Measure It: Proper Wheelchair Fit Is Key to Ensuring Function while Protecting Skin Integrity.

GENERAL PURPOSE: To review the biomechanics of posture, appropriate means to configure a wheelchair to permit proper postural support, and common problems arising from improper wheelchair fit. TARGET AUDIENCE: This continuing education activity is intended for physicians, physician assistants, nurse practitioners, and nurses with an interest in skin and wound care. LEARNING OBJECTIVES/OUTCOMES: After participating in this educational activity, the participant will:1. Synthesize the concepts influencing proper wheelchair fit.2. Identify the biomechanics of posture as they apply to wheelchair fit.3. Summarize the appropriate assessment guidelines for determining and preparing to adjust wheelchair fit.

A variety of problems can arise from sitting persons in poorly fitted wheelchairs, including contractures, pain, and pressure injuries. These complications can result in functional consequences for the patient, such as reduced independence and activity. This article focuses specifically on proper wheelchair fit, describing the impact of proper wheelchair fit on the posture and function of wheelchair users. The author aims to help clinicians better recognize the basic biomechanics of posture, describe the appropriate means to configure a wheelchair to permit proper postural support, and identify common problems arising from improper wheelchair fit.

Does Sacrococcygeal Skeletal Morphology and Morphometry Influence Pressure Injury Formation in Adults?

GENERAL PURPOSE: To present a study that investigated sacrococcygeal skeletal structure as a possible nonmodifiable intrinsic risk factor for pressure injury and identify possible issues caused by its morphology. TARGET AUDIENCE: This continuing education activity is intended for physicians, physician assistants, nurse practitioners, and nurses with an interest in skin and wound care. LEARNING OBJECTIVES/OUTCOMES: After participating in this educational activity, the participant will:1. Recognize the background information the authors considered when planning and conducting their study of sacrococcygeal skeletal structure as a possible pressure injury risk factor.2. Identify the characteristics of the two groups of study participants.3. Choose the results of the study clinicians may consider when implementing evidence-based practice.

To determine if sacrococcygeal skeletal morphology and morphometry characteristics were possible pressure injury (PI) intrinsic risk factors; determine the exact location of these PIs; and generate hypotheses and determine methodological considerations required for future larger studies. This case-control pilot study compared 30 patients who had an MRI scan­15 patients had a PI and 15 patients did not. Key sacrococcygeal morphology and morphometry parameters were assessed. On average, patients with PIs had less of a lumbosacral and sacrococcygeal angle and a greater sacral curvature and intercoccygeal angle than did patients without a PI. Patients with PIs had more variable coccyx types. Tissue and bone destruction precluded several measurements in some patients. The most common area of destruction was located distally. Sacrococcygeal measurements differed in patients with PIs, and PIs were predominately located distally. Authors recommend replicating this study on a larger scale because certain key attributes warrant further investigation to determine their influence on sacrococcygeal PIs. Sacrococcygeal morphology and morphometry parameters have not been previously studied as possible intrinsic risk factors for PIs; yet, this is the most common location for their occurrence. Knowledge regarding possible injury mechanisms due to the forces from overlying skeletal structures with respective tissue loading over the sacrococcygeal area has the potential to inform practice; preventive strategies; and equipment, products, and technology developed.

Friction characteristics of preventative wound dressings under clinically-relevant conditions.

Wound dressings can be used prophylactically or during actual treatment. Preventative dressings have become a standard of care to prevent pressure ulcers in patients while in bed. While the mechanism of the preventative benefit has not been completely explained, the friction between the dressing and linen is hypothesized as being a key performance factor. The objective of this project was to quantify the static and kinetic coefficients of friction (COF) of various brands of prophylactic dressings under the stresses experienced in situ, while the dressings are in contact with bed linen materials. The COF of six commercial dressings were calculated using tribometer measurements. The ranges of static COF were 0.333-0.542 and kinetic COF were 0.333-0.513. Four dressings exhibited COF that were consistent with skin-linen values reported in the literature and all dressing COF appear to be lower than the COF of moist skin against linen.

Pressure Ulcer Risk Factors in Persons with Mobility-Related Disabilities.

