Impact of Race, gait speed and arch height on plantar loading.

Diabetes is a leading cause for death in the United States, with African Americans (AA) being twice as likely to die from diabetes than White Americans (WA). AA are twice as likely to experience diabetes-related foot amputation due to foot ulcers, which are most often caused by high plantar pressure. While it is known that arch height, sex, family history of diabetes, Body Mass Index (BMI), age, and gait speed can impact plantar loading, there is a need to test the hypothesis that race in combination with the previously mentioned variables are significant predictors of plantar loading. To answer this question, plantar loading data was collected from 107 participants using an EMED pressure-measurement system (Novel Electronics, Inc, St Paul, MN, USA). Each participant walked barefoot at a self-selected walking pace ten times. Contact area, maximum force, and were force-time integral collected for each step on the pressure plate. A multiple linear regression was used to test if race, age, Arch Height Index (AHI), gait speed, sex assigned at birth, family history of diabetes, and BMI significantly predicted plantar loading. Race, age, AHI, gait speed, sex, and BMI were considered significant predictor variables for plantar loading. Most importantly, race was a significant predictor of maximum force in the hallux (ß = 6.46, p < 0.001), rearfoot (ß = -6.36, p < 0.001), and lateral midfoot (ß = -2.72, p < 0.001), and the force-time integral in the hallux (ß = 2.37, p < 0.001), rearfoot (ß = -2.14, p < 0.001), and lateral midfoot (ß = -0.65, p < 0.001). These findings could help with understanding why AA are more likely to develop diabetic foot ulcers than WA.

Development of a finite element-based model for the thermal assessment of transtibial prosthetic liners.

BACKGROUND: Thermal discomfort because of elevated residual limb skin temperatures and/or perspiration within the prosthetic socket is frequently reported among people with amputation. OBJECTIVE: To evaluate the impact of the thermal conductivity characteristics of prosthetic liners on transtibial prosthesis heat dissipation, following postactivity rest. STUDY DESIGN: Time-dependent heat transfer study in solids using finite element analysis. METHODS: A three-dimensional model of the transtibial residual limb was developed by simplifying the geometry to tapered, layered cylinders. Four prosthetic socket liners of varying thermal conductivities were then added to the exterior, and the final surface temperatures of the skin layer were analyzed. RESULTS: Warmer temperatures were observed near regions with greater muscle volume; cooler temperatures were observed at the distal end of the simplified model. The final residual limb skin temperatures for each prosthetic liner were found to be significantly different from one another. Overall, the average final surface temperatures of the skin layer at the end of postactivity rest was 3.85°C ± 0.12°C greater than the initial surface temperatures of skin layer. CONCLUSIONS: None of the prosthetic liners made a significant reduction in residual limb skin temperatures after activity. The results indicate that the focus should be on other material properties of the prosthetic liners or active cooling systems.

The Structural Effects of Diabetes on Soft Tissues: A Systematic Review.

Hyperglycemia, which is associated with diabetes, increases the production of advanced glycation end products. Advanced glycation end products lead to the structural degradation of soft tissues. The structural degradation of diabetic soft tissues has been investigated in humans, rodents, and canines. Therefore, the objective of this review is to unify the various contributions to diabetes research through the mechanical properties and geometric characteristics of soft tissues. A systematic review was performed and identified the effects of diabetes on mechanical and geometric properties of soft tissues via experimental testing or in vivo - driven finite element analysis. The literature concludes that diabetes contributes to major structural changes in soft tissues but does not cause the same structural changes in all soft tissues (e.g., diabetic tendons are weaker and diabetic plantar tissues are tougher). Diabetes stiffens and toughens soft tissues, thus altering viscoelastic behavior (e.g., poor strain and stress response). However, diabetes management routines can prevent or minimize the effects of diabetes on the mechanical and geometric properties of soft tissues. Unification of the structural effects of diabetes on soft tissues will contribute to the pathophysiology of diabetes.

Impact of screw thread shape on stress transfer in bone: a finite element study.

Gradual screw loosening is a well-known failure mechanism in internal fixation. Loosening is primarily due to progressive bone loss caused by stress shielding, a phenomenon in which a medical device absorbs a disproportionate amount of load within the screw-bone construct. The proximity of elastic moduli of magnesium and bone presents the potential for alleviating screw loosening by allowing optimum stress to be transferred between screw and bone, and in turn, supporting bone remodeling around the screw. In this study, the effect of thread profile on stress transfer in a magnesium fixation was simulated using a 2-D finite element model. Modified stress parameters from a previous study were used to estimate stress transfer across three thread profiles. Results showed highest stress transfer in trapezoidal-shaped magnesium screw thread. In accordance, this study corroborates the potential for magnesium as an ultimate screw material to eliminate progressive screw loosening.

Design of a new magnesium-based anterior cruciate ligament interference screw using finite element analysis.

