Long-term follow-up of Van Nes rotationplasty in patients with congenital proximal focal femoral deficiency.

Van Nes rotationplasty may be used for patients with congenital proximal focal femoral deficiency (PFFD). The lower limb is rotated to use the ankle and foot as a functional knee joint within a prosthesis. A small series of cases was investigated to determine the long-term outcome. At a mean of 21.5 years (11 to 45) after their rotationplasty, a total of 12 prosthetic patients completed the Short-Form (SF)-36, Faces Pain Scale-Revised, Harris hip score, Oswestry back pain score and Prosthetic Evaluation Questionnaires, as did 12 age- and gender-matched normal control participants. A physical examination and gait analysis, computerised dynamic posturography (CDP), and timed 'Up & Go' testing was also completed. Wilcoxon Signed rank test was used to compare each PFFD patient with a matched control participant with false discovery rate of 5%. There were no differences between the groups in overall health and well-being on the SF-36. Significant differences were seen in gait parameters in the PFFD group. Using CDP, the PFFD group had reduced symmetry in stance, and reduced end point and maximum excursions. Patients who had undergone Van Nes rotationplasty had a high level of function and quality of life at long-term follow-up, but presented with significant differences in gait and posture compared with the control group.

Mechanical characterization of fourth generation composite humerus.

Mechanical data on upper extremity surrogate bones, supporting use as biomechanical tools, is limited. The objective of this study was to characterize the structural behaviour of the fourth-generation composite humerus under simulated physiologic bending, specifically, stiffness, rigidity, and mid-diaphysial surface strains. Three humeri were tested in four-point bending, in anatomically defined anteroposterior (AP) and mediolateral (ML) planes. Stiffness and rigidity were derived using load-displacement data. Principal strains were determined at the anterior, posterior, medial, and lateral surfaces in the humeral mid-diaphysial transverse plane of one specimen using stacked rosettes. Linear structural behaviour was observed within the test range. Average stiffness and rigidity were greater in the ML (918 +/- 18 N/mm; 98.4 +/- 1.9 Nm2) than the AP plane (833 +/- 16 N/mm; 89.3 +/- 1.6 Nm2), with little inter-specimen variability. The ML/AP rigidity ratio was 1.1. Surface principal strains were similar at the anterior (5.41 micro epsilon/N) and posterior (5.43 micro epsilon/N) gauges for AP bending, and comparatively less for ML bending, i.e. 5.1 and 4.5 micro epsilon/N, at the medial and lateral gauges, respectively. This study provides novel strain and stiffness data for the fourth-generation composite humerus and also adds to published construct rigidity data. The presented results support the use of this composite bone as a tool for modelling and experimentation.

Analysis of postural stability following posterior spinal fusion in adolescents with idiopathic scoliosis.

This study uses experimental data acquired from adolescents with idiopathic scoliosis to assess their postural control during quiet standing before and after posterior spinal fusion. Statistically significant differences were seen when comparing the pre- and post-surgical measures of balance calculated from data for three different test conditions.

Using a bi-planar postural stability model to assess children with scoliosis.

This study examines the postural stability of children with idiopathic scoliosis, using experimental data and a model of sway that includes mediolateral (ML) and anterioposterial (AP) components. The experimental data includes center of pressure (COP) measurements calculated from data acquired using two Advanced Medical Technology, Inc. (AMTI) force plates. Sway metrics are computed and compared with the model simulation, which successfully reproduced the clinical data from 16 children with scoliosis and 20 typically-developing children. This study is part of the first phase of a multi-year study designed to systematically assess whether fusing the spine to L4 in children with scoliosis has a significant impact on physical function and quality of life.

Application of a bi-planar postural stability model in children with cerebral palsy.

This study presents initial results from a bi-planar model used to investigate the neurological factors affecting balance deficits in children with diplegic cerebral palsy (CP). The model uses an inverted pendulum to describe sway in both the anteroposterior (AP) and mediolateral (ML) planes. The study presents Center of Pressure (COP) data from 17 children diagnosed with spastic diplegic CP using two standard AMTI force plates. Sway metrics in the time and frequency domains in the AP and ML planes were calculated and compared to simulations produced by the model. The proposed bi-planar model successfully reproduced sway signals acquired from experimental (clinical) data.

Biomechanical implications of the negative heel rocker sole shoe: gait kinematics and kinetics.