OBJECTIVE: To assess pressure ulcer (PU) risk in persons with mobility impairments using a large data set to identify demographic, laboratory, hemodynamic, and pharmacologic risk factors. METHODS: The cohort of interest was persons with disabilities who have mobility impairments and are diagnostically at risk of PUs. To define this cohort, diagnoses that qualify patients for skin protection wheelchair cushions were used. Data were obtained from the Cerner Health Facts data warehouse. Two cohorts were defined: persons with and without a history of PUs. Analysis included descriptive statistics and multivariate logistic regression modeling. Variables retained in the model were identified using LASSO, gradient boosting, and Bayesian model averaging. MAIN RESULTS: The resulting cohorts included more than 87,000 persons with a history of PUs and more than 1.1 million persons who did not have a PU. The data revealed seven disability groups with the greatest prevalence of PUs: those with Alzheimer disease, cerebral palsy, hemiplegia, multiple sclerosis, paraplegia/quadriplegia, Parkinson disease, and spina bifida. Ulcers in the pelvic region accounted for 82% of PUs. Persons with disabilities who were male or black had a greater prevalence of PUs. Physiologic risk factors included the presence of kidney or renal disease, decreased serum albumin, and increased serum C-reactive protein. CONCLUSIONS: The results indicate that, although persons with disabilities can exhibit a wide functional range, they remain at risk of PUs and should be evaluated for proper preventive measures, including support surfaces and wheelchair cushions.

Seated buttocks anatomy and its impact on biomechanical risk.

AIM: The objective of this study was to describe the amount, types, and shapes of tissue present in the buttocks during sitting (i.e., seated buttocks soft tissue anatomy), and the impact of seated buttocks soft tissue anatomy on biomechanical risk. MATERIALS AND METHODS: The buttocks of 35 people, including 29 full-time wheelchair users with and without a history of pelvic pressure ulcers were scanned sitting upright on 3" of flat HR45 foam in a FONAR Upright MRI. Multi-planar scans were analyzed to calculate bulk tissue thickness, tissue composition, gluteus maximus coverage at the ischium, the contour of the skin, and pelvic tilt. RESULTS: Bulk tissue thickness varied from 5.6 to 32.1 mm, was composed mostly of adipose tissue, and was greatest in the able-bodied cohort. Skin contours varied significantly across status group, with wheelchair users with a history of pressure ulcers having tissue with a peaked contour with a radius of curvature of 65.9 mm that wrapped more closely to the ischium (thickness at the apex = 8.2 mm) as compared to wheelchair users with no pressure ulcer history (radius of curvature = 91.5 mm and apex thickness = 14.5 mm). Finally, the majority of participants presented with little to no gluteus coverage over their ischial tuberosity, regardless of status group. CONCLUSIONS: This study provides quantitative evidence that Biomechanical Risk, or the intrinsic characteristic of an individual's soft tissues to deform in response to extrinsic applied forces, is greater in individuals at greater risk for pressure ulcers.

Visualizing Tissue Strain Under the Sacrum and Coccyx in Different Supine Postures: A Case Series.

OBJECTIVE: To visually assess and report the influence of supine positioning and sacrum and coccyx anatomy on tissue deformation. METHODS: A convenience sample of three participants was scanned using MRI. All participants were scanned in a supine position with a rig oriented in a flat or horizontal position and with the torso portion of the rig elevated to 30° to simulate head-of-bed elevation. Representative images were identified to visualize and depict (1) the differences in tissue thickness and deformation in response to changes in supine positioning (0° and 30°), (2) the relative displacement of the skeleton relative to the skin during 30° incline, and (3) differences in sacrococcygeal morphology. RESULTS: The tissue thickness under the sacrum stayed the same or increased when torsos were elevated. Skeletons were displaced relative to the skin when the rig was elevated regardless of the pelvis location. Further, in the elevated position, coccyges flexed when pelvises were placed on the elevated segment but did not flex when pelvises were placed on the horizontal segment. CONCLUSIONS: This case series is useful in defining new areas of research that can (1) identify the deformation induced by normal and frictional forces resulting from different positions of the bed chassis, (2) assess the impact of positioning the pelvis on elevated versus horizontal segments of the bed chassis, and (3) define the association between sacral and coccyx morphology and pressure ulcer occurrence in hospitalized patients.

The Characterization of Plantar Skin Across Environmental Condition and Time.

