Loss of bone density and bone strength following premenopausal risk-reducing bilateral salpingo-oophorectomy: a prospective controlled study (WHAM Study).

Prophylactic oophorectomy is recommended for women at high risk for ovarian cancer, but the associated impact on bone health is of clinical concern. This prospective, controlled study demonstrated substantial loss of bone density and bone strength following surgical menopause. Postoperative hormone therapy alleviated, but not fully prevented, spinal bone loss. INTRODUCTION: This prospective study investigated bone health in women following premenopausal oophorectomy. METHODS: Dual-energy x-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and pQCT-based finite element analysis (pQCT-FEA) were used to assess bone health between systemic hormone therapy (HT) users and non-users after premenopausal risk-reducing bilateral salpingo-oophorectomy (RRBSO) compared with premenopausal controls over 24-month follow-up. RESULTS: Mean age was 42.4 ± 2.6 years (n = 30) for the surgery group and 40.2 ± 6.3 years for controls (n = 42), and baseline bone measures were similar between groups. Compromised bone variables were observed at 24 months after RRBSO, among which areal bone mineral density (aBMD) at the lumbar spine, tibial volumetric cortical density (Crt vBMD), and tibial bending stiffness (kbend) had decreased by 4.7%, 1.0%, and 12.1%, respectively (all p < 0.01). In non-HT users, significant losses in lumbar spine (5.8%), total hip (5.2%), femoral neck (6.0%) aBMD, tibial Crt vBMD (2.3%), and kbend (14.8%) were observed at 24 months (all p < 0.01). HT prevented losses in kbend, tibial Crt vBMD, and aBMD, except for modest 2.3% loss at the lumbar spine (p = 0.01). CONCLUSION: This prospective, controlled study of bone health following RRBSO or premenopausal oophorectomy demonstrated substantial loss of bone density and bone strength following RRBSO. HT prevented loss of bone density and bone stiffness, although there was still a modest decrease in lumbar spine aBMD in HT users. These findings may inform decision-making about RRBSO and clinical management following premenopausal oophorectomy.

Peripheral quantitative computed tomography (pQCT)-based finite element analysis provides enhanced diagnostic performance in identifying non-vertebral fracture patients compared with dual-energy X-ray absorptiometry.

Due to limitations of the predominant clinical method for diagnosing osteoporosis, an engineering model based on a dedicated CT scanner for bone density and structure was applied in fracture patients and controls. Improved diagnostic performance was observed, which supports its potential use in future research and clinical practice. INTRODUCTION: Dual-energy X-ray absorptiometry (DXA), the predominant clinical method for diagnosing osteoporosis, has limitations in identifying individuals with increased fracture risk. Peripheral quantitative computed tomography (pQCT) provides additional information and can be used to generate finite element (FE) models from which bone strength properties can be estimated. We investigated the ability of pQCT-FE properties to distinguish peripheral low-trauma fracture patients from healthy controls, by comparison with DXA and standard pQCT. METHODS: One hundred and eight fracture patients (77 females aged 67.7 ± 7.9 years, 31 males aged 69.7 ± 8.9 years) were recruited from a hospital fracture liaison service. One hundred and twenty healthy community controls (85 females aged 69.8 ± 8.5 years, 35 males aged 68.9 ± 7.2 years) were recruited. RESULTS: Significant differences between groups were observed in pQCT-FE properties, especially at the 4% tibia site. Fracture odds increased most per standard deviation decrease in pQCT-FE at this location [shear stiffness estimate, kshear, in females, OR = 10.34, 95% CI (1.91, 43.98); bending stiffness estimate, kbend, in males, OR = 8.32, 95% CI (4.15, 33.84)]. Area under the receiver operating characteristics curve (AUROC) was observed to be highest with pQCT-FE properties at 4% the tibia site. In females, this was 0.83 for the pQCT-FE variable kshear, compared with 0.72 for DXA total hip bone density (TH aBMD) and 0.76 for pQCT tibia trabecular density (Trb vBMD); in males, this was 0.81 for the pQCT-FE variable kbend at the 4% tibia site, compared with 0.62 for TH aBMD and 0.71 for Trb vBMD. There were significant differences in AUROC between DXA and pQCT-FE variables in both females (p = 0.02) and males (p = 0.03), while no difference was observed in AUROC between primary pQCT and pQCT-FE variables. CONCLUSIONS: pQCT-FE modeling can provide enhanced diagnostic performance compared with DXA and, given its moderate cost, may be useful in clinical settings.

