Seat cushion with adjustable contour and method of adjusting the contour of a seat cushion

A flexible support structure of a seat cushion, such as a wheelchair cushion, has an upper surface with a support contour having relief areas for establishing relatively less pressure on skin adjacent to bony prominences of a user's pelvis and having a support area for establishing relatively more pressure on skin covering a tissue mass spaced from the bony prominences. A slit is formed in the rear corner of the support structure and an insertion member is inserted into the slit to change a position of the support area to thereby adjust the support contour for better support of the pelvic area. A cover encases the support structure to resist outward deformation of the support structure. The cover has an extension portion that expands the cover at the rear corner to increase a dimension of the cover to encase an increase dimension of the corner caused by the insertion of the insertion member.

FIELD OF THE INVENTION

This invention relates to seat cushions, and more particularly, to a new and improved seat cushion having an adjustable support contour that provides a range of users with a proper orientation of posture while reducing or eliminating the incidence of pressure ulcers. The support contour offloads or isolates pressure and shear forces from skin tissue surrounding the bony prominences of the pelvic skeletal bone structure, such as the ischial tuberosities, greater trochanters, coccyx and sacrum, thereby removing pressure and shear forces from those areas which are susceptible to injury from prolonged sitting. Proper postural alignment is achieved by transferring the pressure from the offloaded areas to greater masses of tissue not associated with bony prominences, such as the proximal thighs and the posterior lateral buttocks. The additional support from these areas encourages improved postural alignment and control.

BACKGROUND OF THE INVENTION

A wheelchair seat cushion must perform a number of important functions. The seat cushion should be comfortable and capable of providing proper support for optimal posture and posture control for a considerable length of time. The seat cushion should also assist, or at least not materially hinder, the user in maneuvering the wheelchair, permit a useful range of motion from the pelvis and upper torso of the person, and create stability and security for the person within the wheelchair. Perhaps most importantly, the seat cushion should help prevent and reduce the incidence of pressure ulcers created by prolonged sitting on the cushion without adequate pressure relief. Pressure ulcers can become a very serious health problem for individuals who must remain constantly in contact with the support cushion, and it is important to avoid such pressure ulcers.

Wheelchair users, like everyone, are of substantially different sizes, weights and shapes. Many wheelchair users have physical disabilities and associated posture and postural control impairments such as those typically caused by congenital disorders. Other wheelchair users, such as those who have been disabled by acquired or traumatic injuries, may have a more typical size and shape. In all of these cases, the support contour of the wheelchair seat cushion must safely support the anatomy of the user, whether the anatomy is abnormal or more typical. Wheelchair seat cushions must fit and perform properly to prevent further physical impairment and pressure ulcers. The cushion must also enhance the functional capabilities of the user by supporting independence in activities of daily living. There are a number of different theories or approaches for configuring the support contour of a wheelchair seat cushion to avoid pressure ulcers and to provide adequate postural alignment.

One approach to configuring the support contour of a wheelchair seat cushion is a single generic support contour which attempts to accommodate all types of pelvic bone-structure configurations, whether more abnormal or more typical. In general, this generic approach involves using a soft, flowable or adaptable material, such as air or gel, as the support material within the wheelchair cushion. This adaptable material adjusts and redistributes in response to the weight and shape of the user to create a support contour which conforms to the anatomy of the user. By conforming to the anatomy of the user, the pressure on the skin of the user is usually distributed relatively evenly over the area of contact. The extent of the uniform pressure distribution depends on the capability of the cushion to accept and conform to the user's anatomy without displacing the adaptable material and resulting in firm contact with a support structure.

The substantially equal pressure distribution is theorized to reduce the incidence of pressure ulcers, by decreasing peak pressures on the skin in the pelvic area associated with bony prominences, most notably the ischial tuberosities, coccyx, sacrum, and greater trochanters. However, as individuals age with their disabilities, the quality of their skin is further compromised in its ability to tolerate pressure and shear forces. The decreased tolerance for pressure and shear forces, no matter how well those forces are distributed, increases the incidence of pressure ulcers.

