniques used to define WBAM vary and make comparisons between studies difficult. To address this problem, WBAM about each anatomical axis of rotation from a healthy control population during normal gait were investigated within four metrics: 1) range of WBAM, 2) integrated WBAM, 3) statistical parametric mapping (SPM), and 4) principal component analysis (PCA). These data were studied as a function of walking speed and normalization. Normalization techniques included: 1) no normalization, 2) normalization by height, body mass and walking speed, and 3) normalization by height, body mass and a scalar number, gravity×height, that is independent of walking velocity. Significant results were obtained as a function of walking speed regardless of normalization technique. However, the interpretation of significance within each metric was dependent on the normalization technique. Method 3 was the most robust technique as the differences were not altered from the expected relationships within the raw data. Method 2 actually inverted the expected relationship in WBAM amplitude as a function of walking speed, which skewed the results and their interpretation. Overall, SPM and PCA statistical methods provided better insights into differences that may be important. However, depending on the normalization technique used, caution is advised when interpreting significant findings when comparing participants with disparate walking speeds.

The Impact of Design Factors on User Behavior in a Virtual Hospital Room to Explore Fall Prevention Strategies.

OBJECTIVES: Falls in hospitals pose a significant safety risk, leading to injuries, prolonged hospitalization, and lasting complications. This study explores the potential of augmented reality (AR) technology in healthcare facility design to mitigate fall risk. BACKGROUND: Few studies have investigated the impact of hospital room layouts on falls due to the high cost of building physical prototypes. This study introduces an innovative approach using AR technology to advance methods for healthcare facility design efficiently. METHODS: Ten healthy participants enrolled in this study to examine different hospital room designs in AR. Factors of interest included room configuration, door type, exit side of the bed, toilet placement, and the presence of IV equipment. AR trackers captured trajectories of the body as participants navigated through these AR hospital layouts, providing insights into user behavior and preferences. RESULTS: Door type influenced the degree of backward and sideways movement, with the presence of an IV pole intensifying the interaction between door and room type, leading to increased sideways and backward motion. Participants displayed varying patterns of backward and sideways travel depending on the specific room configurations they encountered. CONCLUSIONS: AR can be an efficient and cost-effective method to modify room configurations to identify important design factors before conducting physical testing. The results of this study provide valuable insights into the effect of environmental factors on movement patterns in simulated hospital rooms. These results highlight the importance of considering environmental factors, such as the type of door and bathroom location, when designing healthcare facilities.

Extended physiological proprioception is affected by transhumeral Socket-Suspended prosthesis use.

The objective of this study was to define targeted reaching performance without visual information for transhumeral (TH) prosthesis users, establishing baseline information about extended physiological proprioception (EPP) in this population. Subjects completed a seated proprioceptive targeting task under simultaneous motion capture, using their prosthesis and intact limb. Eight male subjects, median age of 58 years (range 29-77 years), were selected from an ongoing screening study to participate. Five subjects had a left-side TH amputation, and three a right-side TH amputation. Median time since amputation was 9 years (range 3-54 years). Four subjects used a body-powered prosthetic hook, three a myoelectric hand, and one a myoelectric hook. The outcome measures were precision and accuracy, motion of the targeting hand, and joint angular displacement. Subjects demonstrated better precision when targeting with their intact limb compared to targeting with their prosthesis, 1.9 cm2 (0.8-3.0) v. 7.1 cm2 (1.3-12.8), respectively, p = 0.008. Subjects achieved a more direct reach path ratio when targeting with the intact limb compared to with the prosthesis, 1.2 (1.1-1.3) v. 1.3 (1.3-1.4), respectively, p = 0.039 The acceleration, deceleration, and corrective phase durations were consistent between conditions. Trunk angular displacement increased in flexion, lateral flexion, and axial rotation while shoulder flexion decreased when subjects targeted with their prosthesis compared to the intact limb. The differences in targeting precision, reach patio ratio, and joint angular displacements while completing the targeting task indicate diminished EPP. These findings establish baseline information about EPP in TH prosthesis users for comparison as novel prosthesis suspension systems become more available to be tested.

