Brian L. Davis

Temperature as a predictive tool for plantar triaxial loading.

Diabetic foot ulcers are caused by moderate repetitive plantar stresses in the presence of peripheral neuropathy. In severe cases, the development of these foot ulcers can lead to lower extremity amputations. Plantar pressure measurements have been considered a capable predictor of ulceration sites in the past, but some investigations have pointed out inconsistencies when solely relying on this method. The other component of ground reaction forces/stresses, shear, has been understudied due to a lack of adequate equipment. Recent articles reported the potential clinical significance of shear in diabetic ulcer etiology. With the lack of adequate tools, plantar temperature has been used as an alternative method for determining plantar triaxial loading and/or shear. However, this method has not been previously validated. The purpose of this study was to analyze the potential association between exercise-induced plantar temperature increase and plantar stresses. Thirteen healthy individuals walked on a treadmill for 10 minutes at 3.2km/h. Pre and post-exercise temperature profiles were obtained with a thermal camera. Plantar triaxial stresses were quantified with a custom-built stress plate. A statistically significant correlation was observed between peak shear stress (PSS) and temperature increase (r=0.78), but not between peak resultant stress (PRS) and temperature increase (r=0.46). Plantar temperature increase could predict the location of PSS and PRS in 23% and 39% of the subjects, respectively. Only a moderate linear relationship was established between triaxial plantar stresses and walking-induced temperature increase. Future research will investigate the value of nonlinear models in predicting plantar loading through foot temperature.

Design of a novel prosthetic socket: Assessment of the thermal performance

Prosthetic liners and sockets insulate the residual limb, causing excessive sweating and concomitant skin maceration. When coupled with atypical loading conditions, further dermatologic problems can arise. This can significantly reduce the quality of life of an amputee patient. Improving the design of the prosthetic socket has been proposed as a means of reestablishing a normal thermal environment around the residual limb. In this study, a prosthetic socket was modified by incorporating a helical cooling channel within the socket wall using additive manufacturing techniques. Two sockets were modeled: a control socket, and a modified socket containing a 0.48 cm diameter cooling channel. Computer simulations and bench-top testing were used to assess the designs ability to create a greater temperature differential across the socket wall. A greater temperature drop across the socket wall suggested that the socket could provide cooling benefits to the residual limb by allowing for heat to be drawn away from the limb. The temperature difference across the socket wall was calculated for both sockets in each aspect of the study. Both socket type (p=0.002) and location on the socket (p=0.014) were statistically significant factors affecting the temperature difference between inner and outer socket walls. Compared with the control socket, the modified socket containing a helical cooling channel exhibited greater temperature differences across its wall of 11.1 °C and 6.4 °C in the computer simulations and bench-top testing, respectively. This finding suggested that socket modifications, such as the cooling channel presented, could provide a beneficial cooling effect to an amputee patients residual limb.

Association Between Plantar Temperatures and Triaxial Stresses in Individuals With Diabetes

Diabetic foot ulcers have a biomechanical etiology related to triaxial plantar stresses (3DS) (1). Bergtholdt and Brand (2) suggested that the foot would heat up before breaking down, indicating that elevated 3DS in the diabetic foot would result in inflammation that could be monitored by thermography. The purpose of this study was to explore the hypothesized relationship between 3DS and plantar temperatures. Twenty-eight individuals with diabetes, 14 with peripheral neuropathy (DN) and 14 without (DC), walked at self-selected speeds across a custom-built plate that quantified 3DS. After 10 min of acclimation, resting barefoot temperatures were recorded using a Fluke infrared thermal camera. Linear regressions were used to reveal associations between magnitudes of 3DS and resting temperatures. Associations between locations of peak 3DS and peak temperatures were also examined. As assessed by linear regression, temperature was a statistically significant predictor of peak shear stress (PS) and shear-time integral magnitudes at the hallux. No significant association was found …

Plantar Shear Stress Distribution in Patients with Rheumatoid Arthritis Relevance to Foot Pain

