Biomedical subjects

William R Ledoux

Publications and source records attributed to William R Ledoux.

14 recordsLinked to original sources

PubMed2006

Effect of foot shape on the three-dimensional position of foot bones.

To eliminate some of the ambiguity in describing foot shape, we developed three-dimensional (3D), objective measures of foot type based on computerized tomography (CT) scans. Feet were classified via clinical examination as pes cavus (high arch), neutrally aligned (normal arch), asymptomatic pes planus (flat arch with no pain), or symptomatic pes planus (flat arch with pain). We enrolled 10 subjects of each foot type; if both feet were of the same foot type, then each foot was scanned (n=65 total). Partial weightbearing (20% body weight) CT scans were performed. We generated embedded coordinate systems for each foot bone by assuming uniform density and calculating the inertial matrix. Cardan angles were used to describe five bone-to-bone relationships, resulting in 15 angular measurements. Significant differences were found among foot types for 12 of the angles. The angles were also used to develop a classification tree analysis, which determined the correct foot type for 64 of the 65 feet. Our measure provides insight into how foot bone architecture differs between foot types. The classification tree analysis demonstrated that objective measures can be used to discriminate between feet with high, normal, and low arches.

Biomechanical Phenomena↗

PubMed2006

A three-dimensional finite element model of the transibial residual limb and prosthetic socket to predict skin temperatures.

Amputees who wear prosthetic limbs often experience discomfort from blisters and sores due to mechanical insult; these skin conditions are exacerbated by elevated skin temperatures and excessive perspiration within the prosthetic socket. The goal of this study was to create a tool for developing new prostheses that accommodate varying thermal loads arising from everyday activities. A three-dimensional thermal model of a transtibial residual limb and prosthesis was constructed using the finite element (FE) method. Transverse computerized tomography (CT) scans were used to specify the geometry of the residual limb and socket. Thermal properties from the literature were assigned to both biological tissue and prosthetic socket elements. The purpose of this work was to create a model that would aid in testing the effect of new prosthesis designs on skin temperature. To validate its output, the model was used to predict the skin temperature distribution in a common prosthetic socket system (silicone liner, wool sock, and carbon fiber socket) at rest with no mechanical loading. Skin temperatures were generally elevated near muscle and decreased anteriorly and at the distal end. Experimental temperature measurements taken at the skin-prosthesis interface of five human subjects were used to validate the model. Data extracted from the thermal model at anterior, posterior, lateral, and medial locations were typically within one standard deviation of experimental results; the mean temperatures were within 0.3 degree C for each section and were within 0.1 degree C overall.

Amputees↗

PubMed2005

The midtarsal joint locking mechanism.

BACKGROUND: The midtarsal joint, consisting of the talo-navicular and the calcaneocuboid joints, is presumed to be responsible for the foot being both flexible and rigid during different parts of the stance phase of gait. However, this mechanism has never been well quantified. This study explores the midtarsal joint locking mechanism by comparing the effect of hindfoot inversion and eversion on midfoot and forefoot mobility. METHODS: Motion of the tibia, talus, calcaneus, navicular, cuboid and the first, second, and fifth metatarsals were measured in nine cadaver feet using Polhemus Fastrak electromagnetic sensors (EST GmbH and Co. KG, Kaiserslautern, Germany). The talus was fixed to the tibia, and then the forefoot was maximally dorsiflexed, plantarflexed, inverted, and everted, with the hindfoot in maximal eversion and inversion, for a total of eight test positions. The range of motion of the individual bones between maximal forefoot dorsiflexion and plantarflexion and between maximal forefoot inversion and eversion was calculated for the hindfoot in maximal eversion and inversion. RESULTS: For the range of motion from maximal dorsiflexion to maximal plantarflexion there was significantly increased movement of the first, second, and fifth metatarsals in the sagittal plane (p-value = 0.003, 0.007, and 0.002, respectively) when the calcaneus was maximally everted compared to when the calcaneus was maximally inverted. No significant differences were detected for the range of motion from forefoot inversion to eversion for the two hindfoot positions. CONCLUSIONS: This study demonstrated that motion in the forefoot is influenced by hindfoot position through the midtarsal joint. Specifically, the sagittal plane range of motion of the metatarsals is increased when the hindfoot is in valgus.

