Predictors of pressure ulcer incidence following traumatic spinal cord injury: a secondary analysis of a prospective longitudinal study.

STUDY DESIGN: Secondary analysis of data from a prospective cohort study. OBJECTIVES: The objective of this study was to identify the medical and demographic factors associated with the development of pressure ulcers during acute-care hospitalization and inpatient rehabilitation following acute spinal cord injury. SETTING: The study was carried out at acute hospitalization, inpatient rehabilitation and outpatient rehabilitation sites at a university medical center in the United States. METHODS: Adults with acute traumatic spinal cord injury (n=104) were recruited within 24-72 h of admission to the hospital. Pressure ulcer incidence was recorded. RESULTS: Thirty-nine participants out of 104 (37.5%) developed at least one pressure ulcer during acute-care hospitalization and inpatient rehabilitation. Univariate logistic regression analyses revealed significant association of pressure ulcer incidence for those with pneumonia and mechanical ventilation (P=0.01) and higher injury severity (ASIA A) (P=0.01). Multiple logistic regression showed that the odds of formation of a first pressure ulcer in participants with ASIA A was 4.5 times greater than that for participants with ASIA B, CI (1-20.65), P=0.05, and 4.6 times greater than that for participants with ASIA C, CI (1.3-16.63), P=0.01. CONCLUSION: Among individuals with acute traumatic SCI, those with high-injury severity were at an increased risk to develop pressure ulcers. Pneumonia was noted to be associated with the formation of pressure ulcers.

Evaluation of wheelchair sling seat and sling back crashworthiness.

Many wheelchairs are used as vehicle seats by those who cannot transfer to a vehicle seat. Although ANSI/RESNA WC-19 has been recently adopted as a standard to evaluate crashworthiness of the wheelchairs used as motor vehicle seats, replacement or after-market seats may not be tested to this standard. This study evaluated the crashworthiness of two specimens each of three unique sling backs and three unique sling seats using a static test procedure intended to simulate crash loading conditions. To pass the test, a sling back is required to withstand a 2290 lb load, and a sling seat should be capable of withstanding a 3750 lb load. All, but two sling back specimens which failed at 1567 lb and 1787 lb, withstood the test criterion load. Two of six tested sling seats failed to pass the test: one failed at 3123 lb and the other failed to sustain the load for 5 s although it reached the test criterion load. Most of the failures occurred at the seams of the side openings of upholsteries where the wheelchair frame inserts for attachment.

Evaluation of wheelchair drop seat crashworthiness.

Wheelchair seating crash performance is critical to protecting wheelchair users who remain seated in their wheelchairs during transportation. Relying upon computer simulation and sled testing seat loads associated with a 20 g/48 kph (20 g/30 mph) frontal impact and 50th percentile male occupant were estimated to develop test criteria. Using a static test setup we evaluated the performance of various types of commercially available drop seats against the loading test criteria. Five different types of drop seats (two specimens each) constructed of various materials (i.e. plastics, plywood, metal) were evaluated. Two types of drop seats (three of the total 10 specimens) met the 16650 N (3750 lb) frontal impact test criteria. While additional validation of the test protocol is necessary, this study suggests that some drop seat designs may be incapable of withstanding crash level loads.

The relationship between pressure ulcer incidence and buttock-seat cushion interface pressure in at-risk elderly wheelchair users.

OBJECTIVE: To investigate the relation between pressure ulcer incidence and buttock-wheelchair seat cushion interface pressure measurements. DESIGN: Secondary analysis of data from a randomized clinical trial. SETTING: Skilled nursing facility. PATIENTS: Thirty-two elderly patients (age, > or = 65 yr), with Braden score < or = 18 and Braden mobility and activity subscale score < or = 5, who used wheelchairs > or = 6 hr/d, were free of existing sitting-induced pressure ulcers, and weighed < or = 250 lb. INTERVENTIONS: Generic foam seat cushion or pressure-reducing seat cushion. MAIN OUTCOME MEASURES: The incidence of sitting-induced pressure ulcers over a 1- to 12-month period was compared with pressure measured between patients' buttocks and wheelchair seat cushions. A flexible pad with a 15 x 15 pressure sensor array was used to measure interface pressure. RESULTS: Interface pressure measured on wheelchair seat cushions was higher (p < or = .01 for both peak pressure and average of highest 4 pressures) for patients who developed sitting-acquired pressure ulcers compared with those patients who did not. CONCLUSIONS: Results indicated that higher interface pressure measurements are associated with a higher incidence of sitting-acquired pressure ulcers for high-risk elderly people who use wheelchairs.

Evaluation of wheelchair seating system crashworthiness: "drop hook"-type seat attachment hardware.