A method for fatigue testing of equine McIII subchondral bone under a simulated fast workout training programme.

BACKGROUND: Standard fatigue testing of bone uses a single load and frequency applied until failure. However, in situ, the subchondral bone of Thoroughbred racehorses is subjected to a combination (or a spectrum) of loads and frequencies during training and racing. OBJECTIVE: To investigate the use of a fatigue testing method for equine third metacarpal (McIII) subchondral bone under a spectrum of loading conditions which a racehorse is likely to experience during a fast workout. STUDY DESIGN: In vitro biomechanical experimental study. METHODS: McIII subchondral bone specimens (n = 12) of racehorses were harvested from left and right medial condyles. A novel fatigue loading protocol was developed based upon a standard sequence of gaits during a typical fast workout protocol. This loading pattern, or loading loop, was repeated until the failure of the specimen. RESULTS: The mean ± standard deviation for all specimens for total time-to-failure was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 fast workouts). Ten of twelve specimens withstood at least one complete loop equivalent to a fast workout. All specimens failed during simulated gallop loading. MAIN LIMITATIONS: The resting time between loops was much shorter than in vivo resting time and specimens were unconfined during compressive testing. CONCLUSIONS: This novel fatigue loading protocol more closely mimics in vivo fatigue loading of McIII subchondral bone and demonstrates the importance of the highest speeds in the development of subchondral bone injury.

Lumbar model generator: a tool for the automated generation of a parametric scalable model of the lumbar spine.

Low back pain is a major cause of disability and requires the development of new devices to treat pathologies and improve prognosis following surgery. Understanding the effects of new devices on the biomechanics of the spine is crucial in the development of new effective and functional devices. The aim of this study was to develop a preliminary parametric, scalable and anatomically accurate finite-element model of the lumbar spine allowing for the evaluation of the performance of spinal devices. The principal anatomical surfaces of the lumbar spine were first identified, and then accurately fitted from a previous model supplied by S14 Implants (Bordeaux, France). Finally, the reconstructed model was defined according to 17 parameters which are used to scale the model according to patient dimensions. The developed model, available as a toolbox named the lumbar model generator, enables generating a population of models using subject-specific dimensions obtained from data scans or averaged dimensions evaluated from the correlation analysis. This toolbox allows patient-specific assessment, taking into account individual morphological variation. The models have applications in the design process of new devices, evaluating the biomechanics of the spine and helping clinicians when deciding on treatment strategies.

Biomechanical testing of the calcified metacarpal articular surface and its association with subchondral bone microstructure in Thoroughbred racehorses.

BACKGROUND: Palmar/plantar osteochondral disease (POD) and third metacarpal/-tarsal condylar fractures are considered fatigue injuries of subchondral bone (SCB) and calcified cartilage due to repetitive high loads in racehorses. In combination with adaptive changes in SCB in response to race training, the accumulation of SCB fatigue is likely to result in changes of joint surface mechanical properties. OBJECTIVES: To determine the spatial relationship and correlation of calcified articular surface biomechanical properties with SCB microstructure and training history in the distal palmar metacarpal condyle of Thoroughbred racehorses. STUDY DESIGN: Cross-sectional study. METHODS: Third metacarpal condyles were examined from 31 Thoroughbred horses with micro-computed tomography (microCT). Hyaline cartilage was removed and reference point indentation (RPI) mechanical testing of the calcified articular surface was performed. Training histories were obtained from trainers. The association among indentation distance increase (IDI, an inverse RPI measure of toughness), and microCT and training variables was assessed using a mixed-effects generalised linear model. RESULTS: Untrained horses had higher IDI than horses that had commenced training (P<0.001). Death as a result of musculoskeletal bone fatigue injury (P = 0.044) and presence of POD (P = 0.05) were associated with higher IDI. The microCT variables connectivity density and trabecular pattern factor were positively (P = 0.002) and negatively (P<0.001) correlated with IDI respectively. MAIN LIMITATIONS: The application of RPI to the calcified articular surface is novel and there is a potential for measurement variability with surface unevenness. CONCLUSION: Commencement of race training is associated with altered material properties of the calcified articular surface in horses. Reduced articular surface material properties can also be detected in horses that have fatigue injuries of the distal metacarpus and at other sites in the skeleton. Measures of SCB connectivity and trabecular surface shape may be more important determinants of resistance to failure of the calcified articular surface than traditional measures such as SCB volume and density.

