by Quyen Catania, PT, DPT, CWS, CLT; Erin Michael, PT, DPT, ATP/SMS; and Marjorie Morgan, PTA
According to the National Spinal Cord Injury Statistical Center, approximately 291,000 people are currently living with a spinal cord injury (SCI) in the United States. There are roughly 17,730 new cases each year.1 Neurological impairments including decreased mobility and impaired sensation place clients with SCI at high risk for developing pressure injuries (PrIs). The incidence of PrIs in community-dwelling adults with SCI is greater than 30% per year and up to 95% over the course of a lifetime.2,3
To date, there is limited research to determine whether injury patterns in clients with SCI affect risk of pressure injury development. A 4-year retrospective case study was performed at Kennedy Krieger Institute’s International Center for Spinal Cord Injury, Baltimore, to determine whether clients with lower motor neuron (LMN) injuries were more likely to report PrIs than clients with upper motor neuron (UMN) injuries. To review, SCI is classified according to the extent of injury (last intact root above the injured portion of the spinal cord and completeness of lesion) and type of injury pattern (upper motor neuron and lower motor neuron dysfunction). Those with LMN injury exhibit flaccid paralysis, severe muscle atrophy, and decreased or absent deep tendon reflex as a result of disruption of the peripheral motor pathways.4 In contrast, UMN injuries are categorized by disruption of the primary motor pathways and manifest as increased muscle tone, overactive reflexes, and positive Babinski reflex.4
All study subjects with traumatic and non-progressive myelopathy, neurological levels T8 and below, who reported PrI or history of PrI upon admission were selected for the retrospective review. For the purpose of the study, study subjects were separated into UMN vs. LMN groups based solely on spasticity. The LMN group was defined as having a score of 0 on the Modified Ashworth Scale (MAS), a scale measuring muscle tone, and without pharmacological management for spasticity. The UMN group was defined as having any number greater than 0 on the MAS, with or without pharmacological management. For both categories, outcome measurements collected included: presence of PrI, history of PrI, requirement of flap closure, demographics, International Standards for Neurological Classification of SCI, neurological level, Modified Ashworth Scale, Spinal Cord Independent Measures-III, Braden Scale, and use of anti-spasticity medication.
Data from 180 study subjects were collected: 31 for the LMN group and 149 for the UMN group. The UMN group comprised 65% males whereas the LMN group comprised of 58% male, averaging 4-7 years after injury. The LMN group averaged 26 years of age and had more motor complete injuries, while the UMN group averaged 38 years of age and had more motor incomplete injuries. Results indicated that study subjects with LMN were more likely to report PrI upon admission, in addition to having had a history of PrI. Equally interesting, clients with UMN were more likely to never have had a PrI and less likely to report a PrI at admission. Furthermore, even though it wasn’t statistically significant, study subjects with LMN were more likely to require flap surgeries when compared to their counterparts.
An MRI investigation published in 2017 showed that participants with SCI tended to have less muscle tissue volume beneath their ishcial tuberosities (IT) while sitting compared to participants without SCI. This reduction of muscle and fat volumes can cause tissue deformation and ischemia-related tissue damages.5 Moreover, in patients with LMN muscle fibers have been found to be replaced by adipose and fibrous tissues. These severe structural changes were not present in patients with UMN, even 20 years after thoracic-level SCI.6
One way in which clinicians can play an active role in reducing risk of PrI development in the SCI population is to prescribe individualized wheelchair cushions. Cushions can diminish sitting pressures, correct flexible asymmetries or accommodate fixed ones, reduce tissue strain, regulate skin temperature, and minimize moisture.7,8 The proper seat cushion can serve as the first line of defense against PrIs for the active wheelchair user.
Immersion and Envelopment.
These are the principles behind a majority of cushion models and cushion materials. The idea is that the user sinks into the cushion. The further the body drops into the cushion, the larger the surface area for pressure redistribution. This results in lower pressures under the boney prominences.
Off-loading cushion (OLC). This cushion is foam-based and developed like a prosthetic or orthotic. The pressure is displaced to lower-risk soft tissues, while the higher-risk boney areas (ischial tuberosities, sacrum, coccyx and greater trochanter) are off-loaded. Due to being built off orthotic principles, this cushion type can also enhance pelvic alignment and create a more functional posture.