OBJECTIVE: To evaluate the crashworthiness of commercially available hardware that attaches seat surfaces to the wheelchair frame. DESIGN: A low cost static crashworthiness test procedure that simulates a frontal impact motor vehicle crash. SETTING: Safety testing laboratory. SPECIMENS: Eleven unique sets of drop-hook hardware made of carbon steel (4), stainless steel (4), and aluminum (3). INTERVENTIONS: Replicated seat-loading conditions associated with a 20g/48 kph frontal impact. Test criterion for seat loading was 16,680 N (3750 lb). MAIN OUTCOME MEASURES: Failure load and deflection of seat surface. RESULTS: None of the hardware sets tested met the crashworthiness test criterion. All failed at less than 50% of the load that seating hardware could be exposed to in a 20g/48 kph frontal impact. The primary failure mode was excessive deformation, leading to an unstable seat support surface. CONCLUSIONS: Results suggest that commercially available seating drop hooks may be unable to withstand loading associated with a frontal crash and may not be the best option for use with transport wheelchairs.

A randomized control trial to evaluate pressure-reducing seat cushions for elderly wheelchair users.

OBJECTIVE: To determine if the use of pressure-reducing wheelchair cushions for elderly nursing home resident wheelchair users who are at high risk for developing sitting-acquired pressure ulcers would result in a lower incidence rate of pressure ulcers, a greater number of days until ulceration, and lower peak interface pressures compared with the use of convoluted foam cushions over a 12-month period. To determine the feasibility of conducting a subsequent full-scale definitive trial to evaluate the use of pressure-reducing seat cushions for elderly nursing home resident wheelchair users. DESIGN: Randomized control trial SETTING: 2200-bed skilled nursing facilities (1 suburban and 1 urban academic medical center) PATIENTS: 32 male and female at-risk nursing home residents who were wheelchair users > or = 65 years of age. Participants had Braden Scale scores < or = 18, Braden Activity and Mobilitysubscale scores < or = 5, no sitting surface pressure ulcers, and a daily wheelchair sitting tolerance of more than 6 hours. All met criteria for using the ETAC Twin wheelchair. INTERVENTIONS: Seating evaluation with pressure-mapping and subsequent seating prescription. Subjects were assigned to either a foam (n=17) or pressure-reducing cushion (n=15) group and weekly assessments of skin and pressure ulcer risk were made. MAIN OUTCOME MEASURES: Incidence of pressure ulcers, days to ulceration, and peak interface pressure. MAIN RESULTS: At a 95% confidence interval, a 2-tailed analysis showed no differences between the FOAM and pressure-reducing cushion groups for pressure ulcer incidence, total days to pressure ulcer, or initial peak interface pressure. Pressure-reducing cushions were more effective in preventing sitting-acquired (ischial) pressure ulcers (P<.005). Higher interface pressures were associated with a higher incidence of pressure ulcers (P<.001). CONCLUSIONS: A definitive randomized control multicenter cushion trial is feasible with a sample size of 50 to 100 per study group. In the definitive trial, the definition of sitting-acquired pressure ulcers should be limited to lesions occurring over the ischial tuberosities.

Wheelchair integrated occupant restraints: feasibility in frontal impact.

Individuals often use their wheelchair as a motor vehicle seat when traveling in motor vehicles. The current use of fixed vehicle-mounted wheelchair occupant restraint systems (FWORSs) often results in poor belt fit and discomfort. Additionally, satisfaction, usability and usage rate of FWORSs during transit use are often low. The automotive industry has shown improved occupant restraint usage, belt fit and injury protection when integrating the upper torso and pelvic restraint in a motor vehicle seat. This study compared occupant injury measures of a FWORS to a concept wheelchair integrated restraint system (WIRS) using a 20g frontal sled impact test with a 30 mph change in velocity. Neck loads, neck moments, head, pelvis and chest acceleration, sternum compression and knee and head excursion data were recorded from the wheelchair seated 50th percentile male hybrid III anthropomorphic test dummy (ATD). The WIRS resulted in a lower head injury criteria (HIC) value, lower sternum compression and a lower upper-torso restraint load than the FWORS. Compared with the FWORS, increased head, knee and wheelchair excursions and higher neck loads and moments were measured in the WIRS test. Both restraint scenario injury parameters were complied with occupant injury criteria based on General Motors Injury Assessment Reference Values (GM-IARVs) and occupant kinematic requirements defined by the Society of Automotive Engineers (SAE) voluntary standard, J2249. A higher motion criteria index was calculated for the WIRS scenario and a comparable combined injury criteria index was calculated for both restraint scenarios. The sled impact test showed WIRS concept feasibility, facilitating further development by industrial manufacturers who might further want to pursue this restraint principle to increase wheelchair occupant safety and comfort during transport in motor vehicles.

