Goal: This paper presents an algorithm for accurately estimating pelvis, thigh, and shank kinematics during walking using only three wearable inertial sensors. Methods: The algorithm makes novel use of a constrained Kalman filter (CKF). The algorithm iterates through the prediction (kinematic equation), measurement (pelvis position pseudo-measurements, zero velocity update, flat-floor assumption, and covariance limiter), and constraint update (formulation of hinged knee joints and ball-and-socket hip joints). Results: Evaluation of the algorithm using an optical motion capture-based sensor-to-segment calibration on nine participants (7 men and 2 women, weight 63.0 6.8 kg, height 1.70 0.06 m, age 24.6 3.9 years old), with no known gait or lower body biomechanical abnormalities, who walked within a $4 \times 4 m^2$ capture area shows that it can track motion relative to the mid-pelvis origin with mean position and orientation (no bias) root-mean-square error (RMSE) of 5.21 1.3 cm and 16.1 3.2, respectively. The sagittal knee and hip joint angle RMSEs (no bias) were 10.0 2.9 and 9.9 3.2, respectively, while the corresponding correlation coefficient (CC) values were 0.87 0.08 and 0.74 0.12. Conclusion: The CKF-based algorithm was able to track the 3D pose of the pelvis, thigh, and shanks using only three inertial sensors worn on the pelvis and shanks. Significance: Due to the Kalman-filter-based algorithm's low computation cost and the relative convenience of using only three wearable sensors, gait parameters can be computed in real-time and remotely for long-term gait monitoring. Furthermore, the system can be used to inform real-time gait assistive devices.

We used body-worn inertial sensors to quantify differences in semi-free-living gait between stairs and on normal flat ground in older adults, and investigated the utility of assessing gait on these terrains for predicting the occurrence of multiple falls. Eighty-two community-dwelling older adults wore two inertial sensors, on the lower back and the right ankle, during several bouts of walking on flat surfaces and up and down stairs, in between rests and activities of daily living. Derived from the vertical acceleration at the lower back, step rate was calculated from the signal's fundamental frequency. Step rate variability was the width of this fundamental frequency peak from the signal's power spectral density. Movement vigor was calculated at both body locations from the signal variance. Partial Spearman correlations between gait parameters and physiological fall risk factors (components from the Physiological Profile Assessment) were calculated while controlling for age and gender. Overall, anteroposterior vigor at the lower back in stair descent was lower in subjects with longer reaction times. Older adults walked more slowly on stairs, but they were not significantly slower on flat surfaces. Using logistic regression, faster step rate in stair descent was associated with multiple prospective falls over 12 months. No significant associations were shown from gait parameters derived during walking upstairs or on flat surfaces. These results suggest that stair descent gait may provide more insight into fall risk than regular walking and stair ascent, and that further sensor-based investigation into unsupervised gait on different terrains would be valuable.

Background: Patient satisfaction is an important measurement in healthcare for administrators, clinicians and patients. Objectives: This study investigated the role of gait deviation in patient satisfaction following lower-limb amputation and prosthesis prescription. Study design: A cross-sectional study was done. Methods: Twenty community-based unilateral lower-limb amputees, 12 transtibial and 8 transfemoral, were recruited from support groups. Participants completed the prosthesis evaluation questionnaire (PEQ) with embedded satisfaction-related questions, the timed-up-and-go test and the six-minute walk test, and also underwent quantitative three-dimensional analysis. Kinematic deviation was summarized using the gait profile score (GPS). Results: Satisfaction levels were generally high (median 80 + /100). Sociodemographic variables did not correlate significantly with any of the satisfaction measures (−0.35 ≤ r ≤ 0.54). Satisfaction correlated strongly with the PEQ scales, particularly ambulation, prosthetic utility, frustration, perceived response and social burden (r ≥ 0.70). By contrast, the relationships between satisfaction and performance-based outcome measures were not significant (−0.45 ≤ r ≤ 0.43), and the GPS did not correlate with any satisfaction measures (−0.23 ≤ r ≤ 0.15). Conclusions: In this study of high functioning amputees, gait deviation was unimportant to the amputee, while self-reported functional ability and attitudes toward the prosthesis were the strongest correlates of satisfaction following lower-limb amputation. Clinical relevance For the high functioning individuals with lower-limb amputation in this study, gait deviation was not a significant correlate of patient satisfaction. Results suggest that improving self-perceived functional ability and attitudes toward the prosthesis, rather than minimizing gait deviation, will improve patient satisfaction.

The suitability of finite element analysis (FEA) for standardizing the mechanical characterization of energy storage and return (ESAR) prostheses was investigated. A methodology consisting of both experimental and numerical analysis was proposed and trialed for the Vari-flex^® Modular^TM, Flex-foot Cheetah and Cheetah Xtreme by Össur^® and a 1E90 Sprinter by Ottobock^®. Gait analysis was conducted to determine suitable orientation angles for non-destructive testing (NDT) of the ESAR prostheses followed by a quasi-static inverse FEA procedure within COMSOL Multiphysics^®, where the NDT conditions were replicated to determine the homogenized material properties of the prostheses. The prostheses' loading response under bodyweight for an 80kg person was then simulated, using both Eigenfrequency and time-dependent analysis. The apparent stiffness under bodyweight was determined to be 94.7, 48.6, 57.4 and 65.0Nmm^-1 for the Vari-flex^® Modular^TM, Flex-foot Cheetah, Cheetah Xtreme and 1E90 Sprinter, respectively. Both the energy stored and returned by the prostheses varied negatively with stiffness, yet the overall efficiency of the prostheses were similar, at 52.7, 52.0, 51.7 and 52.4% for the abovementioned prostheses. The proposed methodology allows the standardized assessment and comparison of ESAR prostheses without the confounding influences of subject-specific gait characteristics.

The prediction of conditions that may result in thrombus formation is a useful application of computational fluid dynamics. A number of techniques exist, based on the consideration of wall shear stress and regions of low blood flow; however, no clear guideline exists for the best practice of their use. In this paper, the sensitivity of each parameter and the specific mechanical forces are explained, before the optimal indicator of thrombosis risk is outlined. An extracorporeal access device cavity provides a suitable geometry to test the methodology. The recommended method for thrombus prediction considers areas with a calculated residence time (RT) and shear strain rate (SSR) thresholds, here set to RT>1 and SSR < 10 s(- 1). Evidence of thrombosis was found for physiological waveforms with an absence of reverse flow, which is expected to 'wash out' the cavity. The predicted thrombosis sites compare well with evidence collected from explanted devices.