A simple, isotropic depolarized light source.

Unpolarized light can be an important tool in optical experiments. Producing it, however, can prove to be a challenge. Natural sources of light that are commonly thought of as unpolarized are, in fact, either weakly polarized or not practical sources of light in a laboratory setting. Standard, commercially available light depolarizers produce unpolarized light only after the polarization state of the light across the diameter of the output beam has been averaged. Locally, such beams are highly polarized. In this work, we report a simple, low cost light depolarizer capable of producing light with a total polarization of less than 1% for a 15-mm diameter output beam. Based upon diffuse scattering, the light transmitted through the depolarizer discussed here produces only small polarizations locally, with the total polarization for a 1.25-mm diameter area being <6%. The effects of the depolarizer on the transmitted beam's intensity are also reported.

Changes in frontal plane kinematics over 12-months in individuals with the Percutaneous Osseointegrated Prosthesis (POP).

BACKGROUND: A bone-anchored prosthesis (BAP) eliminates the need for a conventional socket by attaching a prosthesis directly to the user's skeleton. Currently, limited research addresses changes in gait mechanics post BAP implantation. OBJECTIVE: Examine changes in frontal plane movement patterns after BAP implantation. METHODS: Participants were individuals with unilateral transfemoral amputation (TFA) enrolled in the US Food and Drug Administration (FDA) Early Feasibility Study examining the Percutaneous Osseointegrated Prosthesis (POP). The participants completed overground gait assessments using their conventional socket and at 6-weeks, 12-weeks, 6-months, and 12-months following POP implantation. Statistical parameter mapping techniques were used in examining changes in frontal plane kinematics over the 12-months and differences with reference values for individuals without limb loss. RESULTS: Statistically significant deviations were found pre-implantation compared to reference values for hip and trunk angles during prosthetic limb stance phase, and for pelvis and trunk relative to the pelvis angles during prosthetic limb swing. At 6-weeks post-implantation, only the trunk angle demonstrated a statistically significant reduction in the percent of gait cycle with deviations relative to reference values. At 12-months post-implantation, results revealed frontal plane movements were no longer statistically different across the gait cycle for the trunk angle compared to reference values, and less of the gait cycle was statistically different compared to reference values for all other frontal plane patterns analyzed. No statistically significant within-participant differences were found for frontal plane movement patterns between pre-implantation and 6-weeks or 12-months post-implantation. CONCLUSIONS: Deviations from reference values displayed prior to device implantation were reduced or eliminated 12-months post-implantation in all frontal plane patterns analyzed, while within-participant changes over the 12-month period did not reach statistical significance. Overall, the results suggest the transition to a BAP aided in normalizing gait patterns in a sample of relatively high functioning individuals with TFA.

High and low performers in internal rotation after reverse total shoulder arthroplasty: a biplane fluoroscopic study.