Aged, 80 and over↗

PubMed2004

Clinical biomechanics of the peritalar joint.

The peritalar joint includes the articulations between the talus and calcaneus and the talus and navicular. Motion between the talus and calcaneus is described most often as rotation about an axis that points medially, anteriorly, and superiorly. This motion is considered to be triplanar, with inversion, plantar flexion, and adduction occurring together, whereas eversion, dorsiflexion, and abduction are associated. Similar motions have been described between the talus and navicular. Foot deformity, such as a pes planus or a pes cavus foot type, and hindfoot or midfoot joint fusion can alter the biomechanics of the peritalar joint.

Arthrodesis↗

PubMed2004

A quasi-linear, viscoelastic, structural model of the plantar soft tissue with frequency-sensitive damping properties.

Little is known about the structural properties of plantar soft-tissue areas other than the heel; nor is it known whether the structural properties vary depending on location. Furthermore, although the quasi-linear viscoelastic (QLV) theory has been used to model many soft-tissue types, it has not been employed to model the plantar soft tissue. The structural properties of the plantar soft tissue were quantified via stress relaxation experiments at seven regions (subcalcaneal, five submetatarsal, and subhallucal) across eight cadaveric feet. The cadaveric feet were 36.9 +/- 17.4 (mean +/- S.D.) years of age, all free from vascular diseases and orthopedics disorders. All tests were performed at a constant environmental temperature of 35 degrees C. Stress relaxation experiments were performed; different loads were employed for different areas based on normative gait data. A modification of the relaxation spectrum employed within the QLV theory allowed for the inclusion of frequency-sensitive relaxation properties in addition to nonlinear elastic behavior. The tissue demonstrated frequency-dependent damping properties that made the QLV theory ill suited to model the relaxation. There was a significant difference between the elastic structural properties (A) of the subcalcaneal tissue and all other areas (p = 0.004), and a trend (p = 0.067) for the fifth submetatarsal to have less viscous damping (c1) than the subhallucal, or first, second, or third submetatarsal areas. Thus, the data demonstrate that the structural properties of the foot can vary across regions, but careful consideration must be given to the applied loads and the manner in which the loads were applied.

Adolescent↗

PubMed2003

Triangular osteosynthesis and iliosacral screw fixation for unstable sacral fractures: a cadaveric and biomechanical evaluation under cyclic loads.

OBJECTIVE: To conduct a biomechanical comparison of a new triangular osteosynthesis and the standard iliosacral screw osteosynthesis for unstable transforaminal sacral fractures in the immediate postoperative situation as well as in the early postoperative weight-bearing period. DESIGN: Twelve preserved human cadaveric lumbopelvic specimens were cyclicly tested in a single-limb-stance model. A transforaminal sacral fracture combined with ipsilateral superior and inferior pubic rami fractures were created and stabilized. Loads simulating muscle forces and body weight were applied. Fracture site displacement in three dimensions was evaluated using an electromagnetic motion sensor system. INTERVENTION: Specimens were randomly assigned to either an iliosacral and superior pubic ramus screw fixation or to a triangular osteosynthesis consisting of lumbopelvic stabilization (between L5 pedicle and posterior ilium) combined with iliosacral and superior pubic ramus screw fixation. MAIN OUTCOME MEASURES: Peak loaded displacement at the fracture site was measured for assessment of initial stability. Macroscopic fracture behavior through 10,000 cycles of loading, simulating the early postoperative weight-bearing period, was classified into type 1 with minimal motion at the fracture site, type 2 with complete displacement of the inferior pubic ramus, or type 3 with catastrophic failure. RESULTS: The triangular osteosynthesis had a statistically significantly smaller displacement under initial peak loads (mean +/- standard deviation [SD], 0.163 +/- 0.073 cm) and therefore greater initial stability than specimens with the standard iliosacral screw fixation (mean +/- SD, 0.611 +/- 0.453 cm) ( = 0.0104), independent of specimen age or sex. All specimens with the triangular osteosynthesis demonstrated type 1 fracture behavior, whereas iliosacral screw fixation resulted in one type 1, two type 2, and three type 3 fracture behaviors before or at 10,000 cycles of loading. CONCLUSION: Triangular osteosynthesis for unstable transforaminal sacral fractures provides significantly greater stability than iliosacral screw fixation under in vitro cyclic loading conditions. In vitro cyclic loading, as a limited simulation of early stages of patient mobilization in the postoperative period, allows for a time-dependent evaluation of any fracture fixation system.