Modelling apical columnar epithelium mechanics from circumferential contractile fibres.

Simple columnar epithelia are formed by individual epithelial cells connecting together to form single cell high sheets. They are a main component of many important body tissues and are heavily involved in both normal and cancerous cell activities. Prior experimental observations have identified a series of contractile fibres around the circumference of a cross section located in the upper (apical) region of each cell. While other potential mechanisms have been identified in both the experimental and theoretical literature, these circumferential fibres are considered to be the most likely mechanism controlling movement of this cross section. Here, we investigated the impact of circumferential contractile fibres on movement of the cross section by creating an alternate model where movement is driven from circumferential contractile fibres, without any other potential mechanisms. In this model, we utilised a circumferential contractile fibre representation based on investigations into the movement of contractile fibres as an individual system, treated circumferential fibres as a series of units, and matched our model simulation to experimental geometries. By testing against laser ablation datasets sourced from existing literature, we found that circumferential fibres can reproduce the majority of cross-sectional movements. We also investigated model predictions related to various aspects of cross-sectional movement, providing insights into epithelium mechanics and demonstrating the usefulness of our modelling approach.

Bone fatigue and its implications for injuries in racehorses.

Musculoskeletal injuries are a common cause of lost training days and wastage in racehorses. Many bone injuries are a consequence of repeated high loading during fast work, resulting in chronic damage accumulation and material fatigue of bone. The highest joint loads occur in the fetlock, which is also the most common site of subchondral bone injury in racehorses. Microcracks in the subchondral bone at sites where intra-articular fractures and palmar osteochondral disease occur are similar to the fatigue damage detected experimentally after repeated loading of bone. Fatigue is a process that has undergone much study in material science in order to avoid catastrophic failure of engineering structures. The term 'fatigue life' refers to the numbers of cycles of loading that can be sustained before failure occurs. Fatigue life decreases exponentially with increasing load. This is important in horses as loads within the limb increase with increasing speed. Bone adapts to increased loading by modelling to maintain the strains within the bone at a safe level. Bone also repairs fatigued matrix through remodelling. Fatigue injuries develop when microdamage accumulates faster than remodelling can repair. Remodelling of the equine metacarpus is reduced during race training and accelerated during rest periods. The first phase of remodelling is bone resorption, which weakens the bone through increased porosity. A bone that is porous following a rest period may fail earlier than a fully adapted bone. Maximising bone adaptation is an important part of training young racehorses. However, even well-adapted bones accumulate microdamage and require ongoing remodelling. If remodelling inhibition at the extremes of training is unavoidable then the duration of exposure to high-speed work needs to be limited and appropriate rest periods instituted. Further research is warranted to elucidate the effect of fast-speed work and rest on bone damage accumulation and repair.

Shod landing provides enhanced energy dissipation at the knee joint relative to barefoot landing from different heights.

Athletic shoes can directly provide shock absorption at the foot due to its cushioning properties, however it remains unclear how these shoes may affect the level of energy dissipation contributed by the knee joint. This study sought to investigate biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. Twelve healthy male recreational athletes were recruited and instructed to perform double-leg landing from 0.3-m and 0.6-m heights in barefoot and shod conditions. The shoe model tested was Brooks Maximus II. Markers were placed on the subjects based on the Plug-in Gait Marker Set. Force-plates and motion-capture system were used to capture ground reaction force (GRF) and kinematics data respectively. 2×2-ANOVA (barefoot/shod condition×landing height) was performed to examine differences in knee kinematics, kinetics and energetics between barefoot and shod conditions from different landing heights. Peak GRF was not significantly different (p=0.732-0.824) between barefoot and shod conditions for both landing heights. Knee range-of-motion, flexion angular velocity, external knee flexion moment, and joint power and work were higher during shod landing (p<0.001 to p=0.007), compared to barefoot landing for both landing heights. No significant interactions (p=0.073-0.933) were found between landing height and barefoot/shod condition for the tested parameters. While the increase in landing height can elevate knee energetics independent of barefoot/shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights.