Generic seat cushions which use flowable support material are usually incapable of providing adequate postural alignment. In general terms, adequate postural alignment is assisted by using the support contour of the seat cushion to encourage proper posture by providing a foundation for dynamic posture control. To do so, the support contour must have the capability of applying some support pressure to the pelvic area because alignment of the pelvic area is fundamental for proper posture. The adaptable support material of generic seat cushions is intended to move and redistribute itself, and consequently, is generally unstable and incapable of applying the support pressure or force in certain areas of the pelvic anatomy to optimize postural control and alignment.

Many of the disadvantages associated with generic wheelchair cushions may be overcome by using a custom wheelchair seat cushion having a support contour constructed specifically to accommodate the individual anatomical aspects of a particular user. In such cases, it is necessary to capture the anatomical shape of the individual which will contact the custom seat cushion, and then use that anatomical shape to make the custom seat cushion.

The cost of fabricating a custom wheelchair seat cushion can be substantial, for example, approximately $3000 or more. Much of the expense of a custom wheelchair seat cushion results from the amount of time consumed, and the cost of the relatively sophisticated equipment which must be used to capture and transfer the anatomical shape of the user into the support contour of the seat cushion. Moreover, despite the use of sophisticated equipment, it is nevertheless difficult to capture the anatomical shape of the user and transfer it into a customized support contour. An appreciation of some of these difficulties in creating customized wheelchair seat cushions is discussed in the above-referenced U.S. patent application Ser. No. 10/628,858.

Even if the support contour of the custom cushion is initially satisfactory to the user, changes in tissue and musculature may dictate changes in the optimal support contour of the custom seat cushion. Tissue will typically atrophy over time, particularly for first-time wheelchair users. Tissue atrophy and other tissue changes alter the pressure distribution over the support contour. Those changes may result in increased pressure on tissues surrounding the bony prominences, thereby ultimately increasing the risks of pressure ulcers. Moreover, as the muscle strength diminishes, the user relies more on the support contour of the seat to hold the proper posture. In doing so, parts of the pelvic anatomy press more directly on certain parts of the support contour as a foundation for postural alignment. The increased pressure from a change in tissue mass and postural alignment increases the pressure and shear forces on the skin in those areas, again increasing the risk of pressure ulcers.

In those types of existing wheelchair cushions having individualized support contours intended to interact with the anatomy of a specific user, slight discrepancies in capturing the shape of the individualized support may be compensated for by adding shims or other additional external support structures to the seat cushion or to a structural base upon which the cushion resides. The addition of shims or other support structures to an individualized support contour is relatively imprecise in achieving the desired effect, and requires considerable time and effort due to the number of trial fittings that are typically required. A similar situation exists with respect to anatomical changes that occur after the individualized cushion has been used for some amount of time. In both circumstances, the support capabilities of the cushion are inhibited by the trial and error approach to correcting for shape-capturing discrepancies and anatomical changes. Furthermore, the added shims and external support structures complicate the use of the cushion, because the added parts must be kept in alignment with the cushion when in use.

In those types of existing wheelchair cushions which establish an individualized or specific support contour, certain areas of the support contour may be subject to excessive deformation of the flexible support material from which the cushion is constructed. The wheelchair cushions must be constructed of material which offers some amount of flexibility or resiliency in order to function adequately as a cushion. The flexible or resilient material is subject to deformation in areas of significant curvature or areas which laterally support the anatomical structure of the user. These areas of the support contour may have generally thinner dimensions than the portions of the seat cushion directly beneath the user, or there is no support from any lateral structure to reinforce these areas because of the seat support structure beneath the cushion. Excessively flexible portions of the wheelchair cushion, or portions which may become excessively flexible through use over time, are usually not capable of providing pelvic orientation and alignment as may be required by the wheelchair user.

Because of these and other deficiencies, seat cushions with inadequate support may be used long past the time when they have become ineffective in providing proper support, either because of the cost associated with replacement of the cushion or the failure of the user to recognize the problem until pressure ulcers or other difficulties appear.

Many of the same considerations applicable to wheelchair seat cushions also apply with varying levels of criticality to other types of seat cushions used in other seating environments and applications. For example, seat cushions used in office environments are required to support the user in a comfortable manner and in a manner which encourages proper posture and without creating risks of medical problems, for example inducing blood circulatory problems.

