INTRODUCTION
Wheelchairs are classified as medical devices, but they are better described as functional devices with health implications. One health implication of mobility-disability is tissue health. An analysis of 87,000 persons with mobility-related disabilities who experienced a pressure injury (PI) reported the seven disability groups with the greatest prevalence of PIs: patients with Alzheimer disease, cerebral palsy, hemiplegia, multiple sclerosis, paraplegia/quadriplegia, Parkinson disease, and spina bifida.1 This list embodies a wide range of clinical diagnoses, not all of which are always recognized as being at high risk.
People use wheelchairs for a variety of reasons but share the functional need for assistance in mobility. The seated posture is a functional posture, especially for wheelchair users. Some wheelchair users will transfer out of the wheelchair and sit elsewhere after reaching their destination, whereas other users may remain seated in their wheelchairs during a variety of functional activities. For these users, a wheelchair goes beyond a means of conveyance and is used as the base of support while eating, exercising, recreating, working, learning, and so on. Often, these two user groups require different types of wheelchairs and seating systems, but in both cases, they need a wheelchair that fits well and supports them in a functional seated posture.
Consideration of posture includes both the wheelchair itself and the seating system, which typically consists of a seat cushion and sometimes a back/trunk support. Other postural influences include the wheelchair user himself or herself, as well as the environment and task. Wheelchairs provide structural support for the trunk, pelvis, and extremities. Supporting surfaces such as cushions, back/trunk supports, and footplates have a direct impact on the user interface. Both the wheelchair and supporting surfaces have a significant impact on overall posture.
A seat, especially one that will be used for lengthy durations, should support the body in an upright and functional posture. The importance of posture and wheelchair fit has been described with various cohorts of wheelchair users.2-5 Recently, clinicians and researchers have also highlighted the need to ensure a proper match between the equipment and wheelchair user.6-12
Samuelsson et al9 evaluated complaints about wheelchair systems from 38 users who attended a seating clinic. More than 90% reported seating discomfort or pain as their primary complaint. Assessing outcomes, the authors found that seating interventions had a positive effect on 80% of the clients. The most common intervention was delivery of a more adjustable wheelchair that could be properly fit to the user. Further, 15% of the clients simply required their current equipment to be adjusted properly. One interesting finding was that wheelchair users also reported functional benefits from interventions that reduced their seating discomfort, providing an important link between these constructs.
Two other studies also documented outcomes after a seating and mobility evaluation. In a survey of 117 persons with spinal cord injury, Gallagher et al11 assessed user satisfaction with the entire process of wheelchair evaluation, prescription, and delivery. After evaluation and delivery, most respondents (83%) reported that the wheelchair was the correct size (86%) and properly adjusted (84%). In a retrospective study of 258 nursing home residents who underwent a seating evaluation, significant improvements were found in the independence and safety domains of the Functioning Everyday with a Wheelchair instrument13 postintervention.14
In contrast, studies that did not state whether a seating evaluation was performed when prescribing wheelchairs reported less-positive outcomes. Cherubini and Melchiorri8 assessed how well 15 different wheelchair attributes and configurations met the needs of 150 individual users. Three physicians independently deemed wheelchair attributes as suitable or not suitable. Overall, 68% of wheelchairs had attributes deemed not suitable, with the most common areas of deficiency being cushions, trunk postural support, and pelvic postural support. Adjustable components such as armrests and footplates tended to be suitable more often than nonadjustable components. For example, 40% of wheelchairs had improper seat dimensions (width and/or depth). Similar results were found in a study of nursing home residents who used wheelchairs.15 Approximately 60% of resident wheelchair users had an identified need for better wheelchairs and/or seating. Pain/discomfort, a need for repositioning, and inefficiency in wheelchair propulsion were the most prevalent problems. Nearly half of the residents (46%) had a seating need that was related to skin integrity.