Rocker sole shoes are commonly prescribed to diabetic patients with insensate feet. Recent passage of the therapeutic shoe bill has drawn an increased focus to prescription rehabilitative footwear. The purpose of this work is to investigate the dynamics of lower extremity joints (hip, knee and ankle) with the application of a negative heel rocker sole shoe under controlled lab conditions. Forty normal adults volunteered for gait evaluations using controlled baseline and prescription negative heel rocker sole shoes. Three-dimensional motion analysis techniques were used to acquire kinematic and kinetic data using a six-camera Vicon 370 motion system and two AMTI force plates. No significant change in walking speed or stride length was seen with the negative heel rocker shoe, although cadence was increased. The most significant kinematic changes with the application of the negative heel shoe occurred at the ankle in the sagittal plane with increased plantarflexion at terminal stance. Significant hip and knee changes were also noted with increased mid-stance hip extension and knee flexion. The most significant kinetic effects were seen in the transverse plane followed by changes in the sagittal and coronal planes. Changes in power were mostly noted in the sagittal plane. Other statistically significant changes in gait kinematics and kinetics were observed, although the magnitudes and durations were limited and as a result were not considered clinically significant. The study results indicated the negative heel rocker shoe significantly altered proximal joint metrics (hip and knee). The most significant distal joint alterations were seen in sagittal plane ankle kinetics. These kinematic and kinetic changes, along with previously studied effects of pressure relief at the metatarsal heads, should aid medical professionals in prescribing prophylactic footwear.

A dynamic model of the upper extremities for quantitative assessment of Lofstrand crutch-assisted gait.

Appropriate models for quantitative evaluation of upper extremity dynamics in children with myelomeningocele are limited. Therefore, a three-dimensional (3D) biomechanical model of the upper extremities was developed for quantification during Lofstrand crutch-assisted gait in children with myelomeningocele. The model accurately tracks the joint angles of the trunk, shoulders, elbows, wrists, and crutches. Lofstrand crutches are instrumented with six-axis load cells to obtain force and moment components. The model is applied while performing crutch-assisted ambulatory patterns (alternate gait and swing-through gait). Analysis indicates that the model is suitable for quantifying upper extremity motion during crutch-assisted gait. This model has been designed for dynamic assessment of ambulatory patterns (upper and lower extremities) that present with pediatric myelomeningocele. It is hoped that the study findings will prove useful through advances in treatment monitoring, crutch prescription and therapeutic planning.

Combined sagittal and coronal plane postural stability model.

We present a preliminary study of combined anterior posterior (AP) and medial lateral (ML) sway assuming a classic inverted pendulum with included subtalar movement. Based on a feedback control posture model in the sagittal plane as presented by Maurer and Peterka, we have investigated parameters needed to model ML sway components. Center of pressure (COP) data was collected from a population of 8 normal adults (age 18 to 30 years) using a dual AMTI force plate system. Fourteen different sway metrics were calculated. The collected data was successfully compared to numerous simulations of the model where model parameters were varied and the goal was to reproduce both AP and ML components.

Biomechanics of cranial dynamics during daily living activities.

Motion tracking capabilities of a head-mounted accelerometer apparatus were investigated in conjunction with three-dimensional motion analysis techniques during activities of daily living. In this report, measures between systems are compared for jogging, toe-touching, and start-from-rest tasks. Good fidelity was found for most measures between systems; some phase shifts and amplitude discrepancies were observed, and attributed to transducer orientation and system asynchrony. This preliminary work demonstrates the potential benefits of hybrid motion analysis systems.

Quantification of reaching during stroke rehabilitation using unique upper extremity kinematic model.

Quantification of rehabilitation progress is necessary for accurately assessing clinical treatments. A three-dimensional (3D) biomechanical model of the upper extremity was developed for quantification of stroke rehabilitation. The model was designed to accurately track the 3D orientation of the trunk, shoulder, elbow and wrist. This study explains the application of the upper extremity model. Strict validation of the model confirmed the system's accuracy and resolution. The model was applied to eight hemiparetic stroke patients with spasticity, while completing a set of reaching tasks. The model successfully detected statistical differences in elbow range of motion and angular velocity between the nonparetic (unaffected) and paretic (affected) arms. Both simple and complex biomechanical indices for assessment were developed. This model may aid in the assessment and planning of stroke rehabilitation, and help to decrease recovery time.

Stress analysis of unilateral cleft palate using a three dimensional finite element model of pediatric subject-specific maxilla.