A compound sensor for biomechanical analyses of buttock soft tissue in vivo.

A sensor for in vivo biomechanical characterization of buttock soft tissue has been developed and evaluated. The sensor measures interface pressure, applied force, tilt, and rotation angle of the sensor head, and the thicknesses of multiple soft tissue layers. A composite ultrasonic transducer using a 1-3 ceramic-polymer structure was developed for the sensor. The sensor can identify subcutaneous soft tissue interfaces 5 to 65 mm below the skin surface with a 0.26-mm axial resolution, pressure over the range of 0 to 68 kPa, and force over the range of 0 to 3.6 kg. Our purpose for developing the sensor was to study the biomechanical characteristics of buttock soft tissues. Successful identification of distinguishing characteristics in persons with a susceptibility to pressure ulcers may result in the development of a risk assessment tool based on tissue characterization.

Proposed test method for and evaluation of wheelchair seating system (WCSS) crashworthiness.

Safety of motor vehicle seats is of great importance in providing crash protection to the occupant. An increasing number of wheelchair users use their wheelchairs as motor vehicle seats when traveling. A voluntary standard requires that compliant wheelchairs be dynamically sled impact tested. However, testing to evaluate the crashworthiness of add-on wheelchair seating systems (WCSS) independent of their wheelchair frame is not addressed by this standard. To address this need, this study developed a method to evaluate the crash-worthiness of WCSS with independent frames. Federal Motor Vehicle Safety Standards (FMVSS) 207 test protocols, used to test the strength of motor vehicle seats, were modified and used to test the strength of three WCSS. Forward and rearward loads were applied at the WCSS center of gravity (CGSS), and a moment was applied at the uppermost point of the seat back. Each of the three tested WCSS met the strength requirements of FMVSS 207. Wheelchair seat-back stiffness was also investigated and compared to motor vehicle seat-back stiffness.

Evaluation of wheelchair back support crashworthiness: combination wheelchair back support surfaces and attachment hardware.

Automotive seats are tested for compliance with federal motor vehicle safety standards (FMVSS) to assure safety during impact. Many wheelchair users rely upon their wheelchairs to serve as vehicle seats. However, the crashworthiness of these wheelchairs during impact is often unknown. This study evaluated the crashworthiness of five combinations of wheelchair back support surfaces and attachment hardware using a static test procedure simulating crash loading conditions. The crashworthiness was tested by applying a simulated rearward load to each seat-back system. The magnitude of the applied load was established through computer simulation and biodynamic calculations. None of the five tested wheelchair back supports withstood the simulated crash loads. All failures were associated with attachment hardware.

A method for custom-contoured cushion design using interface pressure measurements.

The interface pressure distributions between flat foam cushions and the buttocks of seated test subjects were compared to custom-contoured cushion surface shapes generated with a seated-buttock contour gauge. Our hypothesis was that pressure measurements could be used to generate a contour equivalent to that obtained with a force-deflection contour gauge. The study was performed in a university medical center using spinal cord injured (SCI) (12) and elderly (30) test subjects. Interface pressure was measured using a pressure mapping pad. Contour shape was measured using an electronic force-deflection contour gauge. Pressure and contour information were reduced prior to analysis using singular value decomposition. Polynomial regressions were performed on the values in the first singular vectors of the corresponding pressure and contour decompositions. Relationships best described by cubic polynomials were detected between pressure and contour shape suggesting that interface pressure predicts optimal contour shape.

Seat cushion optimization: a comparison of interface pressure and tissue stiffness characteristics for spinal cord injured and elderly patients.

OBJECTIVE: A method for designing tissue deformation minimizing seat surfaces was evaluated. Pressure and stiffness criteria were used to optimize surface shape. The method's efficacy for patients with spinal cord injuries (SCI) and a comparison of cushion performance and interface characteristics with a group of 30 elderly patients are presented. DESIGN: Repeated measures, prospective study. SETTING: University medical center. PATIENTS: SCI (n=12), elderly (age 65 + years) [n=30]. INTERVENTIONS: One flat and two custom foam seat cushions. MAIN OUTCOME MEASURES: Interface pressure measured using a pressure sensing pad; tissue stiffness and pressure recorded on a rigid programmable seat surface. RESULTS: Pressure distributions on contoured cushions for the SCI group contained lower values than distributions on flat cushions. A comparison of the pressure data between the elderly and SCI showed that significant differences exist between interface characteristics. The SCI group had higher peak interface pressures for all cushions tested. Tissue stiffness measurements were similar for each group. CONCLUSIONS: Results showed improved effectiveness of custom contoured foam seat cushions versus flat foam cushions. The results suggest that pressure distributions for SCI are more sensitive to support cushion characteristics than for the elderly. Further research is needed to determine the extent of the difference between the populations represented by these groups.

