Biomedical Engineering Faculty Research and Publications

A Database for Estimating Organ Dose for Chest and Head CT Scans for Arbitrary Spectra and Angular Tube Current Modulation

Franco Rupcich et al. — Tue, 05 Mar 2013 13:55:05 PST

Purpose: The purpose of this study was to develop a database for estimating organ dose in a voxelized patient model for coronary angiography and brain perfusion CT acquisitions with any spectra and angular tube current modulation setting. The database enables organ dose estimation for existing and novel acquisition techniques without requiring Monte Carlo simulations. Methods: The study simulated transport of monoenergetic photons between 5 and 150 keV for 1000 projections over 360◦ through anthropomorphic voxelized female chest and head (0◦ and 30◦ tilt) phantoms and standard head and body CTDI dosimetry cylinders. The simulations resulted in tables of normalized dose deposition for several radiosensitive organs quantifying the organ dose per emitted photon for each incident photon energy and projection angle for coronary angiography and brain perfusion acquisitions. The values in a table can be multiplied by an incident spectrum and number of photons at each projection angle and then summed across all energies and angles to estimate total organ dose. Scanner-specific organ dose may be approximated by normalizing the database-estimated organ dose by the database-estimated CTDIvol and multiplying by a physical CTDIvol measurement. Two examples are provided demonstrating how to use the tables to estimate relative organ dose. In the first, the change in breast and lung dose during coronary angiography CT scans is calculated for reduced kVp, angular tube current modulation, and partial angle scanning protocols relative to a reference protocol. In the second example, the change in dose to the eye lens is calculated for a brain perfusion CT acquisition in which the gantry is tilted 30◦ relative to a nontilted scan. Results: Our database provides tables of normalized dose deposition for several radiosensitive organs irradiated during coronary angiography and brain perfusion CT scans. Validation results indicate total organ doses calculated using our database are within 1% of those calculated using Monte Carlo simulations with the same geometry and scan parameters for all organs except red bone marrow (within 6%), and within 23% of published estimates for different voxelized phantoms. Results from the example of using the database to estimate organ dose for coronary angiography CT acquisitions show 2.1%, 1.1%, and −32% change in breast dose and 2.1%, −0.74%, and 4.7% change in lung dose for reduced kVp, tube current modulated, and partial angle protocols, respectively, relative to the reference protocol. Results show −19.2% difference in dose to eye lens for a tilted scan relative to a nontilted scan. The reported relative changes in organ doses are presented without quantification of image quality and are for the sole purpose of demonstrating the use of the proposed database. Conclusions: The proposed database and calculation method enable the estimation of organ dose for coronary angiography and brain perfusion CT scans utilizing any spectral shape and angular tube current modulation scheme by taking advantage of the precalculated Monte Carlo simulation results. The database can be used in conjunction with image quality studies to develop optimized acquisition techniques and may be particularly beneficial for optimizing dual kVp acquisitions for which numerous kV, mA, and filtration combinations may be investigated. © 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4739243]

Long-term Follow up of Van Nes Rotationplasty for Congenital Proximal Focal Femoral Deficiency