For children with cleft palate, oral function is impaired. The hypothesis is that the stress and strain distribution within the affected maxilla with a cleft during functional tasks such as biting and chewing is abnormal and can significantly affect bone development in the growing child. To test this hypothesis, a three-dimensional finite element model of a pediatric subject-specific maxilla with and without unilateral cleft palate was established based upon pediatric subject-specific bony geometry. The stress and strain distribution of the maxillary alveolar region subjected to typical functional loads was analyzed. The preliminary results revealed that both Von Mises stress and maximum principle stress as well as principle strain distribution were unevenly distributed between the hemi-maxillae.

Kinematic analysis of upper extremity joint motion in children using posterior walkers.

This study applies an upper extremity model to analyze motion in 25 children with cerebral palsy using posterior walkers. The study indicates that throughout a gait cycle, the shoulders and wrist are in extension and the elbows are flexed. It also reveals that the elbows are the most asymmetrical joint of the upper extremities during walker-assisted ambulation.

Biomechanics of the double rocker sole shoe: gait kinematics and kinetics.

This paper reports the kinematic and kinetic changes in gait with bilateral double rocker sole shoe modifications. Three-dimensional motion analysis techniques were used to evaluate gait characteristics (temporal-spatial, kinematic, and kinetic measures) of forty (40) subjects while wearing baseline and double rocker sole shoes. Walking speed was unchanged by the double rocker modification. Sagittal plane motions showed significant change at the pelvis, hip, knee, and ankle. (p = 0.01). The toe-only rocker consistently resulted in increase in posterior pelvic tilt (p =0.01). Kinetic changes were observed at the hip in the sagittal and transverse planes, and at the knee and ankle in the sagittal planes. Changes in pelvic tilt and hip rotation were hypothesized to result from feelings of imbalance during ambulation with the double rocker sole shoe.

Development of a computer assisted craniofacial surgery planning system.

Based upon the idea that both facial appearance and functional outcomes of the craniofacial surgery need to be predicted in the pre-surgery planning stage, a CACSP system has been established. In this system, the input is in vivo CT/MRI scan data of patient with craniofacial deformity, anatomical restoration is simulated using the medical visualization packages ANALYZE, and the finite element analysis of the masticatory system has been integrated to predict the functional improvement such as bite force alteration. Preliminary studies in this laboratory have revealed the potential of this system.

Finite element (FE) modeling of the mandible: from geometric model to tetrahedral volumetric mesh.

This paper presents our experience in using FE modeling of clinically relevant cases specifically in mandibular surgery. A semi-automatic procedure integrated with a group of Virtual Basic-based codes has been developed to clean the geometric models. Consequently, the time required for generate the tetrahedral volumetric mesh of mandible from patient-specific CT data has been reduced to less than 40 hours. Pre- and post-operation FE meshes are shown to be consistent and can be used for further modeling and analysis.

Walker-assisted gait in rehabilitation: a study of biomechanics and instrumentation.

While walkers are commonly prescribed to improve patient stability and ambulatory ability, quantitative study of the biomechanical and functional requirements for effective walker use is limited. To date no one has addressed the changes in upper extremity kinetics that occur with the use of a standard walker, which was the objective of this study. A strain gauge-based walker instrumentation system was developed for the six degree-of-freedom measurement of resultant subject hand loads. The walker dynamometer was integrated with an upper extremity biomechanical model. Preliminary system data were collected for seven healthy, right-handed young adults following informed consent. Bilateral upper extremity kinematic data were acquired with a six camera Vicon motion analysis system using a Micro-VAX workstation. Internal joint moments at the wrist, elbow, and shoulder were determined in the three clinical planes using the inverse dynamics method. The walker dynamometer system allowed characterization of upper extremity loading demands. Significantly differing upper extremity loading patterns were identified for three walker usage methods. Complete description of upper extremity kinetics and kinematics during walker-assisted gait may provide insight into walker design parameters and rehabilitative strategies.

Surgical rehabilitation of the planovalgus foot in cerebral palsy.

The objectives of this study were to quantitatively determine the effects of subtalar arthrodesis on the planovalgus foot using three-dimensional (3-D) gait analysis and plantar pressure measurements. Twelve children and adolescents with planovalgus foot deformity secondary to spastic cerebral palsy participated in this outcome study. The pediatric population were evaluated preoperatively and following subtalar fusion. Seventeen feet were operated for the correction of the planovalgus foot deformity. A Holter-type microprocessor-based portable in-shoe data acquisition system was used in this study to collect the multistep dynamic plantar pressure history, while a five-camera Vicon-based gait analysis system was used to track the lower extremity joint kinematics. The results obtained from the plantar pressure measurement showed significant increases in mean peak vertical plantar pressures postoperatively at the lateral midfoot and lateral metatarsal heads. Mean contact durations and mean pressure-time integrals were also significantly increased at these plantar locations following foot surgery. This redistribution in pressure metrics suggests the formation of new lateral plantar weight bearing areas. The 3-D gait analysis system, using standardized lower extremity measurements, was unable to reveal any significant changes in joint kinematics, particularly at the foot and ankle where the surgery was performed. This suggests the need for a more refined system to track the complex motion of the pediatric foot and ankle during gait.