These studies illustrate two important points. First, a mismatch between the user and his or her wheelchair can lead to adverse impacts on function, independence, and comfort. The presence of pain or discomfort is a simple metric indicating the need to improve the wheelchair and seating environment. Second, conducting a seating evaluation can result in positive outcomes. All of the articles advocated for a proper evaluation to inform the wheelchair prescription and fitting process. This is a prudent suggestion that has potential benefits for function and PI prevention.
An efficacy study of wheelchair cushions in nursing home residents explicitly stated that cushions alone cannot protect the skin; rather, a properly fitted wheelchair is also needed.10 The authors state: "Poorly fitting wheelchairs are likely to result in poor posture that will result in higher pressure and increased pressure ulcer risk." The authors found that persons who were independently mobile had significantly fewer PIs than those participants who were dependent in their mobility.10 This is an important result because it highlights the value of function by linking activity to PI prevention.
Taken collectively, these studies provide a link between good posture, proper postural support, and PI prevention: Good posture leads to better function, which results in improved health outcomes. A simple review of posture can refresh clinicians' knowledge of seating, which can be applied to wheelchair users and non-wheelchair users alike. The principles of biomechanics as applied to posture are applicable across a wide span of persons, seats, chairs, and environments. In this article, the author focuses on the wheelchair and, specifically, proper wheelchair fit, to elucidate its impact on the posture and function of wheelchair users.
BIOMECHANICS OF POSTURE
The seated posture has been extensively studied for decades, with particular emphasis from ergonomic perspectives.16-22 One important ergonomic finding is that seating is not a static activity,23-27 and moving while seated has positive implications for both function and health. Simply put, we need to move even while seated, and this applies to wheelchair users as well. However, the biomechanics of posture can be complex when including dynamic activity, so this discussion will limit postural biomechanics to forces and anthropometry during quiet sitting.
In sitting, the majority of the body mass is transmitted through the pelvis to the buttocks and onto the seat surface. This results in the pelvis being the most important load-bearing site, and accordingly, it should garner substantial attention when evaluating posture. Body weight is also transmitted to the backrest through the trunk and to the floor or footplates via the lower extremities and feet. These forces result from the gravitational influence on body mass, but the seating system has a significant impact on how these forces are distributed over the contact areas. Remembering that pressure = force/area, and localized pressure is the defining cause of PIs, the relationship between the distribution of force onto the supporting surfaces and tissue integrity becomes evident.
Gravitational forces act downward and are responsible for the pressures on the body. Body weight dictates these forces, but how well they are distributed is a function of posture. For example, you can easily increase the pressure on your buttocks by leaning forward off your backrest or raising your feet off the ground. This is a simple exercise of decreasing the contact area between your seat and body. However, another important force is ever present during a seated posture: friction. Frictional forces also exist at the seat surface, backrest, and foot support. Friction, by definition, is the force that resists sliding between two bodies. Friction is directly related to the normal force between the bodies and the surface of contact. So, both normal and frictional forces are a function of the mass of the body segment and the postural alignment of the body with respect to the seat. Figure 1 illustrates the normal and frictional forces that are imparted onto the body by the chair and the ground.
To illustrate, consider sitting in a regular chair. Anytime a person leans against the backrest, the backrest imparts an equal and opposite force that serves to push the person out of the chair. This reaction force is counteracted by frictional forces at the seat and feet. This is easy to experience. Sit on a chair (a hard seat, like a dining room chair is best for this demonstration); lean against the backrest, and you will feel yourself sliding forward. This sliding tendency is counteracted by the friction on the seat. If you can lift your feet off the ground, you will experience this sliding tendency even more. Then, lean forward slightly so your back is no longer contacting the backrest. The sliding tendency will decrease. Because this forward-sliding tendency is ever present when sitting with a backrest, achieving a stable and functional posture includes the need to manage this sliding tendency. Improper fit of a seating system can result in situations that do not provide requisite stability and can lead to poor posture that adds risk to skin integrity and lessens function.