Biomechanical Phenomena↗

PubMed2003

Muscular imbalances resulting in a clawed hallux.

A clawed hallux is a deformity of the great toe resulting from a muscular imbalance. Using a cadaveric foot-loading frame, we quantitatively assessed the role of the peroneus longus (PL), extensor hallucis longus (EHL), and flexor hallucis longus (FHL) on position and pressure distribution of the first ray by simulating muscle imbalances. The experimental protocol included applying seven different combinations of simulated disproportionate loads ("overpulls") for these three muscles using midstance force values derived from the literature. This study quantified the angular change in the joints of the first ray and measured the plantar pressure beneath the head of the first metatarsal and the hallux. The results indicated that the peroneus longus was statistically the greatest contributor to the elevation of plantar pressure beneath the first metatarsal, while the EHL and FHL were primarily responsible for the angular changes resulting in the clawed hallux deformity.

Aged↗

PubMed2003

Biomechanical differences among pes cavus, neutrally aligned, and pes planus feet in subjects with diabetes.

The purpose of this study was to quantify differences in joint range of motion, foot deformity, and foot morphology among pes cavus, neutrally aligned, pes planus rigid, and pes planus flexible feet. A cohort of 1047 veterans with diabetes (contributing 2047 feet) was enrolled in a prospective study of diabetic ulcer risk factors (the Seattle Diabetic Foot Study). Significant differences between foot types were found. Pes cavus feet had an increased percentage of prominent metatarsal heads, bony prominences, and hammer/claw toes (p < .0001), as well as significantly increased amounts of hallux dorsiflexion and decreased amounts of hallux plantarflexion (p < .0001) with a total range of motion equal to the other foot types (p = .3). Neutrally aligned feet had a lower percentage of intrinsic muscle atrophy, bony prominences, and hammer/claw toes (p < .0001). Pes planus feet had an increased lateral talometatarsal angle (p < .0001) and an increased second metatarsal length. These data demonstrate structural differences between foot types in a population with diabetes.

Biomechanical Phenomena↗

PubMed2002

The distributed plantar vertical force of neutrally aligned and pes planus feet.

The distributed vertical ground reaction forces were determined for a normative population and contrasted with data from subjects with flat feet. Nineteen asymptomatic subjects, 11 with a neutrally aligned foot type (normal arch) and 8 with a pes planus foot type (low arch), were studied as they walked barefoot across a pressure plate. The pressure plate data were converted to force values at seven locations (subhallucal, five submetatarsal and subcalcaneal) on the plantar aspect of the foot. The distributed loading pattern of the plantar soft tissue throughout the stance phase of gait was determined. Pes planus feet had significantly more force at the subhallucal area with no difference seen under the other areas. These data are indicative of aberrant first ray mechanics in pes planus feet.

Adult↗

PubMedDate not supplied

Residual-limb skin temperature in transtibial sockets.

The insulated environment of the lower-limb prosthesis can result in elevated residual-limb skin temperatures that may contribute to skin irritation, blistering, and a reduced quality of life. The design and materials of the prosthetic socket, suspension system, and liner can potentially alleviate these conditions, but the thermal load may vary with activity and location within the socket. To characterize the thermal environment at the skin-prosthesis interface, we made temperature measurements on five transtibial amputees at 14 locations on the residual limbs. After the participants donned their prosthesis and rested in the seated position for 15 min, the mean skin temperatures of their residual limbs increased by 0.8 degrees Celcius. Subsequent walking for 10 min resulted in a 1.7 degrees Celsius total increase in mean skin temperature. Thermal contour maps revealed the skin was coolest at the anterior proximal location and warmest across the posterior section, correlating with areas of low and high perfusion. From the results, we determined that residual-limb skin temperature depends on activity and locality. This information may aid in understanding where and why skin problems develop on lower-limb residual limbs and may provide design requirements for new prosthetic socket systems intended to alleviate temperature-related discomfort.

Adult↗

PubMedDate not supplied

A shear and plantar pressure sensor based on fiber-optic bend loss.