Haluk Altiok et al. — Tue, 05 Mar 2013 13:17:46 PST

INTRODUCTIONProximal focal femoral deficiency (PFFD) is a congenital anomaly that presents challenges for orthopaedic and prosthetic management. The Van Nes rotationplasty is one treatment in which the extremity is surgically rotated to utilize the ankle and foot as a functional knee joint in a prosthesis. The purpose of this study is to determine the long-term functional and quality of life (QOL) outcomes for individuals who have undergone rotationplasty surgery for congenital PFFD compared to age and gender matched controls. METHODSThis prospective study had 12 prosthetic participants (PFFD Group: 8 M, 4F, age range 16-57 years) average 31.6±13.5 years and 12 control participants (Control Group: 8M, 4F) with an average age 32.6±14.1 years. Participants completed the following outcome questionnaires: SF-36, Revised-Faces Pain Scale, Harris Hip Score, Oswestry back pain score; and underwent lower extremity range of motion (ROM), hand held dynamometry, gait analysis, computerized dynamic posturography and Timed ‘Up& Go’ (TUG) testing. The PFFD Group also completed the Prosthetic Evaluation Questionnaire© (PEQ). The Wilcoxon Signed rank test was used to statistically compare each PFFD Group participant to the matched Control Group participant with values statistically significant at p< 0.0123. RESULTSParticipants had rotationplasty performed at an average age of 6.5±3.9 years with follow up testing done 25.1±11.2 years later. All adult subjects were working full time in a variety of manual and office/desk jobs. No significant issues were seen for body image. Pain: The PFFD and Control Groups both reported similar low back pain with 6.8±9.7% and 7.0±13.0% disability respectively on the Oswestry back pain questionnaire. On the day of testing, only one PFFD participant reported mild low back pain on the Revised- Faces Pain Scale. The average Harris Hip Score for the PFFD Group was 92.7±9.2 out of 100, indicating excellent outcome. Two participants reported pain on their non-prosthetic hip. ROM: The PFFD Group showed significantly decreased hip flexion and ankle dorsiflexion, and increased ankle plantarflexion strength on the prosthetic side compared to the Control Group. The PFFD Group had significantly greater ankle abduction strength on their non-prosthetic side compared to the Control Group. Strength: The PFFD Group demonstrated significantly weaker hip flexion, hip abduction and ankle plantarflexion on the prosthetic side compared to the Control Group. TUG: The PFFD Group scored an average of 8.5±1.6 seconds on the TUG, demonstrating a low fall risk. The Control Group scored significantly lower with an average of 6.5 ±1.0 seconds. SF-36: There were no significant differences between the groups in overall health and well-being. PEQ©: The PFFD Group scored lower in areas of satisfaction, appearance, and sounds of the prosthesis. However, participants reported that others perceived them well and they did not see themselves as a social burden. Gait Analysis: Temporal-spatial gait parameters for the PFFD Group demonstrated significant decrease in cadence, stride time, opposite foot off, single support and walking speed compared to Control Group. Posturography: The PFFD Group showed significant decrease in symmetry in stance, as well as a decrease in end point and maximum excursion in limits of stability testing compared to the Control Group. DISCUSSION AND CONCLUSIONOverall, long-term follow up of teens and adults who underwent Van Nes rotationplasty showed that they maintained a high level of function, participation and QOL. They did present with significant differences in temporal spatial and posturography parameters compared to the Control Group.

Static and Dynamic Calibration of an Eight-Camera Optical System for Human Motion Analysis

Jeffrey D. Kertis et al. — Fri, 01 Feb 2013 11:47:18 PST

An eight-camera Optitrack motion capture system was evaluated by performing static, linear dynamic, and angular dynamic calibrations using marker distances associated with upper and lower extremity gait and wheelchair models. Data were analyzed to determine accuracy and resolution within a defined capture volume using a standard Cartesian reference system. Static accuracy ranged from 99.31 to 99.90%. Static resolution ranged from 0.04 ± 0.15 to 0.63 ± 0.15 mm at the 0.05 level of significance. The dynamic accuracy ranged from 94.82 to 99.77%, and dynamic resolution ranged from 0.09 ± 0.26 to 0.61 ± 0.31 mm at the 0.05 level of significance. These values are comparable to those reported for a standard Vicon 524 (Oxford Metrics, Oxford, England) motion analysis system. The results support application of the lower cost Optitrack system for 3D kinematic assessment of upper and lower extremity motion during gait, assisted ambulation, and wheelchair mobility.

Effect of Fine Wire Electrode Insertion on Gait Patterns in Children with Hemiplegic Cerebral Palsy

Joseph Krzak et al. — Fri, 01 Feb 2013 09:58:01 PST

Background

Fine wire electromyography (EMG) is commonly used for surgical decision making in equinovarus foot deformity. However, this invasive technique may have the unwanted effect of altering the gait of children with cerebral palsy (CP). The purpose of this study was to determine if fine wire insertion into the posterior tibialis muscle affects temporal-spatial parameters and hindfoot kinematics during gait in children with equinovarus secondary to hemiplegic CP.

Methods

12 children with hemiplegic CP who presented with an equinovarus foot (mean age 12.5 yrs, four right-sided, eight left-sided) were recruited. Temporal-spatial parameters and 3-D segmental foot and ankle kinematic gait data were collected utilizing standard gait analysis and the Milwaukee Foot Model (MFM). Three representative trials with and without fine wire electrode insertion were compared to determine the effect of electrode placement in the posterior tibialis on temporal spatial-parameters and hindfoot sagittal, coronal and transverse plane kinematic peaks, timing of kinematic peaks, and excursions.

Results

No significant differences in any temporal-spatial or kinematic parameters were observed between “with wire” and “without wire” conditions. Strong correlations were observed among the gait parameters, with the exception of cadence, for the two conditions.