Types of Poor Posture
With regard to wheelchair seating, the most common poor postures can be described as (1) a slouched, kyphotic posture and (2) asymmetry due to pelvic obliquity. By identifying these postures, clinicians can begin the process of identifying the causes and design proper interventions.
Slouched, kyphotic posture
This type of posture is characterized by posterior pelvic tilt and kyphotic spine (Figure 2). This results in loading at the sacrum/coccyx, hyperextension of the cervical spine to maintain forward gaze, and an increased forward-sliding tendency in response to the poor trunk and pelvic support. Posterior pelvic tilt results in the sacrum and coccyx bearing more load than in an erect posture. This is significant from a skin integrity standpoint. Considering the superficial location of this bony complex and its rough surface anatomy, an unnecessary increase in load-bearing exposes tissue to unnecessary stress. Unfortunately, a slouched, kyphotic posture is fairly common because it results from many instances of poor fit.
Several anatomical markers can be used to identify a slouched posture. Palpating the anterior and posterior iliac spines is a direct way to assess posterior pelvic tilt, but the posterior iliac spine can be difficult to palpate when a person is sitting against a backrest. Palpating the coccyx with respect to the seat cushion is simpler and offers assessment of the sacral-coccyx orientation in the sagittal plane as well as its load-bearing status. Moving up the body, a kyphotic thoracic spine can be identified by the relative locations of the acromion and mastoid processes. These should be aligned in an erect posture. As kyphosis increases, the head translates forward with a concomitant extension of the cervical spine (Figure 2). So, in addition to potentially exposing the sacrum and coccyx to unnecessary forces, the slouched kyphotic posture can result in musculoskeletal pain and discomfort.
Asymmetry due to pelvic obliquity
Pelvic obliquity is an asymmetric posture in the frontal plane. It can be identified by palpating the iliac crests and occurs when one side is lower than the other. A pelvic obliquity can be a fixed deformity that is not readily corrected or a flexible asymmetry that can be corrected with proper postural support. A seating evaluation, often performed by a physical or occupational therapist, can distinguish a fixed versus correctable pelvic obliquity. A correctable pelvic obliquity can result from a variety of reasons linked to a poor wheelchair fit such as sitting slightly to one side of a sling wheelchair seat or from having to lean over to reach an armrest.
With respect to tissue integrity, the impact of an obliquity is fairly intuitive. This asymmetric posture leads to heightened pressure on the lower side, with both the ischia and trochanters bearing the additional load. If the obliquity induces postural instability, the person may have to lean on the armrest to remain upright. In extreme cases, this forces the person to use the arm as a postural support.
MATCHING WHEELCHAIR DIMENSIONS TO THE USER
The biomechanics of wheelchair seating can be considered a subset of the larger realm of seating biomechanics. One difference is that the function of the wheelchair user is impaired in some manner that necessitates the use of the wheelchair. This reduced function extends beyond the lower extremities and can involve all parts of the upper body that are needed to achieve proper postural support. This fact, coupled with the fact that wheelchair users sit for extended periods, highlights the importance of a good seating system. Several authors have written about wheelchair seating, the importance of evaluation, and consequences of poor posture and poor wheelchair fit.2-8 Readers are encouraged to access these for additional information and fuller insight into the concepts presented in this article.
A wheelchair is a simple device with a substantial number of components. Figure 3 illustrates the key components of a standard wheelchair. Several of these components are involved in properly fitting a wheelchair to its user. To properly fit a wheelchair to a person, a minimum of six measurements must be considered (Figure 4), including measurements of the supporting surfaces of the buttocks, trunk, and upper and lower extremities. Not all these measurements are treated equally, as will be discussed, and a few measurements tend to dominate the selection of a proper wheelchair. However, wheelchairs should be ordered and adjusted to match all six of measurements to the user.