BACKGROUND: Internal rotation in adduction is often limited after reverse total shoulder arthroplasty (rTSA), but the origins of this functional deficit are unclear. Few studies have directly compared individuals who can and cannot perform internal rotation in adduction. Little data on underlying 3D humerothoracic, scapulothoracic, and glenohumeral joint relationships in these patients are available. METHODS: Individuals >1-year postoperative to rTSA were imaged with biplane fluoroscopy in resting neutral and internal rotation in adduction poses. Subjects could either perform internal rotation in adduction with their hand at T12 or higher (high, N = 7), or below the hip pocket (low, N = 8). Demographics, the American Shoulder and Elbow Surgeons score, Simple Shoulder Test, and scapular notching grade were recorded. Joint orientation angles were derived from model-based markerless tracking of the scapula and humerus relative to the torso. The 3D implant models were aligned to preoperative computed tomography models to evaluate bone-implant impingement. RESULTS: The Simple Shoulder Test was highest in the high group (11 ± 1 vs. 9 ± 2, P = .019). Two subjects per group had scapular notching (grades 1 and 2), and 3 high group and 4 low group subjects had impingement below the glenoid. In the neutral pose, the scapula had 7° more upward rotation in the high group (P = .100), and the low group demonstrated 9° more posterior tilt (P = .017) and 14° more glenohumeral elevation (P = .047). In the internal rotation pose, axial rotation was >45° higher in the high group (P ≤ .008) and the low group again had 11° more glenohumeral elevation (P = .058). Large rotational differences within subject groups arose from a combination of differences in the resting neutral and maximum internal rotation in adduction poses, not only the terminal arm position. CONCLUSIONS: Individuals who were able to perform high internal rotation in adduction after rTSA demonstrated differences in joint orientation and anatomic biases versus patients with low internal rotation. The high rotation group had 7° more resting scapular upward rotation and used a 15°-30° change in scapular tilt to perform internal rotation in adduction versus patients in the low group. The combination of altered resting scapular posture and restricted scapulothoracic range of motion could prohibit glenohumeral rotation required to reach internal rotation in adduction. In addition, inter-patient variation in humeral torsion may contribute substantially to postoperative internal rotation differences. These data point toward modifiable implant design and placement factors, as well as foci for physical therapy to strengthen and mobilize the scapula and glenohumeral joint in response to rTSA surgery.

Intrinsic factors contributing to elevated intra-abdominal pressure.

Pelvic floor disorders affect 24% of US women, and elevated intra-abdominal pressure may cause pelvic injury through musculoskeletal strain. Activity restrictions meant to reduce pelvic strain after traumatic events, such as childbirth, have shown little benefit to patients. Reported high variability in abdominal pressure suggests that technique plays a substantial role in pressure generation. Understanding these techniques could inform evidence-based recommendations for protective pelvic care. We hypothesized use of a motion-capture methodology could identify four major contributors to elevated pressure: gravity, acceleration, abdominal muscle contraction, and respiration. Twelve women completed nineteen activities while instrumented for whole body motion capture, abdominal pressure, hip acceleration, and respiration volume. Correlation and partial least squares regression were utilized to determine primary technique factors that increase abdominal pressure. The partial least squares model identified two principal components that explained 59.63% of relative intra-abdominal pressure variability. The first component was primarily loaded by hip acceleration and relative respiration volume, and the second component was primarily loaded by flexion moments of the abdomen and thorax. While reducing abdominal muscle use has been a primary strategy in protective pelvic floor care, the influence of hip acceleration and breathing patterns should be considered with similar importance in future work.

Powered Hip Exoskeleton Reduces Residual Hip Effort Without Affecting Kinematics and Balance in Individuals With Above-Knee Amputations During Walking.

OBJECTIVE: A unilateral, lightweight powered hip exoskeleton has been shown to improve walking economy in individuals with above-knee amputations. However, the mechanism responsible for this improvement is unknown. In this study we assess the biomechanics of individuals with above-knee amputations walking with and without a unilateral, lightweight powered hip exoskeleton. We hypothesize that assisting the residual limb will reduce the net residual hip energy. METHODS: Eight individuals with above-knee amputations walked on a treadmill at 1 m/s with and without a unilateral powered hip exoskeleton. Flexion/extension assistance was provided to the residual hip. Motion capture and inverse dynamic analysis were performed to assess gait kinematics, kinetics, center of mass, and center of pressure. RESULTS: The net energy at the residual hip decreased from 0.05±0.04 J/kg without the exoskeleton to -0.01±0.05 J/kg with the exoskeleton (p = 0.026). The cumulative positive energy of the residual hip decreased on average by 18.2% with 95% confidence intervals (CI) (0.20 J/kg, 0.24 J/kg) and (0.16 J/kg, 0.20 J/kg) without and with the exoskeleton, respectively. During stance, the hip extension torque of the residual limb decreased on average by 37.5%, 95% CI (0.28 Nm/kg, 0.36 Nm/kg), (0.17 Nm/kg, 0.23 Nm/kg) without and with the exoskeleton, respectively. CONCLUSION: Powered hip exoskeleton assistance significantly reduced the net residual hip energy, with concentric energy being the main contributor to this change. We believe that the reduction in residual hip extension torque during early stance is the main contributor to this reduction. SIGNIFICANCE: This analysis shows that by assisting the residual hip, the exoskeleton significantly decreased the net hip energy produced by the residual limb, which may explain the improvements in walking economy previously observed.