The existing types of cushion materials are air, fluid (or gel), foam, and honeycomb. Each has its own set of benefits and drawbacks.
Air. The evidence behind the effectiveness of air-cell based (ACB) cushions in reducing pressures is substantial. The immersion and envelopment principle of these cushions evenly distributes pressure over a larger contact area or the entire seating surface.9,10 Air cushions are lightweight, waterproof, and easily cleaned. Due to air being a more dynamic surface, achieving postural support can be a challenge as stability is reduced. Maintenance for this style of cushion is high. Inflation levels must be checked regularly; the pressure-relieving properties rely on proper inflation levels. Air is influenced by environmental temperatures; a change in temperature can influence the overall inflation level of the cushion. Lastly, a leak or hole could be devastating to skin health.
Fluid. These cushions are gel-based and easily conform or contour to the user. Research shows that they may reduce skin temperature, as compared to a flat foam or ACB cushion.7 The gel surface is dynamic, but typically there is a foam base allowing easy modification for positioning needs. Fluid cushions may require daily kneading or repositioning of the gel, but are lower maintenance than the standard ACB cushion. They tend to be heavier than other varieties and have the potential for leaking. They may be influenced by environmental temperature — becoming more or less viscous — which impacts user immersion.
Foam. Foam comes in many varieties or densities. These varieties can be layered to customize the cushion set-up and create postural support versus pressure relief. They can be molded to create a custom fit. Foam is relatively low maintenance and lightweight. However, increases in skin temperature are seen after prolonged sitting on some foam varieties,7 and it has been found to place high stress on muscle, fat and skin.11 Some foam types compress easily and can lose their resiliency over time. Generally, it is not moisture resistant, which can be an issue for people who struggle with incontinence or hyperhidrosis.
Hybrid. This style of cushion has become increasingly more popular, as it combines multiple materials to utilize each where it is most advantageous. Air or gel can be placed under high-risk areas, as they provide superior pressure relief, while foam can be used in areas that are not as susceptible to pressure, like the gluteal tissue or thighs, to promote stability and permit adequate postural support.
Honeycomb. These cushions look like a beehive — hence, the name — and are made from thermoplastics. Their design allows for good airflow and decreased moisture, and they are lightweight and easy to clean. They are limited in their ability to provide postural support, compress over time, and tend to have higher interstitial pressures than other cushion types.
Our wound team has established that clients with LMN injuries are more likely to report history of PrI and likely have PrI upon admission. Additionally, our seating team has discovered that a majority of cushion types do not adequately reduce pressure over boney prominences in clients with LMN as muscle atrophy and tissue changes are too significant. For many, even on the gold standard ACB cushions, the ITs would still receive too much pressure, lighting up red on our pressure mapping system. Promising research has found decreased interface pressures in the IT and sacral/coccygeal regions7 and decreased tissue strain8 when sitting on an orthotic offloading wheelchair cushion versus air cushion.
Historically, OLCs had been avoided, as it was thought that taking pressure away from one area must cause greater pressure in another. However, when comparing the OLC to ACB cushions by measuring tissue deformation under the ITs, decreased soft-tissue thickness was noted when participants were on the ACB cushion, suggesting greater tissue strain and increased tissue risk compared to OLCs. Additional MRI evidence is emerging to debunk the historic views of OLCs.10
Most importantly, significant and recurring evidence exists to support and reinforce the necessity for a comprehensive and individualized evaluation. For example, MRI imaging of six participants and six cushion varieties, each functioning off of the immersion and envelopment principles,12 found great variability in cushion effectiveness. No one cushion type performed well for all individuals.
Clinicians should monitor clients with SCI who have decreased spasticity more closely for PrI development throughout their lifetime. Additionally, for wheelchair users, cushions should be used to decrease risk of PrI development. Each patient requires an individualized team approach to cushion selection and management as there are benefits and drawbacks to each cushion type. RM
Quyen Catania, PT, DPT, CWS, CLT, graduated from University of Notre Dame with a Bachelor of Science and Washington University in St. Louis with her Doctorate in Physical Therapy. She obtained her Certified Wound Specialist in 2016 and Certified Lymphedema Therapist in 2017. She is currently a level III physical therapist and has been an integral part of creating and expanding lymphedema and wound care services at Kennedy Krieger Institute, International Center for Spinal Cord Injury.