Seat Width
Wheelchairs tend to be categorized by seat width because it is a nonadjustable feature. As a result, most wheelchairs are ordered or selected for a person according to seat width. Wheelchairs come in a wide range of seat widths, but many adult models progress in 2-inch increments starting at 16 inches. Seated hip width is the anthropometric measurement that is used to correctly prescribe wheelchair width. The proper wheelchair has the narrowest seat width that allows the user to sit without direct pressure on his or her hips. Direct pressure can come from the armrests, clothing guards, or tires and can lead to discomfort or skin problems.
Most seat width problems arise from placing someone in a wheelchair that is too wide. Using a wider wheelchair than is necessary reduces maneuverability and accessibility. Maneuvering a wider chair through doorways and other indoor spaces is a lot more difficult, so there is no benefit from using an unnecessarily wide chair. Further, access to the handrims is hindered if the chair is too wide, reducing the user's ability to propel the wheelchair efficiently (Supplemental Figure 1, http://links.lww.com/NSW/A144).
Seat Depth
Seat depth is the second dimension that defines many wheelchair models. A 16-inch seat depth is the most common, but longer seat depths are also available and should be considered for some users. The buttock-to-popliteal length is the anthropometric measurement that defines seat depth (Figure 5). Proper wheelchair seat depth is typically a little longer than the seat depths in desk or dining room chairs because greater support is needed under the thighs. A good guideline is to have approximately 1 inch between the popliteal fossa and front edge of the seat.
If seated in a chair that is too long, contact at the popliteal fossa will result in discomfort and the person will slide forward into a slouched, kyphotic posture, which can lead to unnecessary pressures on the sacrum and coccyx, as well as musculoskeletal discomfort. Conversely, if the seat depth is too short (Supplemental Figure 2, http://links.lww.com/NSW/A144), proper support is not provided. The hip may rotate internally or externally because of poor thigh stability, and there may be less stability of the buttocks on the seat because of reduced contact surface area.
Seat Height
Seat height has a direct impact on posture, propulsion, and transfers. In most wheelchairs, seat height is greater than that of everyday chairs simply because wheelchairs are designed so that the feet are off the ground. Standard wheelchair seat heights are 19 inches before the addition of a cushion. Therefore, the total seat height is typically greater.
Proper seat height is dependent on the height of the wheelchair user and his or her means of propulsion. Users who propel only with their hands will use footplates for support. These users should sit with properly adjusted footplates so that their thighs are fully supported on the seating surface. Persons who propel with one or both legs require better access to the ground and thus a lower seated height. If a user who propels by foot is placed in a seat that is too high, he or she will slide forward in the seat in order to extend the hip and reach the ground, resulting in a slouched, kyphotic posture (Figure 6). This sliding tendency is even greater for users who foot propel because foot propulsion acts to pull a person forward in the seat. These users require extra attention to ensure a stable seated posture. Sitting height can be lowered using a drop seat; these are commercially available from many sources. A few cushions are also designed to facilitate foot propulsion by allowing the user to sit lower in the seat compared with sitting on a traditional wheelchair cushion.
A slight conflict arises from the fact that transfers are made easier when getting into and out of a slightly higher seat (Figure 7). The need to keep the seat low to reach the ground to propel is in conflict with a desire to facilitate transfers into and out of the wheelchair. This underscores the need for individual evaluation for proper wheelchair fit. Fortunately, most wheelchairs can be adjusted to different seat heights by changing the axle positions of the drive wheels and casters. This relatively simple adjustment is illustrated in Figure 8. In this particular example, the drive wheels can be placed in either of two positions, and the caster forks have three possible axle positions. The forks offer multiple axle positions to accommodate casters with different diameters and enable changes in seat height. One added functionality is that the caster axle position can also be used to alter the seat angle, but this adjustment is best done by someone experienced in adjusting wheelchairs.
