Peter A. Smith

Biomechanical model for evaluation of pediatric upper extremity joint dynamics during wheelchair mobility

Pediatric manual wheelchair users (MWU) require high joint demands on their upper extremity (UE) during wheelchair mobility, leading them to be at risk of developing pain and pathology. Studies have examined UE biomechanics during wheelchair mobility in the adult population; however, current methods for evaluating UE joint dynamics of pediatric MWU are limited. An inverse dynamics model is proposed to characterize three-dimensional UE joint kinematics and kinetics during pediatric wheelchair mobility using a SmartWheel instrumented handrim system. The bilateral model comprises thorax, clavicle, scapula, upper arm, forearm, and hand segments and includes the sternoclavicular, acromioclavicular, glenohumeral, elbow and wrist joints. A single 17 year-old male with a C7 spinal cord injury (SCI) was evaluated while propelling his wheelchair across a 15-meter walkway. The subject exhibited wrist extension angles up to 60°, large elbow ranges of motion and peak glenohumeral joint forces up to 10% body weight. Statistically significant asymmetry of the wrist, elbow, glenohumeral and acromioclavicular joints was detected by the model. As demonstrated, the custom bilateral UE pediatric model may provide considerable quantitative insight into UE joint dynamics to improve wheelchair prescription, training, rehabilitation and long-term care of children with orthopedic disabilities. Further research is warranted to evaluate pediatric wheelchair mobility in a larger population of children with SCI to investigate correlations to pain, function and transitional changes to adulthood.

Design and development of an active marker based system for analysis of 3-D pediatric foot and ankle motion

A unique light emitting diode (LED) based active marker system was developed to track the three dimensional motion of the pediatric foot and ankle. The marker system was used with a six-camera Vicon VX (Oxford Metrics, Oxford, U.K) motion analysis system which was integrated with a three-segment biomechanical model to describe the complex multiplanar motion of the tibia, hindfoot and forefoot. The average static resolution (0.38 mm) and accuracy (99.12%) obtained with this system was better than that obtained with the authors comparable adult foot and ankle system. Spectral analysis revealed a distinct 30 Hz component due to video interlacing. Dynamic testing of this system has confirmed that further clinical trials are supported and feasible.

3D Micron-scale Imaging of the Cortical Bone Canal Network in Human Osteogenesis Imperfecta (OI)

Osteogenesis imperfecta (OI) is a genetic disorder leading to increased bone fragility. Recent work has shown that the hierarchical structure of bone plays an important role in determining its mechanical properties and resistance to fracture. The current study represents one of the first attempts to characterize the 3D structure and composition of cortical bone in OI at the micron-scale. A total of 26 pediatric bone fragments from 18 individuals were collected during autopsy (Nc=5) or routing orthopaedic procedures (NOI=13) and imaged by microtomography with a synchrotron light source (SRμCT) for several microstructural parameters including cortical porosity (Ca.V/TV), canal surface to tissue volume (Ca.S/TV), canal diameter (Ca.Dm), canal separation (Ca.Sp), canal connectivity density (Ca.ConnD), and volumetric tissue mineral density (TMD). Results indicated significant differences in all imaging parameters between pediatric controls and OI tissue, with OI bone showing drastically increased cortical porosity, canal diameter, and connectivity. Preliminary mechanical testing revealed a possible link between cortical porosity and strength. Together these results suggest that the pore network in OI contributes greatly to its reduced mechanical properties.

Rehabilitative orthotics evaluation in children with diplegic cerebral palsy: kinematics and kinetics

Ankle foot orthoses (AFOs) are prescribed for ambulatory children with spastic diplegia to improve biomechanical alignment and functional capability. The purpose of this study was to employ quantitative motion analysis of the lower extremity to investigate two rehabilitative orthotics. The effects of hinged ankle foot orthoses (HAFO) and dynamic ankle foot orthoses (DAFO) for joint ankle management in children with cerebral palsy were compared. Sixteen (16) independently ambulatory children with a diagnosis of spastic diplegic cerebral palsy (7.5 /spl plusmn/ 2.9 yrs.) were included in the study. The biomechanical effects of two AFO designs were compared to barefoot using a 3-D motion analysis system. Significant differences between braced and unbraced conditions were found in peak ankle dorsiflexion, and peak ankle plantarflexion, knee stance peak flexion, knee swing peak flexion, hip stance peak flexion, and peak ankle plantarflexion moment (p < 0.01). Differences between the HAFO and DAFO were not seen in the kinematic and kinetic metrics. Further development of dynamic testing is suggested in order to advance our understanding of orthotic intervention. The value of quantitative description of gait dynamics is clearly indicated for rehabilitative application.

Design and validation of upper extremity support system for dynamic postural stability assessment

The design and validation of a biomechanical measurement system to determine 3D upper extremity support forces during walker assisted standing is presented. The system performs dynamic postural stability testing while recording six axis force and moment information from a pair of instrumented walker handles. The work is part of a larger study of the correlation of postural stability assessment, gait analysis and functional measurement instruments in children with cerebral palsy who require assistive devices to ambulate. The system is found suitable for further testing and patient evaluation.

Clinical validation of a system for the analysis of pediatric foot and ankle kinematics during gait

Kinematic foot and ankle data was acquired from 10 pediatric subjects using a six camera Vicon VX (Oxford Metrics, Oxford, U.K) based active marker system. The system was based on a three segment rigid body model that described the motion of the tibia, hindfoot and forefoot. Radiographic measurements were utilized to index the motion data with respect to the underlying bony anatomy. Data was collected from five normal pediatric subjects who had no prior orthopaedic surgery or indications or symptoms of pathology and from five subjects with an equinovarus deformity secondary to cerebral palsy. The data obtained form the normal controls showed motion of the three segments to be similar to that of mature adult foot and ankle motion. Data collected from subjects with the equinovarus deformity showed a pattern consistent with pathology observed by reviewing slow motion videos.