Erin Michael, PT, DPT, ATP/SMS, is Manager of Patient Advocacy and Special Programs at Kennedy Krieger Institute’s International Center for Spinal Cord Injury (ICSCI) in Baltimore. She received her Doctor of Physical Therapy degree from Ithaca College in 2006. She specializes in treating paralyzing neurological conditions, including multiple sclerosis, transverse myelitis, cerebral palsy, and traumatic and non-traumatic spinal cord injury. Additionally, Michael is the coordinator of the ICSCI Seating and Mobility Clinic and has specialized in seating and mobility for nearly 10 years. She received her assistive technology professional certification in 2011 and her seating and mobility specialist certification in 2013. Michael is a member of the Clinician’s Task Force and of the RESNA Professional Standards Board.
Marjorie Morgan, PTA, is currently a physical therapy assistant at Kennedy Krieger Institute, International Center for Spinal Cord Injury. Morgan has had extensive experience working with patients affected by cerebral palsy and brain injury through Kennedy Krieger’s Specialized Transitional Program and patients with limb deformities at International Center for Limb and Lengthening. In 2008, she transitioned to the International Center for Spinal Cord Injury, where she currently treats patients affected by SCI. For more information, contact [email protected].
1. National Spinal Cord Injury Statistical Center. (2019). 2019 Annual Statistical Report. Birmingham, Alabama: National Spinal Cord Injury Statistical Center.
2. Vaishampayan A, Clark F, Carlson M, Blanche E. Preventing pressure ulcers in people with spinal cord injury: targeting risky life circumstances through community-based interventions. Adv Skin Wound Care. 2011;24(6):275-84.
3. Marin J, Nixon J, Gorecki C. A systematic review of risk factors for development and reoccurrence of pressure injuries in people with spinal cord injuries. Spinal Cord. 2013;51:522-27.
4. Douherty J, Burns A, O’Farell D, Ditunno J. Prevalence of upper motor neuron vs. lower motor neuron lesions in complete lower thoracic and lumbar spinal cord injuries. J Spinal Cord Med. 2002;25:289-92.
5. Brienza D, Vallely J, Karg P, Akins J, Gefen A. An MRI investigation of the effects of user anatomy and wheelchair cushion type on tissue deformation. J Tissue Viability. 2017;27(1):42-53.
6. Kern H, Stramare R, Martino L, Zanato R, Gargiulo P, Carraro U. Permanent LMN denervation of human skeletal muscle and recovery by h-b FES: management and monitoring. Eur J Transl Myol. 2010;20(3):91-104.
7. Hsu TW, Yang SY, Liu JT, Pan CT, Yang YS. The effect of cushion properties on skin temperature and humidity at the body-support interface. Assist Technol. 2016;29:1-8.
8. Krey HC, Calhoun C. Utilizing research in wheelchair and seating selection and configuration for children with injury/dysfunction of the spinal cord. J Spinal Cord Med. 2004;27(1):29-37.
9. Crane B, Wininger M, Call E. Orthotic style off-loading wheelchair seat cushion reduces interface pressure under the ischial tuberosity and sacrococcygeal regions. Arch Phys Med Rehabil. 2016;97(11):1872-1879.
10. Call E, Hetzel T, McLean C, Burton J, Oberg C. Off-loading wheelchair cushion provides best case reduction in tissue deformation as indicated by MRI. J Tissue Viability. 2017;26(3):172-179.
11. Levy A, Kopplin K, Gefen A. An air-cell-based cushion for pressure ulcer protection remarkably reduces tissue stresses in the seated buttocks with respect to foams: finite element studies. J Tissue Viability. 2014;23(1):13-23.
12. Brienza D, Vallely J, Karg P, Akins J, Gefen A. An MRI investigation of the effects of user anatomy and wheelchair cushion type on tissue deformation. J Tissue Viability. 2018;27(1):42-53.