Variability in three-dimensional measurements of back contour with raster stereography in normal subjects.

Forty normal children with a mean age of 9.1 years were investigated by using a Quantec Spinal Image System (QSIS). The QSIS uses computerized raster stereography technology to acquire three-dimensional measurements of back contour. Within a 95-percentile confidence interval (a) coronal-plane QSIS angles ranged from 0.05 to 2.36 degrees; (b) transverse-plane QSIS angles ranged from 0.03 to 1.96 degrees; and (c) sagittal-plane QSIS angles ranged from 36.8 to 44.8 degrees. Trunk-alignment deviation ranged from 3.51 to 7.45 mm within a 95-percentile confidence interval. An intraobserver standard deviation of +/-4.2 degrees was noted across all angular metrics. Normal ranges of QSIS-determined values for a population of 40 children without clinical evidence of pathology are reported.

Hindfoot coronal alignment: a modified radiographic method.

Accurate clinical evaluation of the alignment of the calcaneus relative to the tibia in the coronal plane is essential in the evaluation and treatment of hindfoot pathologic condition. Previously described radiographic views of the foot and ankle do not demonstrate the true coronal alignment of the calcaneus relative to the tibia. Some of these views impose on the patient an unnatural posture that itself changes hindfoot alignment, whereas other methods distort the coronal alignment by the angle of the x-ray beam. Our purpose was to develop a modified radiographic view and measurement method for determining an angular measurement of hindfoot coronal alignment based on a cadaver study of the radiographic characteristics of the calcaneus and motion analysis of standing subjects. The view was obtained by having the subject stand on a piece of cardboard to create a foot template. The template was then positioned so that each foot was x-rayed perpendicular to the cassette while still maintaining the natural base of support. A method using multiple ellipses was developed to determine more accurately the coronal axis of the posterior calcaneus. A study using cadavers was performed in which radio-opaque markers were placed on multiple bony landmarks on the calcaneus. The tibia was held fixed in a vertical position, and the foot was x-rayed using the above techniques in different degrees of rotation without changing the relation of the calcaneus to the tibia. The radiographs of the modified Cobey and our view were examined to verify which markers were visible at different angles of rotation and how the hindfoot alignment measurements changed with foot rotation. To define further the differences between the views, an analysis of postural stability was conducted while the subjects were standing with the feet in the positions for imaging both the Buck modification of the Cobey view and our hindfoot alignment view. The combined results of the cadaver, radiographic measurement, and postural stability segments of the study reveal that this coronal hindfoot alignment view and measurement method is reproducible, more closely measures "true" coronal hindfoot alignment, and is more clinically applicable because the alignment is measured while the patient is standing with a normal angle and base of stance. The modified radiographic measurement method relies on posterior calcaneal anatomic landmarks, is less affected by rotation of the foot and ankle, and is reproducible between observers.

Instantaneous postural stability characterization using time-frequency analysis.

Postural stability assessment is critical to a more accurate understanding of sway and balance control. The center of pressure (COP) metric has been shown to be a suitable output measure for time and frequency analysis. However, the center of pressure is a non-stationary signal. Standard time and frequency analysis methods may not be adequate for monitoring the dynamic changes in the center of pressure signal. In this study a time-frequency method, based on data-adaptive evolutionary spectral estimation, is applied to monitor the dynamic changes of the center of pressure in a non-stationary environment. Metrics including the instantaneous mean frequency (IMF), instantaneous spectral bandwidth (ISB), and instantaneous average power (IAP) are analyzed to characterize the center of pressure signal in both the anterior-posterior (AP) and the medial-lateral (ML) planes. Within the confines of this study, the IMF was found to be inversely proportional to IAP. The inverse proportionality factors were calculated in both eyes-open and eyes-closed trials during upright quiet standing. These findings suggest that the time-frequency analysis provides instantaneous metrics which describe the amplitude changes and frequency shift of the center of pressure under a variety of environmental conditions, thus providing a more reliable quantification of postural control.