Discussion

Fine wire insertion into the posterior tibialis had no measurable effect on the gait of individuals with equinovarus secondary to hemiplegic CP. This suggests that the simultaneous collection of segmental foot and ankle kinematics and fine wire EMG data of the posterior tibialis is acceptable for surgical decision making in this patient population.

Upper Extremity Biomechanical Model for Evaluation of Pediatric Joint Demands during Wheelchair Mobility

Alyssa J. Paul et al. — Fri, 01 Feb 2013 09:39:45 PST

Current methods for evaluating upper extremity (UE) dynamics during pediatric wheelchair use are limited. We propose a new model to characterize UE joint kinematics and kinetics during pediatric wheelchair mobility. The bilateral model is comprised of the thorax, clavicle, scapula, upper arm, forearm, and hand segments. The modeled joints include: sternoclavicular, acromioclavicular, glenohumeral, elbow and wrist. The model is complete and is currently undergoing pilot studies for clinical application. Results may provide considerable quantitative insight into pediatric UE joint dynamics to improve wheelchair prescription, training and long term care of children with orthopaedic disabilities.

Including Aortic Valve Morphology in Computational Fluid Dynamics Simulations: Initial Findings and Application to Aortic Coarctation

David C. Wendell et al. — Mon, 28 Jan 2013 08:20:29 PST

Computational fluid dynamics (CFD) simulations quantifying thoracic aortic flow patterns have not included disturbances from the aortic valve (AoV). 80% of patients with aortic coarctation (CoA) have a bicuspid aortic valve (BAV) which may cause adverse flow patterns contributing to morbidity. Our objectives were to develop a method to account for the AoV in CFD simulations, and quantify its impact on local hemodynamics. The method developed facilitates segmentation of the AoV, spatiotemporal interpolation of segments, and anatomic positioning of segments at the CFD model inlet. The AoV was included in CFD model examples of a normal (tricuspid AoV) and a post-surgical CoA patient (BAV). Velocity, turbulent kinetic energy (TKE), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) results were compared to equivalent simulations using a plug inlet profile. The plug inlet greatly underestimated TKE for both examples. TAWSS differences extended throughout the thoracic aorta for the CoA BAV, but were limited to the arch for the normal example. OSI differences existed mainly in the ascending aorta for both cases. The impact of AoV can now be included with CFD simulations to identify regions of deleterious hemodynamics thereby advancing simulations of the thoracic aorta one step closer to reality.

Estimation of Organ and Effective Dose due to Compton Backscatter Security Scans

Michael Hoppe et al. — Mon, 17 Dec 2012 10:30:20 PST

Purpose: To estimate organ and effective radiation doses due to backscatter security scanners using Monte Carlo simulations and a voxelized phantom set. Methods: Voxelized phantoms of male and female adults and children were used with the GEANT4 toolkit to simulate a backscatter security scan. The backscatter system was modeled based on specifications available in the literature. The simulations modeled a 50 kVp spectrum with 1.0 mm-aluminum-equivalent filtration and a previously measured exposure of approximately 4.6 μR at 30 cm from the source. Photons and secondary interactions were tracked from the source until they reached zero kinetic energy or exited from the simulation’s boundaries. The energy deposited in the phantoms’ respective organs was tallied and used to calculate total organ dose and total effective dose for frontal, rear, and full scans with subjects located 30 and 75 cm from the source. Results: For a full screen, all phantoms’ total effective doses were below the established 0.25 μSv standard, with an estimated maximum total effective dose of 0.07 μSv for full screen of a male child. The estimated maximum organ dose due to a full screen was 1.03 μGy, deposited in the adipose tissue of the male child phantom when located 30 cm from the source. All organ dose estimates had a coefficient of variation of less than 3% for a frontal scan and less than 11% for a rear scan. Conclusions: Backscatter security scanners deposit dose in organs beyond the skin. The effective dose is below recommended standards set by the Health Physics Society (HPS) and the American National Standards Institute (ANSI) assuming the system provides a maximum exposure of approximately 4.6 μR at 30 cm.

