By K. Missy Ball, MT, PT, ATP
Wheelchairs and seating options have evolved over the past 25 years, providing the clinician and rehab supplier numerous equipment choices which can at times be daunting both in choice of options and justification for funding approval. The differences in tilt-in-space versus recline systems, as well as technical aspects in frame design and clinical application for each need to be understood to make informed decisions.
The tilt-in-space frame allows change in a client’s orientation to gravity while maintaining the same seat to back angle and relationship between seating components to client. Recline systems have a change in seat to back angle with an angular and linear relationship change between seating components and client. With recline, there is an increased tendency for downward migration of the client’s center of mass on seat, as well as torso down the back.
Also, changing a client’s orientation in space can impact on perceptual orientation, arousal, cardiopulmonary status, ingestion/swallow, digestion/elimination, endurance, skeletal alignment, soft tissue flexibility, functional access and reflex activation. Perceptual orientation develops from vestibular, visual, and somatosensory stimuli received through the body. Vestibular system monitors change in direction and speed of head movement providing an awareness of body’s orientation to gravity as well as movement in space.
Clients with sensory processing issues, such as low threshold vestibular or tactile, may have difficulty with changes in orientation. Traumatic Brain Injury clientele in the early stage of rehabilitation may have arousal issues, as well as limited head and trunk control. Choosing the degree of tilt to assist with postural control without diminishing arousal is crucial to progress.
Skeletal alignment, tone and reflexive activity can change with seat to back angle adjustments. For example, a client with an extensor thrust, would possibly improve functionally if the hip extensor activity were reduced by closing the seat to back angle to 85 degrees, diminishing full body extension with any movement and potentially allowing controlled movement.
When choosing system tilt the plane the tilt occurs, direction, degree, location of tilt axis on frame and need for adjustable tilt need to be considered. The plane of tilt can be sagittal (anterior/posterior), frontal (lateral tilt), or a combination of the two (oblique tilt). The direction can also be specified with the plane of motion. Many adjustable tilt frames allow 35-45 degrees of posterior tilt, while less provide both posterior and 5-20 degrees of anterior tilt within the same frame. Posterior tilt is often used for clientele with significant muscle weakness, progressive muscle disease or paralysis (SMA, MS, MD), skeletal deformities, or pressure relief.
It can redistribute weight off the ischial tuberosities onto the posterior torso, reduce gravity’s impact on skeletal alignment, assist with maintaining functional posture of head and torso for feeding, communication, assist with hypotension and venous return insufficiency. Anterior tilt (brief periods) can facilitate active hip and spinal extension to improve sitting as well as improve upper extremity reach, feeding, and phonation when applied to the appropriate client. It can also assist elderly clients with muscle weakness in hip and knee extensors achieve standing. Most functional tasks occur in an anterior tilted pelvic position, such as feeding, brushing teeth, school work.
The placement of the tilt axis within the frame can be anterior, posterior, central or floating. Tilt axis placement can be critical when client is obese, or demonstrates extensor thrust or spasms, or has a high threshold tactile or vestibular issue with heavy banging against back canes present. The variable central gravity axis tilt frame maintains the client’s center of mass relatively center in the frame promoting stability even in full rearward tilt. This configuration can produce a smaller footprint for accessibility, but adds considerable weight to the frame making transport more difficult. Placing the tilt axis posterior within the frame design produces knee elevation with tilt, reduces forward reach to a degree, and lowers the sight line, but frame weight is considerably lighter. Most manual wheelchair frames are designed with tilt axis posterior within frame, including Convaid’s Rodeo, Safari and Trekker. The Rodeo provides 0-45 degrees of posterior tilt with 20degrees of seat to back angle adjustment. The Trekker provides 0-45 degrees of adjustable tilt, 5degrees of anterior tilt, and 170 degrees of adjustable recline or seat to back angle adjustment.
Seat to back angle adjustments refer to changes between the superior aspect of the seat and the anterior aspect of the back. Recline is movement of the back posterior from vertical position. Modifications to the seat to back angle can affect cardiopulmonary function, skeletal alignment, muscle tone and reflexes, manual reach, visual field, postural control, transfer capability and perceptual orientation. Indications for a seat to back angle greater than 90 degrees (95-175 degrees) could be limitations in hip flexion secondary to hip dislocation/subluxation, soft tissue tightness or reflexive activity, skeletal deformity, post-surgical needs, respiratory compromise, postural hypotension, comfort, daily needs (g-tube feedings, tracheostomy care, pressure reliefs, or catherization).
Closed seat to back angle can accommodate significant hip flexion contractures, kyphoscoliosis, diminish extensor thrust and improve trunk and UE functionality in active user (the dump-SCI). The combination of tilt and recline in a frame can be most useful. For example, seat to back angle adjustments can accommodate hip issues (extensor thrust or hip flexion range limitations, then coupled with a variable tilt can allow upright torso and head for functional tasks and social engagement.
The Trekker has 5degrees anterior tilt, 0-45 degrees posterior tilt, and 80-170 degrees of seat to back angle adjustment with choice of either Convaid seating or after -market seating for the more complex client. Recline axis is close to client’s anatomical hip to minimize sheer and increase comfort in greater recline. Accessories include adjustable, elevating leg-rests, ventilator tray, and O2 tank holder for the more medically fragile client.
In summary, frame tilt and recline have numerous clinical applications. Combinations of these options can be effective with more involved client. The seating and mobility prescription needs to be individualized to address the client’s specific limitations, strengths and needs. The prescription is only as effective as the quality of the physical assessment of client and the team’s ability to translate those findings into equipment parameters to meet client’s goals.