A Closer Look at Alternating Pressure Air Cushions
Pressure reliefs can be critically important in combatting the development of pressure injuries. But what if a wheelchair user forgets to perform a pressure relief—or is unable to perform one? The result is a reduction in blood flow that establishes conditions for a pressure injury to develop. These injuries can become life-threatening and are costly to treat, so choosing a cushion that reduces the likelihood that a pressure injury will form becomes vitally important.
A Different Approach
Alternating pressure air cushions manufactured by Aquila Corporation, Holmen, Wis, represent a technology that differs from off-the-shelf products. This cushion combines alternating pressure relief with custom offloading to create a seating environment that raises the user’s level of protection against pressure injuries. A look inside the highly specialized Aquila SofTech cushion reveals a design that incorporates all cushion components inside the cushion base as well as an optional moisture control fan that helps reduce skin temperature and moisture of an existing pressure sore and posterior.
Since it may be used to help prevent pressure injuries as well as treat them, the Aquila cushion can be called a dual-purpose wheelchair cushion. The cushion’s automatic alternation stimulates circulation and changes pressure points, which is essential in preventing pressure injuries from forming. For healing, this custom fabricated cushion offloads beneath the pressure injury and thus eliminates upward inflated pressure. At the same time, the rest of the posterior receives the benefits of alternating pressure relief and tissue perfusion.
The cushion’s custom design and automatic pressure-relief functions are important for clients affected by cognitive or physical limitations that may inhibit their ability to perform manual pressure relief every 20 minutes. Aquila cushions can be helpful in these cases since they are designed to automatically interrupt constant pressure every 60 seconds. This action is similar to a manual pressure lift and one that is instrumental in preventing pressure injuries brought on by constant sitting.
The performance of Aquila cushions is backed by an expanse of data about their use that has been reported in clinical studies, peer-reviewed journals, and case reports. Research that used Aquila cushions offers proof about how the cushion assists in the healing of existing pressure injuries of all stages, including stage 4 and unstageable wounds. Among the notable research the cushions were used in a Cleveland Clinic 5-year study that compared conventional and alternating cushion weight shifting in persons with spinal cord injury.
Complex Rehab Solves Mobility Questions
Complex rehabilitation technologies for mobility are oftentimes the vital link that connects people affected by disabilities with the world outside their own homes. Seating solutions that elevate and recline, negotiate curbs, and even place the user into a standing position solve mobility questions and make it possible for many manual and power wheelchair users to reliably and safely access work, school, friends, and family. This brief overview summarizes a few of the exciting advances in today’s mobility market.
Manual mobility users often rely on handrim wheelchair propulsion, which can place a high mechanical load on the shoulder and lead to overuse injuries. Good news for manual device users can be found in motorized power assist devices that are designed to fit nearly any type of manual wheelchair. They are also made to be lightweight and easy to attach or remove. And, for even greater ease of use, some models are designed to be operated with a wearable controller and connect to an app to track usage data.
Another development for manual complex rehab solutions is vibration damping technology that isolates the seat frame from the base frame to provide a smooth ride. This technology applies a two-frame design (separate seat and base) that aims to reduce high-frequency vibrations received by the user’s body. It is also engineered so that seat angle, seat-to-floor height, and center of gravity all are easy to vary.
Advances in drive and control systems have marked some of the most exciting developments for power wheelchair users. Once such development is the arrival of a fully integrated alternative drive system that allows wheelchair users to operate their devices with a head array, sip & puff, tray array, or many types of joysticks. The head array and tray array use embedded sensors that are aesthetically pleasing yet highly responsive to user control. The system is built around a computerized central processing unit that can be used with all types of proximity switches. The system’s programming software is also designed to allow equipment providers, therapists, or users to adjust their control commands, and assign and reassign commands to various types of switches.
Both power and manual wheelchairs enjoy the continuing evolution of tilt technologies that offer the benefits of weight shifting as well as reduce the risk of injury during transfers. One development now on the market is a cast aluminum frame available in folding and rigid configurations. Features of this technology include hand or foot tilt options, adjustable axle position, and up to 45 degrees of posterior tilt. RM