Shear force

Foot ulceration is a diabetic complication estimated to result in over $1 billion worth of medical expenses per year in the United States alone. This multifaceted problem involves the response of plantar soft tissue to both external forces applied to the epidermis and internal changes such as vascular supply and neuropathy. Increasing evidence indicates that a combination of elevated external forces (pressure and shear) and altered tissue properties is key to the etiology of foot ulcers. The overall goal of this research is to develop a platform-type hardware system that will allow a clinician to measure three-dimensional stress tensors (i...

OBJECTIVE: Shear force is believed to affect pressure ulceration. Therefore, dressing materials that reduce shear force may prevent ulceration and facilitate healing. METHOD: We measured the following three properties: the coefficient of friction between the outer layer of the dressings and the patient's clothes; the degree of adhesiveness between the inner layer of the dressing and the patient's skin; the transmissibility of shear force of the dressing. RESULTS: The coefficients of static friction were 1...

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...

OBJECTIVE: This study was designed to measure pressure and shear reduction of a novel insole design. METHODS: We compared three multilayer viscoelastic insoles to a novel insole design (Glide-Soft, Xilas Medical, Inc., San Antonio, TX). The bottom pad of each insole was fabricated from firm-density Plastazote [Apex Foot Products (now Aetrex), South Hackensack, NJ] with an upper of Plastazote, ethyl vinyl acetate, or PORON (Langer Biomechanics Group, Inc., Deer Park, NY)...

Plantar foot ulceration is a diabetic complication whose underlying causative factors are still not fully understood. The goal of the current work was to simultaneously record plantar pressure and shear and examine the interrelationship of these forces; specifically, if peak shear and pressure occurred at the same site/time and whether adjacent shear forces had a greater tendency to be directed towards or away from each other. A custom built 16 transducer array was used to record forefoot shear and pressure during gait initiation in a cohort of 12 neuropathic diabetic individuals...

Vertical plantar forces are known to be a major precipitating factor in the development of foot pathology. It is also postulated that shear forces are important in the pathogenesis of foot ulcers in patients with diabetes mellitus. Various materials are used in insoles designed to reduce forces on the foot. While many foam materials have been tested for their ability to dissipate vertical forces, few studies have tested the effect of these materials on shear forces. This study assessed the effectiveness of five different materials in reducing plantar shear forces and compared two new gel materials with three of the more conventional foam materials...

PURPOSE: We compared pressure and shear among 3 support surfaces in a controlled laboratory setting. METHODS: In this comparative study, interface pressure and shear were measured in 11 healthy subjects with use of 3 different Medicare-approved, group 2 therapeutic support surfaces. Each surface was placed on 1 of 3 identical platforms, allowing for a fixed, 45-degree head-of-bed (HOB) elevation. Multiple pressure readings were taken at each test site and each HOB position until a measurement that was determined to be reliable was obtained...

During gait the plantar surface of the foot experiences distributed shear and compressive stresses due to tangential and vertical forces respectively. At any given point under a foot, the ratio of tangential/vertical forces gives a value (mu Rmin) for the minimum coefficient of friction required to prevent slipping. If mu Rmin is greater than the actual coefficient of friction (mu A), then localized slipping will occur. Three possible scenarios exist which could lead to skin ulceration: at a localized area the skin may tend to slip (i) towards, (ii) away from or (iii) parallel to a neighboring skin region where mu Rmin < or = mu A (i...

Many support surfaces are available, each with advantages and disadvantages, that claim to relieve or reduce the external forces contributing to the development of pressure ulcers. This article describes pressure and shear, and what a patient support surface must do to relieve those forces. Pressure is the vertical force of the weight of the patient's body on the surface. Shear is a horizontal force that causes the bony prominence to move across the tissue as the skin is held in place, and results from patient movement, nurse movement of the patient, and bed movement...

A transducer has been developed to record the shear or horizontal components of force beneath the sole of the foot. When used with a vertical force transducer it has enabled a comprehensive analysis of the mechanical forces acting beneath the foot when walking in various types of footwear. Considerable differences have been recorded between the footwear. Particularly low forces are present in a plaster cast and to a lesser extent with Plastazote insoles. The possible application of these findings to the management of ulceration of the sole of the foot in diabetes mellitus and leprosy is discussed...

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