Footrest Length
Footrest length affects the support of both the feet and the thighs and the clearance of the footplates and the ground. The footplate must be approximately 1 to 2 inches off the ground to permit adequate clearance. If too low, the footplate can catch when traversing door thresholds or grade transitions (eg, when starting to go up a ramp or when transitioning between the ramp and flat ground when descending; Figure 9).28 The danger lies in the fact that a moving wheelchair can tip forward if the footplates suddenly hit an obstacle. In fact, approximately half of wheelchair tips are in the forward direction.29
Therefore, footplate clearance is a safety issue to consider when adjusting the footrest length, but proper adjustment is also reflective of the user's height. The proper footrest length is best determined by assessing the thigh and foot as the footrest height is adjusted. The thigh should contact the cushion surface, and the foot should be fully supported with enough weight to maintain stability on the footplate. A footplate that is too high results in the thigh being raised off the seat surface (Supplemental Figure 3, http://links.lww.com/NSW/A144). This flexes the hip and reduces the contact area at the buttocks, resulting in increased pressure on buttock tissue and decreased ability to overcome the forward-sliding tendency. Conversely, footplates that are too low result in poor foot support. The wheelchair user will seek foot stability by sliding forward in the seat (Supplemental Figure 4, http://links.lww.com/NSW/A144).
Armrest Height
Armrests serve a valuable postural support role for many users. They come in a variety of designs and lengths, all with various benefits and drawbacks. For instance, a desk-length armrest pad is shorter to enable the user to wheel closer to a table or desk; however, because the pad is shorter, it offers less forearm support.
Armrest height is adjustable in many chairs. Proper height is determined by adequate support under the forearms while in a comfortable and erect posture. If too high, armrests force the user to elevate his or her shoulders, leading to discomfort (Supplemental Figure 5, http://links.lww.com/NSW/A144) and, most likely, nonuse of the armrests. Conversely, if too low, the user must lean forward or the side to reach the armrests (Supplemental Figure 6 http://links.lww.com/NSW/A144). Leaning to the side creates a pelvic obliquity and will elevate the pressure under the lower side while forcing the user to laterally flex his or her trunk in order to maintain an erect head orientation. A simple adjustment can mitigate this poor posture.
Backrest Height
The height of the backrest dictates the support afforded to the trunk. Chair backrest heights vary considerably according to the type of chair. For instance, dining room chairs have lower backrest heights than car seats. Typically, chairs with lower backrests permit more arm and trunk movement, whereas chairs with higher backrests offer greater support.
Wheelchairs tend to come with a standard backrest height of 16 inches, although many wheelchairs offer a range of backrest heights. The functional backrest height, relative to the person, is dependent on the person's trunk length and the thickness of the seat cushion. For most people, a 16-inch backrest height will support the thoracic spine below the inferior scapula angle. This is an acceptable level of support for many people, and this height also allows the scapula to move freely.
Sitting with a backrest that is too short can lead to postural instability. A person with little or no trunk control might need a backrest that rises up to the scapular spine. More likely, poor fit results when a backrest is too high for a user. Wheelchair users tend to do a lot of functional activity from a seated position, so they need to reach in various directions and access the wheelchair handrims. This reach and access can be hindered by a backrest that is too tall. In addition, a tall backrest can push the trunk forward too much by contacting the full scapula. This results in postural instability, and the user will respond by sliding forward on the seat into a slouched posture.
ADDITIONAL FEATURES IMPACTING SEATED POSTURE
In addition to the key wheelchair measurements, wheelchair upholstery and elevating footrests also directly impact the seated posture.
Sling Seat and Backrest Upholstery
One of the most common problems is upholstery that needs to be replaced. Upholstery stretches over time, resulting in seats and backrests with too much curvature or "sling." Overstretched sling upholstery offers poor support and promotes a poor seated posture.
Excessive backrest sling allows the trunk to collapse into kyphosis. The poor posterior pelvic support offered by lax upholstery also allows the pelvis to adopt posterior pelvic tilt. The result is a pronounced slouched, kyphotic posture (Figure 10, left).
Sling seat upholstery is a curved support. Although some cushions will adjust for this by using a rigid base, most do not, so the user sits on a curved surface. A slightly curved surface will not have a significant impact, but worn-out and overstretched upholstery will contribute to poor posture. Unless the person sits in the exact middle of the seat, the pelvis will orient into an obliquity (Figure 10, right).