Computational Simulations for Aortic Coarctation: Representative Results From a Sampling of Patients

John F. LaDisa et al. — Fri, 31 Aug 2012 08:29:40 PDT

Treatments for coarctation of the aorta (CoA) can alleviate blood pressure (BP) gradients(D), but long-term morbidity still exists that can be explained by altered indices of hemodynamics and biomechanics. We introduce a technique to increase our understanding of these indices for CoA under resting and nonresting conditions, quantify their contribution to morbidity, and evaluate treatment options. Patient-specific computational fluid dynamics (CFD) models were created from imaging and BP data for one normal and four CoA patients (moderate native CoA: D12 mmHg, severe native CoA: D25 mmHg and postoperative end-to-end and end-to-side patients: D0 mmHg). Simulations incorporated vessel deformation, downstream vascular resistance and compliance. Indices including cyclic strain, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were quantified. Simulations replicated resting BP and blood flow data. BP during simulated exercise for the normal patient matched reported values. Greatest exercise-induced increases in systolic BP and mean and peak DBP occurred for the moderate native CoA patient (SBP: 115 to 154 mmHg; mean and peak DBP: 31 and 73 mmHg). Cyclic strain was elevated proximal to the coarctation for native CoA patients, but reduced throughout the aorta after treatment. A greater percentage of vessels was exposed to subnormal TAWSS or elevated OSI for CoA patients. Local patterns of these indices reported to correlate with atherosclerosis in normal patients were accentuated by CoA. These results apply CFD to a range of CoA patients for the first time and provide the foundation for future progress in this area.

Long-term Follow Up of Van Nes Rotationplasty for Proximal Focal Femoral Deficiency

Haluk Altiok et al. — Tue, 24 Jul 2012 14:38:58 PDT

Proximal focal femoral deficiency (PFFD) is a congenital anomaly that presents challenges for orthopaedic and prosthetic management. The Van Nes rotationplasty is one treatment in which the extremity is surgically rotated to utilize the ankle and foot as a functional knee joint in a prosthesis. The purpose of this study is to determine the long-term functional and quality of life (QOL) outcomes for individuals who have undergone rotationplasty surgery for congenital PFFD compared to age and gender matched controls.

Aortic Coarctation: Recent Developments in Experimental and Computational Methods to Assess Treatments for this Simple Condition

John F. LaDisa et al. — Tue, 10 Jul 2012 13:20:37 PDT

Coarctation of the aorta (CoA) is often considered a relatively simple disease, but long-term outcomes suggest otherwise as life expectancies are decades less than in the average population and substantial morbidity often exists. What follows is an expanded version of collective work conducted by the authors' and numerous collaborators that was presented at the 1st International Conference on Computational Simulation in Congenital Heart Disease pertaining to recent advances for CoA. The work begins by focusing on what is known about blood flow, pressure and indices of wall shear stress (WSS) in patients with normal vascular anatomy from both clinical imaging and the use of computational fluid dynamics (CFD) techniques. Hemodynamic alterations observed in CFD studies from untreated CoA patients and those undergoing surgical or interventional treatment are subsequently discussed. The impact of surgical approach, stent design and valve morphology are also presented for these patient populations. Finally, recent work from a representative experimental animal model of CoA that may offer insight into proposed mechanisms of long-term morbidity in CoA is presented.

Comprehensive Review of the Functional Outcome Evaluation of Clubfoot Treatment: A Preferred Methodology

Adam Graf et al. — Mon, 09 Jul 2012 12:20:53 PDT

Treatment outcome has been a focus of interest in those who manage clubfeet. Because of a lack of a common evaluation protocol, it has become necessary to establish a universally recognized quantitative measurement to compare and better understand the treatment outcome. The outcome is not merely morphological and radiographic, but it should also include functional and quality-of-life measurements. In this article, we will outline the most commonly used methods of long-term evaluation for congenital clubfeet and recommend the data collection parameters that are most appropriate for a comprehensive functional analysis. This will begin with pretreatment classifications that are important in prognosticating the results. The physical examinations and plain radiographs in standing position are also two fundamental evaluations of clubfoot. Several outcome evaluations have been published in the literature and may be useful depending on the desired metrics. Gait analysis is an additional useful technical tool for analyzing the motion of the foot and ankle and its relation to the whole body function; pedobarography added to the dynamics of the evaluation. Functional quality-of-life questionnaires are increasing in popularity for measuring the total body functional status and the quality of life.