BACKGROUND Rheumatoid arthritis is an autoimmune disease that causes chronic, progressive joint inflammation; it commonly affects the joints of the feet. Biomechanical alterations and daily pain in the foot are the common outcomes of the disease. Earlier studies focusing on plantar pressure in such patients reported increased vertical loading along with peak pressure-pain associations. However, footwear designed according to the pressure profiles did not relieve symptoms effectively. We examined plantar shear and pressure distribution in patients with rheumatoid arthritis and compared the findings with those of controls, and we investigated a potential relationship between foot pain and local shear stresses. METHODS A custom-built platform was used to collect plantar pressure and shear stress data from nine patients with rheumatoid arthritis and 14 control participants. Seven patients reported the presence of pain under their feet. Pressure-time and shear-time integral values were also calculated. RESULTS Peak pressure, pressure-time integral, resultant shear-time integral, and mediolateral shear stress magnitudes were higher in the complication group (P < .05). An association between peak shear-time integral and maximum pain locations was observed. CONCLUSIONS Increased mediolateral shear stresses under the rheumatoid foot might be attributable to gait instability in such patients. A correlation between the locations of maximum shear-time integral and pain indicate the clinical significance of plantar shear in patients with rheumatoid arthritis.

Thermal Conductivities of Commercially Available Prosthetic Materials

ABSTRACT Prosthetic liners and sockets play an important role in amputee patient rehabilitation. Current commercially available prosthetic liners and sockets insulate the residual limb, causing the temperature of the residual limb to increase. As a result, the residual limb sweats excessively, which can lead to numerous dermatologic conditions when coupled with the atypical loading of the residual limb tissues. These skin problems can impart unnecessary physical and psychological burdens on the amputee patient and hinder his/her rehabilitation process. This study focused on quantifying the thermal barrier posed by materials currently used in prosthetic liners and sockets by measuring the materials’ thermal conductivities. Elastomer thermal conductivities ranged from 0.145 to 0.155 W/m K, whereas fabric thermal conductivities were 0.045 to 0.074 W/m K. Liners exhibited a 0.116 to 0.143 W/m K range of thermal conductivities, and socket materials had thermal conductivities from 0.133 to 0.189 W/m K. These insulating materials are poor candidates for use in prosthetic components that surround the residual limb for many hours each day. As such, future generations of prosthetic liners and sockets should address the atypical thermal environment around the residual limb by improving the materials used and the design implemented.

Simulation of lower limb axial arterial length change during locomotion

The effect of external forces on axial arterial wall mechanics has conventionally been regarded as secondary to hemodynamic influences. However, arteries are similar to muscles in terms of the manner in which they traverse joints, and their three-dimensional geometrical requirements for joint motion. This study considers axial arterial shortening and elongation due to motion of the lower extremity during gait, ascending stairs, and sitting-to-standing motion. Arterial length change was simulated by means of a graphics based anatomic and kinematic model of the lower extremity. This model estimated the axial shortening to be as much as 23% for the femoropopliteal arterial region and as much as 21% for the iliac artery. A strong correlation was observed between femoropopliteal artery shortening and maximum knee flexion angle (r²=0.8) as well as iliac artery shortening and maximum hip angle flexion (r²=0.9). This implies a significant mechanical influence of locomotion on arterial behavior in addition to hemodynamics factors. Vascular tissue has high demands for axial compliance that should be considered in the pathology of atherosclerosis and the design of vascular implants.

Active functional stiffness of the knee joint during activities of daily living: A parameter for improved design of prosthetic limbs

BACKGROUND Exploring knee joint physiological functional stiffness is crucial for improving the design of prosthetic legs that aim to mimic normal gait. This study hypothesizes that knee joint stiffness varies among different activities of daily living, additionally while the knee performs natural movements; the magnitude of the stiffness indicates the degree of energy storage element sufficiency in terms of harvesting/returning energy. METHODS This study examined sagittal plane knee moment vs. knee flexion angle curves from 12 able-bodied subjects during activities of daily living. Slopes of these curves were assessed to find the calculated stiffness during the peak energy return and harvest phases so that the activities, which can be performed when the prosthetic knee is supplemented by a spring, were identified. FINDINGS For the energy return and harvest phases, the stiffness varied between 0.006 and 0.046 Nm/kg deg. and 0 and 0.052 Nm/kg deg. respectively. The optimum energy return phase stiffness was 0.024 (SD 0.013) Nm/kg deg. and energy harvest phase stiffness was 0.011 (SD 0.018) Nm/kg deg. INTERPRETATION Knee joint stiffness varied significantly during activities of daily living, which indicated that a storage unit with a constant stiffness would not be sufficient in providing energy regenerative gait during all activities. However, by controlling the amount and timing of spring compression and release, an energy-regenerative prosthetic knee device could be developed during most of the activities. This study was directed to the development of a complete data set, which determined the torque-angle properties of the healthy knee joint.