SUMMARY OF THE INVENTION

The present invention involves adjusting a standard support contour of a seat cushion to address the individual needs of a user and to obtain the best conditions for isolating and offloading pressure and shear forces from the skin surrounding the bony prominences of the pelvic area skeletal structure and for transferring greater pressure and providing firmer support to areas of the anatomy which have broader masses of soft and muscle tissue not surrounding bony prominences. Offloading or isolating the pressure and shear force from the skin surrounding the bony prominences of the pelvic skeletal structure reduces the risk of pressure ulcers. Transferring pressure and providing pronounced support to broad tissue masses encourages better balance and alignment. Greater support pressure is applied to and maintained on those areas which bias, orient or encourage alignment of the pelvic structure toward proper postural alignment. By offloading the pressure and shear forces from those areas which are prone to skin ulcers, and transferring support pressure to those areas which encourage proper postural alignment, the support contour of the seat cushion simultaneously achieves the two most important wheelchair cushion functions: avoidance of pressure ulcers, and postural alignment and control.

The adjustment capability of the support contour also makes the cushion adaptable to a wider range of variations in the size and shape of the normal human anatomy, primarily as a result of the additional clearance in the areas of the bony prominences and the additional support in the areas of broader tissue and muscular masses. The greater relief or clearance in the areas of the bony prominences and the greater support in the areas of broader tissue and muscular mass, makes the support contour generally applicable to classes of individuals having generally similar pelvic anatomies.

These and other features of the present invention are realized in an adjustable contoured seat cushion for supporting a person in a seated position. The seat cushion includes a support structure having a top surface with a support contour, the support contour defining relief areas which are positioned to align with bony prominences of the person and support areas that are positioned to align with skin covering tissue masses spaced from the bony prominences. The seat cushion also includes an insertion member and an opening or slits formed in one or both of the rear corners of the support structure to receive the insertion member. The slits are positioned between the top surface and a bottom surface of the support structure. A support area of the support contour changes position relative to other support areas or relief areas when the insertion member is inserted into one of the slits.

Another aspect of the invention involves a method of manufacturing a resilient seat cushion for supporting a person in a seated position. The method comprises forming a support structure by forming generally opposite front and a rear sides and generally opposite left and right sides. The rear side intersects the left and right sides at rear corners of the support structure. The support structure further includes a bottom surface extending between the front and rear sides and between the left and right sides, and a top surface generally opposite of the bottom surface and extending between the front and rear sides and the left and right sides. The top surface defines a support contour of the support structure which has relief areas and support areas. The relief areas align with the bony prominences of the person when the person is seated on the cushion and the support areas align with skin covering tissue masses spaced from the bony prominences including skin covering a posterior lateral buttocks of the person. The method involves forming an opening or slit in each of the rear corners. Each opening is adapted to receive an insertion member, and when the insertion member is inserted, the support contour is adjusted in a manner to better support the user.

Another aspect of the invention involves a method of adjusting a seat cushion to support a person in a seated position on a resilient support structure of the seat cushion. The method involves inserting an insertion member into an opening in a portion of the support structure.

A further aspect of the present invention involves a seat cushion kit which includes a seat support structure having an upper support contour for supporting a user. The support structure includes a portion having an opening. The kit also includes a cover which encases the support contour to protect the support contour and which resists outward deformation of the support structure. The kit also includes a clearance measuring device for measuring clearance between the user's anatomy and the support contour. The insertion member is inserted into the opening to adjust a position of a support area of the support structure to better support the user.

A more complete appreciation of the scope of the invention and the manner in which it achieves the above-noted and other improvements can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and by reference to the appended claims.

DETAILED DESCRIPTION

A wheelchair seat cushion20which incorporates the present invention is shown inFIG. 1. The seat cushion20includes a resilient seat support structure22which is constructed of resilient plastic foam material and a breathable material cover24which together are capable of providing the necessary support to the wheelchair user. A support contour26is preferably constructed or otherwise formed as a part of the support structure22. Preferably, the resilient plastic foam material from which the support structure22is formed is a matrix of polypropylene, polyurethane, polyethylene or other plastic beads which have been adhered together during a molding process in which the support contour26is formed simultaneously with the support structure22, as described more completely in the above-referenced U.S. patent application Ser. No. 10/628,858.