A Coupled Experimental and Computational Approach to Quantify Deleterious Hemodynamics, Vascular Alterations, and Mechanisms of Long-Term Morbidity in Response to Aortic Coarctati

Arjun Menon et al. — Fri, 06 Jul 2012 16:31:49 PDT

Introduction

Coarctation of the aorta (CoA) is associated with morbidity despite treatment. Although mechanisms remain elusive, abnormal hemodynamics and vascular biomechanics are implicated. We present a novel approach that facilitates quantification of coarctation-induced mechanical alterations and their impact on vascular structure and function, without genetic or confounding factors.

Methods

Rabbits underwent thoracic CoA at 10 weeks of age (~ 9 human years) to induce a 20 mm Hg blood pressure (BP) gradient using permanent or dissolvable suture thereby replicating untreated and corrected CoA. Computational fluid dynamics (CFD) was performed using imaging and BP data at 32 weeks to quantify velocity, strain and wall shear stress (WSS) for comparison to vascular structure and function as revealed by histology and myograph results.

Results

Systolic and mean BP was elevated in CoA compared to corrected and control rabbits leading to vascular thickening, disorganization and endothelial dysfunction proximally and distally. Corrected rabbits had less severe medial thickening, endothelial dysfunction, and stiffening limited to the proximal region despite 12 weeks of normal BP (~ 4 human years) after the suture dissolved. WSS was elevated distally for CoA rabbits, but reduced for corrected rabbits.

Discussion

These findings are consistent with alterations in humans. We are now poised to investigate mechanical contributions to mechanisms of morbidity in CoA using these methods.

Role of Glutathione in Lung Retention of 99mTc-Hexamethylpropyleneamine Oxime in Two Unique Rat Models of Hyperoxic Lung Injury

Said H. Audi et al. — Fri, 06 Jul 2012 16:11:31 PDT

Rat exposure to 60% O₂ for 7 days (hyper-60) or to >95% O₂ for 2 days followed by a 24-hour in room air (hyper-95R) confers susceptibility or tolerance, respectively, of the otherwise lethal effects of subsequent exposure to 100% O₂. The objective of this study was to determine if lung retention of the radiopharmaceutical agent ^99mTc-HMPAO (hexamethylpropyleneamine oxime) is differentially altered in hyper-60 and hyper-95R rats. Tissue retention of HMPAO is dependent on intracellular content of the antioxidant glutathione (GSH) and mitochondrial function. HMPAO was injected i.v. in anesthetized rats and planar images were acquired. We investigated the role of GSH in the lung retention of HMPAO by pre-treating rats with the GSH-depleting agent diethyl maleate (DEM) prior to imaging. We also measured GSH content and activities of mitochondrial complex I and IV in lung homogenate. The lung retention of HMPAO increased by ~50% and ~250% in hyper-60 and hyper-95R rats respectively compared to retention in rats exposed to room air (normoxic). DEM decreased retention in normoxic (~26%) and hyper-95R (~56%) rats compared to retention in the absence of DEM. GSH content increased by 19% and 40% in hyper-60 and hyper-95R lung homogenate, compared to normoxic lung homogenate. Complex I activity decreased by ~50% in hyper-60 and hyper-95R lung homogenate compared to activity in normoxic lung homogenate. However, complex IV activity was increased by 32% in hyper-95R lung homogenate only. Furthermore, we identified correlations between the GSH content in lung homogenate and the DEM-sensitive fraction of HMPAO retention, and between the complex IV/complex I activity ratio and the DEM-insensitive fraction of HMPAO retention. These results suggest that increase in the GSH-dependent component of the lung retention of HMPAO may be a marker of tolerance to sustained exposure to hyperoxia.

Optimization of Cardiovascular Stent Design Using Computational Fluid Dynamics

Timothy J. Gundert et al. — Fri, 06 Jul 2012 16:03:53 PDT

Coronarystent design affects the spatial distribution of wall shear stress(WSS), which can influence the progression of endothelialization, neointimal hyperplasia,and restenosis. Previous computational fluid dynamics (CFD) studies have onlyexamined a small number of possible geometries to identify stentdesigns that reduce alterations in near-wall hemodynamics. Based on apreviously described framework for optimizing cardiovascular geometries, we developed amethodology that couples CFD and three-dimensional shape-optimization for use instent design. The optimization procedure was fully-automated, such that solidmodel construction, anisotropic mesh generation, CFD simulation, and WSS quantificationdid not require user intervention. We applied the method todetermine the optimal number of circumferentially repeating stent cells (N_C)for slotted-tube stents with various diameters and intrastrut areas. Optimalstent designs were defined as those minimizing the area oflow intrastrut time-averaged WSS. Interestingly, we determined that the optimalvalue of N_C was dependent on the intrastrut angle withrespect to the primary flow direction. Further investigation indicated thatstent designs with an intrastrut angle of approximately 40 degminimized the area of low time-averaged WSS regardless of vesselsize or intrastrut area. Future application of this optimization methodto commercially available stent designs may lead to stents withsuperior hemodynamic performance and the potential for improved clinical outcomes.

