Design and preliminary evaluation of a multi-robotic system with pelvic and hip assistance for pediatric gait rehabilitation.

This paper presents a modular, computationally-distributed "multi-robot" cyberphysical system designed to assist children with developmental delays in learning to walk. The system consists of two modules, each assisting a different aspect of gait: a tethered cable pelvic module with up to 6 degrees of freedom (DOF), which can modulate the motion of the pelvis in three dimensions, and a two DOF wearable hip module assisting lower limb motion, specifically hip flexion. Both modules are designed to be lightweight and minimally restrictive to the user, and the modules can operate independently or in cooperation with each other, allowing flexible system configuration to provide highly customized and adaptable assistance. Motion tracking performance of approximately 2 mm root mean square (RMS) error for the pelvic module and less than 0.1 mm RMS error for the hip module was achieved. We demonstrate coordinated operation of the two modules on a mannequin test platform with articulated and instrumented lower limbs.

Three-dimensional kinematics of the equine metacarpophalangeal joint using x-ray reconstruction of moving morphology - a pilot study.

X-ray reconstruction of moving morphology (XROMM) uses biplanar videoradiography and computed tomography (CT) scanning to capture three-dimensional (3D) bone motion. In XROMM, morphologically accurate 3D bone models derived from CT are animated with motion from videoradiography, yielding a highly accurate and precise reconstruction of skeletal kinematics. We employ this motion analysis technique to characterize metacarpophalangeal joint (MCPJ) motion in the absence and presence of protective legwear in a healthy pony. Our in vivo marker tracking precision was 0.09 mm for walk and trot, and 0.10 mm during jump down exercises. We report MCPJ maximum extension (walk: -27.70 ± 2.78° [standard deviation]; trot: -33.84 ± 4.94°), abduction/adduction (walk: 0.04 ± 0.24°; trot: -0.23 ± 0.35°) and external/internal rotations (walk: 0.30 ± 0.32°; trot: -0.49 ± 1.05°) indicating that the MCPJ in this pony is a stable hinge joint with negligible extra-sagittal rotations. No substantial change in MCPJ maximum extension angles or vertical ground reaction forces (GRFv) were observed upon application of legwear during jump down exercise. Neoprene boot application yielded -65.20 ± 2.06° extension (GRFv = 11.97 ± 0.67 N/kg) and fleece polo wrap application yielded -64.23 ± 1.68° extension (GRFv = 11.36 ± 1.66 N/kg), when compared to naked control (-66.11 ± 0.96°; GRFv = 12.02 ± 0.53 N/kg). Collectively, this proof of concept study illustrates the benefits and practical limitations of using XROMM to document equine MCPJ kinematics in the presence and absence of legwear.

A pediatric animal model to evaluate the effects of disuse on musculoskeletal growth and development.

Prolonged immobilization in hospitalized children can lead to fragility fractures and muscle contractures and atrophy. The purpose of this study was to develop a lower-extremity disuse rabbit model with musculoskeletal changes similar to those observed in children subjected to prolonged immobilization. Six-week-old rabbits were randomly assigned to control (CTRL, n=4) or bilateral sciatic and femoral neurectomy (bSFN, n=4) groups. Trans-axial helical CT scans of each rabbit׳s hind limbs were acquired after eight weeks. The rabbits were then euthanized and the tibiae and calcanea were harvested from each rabbit. µCT imaging was performed on the tibiae and calcanea mid-diaphysis. Four-point bending, gas pycnometry, and ashing were then performed on each tibia. All comparisons reflect the differences between the bSFN and CTRL rabbits. Significant decreases in tibiae bone mineral density (≥9.41%, p≤0.006), axial rigidity (≥50.47%, p≤0.02), and soft tissue mass (55.25%, p=0.006) were observed from the trans-axial helical CT scans. The µCT results indicated significant detriments in tibia and calcaneus cortical thickness and bone volume fraction (p≤0.011). Significant changes in stiffness, yield load, ultimate load, and ultimate displacement (≥30.05%, p≤0.025) were observed from mechanical testing. These data indicate that limb disuse at a time of rapid musculoskeletal growth severely impairs muscle and bone development, reflecting the musculoskeletal complications observed in children with chronic medical conditions causing immobilization. Interventions to reduce these musculoskeletal complications in children are urgently needed. This disuse rabbit model will be useful in pre-clinical studies evaluating novel interventions for improving pediatric musculoskeletal health.