The support contour26is formed, as shown inFIG. 2, with relief areas28,30and32which align with skin covering bony prominences of the users pelvic area, as shown inFIG. 3. Clearances between the bony prominences of the ischial tuberosities34, the greater trochanters36, and the coccyx38and the sacrum40and the support contour26at the relief areas28,30and32, respectively, offload pressure and shear forces from the skin surrounding these bony prominences. The support contour26is also formed with support areas42,44,46and48which align with anatomical features of the users pelvic area to support the user by contacting the skin over muscular portions of the pelvic area. The support areas42,44,46and48compensate for the increased clearance in the areas28,30and32, by providing greater protrusion for enhanced support where there are relatively large and broad masses of tissue and muscle upon which the greater pressure can be applied without creating localized pressure points.

The support contour26faces upward to contact and support the tissues of the user which surround the skeletal structure of the pelvic area50and the thigh bones52of the user, as shown inFIGS. 2-8. The support contour26includes a relatively deep center cavity54which is positioned in the support contour26to be located directly below ischial tuberosities34of the skeletal structure of the pelvic area50, when the user is seated on the cushion20, as shown inFIG. 4.

In the support contour26, the vertical depth and horizontal dimensions of the cavity54are sufficient to offload pressure and shear force from the skin surrounding the ischial tuberosities34. The depth of the cavity54is sufficient to establish clearances56,58and60between the lower ends of the ischial tuberosities34and the lowermost surface area28, as shown inFIGS. 4 and 5. By offloading the pressure and shear force from the skin surrounding the ischial tuberosities34due to the clearances56,58and60, the risk of pressure ulcers on the skin surrounding the ischial tuberosities34is reduced substantially.

The support contour26rises from the lowermost surface area28on opposite transverse sides of the cavity54to the relief areas30, as shown inFIGS. 2 and 3. The relief areas30are positioned directly below and transversely to the outside of the greater trochanters36on both transverse sides of the support contour26, when the user is seated on the cushion20. The relief areas30establish vertical and transverse clearances62with respect to the greater trochanters36to offload pressure and shear force from the skin surrounding the greater trochanters36, as shown inFIG. 5.

The support contour26also includes a recessed channel area32which extends vertically upward from the lowermost surface area28of the cavity54to an upper rear edge of the support contour26, as shown inFIGS. 4 and 8. The channel area32is located on a rear wall66and extends downwardly and longitudinally forward from the rear wall66toward the lowermost surface area28of the cavity54at a transverse midline of the support contour26, as shown inFIG. 8. The channel area32is positioned in the support contour26to be located directly behind the coccyx38and the sacrum40of the pelvic skeletal structure50, when the user is seated in the cushion20. The channel area32establishes a vertical and horizontal clearance68between the channel area32and the coccyx38and sacrum40, as shown inFIG. 4. The channel area32also establishes a transverse clearance70which extends beyond each opposite lateral side of the coccyx38and sacrum40, as shown inFIG. 8. The amount of the clearances68and70is sufficient to offload pressure and shear force from the skin surrounding the coccyx38and sacrum40.

The support contour26includes the two support areas42and44which are located on the rear wall66in positions on opposite transverse sides of a longitudinal midline72, as shown inFIGS. 2,3and8. The support areas42and44extend forwardly from a midline contour line74(FIG. 8), and therefore provide more projections to create exaggerated pressure and support on the tissue and musculature at the posterior lateral buttocks of the pelvic area which is contacted by the support areas42and44. As shown inFIG. 6, the support area42(the support area44is similar, but not shown inFIG. 6) generally curves vertically downwardly and transversely and longitudinally forwardly from an upper position on the rear wall66toward the lowermost surface area28. The support areas42(and44, not shown inFIG. 6) terminate vertically above the lowermost surface area28. Oriented in this manner, the support areas42and44define forwardly and upwardly facing contact surfaces to contact the skin covering the tissue masses surrounding the pelvic bones50at the lateral posterior buttocks. The posterior lateral buttocks tissue and musculature are devoid of any underlying prominent bone structure. Instead, the considerable mass of posterior lateral buttocks tissue and musculature defines a relatively broad and substantial contact area which is able to accept and transfer the force into the pelvic skeletal structure which does not elevate the risk of developing pressure ulcers at those locations.