Upper-extremity kinematics and interlimb movement correlation in persons with Parkinson Disease on irregular terrain, cross-slope, and under dual-task condition.

Background: A defining clinical characteristics of Parkinson disease is reduced upper-extremity movements. Irregular terrain, the presence of a cross slope, and dual-task conditions have been found to alter the lower-limb gait characteristics of persons with Parkinson disease but there is little information how different environmental and cognitive conditions impact upper-limb kinematics as well as interlimb movement correlation. Research question: Do environmental conditions, such as irregular terrain and the presence of cross slope, as well as dual-task condition impact the upper-extremity kinematics and interlimb movement correlation of persons with Parkinson disease compared to healthy, age-matched controls? Methods: Three-dimensional whole-body gait data were collected for nine participants with mild-to-moderate Parkinson disease and nine healthy age-matched control participants. All participants ambulated on a regular terrain, irregular terrain, with and without cross slope, and under dual and single-task conditions. The primary outcomes were arm swing magnitude, arm swing asymmetry, and normalized cross-correlation between the ipsilateral arms and contralateral legs, which characterized movement correlation. Results: For all conditions, persons with Parkinson disease exhibited reduced arm swing magnitude and greater arm swing asymmetry compared to the healthy controls. All participants increased their arm swing magnitude on the irregular surface and under the dual-task condition. In the healthy group, the arm swing asymmetry was invariant to terrain but declined under the dual-task condition while the persons with Parkinson disease exhibited increased asymmetry on the cross slope, on the irregular terrain, and under the dual-task condition. Interlimb movement correlation decreased on the irregular terrain for the persons with Parkinson disease while the healthy group exhibited decreased interlimb movement correlation on the cross slope as well as under the dual-task condition. Significance: Persons with Parkinson disease were able to increase their arm swing magnitude when their balance was challenged and the most significant threat to their safety as defined by the greatest reduction in the interlimb movement correlation was the irregular terrain.

Personalized practice dosages may improve motor learning in older adults compared to "standard of care" practice dosages: A randomized controlled trial.

Standard dosages of motor practice in clinical physical rehabilitation are insufficient to optimize motor learning, particularly for older patients who often learn at a slower rate than younger patients. Personalized practice dosing (i.e., practicing a task to or beyond one's plateau in performance) may provide a clinically feasible method for determining a dose of practice that is both standardized and individualized, and may improve motor learning. The purpose of this study was to investigate whether personalized practice dosages [practice to plateau (PtP) and overpractice (OVP)] improve retention and transfer of a motor task, compared to low dose [LD] practice that mimics standard clinical dosages. In this pilot randomized controlled trial (NCT02898701, ClinicalTrials.gov), community-dwelling older adults (n = 41, 25 female, mean age 68.9 years) with a range of balance ability performed a standing serial reaction time task in which they stepped to specific targets. Presented stimuli included random sequences and a blinded repeating sequence. Participants were randomly assigned to one of three groups: LD (n = 15, 6 practice trials equaling 144 steps), PtP (n = 14, practice until reaching an estimated personal plateau in performance), or OVP (n = 12, practice 100% more trials after reaching an estimated plateau in performance). Measures of task-specific learning (i.e., faster speed on retention tests) and transfer of learning were performed after 2-4 days of no practice. Learning of the random sequence was greater for the OVP group compared to the LD group (p = 0.020). The OVP (p = 0.004) and PtP (p = 0.010) groups learned the repeated sequence more than the LD group, although the number of practice trials across groups more strongly predicted learning (p = 0.020) than did group assignment (OVP vs. PtP, p = 0.270). No group effect was observed for transfer, although significant transfer was observed in this study as a whole (p < 0.001). Overall, high and personalized dosages of postural training were well-tolerated by older adults, suggesting that this approach is clinically feasible. Practicing well-beyond standard dosages also improved motor learning. Further research should determine the clinical benefit of this personalized approach, and if one of the personalized approaches (PtP vs. OVP) is more beneficial than the other for older patients.