Non-linear flexion relationships of the knee with the hip and ankle, and their relative postures during landing.

The knee joint, together with the hip and ankle, contributes to overall shock absorption through their respective flexion motions during landing. This study sought to investigate the presence of a lower extremity coordination pattern by determining mathematical relationships that associate knee flexion angles with hip flexion and ankle dorsiflexion angles during landing phase, and to determine relative postures of the hip and ankle, with reference to the knee, and examine how these relative postures change during key events of the landing phase. Eight healthy male subjects were recruited to perform double-leg landing from 0.6-m height. Motion capture system and force-plates were used to obtain kinematics and ground reaction forces (GRF) respectively. Non-linear regression analysis was employed to determine appropriate mathematical relationships of the hip flexion and ankle dorsiflexion angles with knee flexion angles during the landing phase. Relative lower extremity postures were compared between events of initial contact, peak GRF and maximum knee flexion, using ANOVA on ranks. Our results demonstrated a lower extremity coordination pattern, whereby the knee flexion angles had strong exponential (R(2) = 0.92-0.99, p < 0.001) and natural logarithmic (R(2) = 0.85-0.97, p < 0.001) relationships with hip flexion and ankle dorsiflexion angles respectively during the landing phase. Furthermore, we found that the s ubjects adopted distinctly different relative lower extremity postures (p < 0.05) during peak GRF as compared to initial contact. These relative postures were further maintained till the end of the landing phase. The occurrence of these relative postures may be a reflexive mechanism for the subjects to efficiently absorb the impact imposed by the peak GRF.

Effect of an anterior-sloped brace joint on anterior tibial translation and axial tibial rotation: a motion analysis study.

BACKGROUND: Anterior tibial translation and axial tibial rotation are major biomechanical factors involved in anterior cruciate ligament injuries. This study sought to evaluate a brace prototype designed with an anterior-sloped joint, in terms of its efficacy in attenuating anterior tibial translation and axial tibial rotation during landing, using a motion analysis approach. METHODS: Ten healthy male subjects performed single-leg landing tasks from a 0.6-m height with and without the brace prototype. Ground reaction force and kinematics data were obtained using a motion-capture system and force-plates. Anterior tibial translation and axial tibial rotation were determined based on tibial and femoral marker reference frames. Vertical and anterior-posterior ground reaction forces, hip, knee and ankle joint range-of-motions and angular velocities, anterior tibial translation and axial tibial rotation were compared between unbraced and braced conditions using Wilcoxon signed-rank test. FINDINGS: We found no significant difference in peak vertical and anterior-posterior ground reaction forces (p=0.770 and p=0.332 respectively) between unbraced and braced conditions. Knee joint range-of-motion and angular velocity were lower (p=0.037 and p=0.038 respectively) for braced condition than unbraced condition. Anterior tibial translation and axial tibial rotation were reduced (p=0.027 and p=0.006 respectively) in braced condition, compared to unbraced condition. INTERPRETATION: The anterior-sloped brace joint helps to attenuate anterior tibial translation and axial tibial rotation present in the knee joint during landing. It is necessary to test the brace prototype in a sporting population with realistic sports landing situations in order to assess its effectiveness in lowering anterior cruciate ligament injury risk.

Extent and distribution of tibial osteochondral disruption during simulated landing impact with axial tibial rotation restraint.