The upward component of curvature from the support areas42and44(FIG. 3) tends to induce an upward lifting force on the posterior/lateral pelvic area, which assists in offloading the pressure from the relief areas28,30and32. The lateral buttocks support areas42and44also provide lateral stability which helps retain the user in contact with the support contour26of the seat cushion20. The lateral support stability is applied from the opposite sides of the rear portion of the users body, and thus tends to inhibit the user from tipping backward or to the side within the cushion. The support areas42and44bias or orient the pelvic area50in a slightly forward pivoted position (counterclockwise as shown inFIG. 4) to encourage the user to maintain his or her pelvic area50in a proper postural alignment position.

The support contour26also provides enhanced support from areas46and48which are located beneath the thigh bone52proximal to the greater trochanters36, as shown inFIGS. 2,3and7. The enhanced support areas46and48contact a relatively broad mass of tissue and muscle extending along the posterior thigh bone52. The posterior thigh bone52extends generally longitudinally and has no prominences in the area where the support areas46and48contact the tissue surrounding the posterior thigh bones52. The support areas46and48are able to transfer a relatively significant amount of pressure into the relatively broad mass of posterior thigh tissue and musculature to thereby support the skeletal structure.

The transfer of significant force into the posterior thigh tissue and musculature at the location of the support areas46and48complements the additional support from the areas42and44to maintain alignment for proper postural position of the pelvic area. The location of the support areas42,44,46and48, as shown inFIG. 2, is approximately at four lateral and longitudinal positions surrounding the pelvic structure to facilitate holding the pelvic structure into a position of proper postural alignment and to stabilize the user when seated on the support contour.

By offloading pressure from the bony prominence areas28,30and32, and by applying the exaggerated support in the broad tissue and musculature areas42,44,46and48, atrophy changes are less likely to have a significant negative impact. In general, the added clearance in the areas of the bony prominences provides an additional tolerance for tissue atrophy.

As described in the referenced U.S. patent application Ser. No. 10/628,860, the support contour26can be configured to fit the particular anatomical shape of a user. However, the support contour26is preferably configured with a standardized shape that is suitable to provide improved support characteristics for a range of users. In some circumstances it may be necessary to make adjustments to the support areas42and44of the support contour26to adapt a standardized support contour26to the individual anatomical shape of the user to achieve the maximum benefit. Moreover, because of changes which occur over time in the anatomical structure of the user, adjustments to the support contour26may be necessary at different times during the use of the seat cushion20.

The present invention offers an improved capability to adjust the support areas42and44of the standardized support contour26of the seat cushion20. As shown in FIGS.1and9-13, adjustment of these support areas is accomplished by the insertion of one or more insertion members, such as wedges76and78into slits80and/or82. The introduction of the wedges76and78forces the slits80or82open and thereby increases a vertical dimension of the support structure22in the locations of the wedges76and78. The expansion of the support structure22in these locations, deforms the support structure22and changes the shape of the support contour26. As shown inFIGS. 10 and 12, the insertion of a wedge76into each of the slits80and82causes the support areas42and44to move upward and transversely inward toward one another. The wedges76and78, as shown inFIGS. 11 and 12, also move the support areas42and44longitudinally forward.

Changing the shape of the support contour26provides the ability to adjust the contour26to the particular needs of an individual user. By inserting one or more wedges76, as shown in FIGS.1and9-13, the positions of the support areas42and44are adjusted and the positions of the user's ischial tuberosities34, greater trochanters36, coccyx38and sacrum40relative to the support contour22of the seat cushion20are adjusted. Inserting wedges76and78in the slits80and82moves the support areas42and44relatively more forward and inward which causes an increase in the vertical clearance56between the ischial tuberosities34and the lower surface area28of the support contour26as well as an increase in the transverse clearance60. The forward change in the position of the support areas42and44caused by the wedges76and78pushes the pelvic bones50forward to counteract the tendency of a user to slouch.

The left and right slits80and82are preferably cut or formed into opposite transverse rear corners84and86of the support structure22, as shown inFIG. 9. The left slit80extends from a rear transversely-extending side90of the seat cushion20to a longitudinally-extending left side92of the cushion (FIGS. 9 and 10) and the right slit82extends from the rear side90to a longitudinally-extending right side94of the cushion20. The slits80and82extend in a plane that is generally parallel to a bottom surface96of the support structure22. The slits80and82are generally triangularly shaped (FIG. 12) and resiliently open to receive the wedges76and78by resiliently deforming the portions of the support structure22above and below the slits80and82.