Shear and pressure under the first ray in neuropathic diabetic patients: Implications for support of the longitudinal arch

OBJECTIVE To assess dynamic arch support in diabetic patients at risk for Charcot neuroarthopathy whose arch index has not yet shown overt signs of foot collapse. METHODS Two indirect measures of toe flexor activation (ratios: peak hallux pressure to peak metatarsal pressure - Ph/Pm; peak posterior hallux shear to peak posterior metatarsal shear - Sh/Sm) were obtained with a custom built system for measuring shear and pressure on the plantar surface of the foot during gait. In addition, the tendency of the longitudinal arch to flatten was measured by quantifying the difference in shear between the 1st metatarsal head and the heel (Sflatten) during the first half of the stance phase. Four stance phases from the same foot for 29 participants (16 control and 13 neuropathic diabetic) were assessed. RESULTS The peak load ratio under the hallux (Ph/Pm) was significantly higher in the control group (2.10±1.08 versus 1.13±0.74, p=0.033). Similarly, Sh/Sm was significantly higher in the control group (1.87±0.88 versus 0.88±0.45, p=0.004). The difference in anterior shear under the first metatarsal head and posterior shear under the lateral heel (Sflatten) was significantly higher in the diabetic group (p<0.01). Together these findings demonstrate reduced plantar flexor activity in the musculature responsible for maintaining the longitudinal arch. CONCLUSIONS With no significant difference in arch index between the two groups, but significant differences in Ph/Pm, Sh/Sm and Sflatten the collective results suggest there are changes in muscle activity that precede arch collapse.

Spatial frequency content of plantar pressure and shear profiles for diabetic and non-diabetic subjects

How high does pressure and shear stress sensor resolution need to be in order to reliably measure the plantar pressure and shear profiles (PPSPs) under normal and diabetic feet? In this study, pressure and shear stress data were collected from 26 total diabetic and control subjects using new instrumentation that measures vertical and horizontal force vectors of the plantar contact surface during multiple instances in the gait cycle. The custom built shear-and-pressure-evaluating-camera-system (SPECS) performs simultaneous recordings of pressure and both components of the horizontal force vector (medio-lateral and antero-posterior) at distinctive regions under one׳s foot, at a spatial resolution for each sensor equal to 1.6mm by 1.6mm. A linear interpolation method was used to simulate the effect of increasing sensor size on PPSPs. Ten square-shaped sensors were included in the analysis, having edge lengths of: (1.6mm, 3.2mm, 4.8mm, 6.4mm, 8mm, 9.6mm, 11.2mm, 12.8mm, 14.4mm, and 16mm). A two-dimensional Discrete Fourier Transform was performed on each data set, for each of the ten sensor sizes. To quantify the difference between sensor sizes, a comparison was made using the maximum pressure and shear stress data over the entire plantar contact surface, equivalent to the peak of the spatial frequency spectrum. A reduction of 5% of any component of the stress vector (i.e., pressure, or medio-lateral shear stress, or anter-posterior shear stress) due to an increase in sensor size was deemed significant. The results showed that a sensor measuring 9.6mm by 9.6mm caused meaningful reductions in all three stress components (p<0.001), whereas sensors measuring 1.6mm by 1.6mm, up to 4.8mm by 4.8mm, can capture the full range of spatial frequencies in both pressure and shear stress data.

Estimating Forces during Exercise Activity Using Non-invasive Kinect Camera

Recognizing errors that may occur during participant exercise performance and reduce the risk of exercise-related injuries is important to improving adherence in wellness management. We demonstrate the feasibility of using Kinect camera for estimating ground reaction forces during a jumping exercise, as an alternative to more expensive and traditionally used force plate platforms. The Kinect camera provides a cost-effective solution for participants in analyzing exercise performance in home-based exercises. The proposed technique, which is based on the conservation of momentum, is easy to implement and can be used to provide feedback to the participant in real-time. Our results indicate that the ground reaction forces that are estimated using the 3D joint data obtained from the Kinect camera closely match the forces obtained using a force plate.