Post-traumatic knee osteochondral injuries are often coupled with anterior cruciate ligament (ACL) injury mechanisms during landing. However, it is not well understood whether restraining axial tibial rotation during landing would influence the extent and distribution of osteochondral disruption. Using ski landing as an example, this study subjected knee specimens to simulated landing impact without and with axial tibial rotation restraint, and investigated the extent and distribution of osteochondral disruption at the tibial plateau. Twenty-one porcine knee specimens were randomly divided into three test conditions, namely: (1) control, (2) impact only (I), and 3) impact with restraint (IR). Simulated landing impact was applied to the specimens based on a single 10 Hz haversine. Osteochondral explants were obtained from anterior, middle and posterior regions of medial and lateral tibial compartments. The extent of cartilage and trabecular disruption in these explants was examined based on histology, SEM and microCT. Only specimens in unrestrained condition incurred ACL failure upon impact. Restraining axial tibial rotation during simulated impact generally inflicted cartilage damage and deformation, and further caused trabecular disruption. Axial tibial rotation restraint did not necessarily restrict anterior tibial translation, as indicated by the presence of relative posterior femoral translation and osteochondral disruption at anterior-posterior tibial regions. While the results obtained in the current study may not be completely translatable to human models, there is likelihood that restraining axial tibial rotation during landing may help to prevent ACL failure, but will also induce osteochondral disruption in most tibial regions.

Direct contribution of axial impact compressive load to anterior tibial load during simulated ski landing impact.

Anterior tibial loading is a major factor involved in the anterior cruciate ligament (ACL) injury mechanism during ski impact landing. We sought to investigate the direct contribution of axial impact compressive load to anterior tibial load during simulated ski landing impact of intact knee joints without quadriceps activation. Twelve porcine knee specimens were procured. Four specimens were used as non-impact control while the remaining eight were mounted onto a material-testing system at 70 degrees flexion and subjected to simulated landing impact, which was successively repeated with incremental actuator displacement. Four specimens from the impacted group underwent pre-impact MRI for tibial plateau angle measurements while the other four were subjected to histology and microCT for cartilage morphology and volume assessment. The tibial plateau angles ranged from 29.4 to 38.8 degrees . There was a moderate linear relationship (Y=0.16X; R(2)=0.64; p<0.001) between peak axial impact compressive load (Y) and peak anterior tibial load (X). The anterior and posterior regions in the impacted group sustained surface cartilage fraying, superficial clefts and tidemark disruption, compared to the control group. MicroCT scans displayed visible cartilage deformation for both anterior and posterior regions in the impacted group. Due to the tibial plateau angle, increased axial impact compressive load can directly elevate anterior tibial load and hence contribute to ACL failure during simulated landing impact. Axial impact compressive load resulted in shear cartilage damage along anterior-posterior tibial plateau regions, due to its contribution to anterior tibial loading. This mechanism plays an important role in elevating ACL stress and cartilage deformation during impact landing.

Sagittal knee joint kinematics and energetics in response to different landing heights and techniques.

Single-leg and double-leg landing techniques are common athletic maneuvers typically performed from various landing heights during intensive sports activities. However, it is still unclear how the knee joint responds in terms of kinematics and energetics to the combined effects of different landing heights and techniques. We hypothesized that the knee displays greater flexion angles and angular velocities, joint power and work in response to the larger peak ground reaction force from 0.6-m height, compared to 0.3-m height. We further hypothesized that the knee exhibits elevated flexion angles and angular velocities, joint power and work during double-leg landing, relative to single-leg landing. Ground reaction force, knee joint kinematics and energetics data were obtained from 10 subjects performing single-leg and double-leg landing from 0.3-m to 0.6-m heights, using motion-capture system and force-plates. Higher peak ground reaction force (p<0.05) was observed during single-leg landing and/or at greater landing height. We found greater knee flexion angles and angular velocities (p<0.05) during double-leg landing and/or at greater landing height. Elevated knee joint power and work were noted (p<0.05) during double-leg landing and/or at greater landing height. The knee joint is able to respond more effectively in terms of kinematics and energetics to a larger landing impact from an elevated height during double-leg landing, compared to single-leg landing. This allows better shock absorption and thus minimizes the risk of sustaining lower extremity injuries.

Effect of landing height on frontal plane kinematics, kinetics and energy dissipation at lower extremity joints.

