Toward real-time detection of deep tissue injury risk in wheelchair users using Hertz contact theory

Agam, L; Gefen, Amit

doi:10.1682/jrrd.2007.07.0114

Cited by 13 publications

(11 citation statements)

References 54 publications

(86 reference statements)

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“…In addition to the capillary occlusion that results from both of these factors [25,45,68] many other etiological mechanisms contribute too, including lymphatic occlusion, reperfusion injury, and tissue deformation [1,3,26,64]. Finite element modeling of the latter, predicts that as dead cells accumulate, the resultant microstructural heterogeneity further deforms surviving cells, thereby aggravating the spread of tissue damage [1,13,14]. These mechanical changes then lead to increased stresses in the injured area, resulting in a "snowball effect" that is difficult to halt [1].…”

Section: Pathophysiologymentioning

confidence: 99%

“…Finite element modeling of the latter, predicts that as dead cells accumulate, the resultant microstructural heterogeneity further deforms surviving cells, thereby aggravating the spread of tissue damage [1,13,14]. These mechanical changes then lead to increased stresses in the injured area, resulting in a "snowball effect" that is difficult to halt [1]. Pathologic changes are more severe in muscle than in skin or subcutaneous tissues [67,73], perhaps reflecting the higher metabolic demands of muscle and explaining the importance and prevalence of deep tissue injury (DTI) [25,66,67,73].…”

Section: Pathophysiologymentioning

confidence: 99%

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Preventing Ischial Pressure Ulcers: I. Review of Neuromuscular Electrical Stimulation

Kaplan

Loeb

2011

Applied Bionics and Biomechanics

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Abstract.Objective: Pressure ulcers (PUs) are common and debilitating wounds that arise when immobilized patients cannot shift their weight. Treatment is expensive and recurrence rates are high. Pathophysiological mechanisms include reduced bulk and perfusion of chronically atrophic muscles as well as prolonged occlusion of blood flow to soft tissues from lack of voluntary postural shifting of body weight. This has suggested that PUs might be prevented by reanimating the paralyzed muscles using neuromuscular electrical stimulation (NMES). A review of the published literature over the past 2 decades is detailed.Outcomes: Historically gluteus maximus (GM) has been an important target for NMES, but results have been difficult to interpret and suitable technology has been lacking.Conclusions: NMES of the buttock muscles appears to be valuable in terms of its trophic effects, improving vascularity and soft tissue bulk. It remains unclear, however, whether GM can actually achieve sufficient unloading of normal forces to permit blood flow in the capillary beds of the skin and muscle. Analysis of the skeletal biomechanics is required to assess the relative value of GM vs. hamstring (HS) hip extensors in this regard.

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Section: Pathophysiologymentioning

confidence: 99%

Section: Pathophysiologymentioning

confidence: 99%

Preventing Ischial Pressure Ulcers: I. Review of Neuromuscular Electrical Stimulation

Kaplan

Loeb

2011

Applied Bionics and Biomechanics

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“…Specifically, we tested viscoelastic cushion A in an indentation test configuration using a half-spherical indenter attached to an electromechanical uniaxial testing machine (Instron 5544; High Wycombe, United Kingdom), which deformed the cushion at a rate of 20 mm/min. We calculated the long-term elastic moduli of cushion A using the Hertz solution for this indenter-cushion contact problem, as described by Agam and Gefen for indentation strains of 60, 70, and 80 percent [19] (typical cushion strains under a body weight [20]), after allowing 1 minute of stress relaxation. Cushions B, C, and D were tested in a compression configuration.…”

Section: Cushionsmentioning

confidence: 99%

Use of weight-bearing MRI for evaluating wheelchair cushions based on internal soft-tissue deformations under ischial tuberosities