OBJECTIVE: In the presence of pathologic conditions such as diabetes or neuropathy and activity-related forces, the plantar surface of the foot is a common place for skin breakdown. With this risk, foundational knowledge of typical plantar skin behavior is needed. The purpose of this study was to characterize the plantar skin properties (tangential stiffness, normal compliance, and thickness) across environmental condition and time. DESIGN AND SETTING: Nonexperimental laboratory design. PATIENTS: Sixteen individuals participated (age range, 19-78 years; mean age, 48.5 ± 19.23 years; mean body mass index, 31.5 ± 7.61 kg/m). MAIN OUTCOME MEASURES: Tangential stiffness, normal compliance, and thickness were assessed with the Tissue Interrogation Device (TID), Myotonometer, and ultrasound, respectively. Measurements were taken at 5 anatomic locations over 4 visits across a day (morning and afternoon), week, and month. Measurements were taken in standard (20° C to 24° C, 35%-50% relative humidity) and shoe conditions (32° C, 66% relative humidity). MAIN RESULTS: Tangential stiffness (P = .000), normal compliance (P = .000), and thickness (epidermis, P = .000; dermis, P = .044) all varied by location. No main effect differences were noted across visits or environment across devices. Reliability varied across visits. CONCLUSIONS: All 3 skin properties were found to vary across location and people. Given skin property consistency over time and device reliability, it is reasonable to take and compare measurements within a week. Environmental conditions should be reported and controlled in research assessing plantar skin.

Measuring the impact of cushion design on buttocks tissue deformation: An MRI approach.

AIM: To establish a research approach for describing how different wheelchair cushion designs impact buttocks tissue deformation during sitting. MATERIALS AND METHODS: The buttocks of 4 individuals with spinal cord injury and significant atrophy were scanned sitting in a FONAR Upright MRI. Scans were collected with the individuals' buttocks fully suspended without pelvic support, and seated on 3 different commercially available wheelchair cushions. Multi-planar scans were analyzed to provide 3D renderings and measurements of tissue thickness and shape. RESULTS: Bulk tissue thicknesses at the ischium, which rarely included muscle, were reduced by more than 60% on enveloping cushion designs studied (i.e., Roho HP and Matrx Vi), and more variably (23-60%) on an orthotic off-loading design (i.e., Java). Adipose was typically displaced posterior and superior from the unloaded condition, with more lateral displacement on the Roho HP and Matrx Vi and more medial displacement present on the Java. Large changes in angle at the sacro-coccygeal joint indicated significant loading on the region. Deformation at the greater trochanter was more consistent across surfaces. Greater interface pressures tended to be associated with greater deformation, but the relationship varied by individuals and was highly non-linear. CONCLUSIONS: The buttocks in this study all deformed significantly, but at different locations and in different manners across all 3 surfaces. Attention needs to be paid to the regions of greatest deformation. A future metric of shape compliance should consider cushion performance at all high risk regions, and changes to the amount and shape of tissue in the regions of interest.

How a diverse research ecosystem has generated new rehabilitation technologies: Review of NIDILRR's Rehabilitation Engineering Research Centers.

Over 50 million United States citizens (1 in 6 people in the US) have a developmental, acquired, or degenerative disability. The average US citizen can expect to live 20% of his or her life with a disability. Rehabilitation technologies play a major role in improving the quality of life for people with a disability, yet widespread and highly challenging needs remain. Within the US, a major effort aimed at the creation and evaluation of rehabilitation technology has been the Rehabilitation Engineering Research Centers (RERCs) sponsored by the National Institute on Disability, Independent Living, and Rehabilitation Research. As envisioned at their conception by a panel of the National Academy of Science in 1970, these centers were intended to take a "total approach to rehabilitation", combining medicine, engineering, and related science, to improve the quality of life of individuals with a disability. Here, we review the scope, achievements, and ongoing projects of an unbiased sample of 19 currently active or recently terminated RERCs. Specifically, for each center, we briefly explain the needs it targets, summarize key historical advances, identify emerging innovations, and consider future directions. Our assessment from this review is that the RERC program indeed involves a multidisciplinary approach, with 36 professional fields involved, although 70% of research and development staff are in engineering fields, 23% in clinical fields, and only 7% in basic science fields; significantly, 11% of the professional staff have a disability related to their research. We observe that the RERC program has substantially diversified the scope of its work since the 1970's, addressing more types of disabilities using more technologies, and, in particular, often now focusing on information technologies. RERC work also now often views users as integrated into an interdependent society through technologies that both people with and without disabilities co-use (such as the internet, wireless communication, and architecture). In addition, RERC research has evolved to view users as able at improving outcomes through learning, exercise, and plasticity (rather than being static), which can be optimally timed. We provide examples of rehabilitation technology innovation produced by the RERCs that illustrate this increasingly diversifying scope and evolving perspective. We conclude by discussing growth opportunities and possible future directions of the RERC program.