Wheeled mobility device database for transportation safety research and standards.

To address the issue of safely accessing and securing wheeled mobility devices in motor vehicles, more information characterizing current-production devices was needed. In a recent effort, frame characteristics of wheeled mobility devices were defined and a database developed for recording characteristics relevant to access and securement. A representative number of devices have been surveyed to measure key characteristics, and these measures have been recorded in the database. This paper details the development of the database and frame characterization scheme, the methods used to survey currently available wheeled mobility devices, and some descriptive statistics resulting from an analysis of the data. A discussion of how this information is being used in research aimed at developing technology and safety standards to ensure vehicle access and safe transportation, as well as other potential uses, is also included.

Seat cushion design for elderly wheelchair users based on minimization of soft tissue deformation using stiffness and pressure measurements.

A method for designing seat support surfaces using interface pressure and soft tissue stiffness criteria was evaluated. An algorithm designed to drive a rigid support surface on a programmable seating system to a shape for which the externally applied pressure is inversely related to the measured stiffness of adjacent soft tissue was evaluated on 30 elderly subjects (age 65 years or older). The resulting support surface shapes were transferred to compliant foam cushions and evaluated using interface pressure measurements. Pressure and stiffness measurements on the seating system indicated the surface shape control algorithm met the desired programmed criteria by achieving an inverse relationship between pressure and stiffness, as it converged to an "optimal" support surface shape. Evaluation of interface pressures on the compliant foam cushions showed that the pressure distributions on the cushions contoured to the optimal surface shapes were more uniform and had lower values than distributions on flat foam cushions and foam cushions contoured to shapes measured using state-of-the-art load-deflection devices. The results suggest that support surfaces designed using tissue stiffness as a criteria can provide loading conditions intended to minimize relative deformation and, thus, stress in load-bearing soft tissue.

Development of test methodologies for determining the safety of wheelchair headrest systems during vehicle transport.

For wheelchair users unable to transfer to a vehicle seat, the wheelchair serves as a means of mobility and postural support during activities of daily living and as a seating support in a vehicle. The performance of commercially available adaptive seating components in a dynamic or impact situation, as well as their effect on the safety of the user, is unknown and should be determined. The main objective of the project was to develop a test methodology to statically determine the crashworthiness of wheelchair headrest systems and show the efficacy of that methodology by applying it to several commercially available headrest systems. The methodology was based on Federal Motor Vehicle Safety Standard (FMVSS) test conditions, which use static test procedures to ensure that vehicle head restraints will perform adequately during actual crash conditions. The procedure developed to evaluate the headrests gave informative and repeatable results. The tests performed calculated the energy associated with a critical deformation of the headrest under quasi-static conditions. The results were used to determine the level of safety provided by the devices and to recommend design improvements. The headrests tested exhibited similar modes of deformation due to bending of a vertical adjustment bar, and several devices were determined to be capable of providing adequate restraint in an impact situation.

Assessment of adaptive transportation technology: a survey of users and equipment vendors.

In order to define the state of adaptive transportation equipment, wheelchair users with spinal cord injury (SCI) and equipment vendors were surveyed about equipment, funding, maintenance, and repair. SCI registries from two states, Virginia and Arkansas, were used to create the sample pool of users and 225 responses were received. A list of equipment vendors and vehicle modifiers was compiled from several national resources, and 123 responses were received from 36 states. User respondents were generally satisfied with their adaptive equipment, which typically required only minor inexpensive (< $100) repairs, if any. Personal or family money was used by over 90% of the respondents for equipment funding. Vendors reported that a substantial amount of custom modification or fabrication of equipment is required to meet the needs of their clients. Lifts, external controls, and six-way power seats were cited by vendors as the equipment requiring the most frequent repair. The survey results provide an examination of the opinions and experiences of users and vendors of adaptive transportation equipment, which should prove useful to those involved in evaluating equipment, equipment availability, and the need for industry-wide standards.

Positioning and securement of riders and their mobility aids in transit vehicles: an analytical review.

Individuals are transported daily in transit vehicles while seated on their mobility aids. Although federal standards exist to regulate this practice, controversy exists over whether the regulations are effective or practical. This article describes an objective and analytical review of information available in several areas relevant to positioning and securing riders and their mobility aids in transit vehicles. The objective of the study was to present the current status of knowledge and to identify gaps in knowledge and related problems. As a result, recommendations are provided on future research needs and options for improvement of policy.