Regulation of whole-body and segmental angular momentum in persons with Parkinson's disease on an irregular surface.

BACKGROUND: Persons with Parkinson's disease have impaired motor control that increases their chance of falling when walking, especially on difficult terrains. This study investigated how persons with Parkinson's disease regulate their dynamic balance on a regular and an irregular surface. METHODS: Nine participants with Parkinson's disease and nine healthy, age-matched control participants ambulated on both a regular and an irregular surface. Whole-body and segmental angular momenta were calculated using three-dimensional motion capture data. Major modes of variability between health groups on the two surfaces were investigated using principal component analysis, while differences within each health group between surfaces was investigated using statistical parametric mapping t-tests. FINDINGS: Between groups, the Parkinson participants had greater sagittal, frontal, and transverse whole-body angular momentum on both surfaces, primarily following heel-strike, and the magnitude difference on the irregular surface was greater than on the regular surface. The greatest between group segmental differences on the irregular compared to the regular surface were the legs in the sagittal plane and the head/trunk/pelvis in the transverse plane, with the Parkinson group having greater magnitudes. The within-group comparison found the Parkinson participants had poorer regulation of whole-body angular momentum in the sagittal plane, while the healthy participants showed no consistent differences between surfaces. INTERPRETATION: On an irregular surface, persons with Parkinson's disease exhibit poor control of dynamic balance in the frontal and sagittal planes. These results emphasize the need for weight transfer techniques and training in both the sagittal and frontal planes to maximize balance and reduce fall risk.

Knee Exoskeleton Reduces Muscle Effort and Improves Balance During Sit-to-Stand Transitions After Stroke: A Case Study.

After a stroke, the weight-bearing asymmetry often forces stroke survivors to compensate with overuse of the unaffected side muscles to stand up. Powered exoskeletons can address this problem by assisting the affected limb during sit-tostand transitions. However, there is currently no experimental evidence demonstrating the efficacy of this intervention with the target population. This study explores controlling a powered knee exoskeleton with EMG signals to assist a stroke patient during sit-to-stand transitions. Our results show decreased peak knee torques by 6.24% and 11.9% on their unaffected and affected sides, respectively, while wearing the exoskeleton. Additionally, the peak value of the EMG signal decreased by 29.3% and 21.9%, and the integrated EMG signal value decreased by 46.7% and 36.1% on their affected vastus medialis and lateralis while wearing the exoskeleton, respectively. Finally, our results indicate improved medial-lateral balance by 61.2%, 81.6%, and 70.0% based on the degree of asymmetry (DOA), the center of pressure (COP), and the center of mass (COM), respectively. These results support the efficacy of using powered exoskeletons for high-torque tasks such as sit-to-stand transitions with stroke survivors.

Reverse Total Shoulder Arthroplasty Alters Humerothoracic, Scapulothoracic, and Glenohumeral Motion During Weighted Scaption.