Toddlers actively reorganize their whole body coordination to maintain walking stability while carrying an object.

Balanced walking involves freely swinging the limbs like pendula. However, children immediately begin to carry objects as soon as they can walk. One possibility for this early skill development is that whole body coordination during walking may be re-organized into loosely coupled collections of body parts, allowing children to use their arms to perform one function, while the legs perform another. Therefore, this study examines: 1) how carrying an object affects the coordination of the arms and legs during walking, and 2) if carrying an object influences stride length and width. Ten healthy toddlers with 3-12 months of walking experience were recruited to walk barefoot while carrying or not carrying a small toy. Stride length, width, speed, and continuous relative phase (CRP) of the hips and of the shoulders were compared between carrying conditions. While both arms and legs demonstrated destabilization and stabilization throughout the gait cycle, the arms showed a reduction in intra-subject coordination variability in response to carrying an object. Carrying an object may modify the function of the arms from swinging for balance to maintaining hold of an object. The observed period-dependent changes of the inter-limb coordination of the hips and of the shoulders also support this interpretation. Overall, these findings support the view that whole-body coordination patterns may become partitioned in particular ways as a function of task requirements.

Sensory enhancing insoles improve athletic performance during a hexagonal agility task.

Athletes incorporate afferent signals from the mechanoreceptors of their plantar feet to provide information about posture, stability, and joint position. Sub-threshold stochastic resonance (SR) sensory enhancing insoles have been shown to improve balance and proprioception in young and elderly participant populations. Balance and proprioception are correlated with improved athletic performance, such as agility. Agility is defined as the ability to quickly change direction. An athlete's agility is commonly evaluated during athletic performance testing to assess their ability to participate in a competitive sporting event. Therefore, the purpose of this study was to examine the effects of SR insoles during a hexagonal agility task routinely used by coaches and sports scientists. Twenty recreational athletes were recruited to participate in this study. Each athlete was asked to perform a set of hexagonal agility trials while SR stimulation was either on or off. Vicon motion capture was used to measure feet position during six successful trials for each stimulation condition. Stimulation condition was randomized in a pairwise fashion. The study outcome measures were the task completion time and the positional accuracy of footfalls. Pairwise comparisons revealed a 0.12s decrease in task completion time (p=0.02) with no change in hopping accuracy (p=0.99) when SR stimulation was on. This is the first study to show athletic performance benefits while wearing proprioception and balance improving equipment on healthy participants. With further development, a self-contained sensory enhancing insole device could be used by recreational and professional athletes to improve movements that require rapid changes in direction.

Sensory Enhancing Insoles Modify Gait during Inclined Treadmill Walking with Load.

INTRODUCTION: Inclined walking while carrying a loaded backpack induces fatigue, which may destabilize gait and lead to injury. Stochastic resonance (SR) technology has been used to stabilize spatiotemporal gait characteristics of elderly individuals but has not been tested on healthy recreational athletes. Herein, we determined if sustained vigorous walking on an inclined surface while carrying a load destabilizes gait and if SR has a further effect. METHODS: Participants were fitted with a backpack weighing 30% of their body weight and asked to walk at a constant self-selected pace while their feet were tracked using an optical motion capture system. Their shoes were fitted with SR insoles that were set at 90% of the participant's sensory threshold. The treadmill incline was increased every 5 min until volitional exhaustion after which the treadmill was returned to a level grade. SR stimulation was turned ON and OFF in a pairwise random fashion throughout the protocol. Spatiotemporal gait characteristics were calculated when SR was ON and OFF for the BASELINE period, the MAX perceived exertion period, and the POST period. RESULTS: Vigorous activity increases variability in the rhythmic stepping (stride time and stride length) and balance control (double support time and stride width) mechanisms of gait. Overall, SR increased stride width variability by 9% before, during, and after a fatiguing exercise. CONCLUSION: The increased stride time and stride length variability may compromise the stability of gait during and after vigorous walking. However, participants may compensate by increasing double support time and stride width variability to maintain their stability under these adverse conditions. Furthermore, applying SR resulted in an additional increase of stride width variability and may potentially improve balance before, during, and after adverse walking conditions.