The wedges76and78, as shown inFIGS. 10 and 11, fit into the slits80and82with the thin edge facing inwardly toward the center of the support structure22and the relatively thick corner aligned with a corner of the support structure22. When the wedge76is inserted in the slit80, the wedge76is flush with the left side92and rear side90of the support structure22. Similarly, when the wedge78is inserted in the slit82, the wedge78is flush with the right side94and the rear side90of the support structure22. The wedges76and78are retained in the slits80and82frictionally or by the use of hook and loop fasteners138and140and are also held in positioned by the cover24.

The hook and loop fasteners138and140are preferably connected to the interior of the slits80and82and to the wedges76and78, as shown in FIGS.8and10-12. The slit includes a hook fastener138on one side and a loop fastener140on the opposite side. In this configuration, the slits80and82are held together and maintained against shear forces by the hook and loop fasteners138and140even when a wedge76and78is not inserted. The wedges76and78preferably have corresponding hook and loop fasteners138and140which align with the hook and loop fasteners138and140of the slits80and82when the wedges76and78are inserted.

The wedges76and78are preferably formed from a higher density or less compressible foam material than the material used for the support structure22. The wedges76and78have a generally triangular shape in a plan view (FIG. 12) and have one edge98is relatively thin and an opposite corner100from the edge is thicker than the other corners, preferably about ½″ to 1″, although other wedge sizes can also be used. Inserting relatively larger wedges76and78, or inserting more than one wedge76and78in a slit80and/or82causes relatively more articulation of the support areas42and44than is accomplished with a relatively smaller wedge76.

In addition to providing the capability of adjusting the support contour26symmetrically by inserting equally-sized wedges76into each of the slits80and82, the support contour26can also be adjusted asymmetrically, as shown inFIG. 13. Asymmetric adjustment is where one corner of the support structure22is articulated forward and inward more than the other corner of the support structure22. In some circumstances a user's anatomy can atrophy on one side more than the other side. To accommodate this condition the support contour26can be adjusted asymmetrically by inserting more wedges76and78, or a larger wedge76and78into one side, than the other side. This has the effect of articulating one of the support areas42or44relatively more upward, forward and transversely inward than the other one of the support areas42or44to contact the user's anatomy with both support areas42and44.

As shown inFIGS. 9 and 10, the cover24includes an access zipper104to provide access to the slits80and82to insert and remove the wedges76and78and for inserting and removing the support structure22from the cover24. The cover24has a continuous sidewall112which fits tightly along longitudinally-extending right and left sides92and94, and around transversely-extending front and rear sides88and90of the support structure22. A top portion108of the cover24, as shown inFIG. 1, is positioned over the support contour26. A bottom portion110of the cover24is positioned below the bottom surface96of the support structure22. The top and bottom portions108and110attach to the sidewall112adjoining the longitudinally-extending right and left sides92and94and along the transversely-extending front and rear walls88and90.

The access zipper104is connected between the bottom portion110of the cover24and the continuous sidewall112. When the cover24is on the support structure22, the zipper104extends from the rear of the longitudinally-extending left side92around the entire rear side90to the rear of the longitudinally-extending right side94of the support structure22(FIG. 1). The access zipper104also includes a handle106for opening and closing the zipper104.

The sidewall112of the cover24includes expansion portions114and116having an expansion capability at the rear corners84and86to accommodate the expanded vertical dimension at the corners84and86when the wedges76and78are inserted in the slits80and82in the corners of the support structure22. The expansion capability of the cover24allows the cover24to expand over the corners84and86when the wedges76and78are inserted, as shown inFIG. 10. In this way the cover24has the capability to enclose the support structure22.

Left and right zippers118and120in the sidewall112are openable to provide the expansion capability by increasing a vertical dimension of the sidewall112at the corners84and86. Gussets122and124are attached to the sidewall112adjacent to the upper teeth to the lower teeth of the zippers118and120, respectively, to limit the increase in vertical dimension of the sidewall112when the zippers118and120are opened. The gussets122and124are folded into the interior of the cover24when the zippers118and120are closed. The gussets122and124are preferably made from the same material as the sidewall112.