BACKGROUND: Reverse total shoulder arthroplasty (rTSA) typically restores active arm elevation. Prior studies in patients with rTSA during tasks that load the arm had limitations that obscured underlying three-dimensional (3D) kinematic changes and the origins of motion restrictions. Understanding the scapulothoracic and glenohumeral contributions to loaded arm elevation will uncover where functional deficits arise and inform strategies to improve rTSA outcomes. QUESTIONS/PURPOSES: In a cohort of patients who had undergone rTSA and a control cohort, we asked: (1) Is there a difference in maximum humerothoracic elevation when scapular plane elevation (scaption) is performed with and without a handheld weight? (2) Is maximum humerothoracic elevation related to factors like demographics, patient-reported outcome scores, isometric strength, and scapular notching (in the rTSA group only)? (3) Are there differences in underlying 3D scapulothoracic and glenohumeral motion during scaption with and without a handheld weight? METHODS: Ten participants who underwent rTSA (six males, four females; age 73 ± 8 years) were recruited at follow-up visits if they were more than 1 year postoperative (24 ± 11 months), had a BMI less than 35 kg/m 2 (29 ± 4 kg/m 2 ), had a preoperative CT scan, and could perform pain-free scaption. Data from 10 participants with a nonpathologic shoulder, collected previously (five males, five females; age 58 ± 7 years; BMI 26 ± 3 kg/m 2 ), were a control group with the same high-resolution quantitative metrics available for comparison. Participants in both groups performed scaption with and without a 2.2-kg handheld weight while being imaged with biplane fluoroscopy. Maximum humerothoracic elevation and 3D scapulothoracic and glenohumeral kinematics across their achievable ROM were collected via dynamic imaging. In the same session the American Shoulder and Elbow Surgeons (ASES) score, the Simple Shoulder Test (SST), and isometric strength were collected. Data were compared between weighted and unweighted scaption using paired t-tests and linear mixed-effects models. RESULTS: When compared with unweighted scaption, maximum humerothoracic elevation decreased during weighted scaption for patients who underwent rTSA (-25° ± 30°; p = 0.03) but not for the control group (-2° ± 5°; p = 0.35). In the rTSA group, maximum elevation correlated with the ASES score (r = 0.72; p = 0.02), and weighted scaption correlated with BMI (r = 0.72; p = 0.02) and the SST (r = 0.76; p = 0.01). Scapular notching was observed in three patients after rTSA (Grades 1 and 2). Four of 10 patients who underwent rTSA performed weighted scaption to less than 90° humerothoracic elevation using almost exclusively scapulothoracic motion, with little glenohumeral contribution. This manifested as changes in the estimated coefficient representing mean differences in slopes in the humerothoracic plane of elevation (-12° ± 2°; p < 0.001) and true axial rotation (-16° ± 2°; p < 0.001), scapulothoracic upward rotation (7° ± 1°; p < 0.001), and glenohumeral elevation (-12° ± 1°; p < 0.001), plane of elevation (-8° ± 3°; p = 0.002), and true axial rotation (-11° ± 2°; p < 0.001). The control group demonstrated small differences between scaption activities (< |2°|), but a 10° increase in humerothoracic and glenohumeral axial rotation (both p < 0.001). CONCLUSION: After rTSA surgery, maximum humerothoracic elevation decreased during weighted scaption by up to 88° compared with unweighted scaption, whereas 4 of 10 patients could not achieve more than 90° of elevation. These patients exhibited appreciable changes in nearly all scapulothoracic and glenohumeral degrees of freedom, most notably a near absence of glenohumeral elevation during weighted scaption. Patients with rTSA have unique strategies to elevate their arms, often with decreased glenohumeral motion and resultant compensation in scapulothoracic motion. In contrast, the control group showed few differences when lifting a handheld weight. CLINICAL RELEVANCE: Functional deficiency in activities that load the shoulder after rTSA surgery can affect patient independence, and they may be prevalent but not captured in clinical studies. Pre- or postoperative rehabilitation to strengthen scapular stabilizers and the deltoid should be evaluated against postoperative shoulder function. Further study is required to determine the etiology of deficient glenohumeral motion after rTSA, and the most effective surgical and/or rehabilitative strategies to restore deficient glenohumeral motion after rTSA.

The impact of ankle-foot orthosis's plantarflexion resistance on knee adduction moment in people with chronic stroke.