Upholstery is simply not designed to last forever. It is a soft good that can be easily replaced. A replacement seat or backrest upholstery can be purchased for US $25 to $60.
Manual Elevating Legrests
If one chooses to order elevating legrests, the purpose should be clearly defined relative to the drawbacks. Elevating legrests permit the user to sit with less knee flexion. This can be useful for someone with a knee flexion contracture or who has a care plan calling for knee flexion restrictions. Those are limited uses and are certainly not the norm.
The problems with elevating legrests are more profound. Because these legrests elevate on their own but do not return to a standard position (because of their ratchet mechanism), they can adversely impact posture. They cause misalignment between the anatomical knee joint and mechanical hinge joint of the legrest. The legrest should be adjusted properly to support the foot in the lowered position (Figure 11, left). When the legrest elevates, the mismatch between the joint axes of rotation results in the legrest being too short to properly support the limb, so the footplate pushes on the foot and elevates the thigh, resulting in poor support (Figure 11, middle). To properly support the limb, the footplate must be rotated upward for support by the calf pad with the foot extending beyond the legrest (Figure 11, right). Because wheelchair users typically cannot rotate the footplate out of the way independently, this does not occur in most cases. Moreover, as the knee extends, it can pull the user into a kyphotic, slouched posture because of hamstring tightness.
In summary, elevating legrests should not be treated as default equipment. They add cost and, in the vast majority of cases, are contraindicated due to poor fit over their range of elevation.
PROVISION OF WHEELCHAIRS
In the US, wheelchairs are categorized as either complex rehabilitation technology (CRT) or standard durable medical equipment (DME). The National Coalition for Assistive and Rehab Technology distinguishes CRT as "medically necessary, individually configured devices that require evaluation, configuration, fitting, adjustment or programming."30 As such, CRT users often have complex medical conditions, and meeting their needs requires individualized, customized, and advanced wheelchair and seating technology. A high level of evaluation and prescription is indicated. The ultralightweight manual wheelchair is the only CRT manual wheelchair, but many levels of power wheelchairs are classified as CRT.
Manual wheelchairs represent the overwhelming majority of wheelchair provisions, with standard DME wheelchairs being the most common. An analysis of wheelchair provisions by a commercial insurance company reported the type of equipment and diagnosis of the beneficiary.31 In 2017, the company purchased more than 81,000 wheelchairs, approximately 86% of which were manual wheelchairs. This percentage is heavily influenced by the number of rental manual standard adult chairs provided. Manual standard adult chairs are prescribed for a variety of uses including long-duration, temporary, and part-time use. Sprigle et al31 found that wheelchair recipients tended to be older women, and their most common diagnoses were musculoskeletal or circulatory disorders.
The process of obtaining wheelchairs typically involves a minimum of three parties: the physician/nonphysician practitioner (NPP), a supplier, and the beneficiary (the user or patient). A fourth party, physical and occupational therapists, is also required for certain types of CRT wheelchairs and, in fact, should probably always be involved. The physician/NPP examines the beneficiary and writes an order (prescription) and sends it to a DME supplier. If the beneficiary requires CRT wheeled mobility, a specialty evaluation must be completed by a certified occupational or physical therapist with special knowledge and experience in wheelchair evaluations. For all wheeled mobility devices, the supplier must receive a prescription before creating a detailed product description, which is then sent back to the physician/NPP for approval before it is submitted to Medicare or other payers.
Wheelchair provision for persons residing in facilities often takes a different approach, with wheelchairs being provided from the fleet of chairs owned by the facility. Selecting a wheelchair from a fleet can hinder the proper matching of the chair to the user and his or her needs, but that should be unacceptable. No one would place a 6'2" resident in a 6-foot bed, so why should a 5'2" resident be given a wheelchair sized for a football linebacker?