The zipper118and the gusset122extend from the left side92of the support structure22to the rear90of the support structure22, and the zipper120and the gusset124extend from the right side94of the support structure22to the rear90. The zippers118and120are conventional zippers that have pull handles106which slide in one direction to close the zipper118and120by securing the teeth in an upper half of the zipper to the teeth in a lower half of the zipper, and slide in another direction to open the zipper118and120by separating the teeth in the upper half from the teeth in the lower half of the zipper118and120.

The zippers118and120preferably end at a point near the transverse center of the rear90of the support structure22so that a vertical dimension of the sidewall112at that location does not change regardless of whether the zippers118and120are opened or closed. Positioning the zippers118and120in this way ensures that the cover24remains taut in the transverse rear center of the support structure22.

By keeping the cover24taut in the transverse rear center of the support structure22, support areas42and44are maintained in a lateral dimension from one another before and while the user is seated. The tautness of the cover24in this area ensures that the insertion of the insertion members76and78into the slits80and82causes adjustment to the position of the support areas42and44rather than causing a change in the shape of the bottom surface96.

The cover24helps the support structure22to maintain the position of the support areas42and44by fitting taut over the support structure22. The sidewall112of the cover24fits tautly over the right and left sides92and94and the front and rear sides88and90of the support structure22to keep the front and rear sides of the support structure22from deforming away from one another. The sidewall112of the cover24, including the expandable portions114and116, fits tautly over the rear side of the support structure22and holds that portion of the support structure22from deforming backwardly.

The top portion108of the cover24is preferably made of a conventional spacer mesh material. The spacer mesh has a padding characteristic and is breathable without permitting substantial stretching in either a longitudinal or transverse direction. The remaining bottom portion110of the cover24is preferably made of a substantially non-stretchable nylon material that is also breathable and which covers the seat support structure22other than the support contour26. The sidewall112is also made of non-stretchable breathable nylon material. Since the top, bottom and sidewall portions of the cover24are non-stretchable, the cover24resists outward deflection of the sides88,90,92and94of the support structure22. In this way the non-stretchable characteristic of the cover24assists in maintaining the shape of the support contour26even when the wheelchair user is seated on the cushion20.

The support structure22has a bottom surface28with a generally convex shape, as shown inFIG. 9, that curves slightly between the left and right sides92and94. The shape of the bottom surface28is a compromise between a flat or planar shape that complements a flat seat support structure126(FIG. 10) of some types of wheelchairs and a generally downward convex shape with a larger curve that complements a sling type seat support structure128(shown inFIG. 13) of other types of wheelchairs.

When the cushion20is placed on a flat seat support structure126(FIG. 10) the cushion20tends to flatten out to conform to the seat support structure126, and in doing so, the support areas42and44will generally move away from one another. In order to compensate for this change in the support contour26, the wedges76and78may be inserted to move the support areas42and44relatively closer to one another. On the other hand, when the cushion20is placed on a sling type seat support structure128,FIG. 13, the cushion20tends to assume a more curved shape to match the seat support structure128. In this instance, the support areas42and44are articulated closer to one another by the downwardly convex curve of the cushion20. Because of this articulation, the cushion20may be utilized for some individuals without the addition of wedges76.

The support structure22and the wedges76and78preferably have a generally vertically aligned rear channels102that allow conventional upright bars (not shown) of the wheelchair to be positioned in the corners of the cushion20. The cover24fits over the rear channels102but allows the bars to push into the channels102when the cushion20is positioned on the wheelchair. Positioning the cushion20on the wheelchair in this way also has the effect of retaining the wedges76positioned in the slits80and82.

As described in the above-referenced U.S. patent application Ser. No. 10/628,890, support and pressure relief characteristics of the support contour26can be determined and adjusted by the technique using an impression foam or clearance measuring device130. The clearance measuring device130allows a therapist to determine whether the users bony prominences have adequate clearance from the surface of the cushion20. This provides the therapist with information that is used to determine the degree of adjustment needed, if any, to fit the cushion20to a particular user.