Effects of ACL reconstruction surgery on muscle activity of the lower limb during a jump-cut maneuver in males and females.

We compared muscle activity of the quadriceps, hamstring, and gastrocnemius muscles when ACL-intact (ACL(INT)) and ACL-reconstructed (ACL(REC)) male and female subjects performed a jump-cut task. Surface electromyography sensors were used to evaluate time to peak muscle activity and muscle activity ratios. Rectus femoris (RF) and vastus medialis (VM) peak timing was 71 and 78 ms earlier in ACL(INT) than in ACL(REC) subjects, respectively. Biceps femoris (BF) peak timing was 90 ms earlier in ACL(INT) than in ACL(REC) subjects and 75 ms earlier in females than in males. Medial gastrocnemius (MG) muscle peak timing was 77 ms earlier in ACL(INT) than in ACL(REC) subjects. Lateral gastrocnemius (LG) and MG muscle peak times were 106 ms and 87 ms earlier in females than in males, respectively. The RF, VM, BF, and MG peaked later in ACL(REC) than in ACL(INT) subjects. There was evidence suggesting that the loading phase quadriceps:hamstring (quad:ham) muscle activity ratio was greater in ACL(REC) than in ACL(INT) subjects. Finally, the injury risk phase quad:ham muscle activity ratio was 4.8 times greater in females than in males. In conclusion, differences exist in muscle activity related to ACL status and sex that could potentially help explain graft failure risk and the sex bias.

Automatic determination of an anatomical coordinate system for a three-dimensional model of the human patella.

Measuring the in vivo 3-D kinematics of the patella requires a repeatable anatomical coordinate system (ACS). The purpose of this study was to develop an algorithm to determine an ACS using the patella's unique morphology. An ACS was automatically constructed that aligned the proximal/distal (PD) axis with the posterior vertical ridge. Inter-subject ACS repeatability was determined by registering all patellae and their associated ACSs to a reference patella. The mean angle between the reference patella ACS and each subject's axes was less than 2.5° and the 95% CI was 1.0°-4.0°. Here, we presented an anatomical coordinate system that is independent of the observer's subjective judgement or orientation of the knee within the scanner.

In Situ, noninvasive, T2*-weighted MRI-derived parameters predict ex vivo structural properties of an anterior cruciate ligament reconstruction or bioenhanced primary repair in a porcine model.