BACKGROUND: An ankle-foot orthosis (AFO) is used to assist gait of people with chronic stroke. It is widely accepted that AFO's plantarflexion resistance affects sagittal knee moments during their gait. However, its effect on the coronal knee moment remains unclear. This study aimed to examine the effects of varying articulated AFO's plantarflexion resistance on knee adduction moment in people with chronic stroke. METHODS: Ten people with chronic stroke participated in this study. Gait performance was measured using a Vicon 3-dimensional motion capture system and a Bertec split-belt instrumented treadmill. The participants walked on the treadmill wearing an articulated AFO whose plantarflexion resistance could be systematically adjusted. The ankle joints were set to four distinct levels of plantarflexion resistance (S1 < S2 < S3 < S4). The coronal ankle and knee joint moment, center of pressure, and ground reaction force were analyzed using Visual3D. RESULTS: The external knee adduction moment increased significantly ( P < .001) and the position of the center of pressure trajectory shifted significantly ( P = .003) in the medial direction as the plantarflexion resistance of the AFO was increased from the least resistive condition (S1) to the most resistive condition (S4). The maximum knee adduction moment (median [interquartile range]) was S1: 0.097 (-0.012 to 0.265) Nm/kg; S2: 0.136 (0.040 to 0.287) Nm/kg; S3: 0.160 (0.465 to 0.289) Nm/kg; and S4: 0.192 (0.080 to 0.288) Nm/kg. CONCLUSIONS: This study demonstrated that varying AFO's plantarflexion resistance altered the knee adduction moment, likely by altering the center of pressure trajectory while walking, in people with chronic stroke.

Kinematic coupling of the glenohumeral and scapulothoracic joints generates humeral axial rotation.

Glenohumeral and scapulothoracic motion combine to generate humerothoracic motion, but their discrete contributions towards humerothoracic axial rotation have not been investigated. Understanding their contributions to axial rotation is important to judge the effects of pathology, surgical intervention, and physiotherapy. Therefore, the purpose of this study was to investigate the kinematic coupling between glenohumeral and scapulothoracic motion and determine their relative contributions towards axial rotation. Twenty healthy subjects (10 M/10F, ages 22-66) were previously recorded using biplane fluoroscopy while performing arm elevation in the coronal, scapular, and sagittal planes, and external rotation in 0° and 90° of abduction. Glenohumeral and scapulothoracic contributions towards axial rotation were computed by integrating the projection of glenohumeral and scapulothoracic angular velocity onto the humeral longitudinal axis, and analyzed using one dimensional statistical parametric mapping and linear regression. During arm elevation, scapulothoracic motion supplied 13-20° (76-94%) of axial rotation, mainly via scapulothoracic upward rotation. The contribution of scapulothoracic motion towards axial rotation was strongly correlated with glenohumeral plane of elevation during arm elevation. During external rotation, scapulothoracic motion contributed 10° (8%) towards axial rotation in 0° of abduction and 15° (15%) in 90° of abduction. The contribution of scapulothoracic motion towards humerothoracic axial rotation could explain the simultaneous changes in glenohumeral plane of elevation and axial rotation associated with some pathologies and surgeries. Understanding how humerothoracic motion results from the functional coupling of scapulothoracic and glenohumeral motions may inform diagnostic and treatment strategies by targeting the source of movement impairments in clinical populations.

Total Ankle Replacement Provides Symmetrical Postoperative Kinematics: A Biplane Fluoroscopy Imaging Study.

BACKGROUND: In vivo measurements of tibiotalar and subtalar joint motion following TAR are unavailable. Using biplane fluoroscopy, we tested the hypothesis that the prosthetic tibiotalar joint and adjacent subtalar joint would demonstrate kinematic and range of motion differences compared to the contralateral untreated limb, and control participants. METHODS: Six patients of 41 identified candidates that all underwent unilateral Zimmer TAR (5.4 ± 1.9 years prior) and 6 control participants were imaged with biplane fluoroscopy during overground walking and a double heel-rise activity. Computed tomography scans were acquired; images were segmented and processed to serve as input for model-based tracking of the biplane fluoroscopy data. Measurements included tibiotalar and subtalar kinematics for the TAR, untreated contralateral, and control limbs. Statistical parametric mapping quantified differences in kinematics throughout overground walking and the double heel-rise activity. RESULTS: Patients with this TAR performed walking and heel-rise activities symmetrically with no significant kinematic differences at the tibiotalar and subtalar joints between limbs. Compared to control participants, patients exhibited reduced dorsi/plantarflexion range of motion that corresponded to decreased peak dorsiflexion, but only in the late stance phase of walking. This reduction in tibiotalar dorsi/plantarflexion range of motion in the TAR group became more apparent with double heel-rise activity. CONCLUSION: Patients with a Zimmer TAR had symmetric kinematics during activities of walking and double heel-rise, but they did exhibit minor compensations in tibiotalar kinematics as compared to controls. CLINICAL RELEVANCE: The lack of significant kinematic compensation at the subtalar joint may explain why secondary subtalar osteoarthritis is reported as being relatively uncommon in patients with some TAR designs.