3D anatomy and deformation of the seated buttocks.

AIM: To describe the 3D anatomy and deformation of the buttocks during sitting. MATERIALS AND METHODS: The buttocks of 4 able-bodied individuals and 3 individuals with spinal cord injury were scanned sitting in a FONAR Upright MRI. T1-weighted Fast Spin Echo scans were collected with the individuals seated on a custom wheelchair cushion to unload the ischial tuberosities (ITs) and seated on a 3 inch foam cushion. Multi-planar scans were analyzed, and the muscle, bone and adipose tissue was manually segmented for 3D rendering and analysis of the quantity, geometry, and location of tissues. RESULTS: The gluteus maximus was positioned lateral and posterior to the IT, covering the inferior portion of the IT for only 2 able-bodied participants. Adipose thickness directly under the IT did not differ by diagnosis, nor did it have a consistent response to loading. However, the envelopment of the IT by the surrounding adipose tissue was much greater in two of the participants with spinal cord injuries. These two subjects also had the most curved skin surface as the tissue wrapped around the IT. Tissue strains around the ischium were most visible in the adipose and connective tissue. The gluteus maximus displaced and distorted upwards, posterior and lateral, away from the inferior IT. CONCLUSIONS: Multi-planar imaging is necessary to investigate anatomy and deformation of the buttocks. 5 out of 7 participants did not sit directly on muscle. The tissue beneath their ITs was predominantly composed of fat and connective tissue, suggesting that these tissues might be most vulnerable to injury.

Impact of Mass and Weight Distribution on Manual Wheelchair Propulsion Torque.

Propulsion effort of manual wheelchairs, a major determinant of user mobility, is a function of human biomechanics and mechanical design. Human studies that investigate both variables simultaneously have resulted in largely inconsistent outcomes, motivating the implementation of a robotic propulsion system that characterizes the inherent mechanical performance of wheelchairs. This study investigates the impacts of mass and mass distribution on manual wheelchair propulsion by configuring an ultra-lightweight chair to two weights (12-kg and 17.6-kg) and two load distributions (70% and 55% on drive wheels). The propulsion torques of these four configurations were measured for a straight maneuver and a fixed-wheel turn, on both tile and carpet. Results indicated that increasing mass to 17.6-kg had the largest effect on straight acceleration, requiring 7.4% and 5.8% more torque on tile and carpet, respectively. Reducing the drive wheel load to 55% had the largest effect on steady-state straight motion and on both turning acceleration and steady-state turning; for tile and carpet, propulsion torque increased by 13.5% and 11.8%, 16.5% and 4.1%, 73% and 5.1%, respectively. These results demonstrate the robot's high sensitivity, and support the clinical importance of evaluating effects of wheelchair mass and axle position on propulsion effort across maneuvers and surfaces.

Measurement of Load Redistribution Properties of Wheelchair Cushions Using a Compliant Cushion Loading Indenter.

The aim of this project was to develop and validate a compliant cushion loading indenter (CCLI) capable of evaluating wheelchair cushion performance by measuring internal pressures and deflection. The design of the CCLI consists of 3 subsystems: 1) an internal substructure with medial and lateral protuberances to mimic the load-bearing ischial tuberosities and trochanters, 2) an elastomeric shell to mimic soft tissue and 3) instrumentation to measure internal pressures at both protuberances and deflection of the elastomer at 7 locations. It is parametrically designed so can be scaled larger or smaller to represent different body sizes. To assess the repeatability and sensitivity of measurements, the model was loaded onto two wheelchair cushions, 3″ flat foam and Jay3, using two loads, 44kgf and 53kgf, representing the average upper body mass of 70kg and 83kg persons, respectively. The results showed a high precision of pressure and deflection measurement across two different cushions and loads. Under both loads, pressure measurements exhibited a standard error of < 1 mm and <3 mmHg. The standard deviations of deflection values were less than 2.5 mm (0.1 in.). The pressures and absolute deflection differed significantly across load and cushion type indicating sensitivity to change.