Current Research and Clinical Applications in Human Motion Analysis

Ken N. Kuo et al. — Fri, 06 Jul 2012 15:54:27 PDT

Upper Extremity Joint Dynamics During Walker Assisted Gait: A Quantitative Approach Towards Rehabilitative Intervention

Katherine A. Konop et al. — Fri, 06 Jul 2012 15:49:29 PDT

Background

Many children with spastic diplegic cerebral palsy (CP) use anterior or posterior walkers to aid ambulation. Prolonged use may lead to upper extremity (UE) pathology later in life, including arthritis and joint contractures.

Purpose

This study analyzes the dynamics (kinematics and kinetics) of the shoulder (glenohumeral), elbow, and wrist joints during anterior and posterior walker use. It also examines the dynamic effects of adjusting handle height and grip rotation.

Methods

Ten children with CP underwent motion analysis with upper and lower extremity marker sets and six-degree-of-freedom instrumented walker handles, while using both anterior and posterior walkers. One child underwent the same analysis, with added trials for wrist derotation (adjusted axial grip rotation) and wrist plus elbow derotation (adjusted handle height). A validated kinematic and kinetic model was applied to calculate UE joint angles, joint reaction forces (JRFs), and joint reaction moments (JRMs).

Results

Surprisingly, no statistically significant differences in UE angles, JRFs, or JRMs were observed between anterior and posterior walkers. Wrist derotation, however, decreased the flexion JRM seen at the wrist, and elbow derotation decreased the flexion JRM seen at the elbow.

Conclusion

Anterior and posterior walkers produce similar UE motion and peak loading values. Wrist and elbow joint derotation alters the dynamic effects experienced by the UEs. UE motion analysis during aided gait can be useful for optimizing UE loading conditions to limit pathology later in life.

Analysis of Push-Off Power During Locomotion in Children with Type 1 Osteogenesis Imperfecta

Joseph Krzak et al. — Fri, 06 Jul 2012 14:19:57 PDT

Background/Purpose

Children with type 1 osteogenesis imperfecta (OI) present with abnormal gait characteristics, including reduced power generation during pushoff. However, the exact biomechanical factors associated with reduced power generation are not clearly understood. The purpose of this study was to investigate the biomechanical factors associated with a reduction in ankle power generation in children with type 1 OI.

Methods

Twenty-four participants with type 1 OI (12.5 ± 3.6 years of age) and 24 typically developing children (12.4 ± 3.7 years of age) were evaluated. Three-dimensional gait analysis, isometric plantar flexion strength using dynamometry, and pedobarography were collected on each participant. Results were statistically compared between the groups and a correlation matrix analyzed the associations among the measures.

Results

Children with OI presented with weaker plantar flexors, reduced ankle power generation, and decreased sagittal plane ankle angular velocity during pushoff. However, they presented with similar moment arm distances and ground reaction force magnitudes as typically seen in developing children. There was a higher incidence of pes valgus, increased subarch angles, increased time spent loading the midfoot, and deceased time spent loading the forefoot in children with OI. Plantar flexion strength and the time spent at the midfoot and forefoot were most associated with ankle power generation.

Conclusion

The presence of pes valgus alone does not indicate a reduction of push-off power in children with type 1 OI, but those individuals who have both a flat foot and reduced time spent loading the forefoot during pushoff are the most likely to have reduced push-off power.

Mechanical Characterization of Fourth Generation Composite Humerus

Prateek Grover et al. — Fri, 06 Jul 2012 14:07:47 PDT

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 µε/N) and posterior (5.43 µε/N) gauges for AP bending, and comparatively less for ML bending, i.e. 5.1 and 4.5 µε/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.

Assessing Spinal Motion at Different Fusion Levels in Adolescents with Idiopathic Scoliosis

Sahar Hassani et al. — Thu, 05 Jul 2012 16:39:35 PDT

Foot and Ankle Motion Analysis Using Dynamic Radiographic (Fluoroscopic) Imaging

Benjamin McHenry et al. — Thu, 05 Jul 2012 16:09:44 PDT