Lower-limb complications associated with diabetes include the development of plantar ulcers that can lead to infection and subsequent amputation. While we know from force-plate analyses that medial/lateral and anterior/posterior shear components of ground-reaction forces exist, little is known about the actual distribution of these stresses during daily activities or about the role that shear stresses play in causing plantar ulceration. Furthermore, one critical reason why these data have not been obtained previously is the lack of a validated, widely used, commercially available shear sensor, partly because of the various technical issues associated with measuring shear. In this study, we present a novel means of transducing plantar pressure and shear stress with a fiber-optic sensor. The pressure/shear sensor consists of an array of optical fibers lying in perpendicular rows and columns separated by elastomeric pads. We constructed a map of normal and shear stresses based on observed macrobending through the intensity attenuation from the physical deformation of two adjacent perpendicular fibers. Initial results show that this sensor exhibits low noise and responds to applied normal and shear loads with good repeatability.

Biomechanical Phenomena↗

PubMedDate not supplied

Foot and ankle ligament morphometry.

This study primarily measured and established a morphometric spectrum of cross-sectional areas for foot and ankle ligaments with the use of a new freeze-fracture technique that was independent of ligament cross-sectional shape. Ligament morphometry measurements were made on a total of 121 bone-ligament-bone preparations that were harvested from 26 fresh (unembalmed) male cadaver feet. We used the traditional digital caliper method to measure length and the freeze-fracture technique to measure cross-sectional area. Cross-sectional area values ranged from 21.36 to 170.48 mm(2) and length values from 5.01 to 37.45 mm. In addition, area-to-length ratios ranged from 0.60 to 27.02 mm. Compared with the freeze-fracture technique, the digital caliper method, which assumed that ligament cross-sectional shape was rectangular, resulted in an approximately 35% difference in cross-sectional area.

Adult↗

PubMedDate not supplied

Relationship between foot type, foot deformity, and ulcer occurrence in the high-risk diabetic foot.

We hypothesized an association between foot type, foot deformity, and foot ulceration and conducted an analysis of a well-characterized, high-risk diabetic population of 398 subjects. The average age was 62 years of age and 74% of the study population were males. Foot-type distributions were 19.5% pes cavus (high arch), 51.5% neutrally aligned (normal arch), and 29.0% pes planus (low arch). We quantified the presence of hallux valgus (23.9%), hammer/claw toes (46.7%), and hallux limitus (24.4%). A significant association was found between foot type and hallux valgus (p = 0.003); pes planus feet had the highest prevalence as compared with neutrally aligned feet (odds ratio [OR] = 2.43, p = 0.0006). Foot type was also significantly associated with fixed hammer/claw toes (p = 0.01); pes cavus feet had the highest prevalence as compared with neutrally aligned feet (OR = 3.89, p = 0.001). Foot type was also significantly associated with hallux limitus (p = 0.006) with pes planus feet having the highest prevalence as compared with neutrally aligned feet (OR = 2.19, p = 0.003). However, foot type was not significantly related to any ulcer outcome (p = 0.7). Fixed hammer/claw toes (OR = 3.91, p = 0.003) and hallux limitus (OR = 3.02, p = 0.006) were associated with increased risk of any ulcer occurrence. This study affirms that foot type and foot deformity are related and that foot deformities are associated with ulcer occurrence.

Age Distribution↗

PubMedDate not supplied

A three-dimensional, anatomically detailed foot model: a foundation for a finite element simulation and means of quantifying foot-bone position.

We generated an anatomically detailed, three-dimensional (3-D) reconstruction of a human foot from 286 computerized topographic (CT) images. For each bone, 2-D cross-sectional data were obtained and aligned to form a stacked image model. We calculated the inertial matrix of each bone from the stacked image model and used it to determine the principal axes. Relative angles between the principal axes of the bones were employed to describe the shape of the foot, i.e., the relationships between the bones of the foot. A 3-D surface model was generated from the stacked image models and a detailed 3-D mesh for each bone was created. Additionally, the representative geometry of the plantar soft tissue was obtained from the CT scans, while the geometries of the cartilage between bones were obtained from the 3-D surface bone models. This model served dual purposes: it formed the anatomical foundation for a future finite element model of the human foot and we used it to objectively quantify foot shape using the relationships between the principal axes of the foot bones.

Aged↗