Effects of wheelchair cushions and pressure relief maneuvers on ischial interface pressure and blood flow in people with spinal cord injury.

OBJECTIVE: To investigate the effectiveness and interactions of 2 methods of pressure ulcer prevention, wheelchair cushions and pressure relief maneuvers, on interface pressure (IP) and blood flow of the buttocks. DESIGN: Within-subject repeated measures. SETTING: Rehabilitation center. PARTICIPANTS: Wheelchair users with a spinal cord injury or disorder (N=17). INTERVENTIONS: Participants performed 3 forward leans and 2 sideward leans with different degrees of lean while seated on each of 3 different wheelchair cushions. MAIN OUTCOME MEASURES: IP measured with a custom sensor and blood flow measured with laser Doppler flowmetry were collected at the ischial tuberosity. RESULTS: Pressure relief maneuvers had a significant main effect on the ischial IP (P<.001); all maneuvers except for the small frontward lean resulted in a significant reduction in IP compared with upright sitting. Blood flow significantly varied across postures (P<.001) with flow during upright sitting and small forward leans being significantly lower than during the full and intermediate leans in both the forward and sideward directions. CONCLUSIONS: The results of the study highlight the importance of positioning wheelchair users in a manner that facilitates in-seat movement. Regardless of the cushion being used, the pressure relief maneuvers resulted in very large reductions in IPs and significant increases in buttock blood flow. Only the small frontward lean was shown to be ineffective in reducing pressure or increasing blood flow. Because these pressure relief maneuvers involved postural changes that can occur during functional activities, these pressure relief maneuvers can become a part of volitional pressure relief and functional weight shifts. Therefore, clinical instruction should cover both as a means to impart sitting behaviors that may lead to better tissue health.

Measure it: proper wheelchair fit is key to ensuring function while protecting skin integrity.

The objectives of this article are to help the clinician to better recognize the basic biomechanics of posture, describe the appropriate means to configure a wheelchair to permit proper postural support, and to identify common problems arising from improper wheelchair fit.

Factors that influence changes in wheelchair cushion performance over time.

Wheelchair cushions can be used for many hours every day. Like all devices, cushions degrade over time, losing the ability to provide adequate support. Little is known about the changes that cushions undergo after typical everyday use. This project was designed to monitor cushion performance over time with the objective to identify the most important factors that predict cushion degradation. Wheelchair users and their cushions were evaluated multiple times. Information was collected about participants' posture and activities, their cushions, and use of their cushions. Cushion performance was determined by measuring interface pressure using a buttock model. Data analysis proceeded in two steps. First, principal component analysis was run to reduce the number of variables. Second, multiple regression determined which variables influenced the interface pressure performance variables. Results indicated that user characteristics and the manner in which the cushion is used have a greater influence on cushion performance than the chronological age of the cushion. This result can be useful to clinicians who should query users about cushion use when investigating the need to replace a cushion. Finally, this information is applicable to policies that govern cushion replacement and indicted that wear on a cushion is not equivocal across users.

Evaluating bottoming-out of bariatric sized wheelchair cushions.

In the United States, wheelchair cushions are classified using HCPCS codes. Cushions classified as Skin Protection cushions are provided for wheelchair users who are at risk of tissue damage. Cushions designed for bariatric users fall into a category of cushions with width of 22 inches or greater. Current coding procedures require tests that are designed for 41-43-cm-wide cushion so cannot evaluate wider cushions. The objective of this study was to evaluate the performance of heavy-duty or bariatric wheelchair cushions using an anthropometrically appropriate buttock model and loading profile. A rigid buttock model, designed to reflect the anthropometry of persons using cushions over 55 cm in width was loaded onto six bariatric-sized wheelchair cushions. Two applied loads, 75 and 88 kg, represented the 50th and 80th percentile of persons who would be expected to use a 55-cm-wide cushion. None of the cushions indicated a bottomed-out state at the 88 kg load, suggesting that they could adequately support users weighing 135 kg. However, when evaluating cushions at their maximum rated loads, two of the six cushions were approaching or had bottomed-out. This study indicates that a more valid approach to classify Skin Protection bariatric cushions is needed.