Lack of the necessary magnitude of energy dissipation by lower extremity joint muscles may be implicated in elevated impact stresses present during landing from greater heights. These increased stresses are experienced by supporting tissues like cartilage, ligaments and bones, thus aggravating injury risk. This study sought to investigate frontal plane kinematics, kinetics and energetics of lower extremity joints during landing from different heights. Eighteen male recreational athletes were instructed to perform drop-landing tasks from 0.3- to 0.6-m heights. Force plates and motion-capture system were used to capture ground reaction force and kinematics data, respectively. Joint moment was calculated using inverse dynamics. Joint power was computed as a product of joint moment and angular velocity. Work was defined as joint power integrated over time. Hip and knee joints delivered significantly greater joint power and eccentric work (p<0.05) than the ankle joint at both landing heights. Substantial increase (p<0.05) in eccentric work was noted at the hip joint in response to increasing landing height. Knee and hip joints acted as key contributors to total energy dissipation in the frontal plane with increase in peak ground reaction force (GRF). The hip joint was the top contributor to energy absorption, which indicated a hip-dominant strategy in the frontal plane in response to peak GRF during landing. Future studies should investigate joint motions that can maximize energy dissipation or reduce the need for energy dissipation in the frontal plane at the various joints, and to evaluate their effects on the attenuation of lower extremity injury risk during landing.

Repeated application of incremental landing impact loads to intact knee joints induces anterior cruciate ligament failure and tibiofemoral cartilage deformation and damage: A preliminary cadaveric investigation.

Anterior cruciate ligament (ACL) injury is a major problem worldwide and prevails during high-impact activities. It is not well-understood how the extent and distribution of cartilage damage will arise from repetitive landing impact loads that can lead to ACL failure. This study seeks to investigate the sole effect of repetitive incremental landing impact loads on the induction of ACL failure, and extent and distribution of tibiofemoral cartilage damage in cadaveric knees. Five cadaveric knees were mounted onto a material testing system at 70 degrees flexion to simulate landing posture. A motion-capture system was used to track rotational and translational motions of the tibia and femur, respectively. Each specimen was compressed at a single 10Hz haversine to simulate landing impact. The compression trial was successively repeated with increasing actuator displacement till a significant compressive force drop was observed. All specimens underwent ACL failure, which was confirmed via magnetic resonance scans and dissection. Volume analysis, thickness measurement and histological techniques were employed to assess cartilage lesion status. For each specimen, the highest peak compressive force (1.9-7.8kN) was at the final trial in which ACL failure occurred; corresponding posterior femoral displacement (7.6-18.0mm) and internal tibial rotation (0.6 degrees -4.7 degrees ) were observed. Significant compressive force drop (79.8-90.9%) was noted upon ACL failure. Considerable cartilage deformation and damage were found in exterior, posterior and interior femoral regions with substantial volume reduction in lateral compartments. Repeated application of incremental landing impact loads can induce both ACL failure and cartilage damage, which may accelerate the risk of developing osteoarthritis.

Modified Bilston nonlinear viscoelastic model for finite element head injury studies.

This paper proposes a modified nonlinear viscoelastic Bilston model (Bilston et al., 2001, Biorheol., 38, pp. 335-345). for the modeling of brain tissue constitutive properties. The modified model can be readily implemented in a commercial explicit finite element (FE) code, PamCrash. Critical parameters of the model have been determined through a series of rheological tests on porcine brain tissue samples and the time-temperature superposition (TTS) principle has been used to extend the frequency to a high region. Simulations by using PamCrash are compared with the test results. Through the use of the TTS principle, the mechanical and rheological behavior at high frequencies up to 10(4) rads may be obtained. This is important because the properties of the brain tissue at high frequencies and impact rates are especially relevant to studies of traumatic head injury. The averaged dynamic modulus ranges from 130 Pa to 1500 Pa and loss modulus ranges from 35 Pa to 800 Pa in the frequency regime studied (0.01 rads to 3700 rads). The errors between theoretical predictions and averaged relaxation test results are within 20% for strains up to 20%. The FEM simulation results are in good agreement with experimental results. The proposed model will be especially useful for application to FE analysis of the head under impact loads. More realistic analysis of head injury can be carried out by incorporating the nonlinear viscoelastic constitutive law for brain tissue into a commercial FE code.

Development of an integrated CAD-FEA process for below-knee prosthetic sockets.