BACKGROUND: Magnetic resonance imaging (MRI) is a noninvasive technology that can quantitatively assess anterior cruciate ligament (ACL) graft size and signal intensity. However, how those properties relate to reconstructed or repaired ligament strength during the healing process is yet unknown. HYPOTHESIS: Magnetic resonance imaging-derived measures of graft volume and signal intensity are significant predictors of the structural properties of an ACL or ACL graft after 15 weeks and 52 weeks of healing. STUDY DESIGN: Controlled laboratory study. METHODS: The current data were gathered from 2 experiments evaluating ACL reconstruction and repair techniques. In the first experiment, pigs underwent unilateral ACL transection and received (1) ACL reconstruction, (2) ACL reconstruction with collagen-platelet composite (CPC), or (3) no treatment. The surgical legs were harvested after 15 weeks of healing. In the second experiment, pigs underwent ACL transection and received (1) ACL reconstruction, (2) ACL reconstruction with CPC, (3) bioenhanced ACL primary repair with CPC, or (4) no treatment. The surgical legs were harvested after 52 weeks. The harvested knees were imaged using a T2*-weighted 3-dimensional constructive interference in steady state (CISS) sequence. Each ligament was segmented from the scans, and the intra-articular volume and the median grayscale values were determined. Mechanical testing was performed to establish the ligament structural properties. RESULTS: Volume significantly predicted the structural properties (maximum load, yield load, and linear stiffness) of the ligaments and grafts (R (2) = 0.56, 0.56, and 0.49, respectively; P ≤ .001). Likewise, the median grayscale values (ie, signal intensity) significantly predicted the structural properties of the ligaments and grafts (R (2) = 0.42, 0.37, and 0.40, respectively; P < .001). The combination of these 2 parameters in a multiple regression model improved the predictions (R (2) = 0.73, 0.72, and 0.68, respectively; P ≤ .001). CONCLUSION: Volume and grayscale values from high-resolution T2*-weighted MRI scans are predictive of structural properties of the healing ligament or graft in a porcine model. CLINICAL RELEVANCE: This study provides a critical step in the development of a noninvasive method to predict the structural properties of the healing ACL graft or repair. This technique may prove beneficial as a surrogate outcome measure in preclinical animal and clinical studies.

Kinematic differences between optical motion capture and biplanar videoradiography during a jump-cut maneuver.

Jumping and cutting activities are investigated in many laboratories attempting to better understand the biomechanics associated with non-contact ACL injury. Optical motion capture is widely used; however, it is subject to soft tissue artifact (STA). Biplanar videoradiography offers a unique approach to collecting skeletal motion without STA. The goal of this study was to compare how STA affects the six-degrees-of-freedom motion of the femur and tibia during a jump-cut maneuver associated with non-contact ACL injury. Ten volunteers performed a jump-cut maneuver while their landing leg was imaged using optical motion capture (OMC) and biplanar videoradiography. The within-bone motion differences were compared using anatomical coordinate systems for the femur and tibia, respectively. The knee joint kinematic measurements were compared during two periods: before and after ground contact. Over the entire activity, the within-bone motion differences between the two motion capture techniques were significantly lower for the tibia than the femur for two of the rotational axes (flexion/extension, internal/external) and the origin. The OMC and biplanar videoradiography knee joint kinematics were in best agreement before landing. Kinematic deviations between the two techniques increased significantly after contact. This study provides information on the kinematic discrepancies between OMC and biplanar videoradiography that can be used to optimize methods employing both technologies for studying dynamic in vivo knee kinematics and kinetics during a jump-cut maneuver.

Knee biomechanics during a jump-cut maneuver: effects of sex and ACL surgery.

PURPOSE: The purpose of this study was to compare kinetic and knee kinematic measurements from male and female anterior cruciate ligament (ACL)-intact (ACLINT) and ACL-reconstructed (ACLREC) subjects during a jump-cut maneuver using biplanar videoradiography. METHODS: Twenty subjects were recruited; 10 ACLINT (5 men and 5 women) and 10 ACLREC (4 men and 6 women, 5 yr postsurgery). Each subject performed a jump-cut maneuver by landing on a single leg and performing a 45° side-step cut. Ground reaction force (GRF) was measured by a force plate and expressed relative to body weight. Six-degree-of-freedom knee kinematics were determined from a biplanar videoradiography system and an optical motion capture system. RESULTS: ACLINT female subjects landed with a larger peak vertical GRF (P < 0.001) compared with ACLINT male subjects. ACLINT subjects landed with a larger peak vertical GRF (P ≤ 0.036) compared with ACLREC subjects. Regardless of ACL reconstruction status, female subjects underwent less knee flexion angle excursion (P = 0.002) and had an increased average rate of anterior tibial translation (0.05%·ms ± 0.01%·ms, P = 0.037) after contact compared with male subjects. Furthermore, ACLREC subjects had a lower rate of anterior tibial translation compared with ACLINT subjects (0.05%·ms ± 0.01%·ms, P = 0.035). Finally, no striking differences were observed in other knee motion parameters. CONCLUSION: Women permit a smaller amount of knee flexion angle excursion during a jump-cut maneuver, resulting in a larger peak vertical GRF and increased rate of anterior tibial translation. Notably, ACLREC subjects also perform the jump cut maneuver with lower GRF than ACLINT subjects 5 yr postsurgery. This study proposes a causal sequence whereby increased landing stiffness (larger peak vertical GRF combined with less knee flexion angle excursion) leads to an increased rate of anterior tibial translation while performing a jump-cut maneuver.