3-dimensional buttocks response to sitting: a case report.

AIM OF THE STUDY: The aim of this study was to describe an individual's 3-dimensional buttocks response to sitting. Within that exploration, we specifically considered tissue (i.e., fat and muscle) deformations, including tissue displacements that have not been identified by research published to date. MATERIALS AND METHODS: The buttocks anatomy of an able-bodied female during sitting was collected in a FONAR Upright MRI. T1-weighted Fast Spin Echo scans were collected with the individual seated on a custom wheelchair cushion with a cutout beneath the pelvis ("unloaded"), and seated on a 3″ foam cushion ("loaded"). 2D slices of the MRI were analyzed, and bone and muscle were segmented to permit 3D rendering and analyses. RESULTS: MRIs indicated a marked decrease in muscle thickness under the ischial tuberosity during loaded sitting. This change in thickness resulted from a combination of muscle displacement and distortion. The gluteus and hamstrings overlapped beneath the pelvis in an unloaded condition, enveloping the ischial tuberosity. But the overlap was removed under load. The hamstrings moved anteriorly, while the gluteus moved posterior-laterally. Under load, neither muscle was directly beneath the apex of the ischial tuberosity. Furthermore, there was a change in muscle shape, particularly posterior to the peak of the ischial tuberosity. CONCLUSION: The complex deformation of buttocks tissue seen in this case study may help explain the inconsistent results reported in finite element models. 3D imaging of the seated buttocks provides a unique opportunity to study the actual buttocks response to sitting.

Visual inspections of wheelchair cushions after everyday use.

The objective of this project was to document the state of wheelchair cushions after everyday use by identifying signs of wear, fatigue, and failure. Visual inspection was done on 202 wheelchair cushions with average and median ages of 2.7 and 2 years, respectively. Most cushions were deemed to be "clean" and the proportion did not change across age groups. A high proportion of cushion covers showed signs of wear with damage to fabric and seams being most prevalent. Foam cushions showed more signs of wear than viscous fluid or air cushions. More than 60% of foam cushions showed signs of permanent deformation, and in nearly half, the foam exhibited granulation or brittleness. About 15% of the bladders used in viscous fluid or air cushions exhibited cracks or breaks in the material. In conclusion, a visual inspection of wheelchair cushions showed that most cushions appeared clean and were in good repair over a wide range of ages and usage patterns. While documenting signs of wear after use can help inform interventions and monitoring, research is needed to document changes in performance of wheelchair cushions overtime as a means to develop better replacement strategies.

Effects of wheels and tires on high-strength lightweight wheelchair propulsion cost using a robotic wheelchair tester.

PURPOSE: This study was designed to investigate the effect of wheel and tire selections on the propulsion characteristics of a high-strength lightweight manual wheelchair using robotic wheelchair propulsion. MATERIALS AND METHODS: Four configurations were compared with differing combinations of drive wheel tires and casters, with the baseline reflecting the manufacturer configuration of a solid mag drive wheel and 8"×1" caster. The robotic wheelchair tester propelled the chair using pre-generated straight and curvilinear manoeuvres using repeatable and reliable cyclic torque profiles. Additionally, energy loss of the components was measured using coast-down deceleration tests to approximate the system-level rolling resistance of each configuration. RESULTS: Results indicate a significant decrease in propulsion cost, increased distance travelled and increased manoeuvrability across all configurations, with upgraded casters and tires. CONCLUSIONS: These results indicated that with better casters and drive wheel tires, the performance of high strength lightweight wheelchairs can be improved and better meet the mobility needs of users.Implications for rehabilitationWheel and tire selection can have a demonstrable impact on the propulsion efficiency of manual wheelchairsCoast-down test protocols can be used as a simple and cost-effective means of assessing representative energy losses across various surfacesWheelchair configurations can be optimized with proper knowledge of the main energetic loss contributions and the environments and contexts of use.