BACKGROUND: Computer-aided design and manufacturing has been successfully used in prosthetic applications since 1980s. It simplifies the socket rectification process and improves reproducibility but does not introduce any new principle into socket design. Integrating finite element analysis to CAD will provide a more objective assessment of socket fit and improve the chance of a successful first fitting. METHODS: Current study aims to establish a finite element model generation technique directly from geometrical information of commercial prosthetic CAD workstation. A program developed in-house automatically performs meshing of the stump geometry and assigns suitable material properties, load and boundary conditions to the model. The model was validated by comparing predicted pressure with experimentally measured values for one amputee subject. FINDINGS: The predicted pressure distribution has an root-mean-square error of 8.8 kPa compared to experimental values at 10%, 25% and 50% of the gait cycle. INTERPRETATION: Current method was able to develop a finite element model to predict interface pressure reasonably well and can be integrated with prosthetic CAD system to provide quantitative feedback to the prosthetist in an automated process.

Static and dynamic pressure profiles of a patellar-tendon-bearing (PTB) socket.

The purpose of this study was to evaluate the pressure distribution at the stump/socket interface in amputees wearing the patellar-tendon-bearing socket. A specially built strain gauged type pressure transducer was used for measuring this pressure distribution in four unilateral transtibial amputees. Pressure and gait parameters were measured simultaneously while they were standing and walking. Pressure profiles were compiled at 10, 25 and 50 per cent of gait cycle and compared with the pressure profiles predicted by Radcliffe in 1961. The subject's anterior-posterior pressure profiles were different from each other. However, at toe-off, each subject exhibited an increase in pressure at the patellar tendon. Their medial-lateral pressure profiles were similar: exhibiting high pressure at the medial proximal and lateral distal regions except for one subject who exhibited high pressure at the lateral proximal region instead. The subjects' pressure profiles did not resemble Radcliffe's anticipated pressure profiles. This was because ground reaction force was not the only factor affecting the resulting pressure profiles.

Stump/socket pressure profiles of the pressure cast prosthetic socket.

OBJECTIVE: The aim was to evaluate stump/socket interface pressure in amputees wearing a socket developed by a pressure casting system.Design. Five unilateral transtibial amputees wore a pressure cast socket and walked at a self-selected speed. BACKGROUND: The socket produces equally distributed pressure at the stump/socket interface, deviating from the conventional belief that pressure varies in proportion to the pain threshold of different tissues in the stump. METHODS: The socket was fabricated while the subject placed his stump in a pressure chamber. Pressure was applied while he adopted a normal standing position. A specially built strain gauged type pressure transducer was used for measuring pressure distribution. Pressure and gait parameters were measured simultaneously while the subjects were standing and walking. RESULTS AND CONCLUSION: The pressure cast technique was able to provide comfortable fitting sockets. A hydrostatic pressure profile was not evident during standing or gait. Results also showed that no standard pressure profile for the pressure cast socket was observed. This was expected as no rectifications were done on the pressure cast socket. Pressure profiles at 10%, 25% and 50% of gait cycle did not correlate with the pressure profiles previously proposed. RELEVANCE: The hydrostatic theory is an attractive concept in socket design as it produces a stump/socket pressure profile that is evenly distributed. Furthermore, it is a method that is easily implemented, independent of a prosthetist's skill and experience and reduces manufacturing time. However, there is still controversy surrounding the efficacy of this hydrostatic theory.

Structural integrity of polypropylene prosthetic sockets manufactured using the polymer deposition technique.

Rapid prototyping (RP) technology has been used recently as a means for automated socket fabrication. Although the technology has proven to be promising and has truly automated the socket fabrication process, the structural integrity of RP sockets remains questionable. For the long term, unsupervised use of these 'unconventional' sockets, their material properties and structural integrity must be determined. This study investigated the structural integrity of polypropylene sockets manufactured using a polymer deposition technique, in which a socket is formed by a continuous strand of partially melted polypropylene that is spirally deposited according to the socket's cross-sectional contour. To investigate the problem of delamination of the socket, the tensile properties of the socket material were determined according to ASTM D638-99. The ultimate tensile strength was found to be approximately 13-23 per cent lower than that of polypropylene sheets that are at present normally used for socket fabrication. In order to improve the load-bearing capacity of the socket, it was reinforced using a double-wall arrangement at the distal region, where failure normally occurs. The structural integrity of the complete prosthesis was then investigated according to ISO 10328 (loading condition II). The prosthesis passed the static loading test registering only 12 mm permanent deformation, and it successfully completed a preliminary cyclic test of 250,000 cycles with no observable failure.