Pressure-Sensing Devices for Assessment of Soft Tissue Loading Under Bony Prominences: Technological Concepts and Clinical U

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Author(s): 
Amit Gefen, PhD

Disclosure: This work was supported by grant no. 6418-6 from the Chief Scientist’s Office of the Ministry of Health, Israel.

Pressure-related chronic wounds, such as diabetic neuropathic foot ulcers and pressure ulcers, are an important health concern that affect millions of patients and costs billions annually.1 Studies conducted at multiple centers in the United States indicate that ulcers in the feet of patients with diabetic neuropathy account for $150 million (US) of the direct annual costs of type 2 diabetes. Deep tissue damage requiring amputation costs about $47,000 per individual case.1 Likewise, the database of the US Centers for Disease Control and Prevention (CDC) indicates that the annual cost of treating pressure ulcers in spinal cord injury (SCI) patients is $1.2 billion in the US alone.2
Pressure-related chronic wounds may occur when soft tissues are compressed between bony prominences—eg, the metatarsal heads in the foot or the ischial tuberosities (IT) in the buttocks and a supporting surface (a shoe insole or a wheelchair sitting surface). Injury occurs when the magnitude of the applied mechanical load or time of exposure to the load, or their combination, exceeds the tissue’s tolerance, which is commonly referred to as “injury threshold.” In such cases, cell death occurs in paths of mechanical breakdown,or ischemic necrosis, or both.3 Pressure-related chronic wounds rarely develop spontaneously in animals, sometimes limiting utilization of animal models for etiological studies.4 Accordingly, much of our understanding of these wounds is based on clinical experience5 that emphasizes a need for objective, quantitative means of measurements of the conditions under which pressure-related chronic wounds develop in humans. Interface pressure data are measures of the spatial and temporal compressive forces per unit area that act on soft tissues contacting a support surface (eg, wheelchair, shoe, etc.). They are basic engineering tools for evaluating the susceptibility of an individual to suffer a pressurerelated wound. Though interface pressure measurements cannot reveal all risk factors for a chronic pressure-related wound (eg, existence of a peripheral vascular disease) they do reflect important biomechanical risk factors, such as loss of tissue thickness that causes higher intensity pressure near bony prominences, foot deformities, regions of callus in plantar tissue, and nonenzymatic glycosylation of collagen that induces stiffening of connective tissues in the plantar foot.6
The purpose of this review is to: 1) describe the current techniques for body-support interface pressure measurements with focus on foot and sitting pressures, 2) list the pressure value ranges measured under the foot in standing and walking, under the buttocks in sitting with particular emphasis on abnormal alterations in foot pressures as result of diabetic neuropathy, and alterations in sitting pressures among paralyzed patients, and 3) discuss clinical utilization of interface pressure measurements in the fitting of diabetic footwear and wheelchair cushions.

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