BACKGROUND/OBJECTIVE: In anterior cruciate ligament â€‹reconstruction, a tendon graft, anchored by interference screws (IFSs), is frequently used as a replacement for the damaged ligament. Generally, IFSs are classified as being either metallic or polymeric. Metallic screws have sharp threads that lacerate the graft, preventing solid fixation. These constructs are difficult to image â€‹and can limit bone--screw integration because of the higher stiffness of the screw. Polymeric materials are often a better match to bone's material properties, but lack the strength needed to hold grafts in place. Magnesium (Mg) is a material of great promise for orthopaedic applications. Mg has mechanical properties similar to bone, ability to be seen on magnetic resonance imagings, and promotes bone healing. However, questions still remain regarding the strength of Mg-based screws. Previous ex vivo â€‹animal experiments found stripping of the screw drive when the full torque was applied to Mg screws during surgery, preventing full insertion and poor graft fixation. The similar design of the Mg screw led to questions regarding the relationship between material properties and design, and the ultimate impact on mechanical behaviour. Thus, the objective of this study was to analyze the stresses in the screw head, a key factor in the stripping mechanism of IFS, then use that information to improve screw design, for this material. METHODS: Using finite element analysis, a comparison study of six drive designs (hexagonal, quadrangle, torx, trigonal, trilobe, and turbine) was performed. This was followed by a parametric analysis to determine appropriate drive depth and drive width. RESULTS: It was observed that with a typical torque (2 â€‹Nm) used for screw insertion during anterior cruciate ligament reconstruction, the maximum von Mises and shear stress values were concentrated in the corners or turns of the drive, which could lead to stripping if the values were greater than the yield stress of Mg (193 â€‹MPa). With a four-time â€‹increase in drive depth to be fully driven and a 30% greater drive width, these maximum stress values were significantly decreased by more than 75%. CONCLUSION: It was concluded that improving the design of a Mg-based screw may increase surgical success rates, by decreasing device failure at insertion. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: The results of this work have the potential to improve designs of degradable IFSs, allowing for greater torque to be applied and thus greater screw fixation between host bone and the graft. Such a fixation will allow greater integration, better patient healing, and ultimately improved patient outcomes.

Moment arms of the ankle throughout the range of motion in three planes.

BACKGROUND: The moment, a force applied at a distance, is responsible for movement and balance. A key component of the moment is the moment arm. The moment arms of nine muscles surrounding the ankle complex during motion in three planes, were studied. MATERIALS AND METHODS: Five cadaveric feet were mounted in a testing device that created moments in the sagittal, coronal and transverse planes. Axial and tendon loads were applied as the foot was passively moved in these planes. Tendon excursions and bone kinematics were monitored. The moment arm was calculated using the tendon excursion method and averaged across all specimens. RESULTS: The largest average moment arm during plantarflexion/dorsiflexion, was the Achilles (mean, 53.1; SD, 5.1 mm). During internal/external rotation the largest moment arm was the peroneus brevis (mean, 20.5; SD, 6.4 mm). During inversion/eversion, the largest moment arm was the peroneus longus (31 mm; SD, 2.3 mm). CONCLUSION: This study quantified the functional moment arms of nine tendons of the ankle/foot. The involvement of multiple tendons in multiple planes of motion should be considered in computational models and when deciding treatments. CLINICAL RELEVANCE: The correlation between moment arms and muscle function has significant effects on treatment efficacy. Information on the balance of moments around the ankle will assist in achieving optimal biomechanical behavior following operative treatments.

Effects of foot orthoses on the work of friction of the posterior tibial tendon.

BACKGROUND: Posterior tibial tendon dysfunction is a significant contributor to flatfeet. Non-operative treatments, like in-shoe orthoses, have varying degrees of success. This study examined changes to the work of friction of the posterior tibial tendon under three conditions: intact, simulated flatfoot, and flatfoot with an orthosis. It was hypothesized that work of friction of the posterior tibial tendon would significantly increase in the flatfoot, yet return to normal with an orthosis. Changes to bone orientation were also expected. METHODS: Six lower limb cadavers were mounted in a foot simulator, that applied axial and a posterior tibial tendon load. Posterior tibial tendon excursion, gliding resistance, and foot kinematics were monitored, and work of friction calculated. Each specimen moved through a range of motion in the coronal, transverse, and sagittal planes. FINDINGS: Mean work of friction during motion in the coronal plane were 0.17 N cm (SD 0.07 N cm), 0.25 N cm (SD 0.09 N cm), and 0.23 N cm (SD 0.09 N cm) for the intact, flatfoot, and orthosis conditions, respectively. Motion in the transverse plane yielded average WoF of 0.36 N cm (SD 0.28 N cm), 0.64 N cm (SD 0.25 N cm), and 0.57 N cm (SD 0.38 N cm) in the same three conditions, respectively. The average tibio-calcaneal and tibio-metatarsal valgus angles significantly increased in the flatfoot condition (5.8 degrees and 9 degrees , respectively). However, the orthosis did slightly correct this angle. INTERPRETATION: The prefabricated orthosis did not consistently restore normal work of friction, though it did correct the flatfoot visually. This implies that patients with flatfeet may be predisposed to developing posterior tibial tendon dysfunction due to abnormal gliding resistance, though bone orientations are restored.