The clearance measuring device130, shown inFIG. 14, is used in accordance with the present invention to measure the clearance between the contacting portion of the individual's anatomy and the support contour26of the seat cushion20(FIG. 1). The clearance measuring device130comprises a pad132of collapsible impression foam confined within a clear flexible envelope134. The foam pad132generally has a longitudinal and transverse horizontal dimensions (as shown inFIG. 14) which are sufficient to cover each of the areas28,30or32of the support contour26(FIG. 2) in which clearance is provided to offload pressure and shear forces from the anatomy in those areas. However, the longitudinal and transverse horizontal dimensions (as shown inFIG. 14) may also be sufficient to cover only a portion of one of the areas28,30and32(FIG. 2). The vertical thickness dimension (as shown inFIG. 14) of the foam pad132is approximately the thickness necessary to achieve a desired degree of collapse of the impression foam, but not to fully collapse the impression foam, when the device130is used.

The clearance measuring device130is used as shown generally inFIGS. 15-16. The device130is placed at a desired location on the support contour26where a clearance is to be measured. In the case of the support contour26shown inFIG. 2, the device would normally be placed to cover all or part of one of the areas28,30or32where a clearance has been configured into the support contour26to offload pressure and shear forces from the user's anatomy. As an example, shown inFIGS. 15 and 16, the device130has been placed at the bottom of the cavity54on the lowermost surface area28. After the device130is placed at the desired location, the user sits down or otherwise contacts the support contour26in the normal manner with the device130positioned between the user's anatomy and that portion of the support contour26where the clearance is to be measured. For example, as shown inFIGS. 15 and 16, the user has seated himself or herself on the support contour26with the device positioned at the lowermost surface area28. The user's ischial tuberosities34and the surrounding tissue contacts the device130and compresses the foam pad132. Collapse, indention or compression of the foam pad132occurs to an extent indicating the amount of clearance between the tissue surrounding the ischial tuberosities34and the lowermost surface area28of the support contour26.

The cushion20can be supplied to a therapist in a seat cushion adjusting kit along with the clearance measuring device130and an assortment of wedges76and78of various sizes. By placing the cushion on the wheelchair and the clearance measuring device130on the cushion20before seating the user on the cushion, the therapist is able to determine if the cushion20, as it is currently configured, is suitable to provide proper postural alignment and pelvic support for the user. If the bony prominences of the seated user are too close to the surface of the support contour26, or other conditions exist where the support contour26is not configured correctly for the user, then the therapist can open the access zipper104and insert one or more wedges76and/or78into one or both of the left or right slits80or82to adjust the position of the support areas42and/or44so that more support is provided by these areas to support the user.

The kit makes it possible for the therapist to stock only one cushion to fit a variety of different users, which saves storage space and eliminates confusion over selecting one of many seating solutions. The adaptability of the cushion20provides the therapist with a broader range of applicability than is available with some other seating devices. The inclusion of the clearance measuring device130and the wedges76and78along with the cushion20provides that therapist with the necessary tools to adjust the cushion20to benefit users with a variety of anatomical configurations. The adjustable nature of the cushion20allows the cushion20to be adjusted to fit the user over a period of time past when conventional non-adjustable cushions must be replaced because of changed user anatomical features or the onset of physical deterioration.

The cushion20is preferably less than two pounds in weight which is believed to be half of the weight of any other cushion currently on the market. The reduced weight of the cushion20makes it an ideal candidate for self-propelled wheelchair where weight is an issue. The cushion20is also ideal for use by wheelchair athletes because of the support given by the cushion20over a range of movements of the pelvic area50and because of the light weight of the cushion20.

The cover24, as well as the support structure22, are made of material that allows air flow around the tissue of the user. This feature is important in the prevention of pressure ulcers since increased temperature and the retention of moisture next to the skin can cause increased stress on the user's skin.

The cover24is also removable from the support structure22so that the cover24can be washed in a conventional washing machine. The support contour22and the wedges76can be rinsed off with running water since the material of the support contour22and the wedges76do not absorb or retain water. The washable nature of the cushion20is especially of benefit to a user who is suffering from problems with incontinence.

The cost of the cushion20to the user is relatively inexpensive in comparison to some other cushions. This is due to the relatively inexpensive nature of the materials used to manufacture the cushion20and the reduced number of hours to produce the cushion20because of the simple yet elegant design. Many other advantages and improvements will be apparent after gaining a full appreciation of the present invention.

A presently preferred embodiment of the present invention and many of its improvements have been described with a degree of particularity. This description is a preferred example of implementing the invention, and is not necessarily intended to limit the scope of the invention. The scope of the invention is defined by the following claims.