Investigating the effects of flexor tendon shortening on active range of motion after finger tendon repair.

Evaluation of surgical effects is often done using simple cadaver experimentation. This study uses a robotic testbed to estimate the best-case clinical outcomes of flexor tendon shortening during repair surgery on cadaver hands. Nine fresh-frozen cadaver subjects were connected to an extrinsic index finger robotic muscle testbed and measurement system. The flexor digitorum profundus tendons were severed and surgically repaired at different shortening levels. The index finger's extrinsic tendons were robotically actuated using Hill-type muscle models to emulate the muscle force-length relationships. Extensor muscles were then activated to estimate the active range of motion (ROM) of the all-finger joints after surgery. The effects of metacarpophalangeal (MCP) joint extension limits and extensor muscle activation were also investigated. The resulting interphalangeal joint ROM was clinically graded. Active ROM of the finger decreases as tendon shortening increases ( ηp2=0.92 ), like passive ROM. This results in a clinical reduction of functionality grade from excellent to good at 10 mm of shortening. Blocking MCP joint ROM and extensor activation also showed significant effects on recovered ROM ( ηp2=0.72 and 0.86). Significant two-way interactions were also observed between shortening and MCP joint blocking ( ηp2=0.80 ) and between shortening and extensor activation ( ηp2=0.78 ). Results support clinical recommendations of limiting shortening to 10 mm. While this article provides additional experimental evidence for current surgical recommendations, it also validates a new robotic-cadaver methodology for predicting active hand recovery in terms of clinical measurements.

Robust Torque Predictions From Electromyography Across Multiple Levels of Active Exoskeleton Assistance Despite Non-linear Reorganization of Locomotor Output.

Robotic exoskeletons can assist humans with walking by providing supplemental torque in proportion to the user's joint torque. Electromyographic (EMG) control algorithms can estimate a user's joint torque directly using real-time EMG recordings from the muscles that generate the torque. However, EMG signals change as a result of supplemental torque from an exoskeleton, resulting in unreliable estimates of the user's joint torque during active exoskeleton assistance. Here, we present an EMG control framework for robotic exoskeletons that provides consistent joint torque predictions across varying levels of assistance. Experiments with three healthy human participants showed that using diverse training data (from different levels of assistance) enables robust torque predictions, and that a convolutional neural network (CNN), but not a Kalman filter (KF), can capture the non-linear transformations in EMG due to exoskeleton assistance. With diverse training, the CNN could reliably predict joint torque from EMG during zero, low, medium, and high levels of exoskeleton assistance [root mean squared error (RMSE) below 0.096 N-m/kg]. In contrast, without diverse training, RMSE of the CNN ranged from 0.106 to 0.144 N-m/kg. RMSE of the KF ranged from 0.137 to 0.182 N-m/kg without diverse training, and did not improve with diverse training. When participant time is limited, training data should emphasize the highest levels of assistance first and utilize at least 35 full gait cycles for the CNN. The results presented here constitute an important step toward adaptive and robust human augmentation via robotic exoskeletons. This work also highlights the non-linear reorganization of locomotor output when using assistive exoskeletons; significant reductions in EMG activity were observed for the soleus and gastrocnemius, and a significant increase in EMG activity was observed for the erector spinae. Control algorithms that can accommodate spatiotemporal changes in muscle activity have broad implications for exoskeleton-based assistance and rehabilitation following neuromuscular injury.