Static and dynamic error of a biplanar videoradiography system using marker-based and markerless tracking techniques.

The use of biplanar videoradiography technology has become increasingly popular for evaluating joint function in vivo. Two fundamentally different methods are currently employed to reconstruct 3D bone motions captured using this technology. Marker-based tracking requires at least three radio-opaque markers to be implanted in the bone of interest. Markerless tracking makes use of algorithms designed to match 3D bone shapes to biplanar videoradiography data. In order to reliably quantify in vivo bone motion, the systematic error of these tracking techniques should be evaluated. Herein, we present new markerless tracking software that makes use of modern GPU technology, describe a versatile method for quantifying the systematic error of a biplanar videoradiography motion capture system using independent gold standard instrumentation, and evaluate the systematic error of the W.M. Keck XROMM Facility's biplanar videoradiography system using both marker-based and markerless tracking algorithms under static and dynamic motion conditions. A polycarbonate flag embedded with 12 radio-opaque markers was used to evaluate the systematic error of the marker-based tracking algorithm. Three human cadaveric bones (distal femur, distal radius, and distal ulna) were used to evaluate the systematic error of the markerless tracking algorithm. The systematic error was evaluated by comparing motions to independent gold standard instrumentation. Static motions were compared to high accuracy linear and rotary stages while dynamic motions were compared to a high accuracy angular displacement transducer. Marker-based tracking was shown to effectively track motion to within 0.1 mm and 0.1 deg under static and dynamic conditions. Furthermore, the presented results indicate that markerless tracking can be used to effectively track rapid bone motions to within 0.15 deg for the distal aspects of the femur, radius, and ulna. Both marker-based and markerless tracking techniques were in excellent agreement with the gold standard instrumentation for both static and dynamic testing protocols. Future research will employ these techniques to quantify in vivo joint motion for high-speed upper and lower extremity impacts such as jumping, landing, and hammering.

Automatic determination of anatomical coordinate systems for three-dimensional bone models of the isolated human knee.

The combination of three-dimensional (3-D) models with dual fluoroscopy is increasingly popular for evaluating joint function in vivo. Applying these modalities to study knee motion with high accuracy requires reliable anatomical coordinate systems (ACSs) for the femur and tibia. Therefore, a robust method for creating ACSs from 3-D models of the femur and tibia is required. We present and evaluate an automated method for constructing ACSs for the distal femur and proximal tibia based solely on 3-D bone models. The algorithm requires no observer interactions and uses model cross-sectional area, center of mass, principal axes of inertia, and cylindrical surface fitting to construct the ACSs. The algorithm was applied to the femur and tibia of 10 (unpaired) human cadaveric knees. Due to the automated nature of the algorithm, the within specimen variability is zero for a given bone model. The algorithm's repeatability was evaluated by calculating variability in ACS location and orientation across specimens. Differences in ACS location and orientation between specimens were low (<1.5mm and <2.5 degrees). Variability arose primarily from natural anatomical and morphological differences between specimens. The presented algorithm provides an alternative method for automatically determining subject-specific ACSs from the distal femur and proximal tibia.