As detailed in this article, just taking a few measurements of a person can help with proper wheelchair selection. In both scenarios, the challenge lies in who will be properly matching the user and his or her needs relative to fit. Physicians/NPPs rarely measure people, and the supplier is not obligated to perform a proper evaluation. However, it is imperative that someone properly determines fit and wheelchair features that impact fit. A therapist or a nurse is probably the best option for these users.
LIMITATIONS AND CONCLUSIONS
This overview of posture and wheelchair fit did not include discussion of wheelchair cushions or refer to diagnoses of wheelchair users. Wheelchair cushions have a direct influence on posture, function, and tissue health, so a full discussion would be an article in and of itself. Any wheelchair user who is at risk for pressure-related tissue damage should be given a cushion that is categorized as a "skin protection" cushion and is correctly sized for them. Just like the wheelchair seat, cushions do not last forever. Simply removing the cover and inspecting the cushion can be a valuable means to assess when a cushion has fatigued and requires replacement. Foam fatigue is reflected by cracks, tears, or loss of resilience. Elastomers and gels can crack or tear when fatigued and if the surrounding membrane (if it has one) is breached, the cushion should be replaced. Any cushion with a bladder, whether for viscous fluid or air, can experience leaks, which often cannot be recognized until the cover is removed.
The decision not to mention diagnoses was volitional for similar reasons, but many references were made to function. Wheelchair use is based on a functional impairment, and people with many diagnoses use wheelchairs. With respect to the content of this article, function includes many parameters, such as the ability to stand or ambulate; postural stability and control, including the ability to reach and lean; and the means by which one propels the wheelchair (upper extremity, lower extremity, or a combination of the two). These and other functional abilities have a direct influence on the type of wheelchair and seating system that should be considered. At a basic level, persons spending little time in a wheelchair will have different needs than someone who sits in a wheelchair for 12 hours a day. A person who is independent in propulsion has different needs than a person who is not. Irrespective of use, however, is the need to properly fit the wheelchair as a means to support the body in a seated posture.
Persons with a high level of postural control will typically need less postural support. This may manifest in a chair with a lower backrest and no arm support that is configured to be less stabile (ie, easier to pop a wheelie). Persons with good trunk control can be expected to perform weight-shifting activities that redistribute loading over the buttocks. Almost all functional movements involving the trunk have an impact on the pressure and blood flow at the buttocks.32 This underscores the need to promote function by putting people in properly fitted wheelchairs.
In contrast, persons with very limited function will rely on the wheelchair and seating system to provide stability. These users may also be less able to reach, lean, and perform weight shifts to protect their skin. People who sit statically are at particular risk of PI development, so other interventions must be considered. Variable-position wheelchairs are available that alter body posture relative to gravity and result in changing the body mass borne by the buttocks. Although a full discussion is beyond the scope of this article, several sources of information can be accessed.33-37
Seating needs can become complex rather quickly. Although all clinicians can and should regularly evaluate posture and fit, engaging a clinician with experience in seating and mobility is needed for persons with more complicated needs. Many problems can arise from sitting persons in poorly fitted wheelchairs. Contractures, pain, and PIs are medical complications that can result in functional consequences such as reduced independence and activity.
Pain is a useful metric to identify problems with the wheelchair and/or seating system. When combined with a quick postural assessment, poor fit or a poor match between user and wheelchair can be identified. Clinicians regularly assess position in bed and evaluate pain in hospital patients and residents as a means to prevent PIs; evaluating posture and pain while seated in a wheelchair is just as important.
PRACTICE PEARLS
* A properly fitted wheelchair enhances comfort and function while preventing PI development.
* A wheelchair cushion cannot overcome a poorly fitted wheelchair to protect skin from breaking down.
* A slouched posture, characterized by posterior pelvic tilt and a kyphotic spine, results in excessive pressure on the sacrum and coccyx.
* Common causes of a slouched posture include seat depth that is too long, a seat that is too high, and footrests that are too low.
* Wheelchair upholstery wears out and should be replaced periodically. The wheelchair itself will last much longer than the upholstery.
REFERENCES