Shabshin¹,

Zoizner²,

Herman³

et al. 2010

JRRD

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Abstract-Deep tissue injury (DTI) is a severe type of pressure ulcer, in which damage initiates under intact skin, in soft tissues that are mechanically deformed by load-bearing bony prominences. Sitting-acquired DTI typically occurs in the gluteus muscles that could sustain deformations by the weightbearing ischial tuberosities (ITs). No clinical method currently exists for measuring internal tissue deformations; so design and selection of wheelchair cushions are based mostly on measuring sitting pressures. Our objective was to evaluate the influence of different commercial cushions on internal soft-tissue deformations under the ITs, using weight-bearing magnetic resonance imaging (MRI). We specifically compared muscle, superficial fat, and effective (muscle and fat together) tissue deformations while subjects (n = 10) sat on four cushions (two viscoelastic and two foam) and directly on a rigid support. Deformations were maximal in muscle tissue (mean ~70%), twice more the amount than in fat (~30%). Effective soft-tissue deformations were ~50% to ~60%. Although cushions mildly reduced muscle deformations in the order of 10%, theoretically, our interpretation suggests that this deformation level adds safe sitting time. This study demonstrated that weightbearing MRI is applicable for evaluating wheelchair cushions and, in the future, may be a tool to systematically support cushion design and selection.

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“…43,46,47 Computer models of the buttocks in seated individuals indicate that the levels of internal pressure are substantially higher than those measured at the surface. 1,5,31,42 Initial validations of these models have been conducted in the hind legs of rodents 6 ; however, empirical measurements of internal pressure from humans or animal models with pelvic anatomy that closely resembles that of humans are not available. Initial measurements of hydrostatic pressure in the deep tissue of pigs were provided by the seminal work of Le et al 30 The goals of the present study were twofold.…”

Section: Introductionmentioning

confidence: 99%

“…The present study focused on: (1) obtaining detailed measures of the distribution of pressure experienced by tissue around the ischial tuberosities, and (2) investigating the effectiveness of intermittent electrical stimulation (IES), a novel strategy for the prevention of DTI, in alleviating pressure in regions at risk of breakdown due to sustained loading. The experiments were conducted in adult pigs.…”

mentioning

confidence: 99%

Distribution of Internal Pressure around Bony Prominences: Implications to Deep Tissue Injury and Effectiveness of Intermittent Electrical Stimulation

et al. 2012

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The overall goal of this project is to develop interventions for the prevention of deep tissue injury (DTI), a form of pressure ulcers that originates in deep tissue around bony prominences. The present study focused on: (1) obtaining detailed measures of the distribution of pressure experienced by tissue around the ischial tuberosities, and (2) investigating the effectiveness of intermittent electrical stimulation (IES), a novel strategy for the prevention of DTI, in alleviating pressure in regions at risk of breakdown due to sustained loading. The experiments were conducted in adult pigs. Five animals had intact spinal cords and healthy muscles and one had a spinal cord injury that led to substantial muscle atrophy at the time of the experiment. A force-controlled servomotor was used to load the region of the buttocks to levels corresponding to 25%, 50% or 75% of each animal's body weight. A pressure transducer embedded in a catheter was advanced into the tissue to measure pressure along a three dimensional grid around the ischial tuberosity of one hind leg. For all levels of external loading in intact animals, average peak internal pressure was 2.01 ± 0.08 times larger than the maximal interfacial pressure measured at the level of the skin. In the animal with spinal cord injury, similar absolute values of internal pressure as that in intact animals were recorded, but the substantial muscle atrophy produced larger maximal interfacial pressures. Average peak internal pressure in this animal was 1.43 ± 0.055 times larger than the maximal interfacial pressure. Peak internal pressure was localized within a ±2 cm region medio-laterally and dorso-ventrally from the bone in intact animals and ±1 cm in the animal with spinal cord injury. IES significantly redistributed internal pressure, shifting the peak values away from the bone in spinally intact and injured animals. These findings provide critical information regarding the relationship between internal and interfacial pressure around the ischial tuberosities during loading levels equivalent to those experienced while sitting. The information could guide future computer models investigating the etiology of DTI, as well as inform the design and prescription of seating cushions for people with reduced mobility. The findings also suggest that IES may be an effective strategy for the prevention of DTI.

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Toward real-time detection of deep tissue injury risk in wheelchair users using Hertz contact theory

Cited by 13 publications

References 54 publications

Preventing Ischial Pressure Ulcers: I. Review of Neuromuscular Electrical Stimulation

Preventing Ischial Pressure Ulcers: I. Review of Neuromuscular Electrical Stimulation

Use of weight-bearing MRI for evaluating wheelchair cushions based on internal soft-tissue deformations under ischial tuberosities

Distribution of Internal Pressure around Bony Prominences: Implications to Deep Tissue Injury and Effectiveness of Intermittent Electrical Stimulation

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