Evaluation process for seating and mobility systems

A seating and mobility system evaluation should address all aspects of a person’s medical and personal lifestyle issues. The following categories should be assessed thoroughly.

Medical History: All medical diagnoses (primary and secondary) are important to identify and document as well as whether the disability is stable, progressive, or fluctuates. Pertinent history that will have an impact on mobility and positioning needs includes history of pressure sores, spasticity management, medications, orthotic use, and sitting tolerance. A detailed interview regarding pressure sore development, management, and successful treatment is important in preventing recurrence. Prior and future surgical interventions, such as spinal fusion, muscle releases, and amputations will affect seating decisions. Prior equipment use and identification of previous problems is helpful in justifying future seating intervention.

Physical Assessment: Physical assessment includes the person’s range of motion, skeletal alignment or posture, motor strength or motor control of the head, trunk and extremities, sitting balance, sensation, interfering tone, or reflexes. Is the muscle tone low or hypotonic? Does the client have hypertonicity, which may require more aggressive seating components to control tonic movement?

Range of Motion: Range of motion of the joints and spine assesses whether postural supports can correct or must accommodate perceived deformities. Flexibility and asymmetries of the hip and pelvis and hamstring tightness are critical areas of assessment. Evaluating asymmetries in hip flexion, scoliosis, and pelvic obliquities and determining whether the deformities are fixed or flexible is important to determining successful solutions. Seating starts from the pelvis and hips, so assessment of pelvic obliquity, scoliosis, tight hamstrings, and hip muscles is critical for ensuring proper positioning.

Reflex-Influenced Posturing: Is reflex-influenced posturing interfering with the patient’s functional potential for maintaining the sitting position? For example, two influential primitive reflexes active in seated posture are the tonic labyrinthine reflex, which causes extension of the head, trunk, and extremities as the body tilts backward or reclines, and asymmetrical tonic neck reflexes, which cause rotation of head, trunk and pelvis and potentially a windswept deformity. At times, this reflex posturing is functionally used to extend the upper extremity in order to drive a power wheelchair or point to a communication device. Persons with athetosis or dyskinetic-type movement disorders may use reflex posturing for stability in order to use their extremities purposefully. The seating device may help inhibit unwanted movements and permit functional movements.⁶

Muscle Strength: Evaluation of muscle strength assesses functional potential with, and the need for, appropriate postural supports. The need for adequate support for sitting balance and pressure distribution versus adequate freedom of movement must be balanced. Overseating can discourage functional potential. For example, a high back on a person with functional low-level tetraplegia would eliminate his or her ability to balance the upper body or to hook the arm over the push handle of a lower back in order to increase forward reach with the opposite arm. Evaluating muscle strength helps determine whether posturing is compensatory for muscle paralysis, weakness, or imbalance. Clients with Duchenne muscular dystrophy have proximal muscle weakness and are able to increase their upper extremity reach by leaning forward and to the side. Restricting trunk motion limits their ability to compensate for proximal weakness in order to reach with and use the distal strength in their hands.

Evaluation of Protective Sensation: Evaluation of protective sensation and assessing for red areas or potential pressure areas helps to determine the appropriate seating surface. History of scar tissue or previous pressure sore intervention can predict areas of high risk. Aging affects the elasticity of the skin and increases risk of damage from shearing, pressure, heat, and moisture.

Seating alignment

Ideal sitting alignment is different for an able-bodied person than for a disabled person, and depends on the individual’s abilities. Sitting is dynamic; it is a continuous process of postural changes whether the position is task oriented or one of rest. For the able-bodied person, a sitting posture with an anterior pelvic tilt and decreased lumbar flexion is the most favorable posture.^17,18,40 Generally three postures of sitting alignment are assumed (Fig. 44-2). Ideally, an upright, symmetrically balanced trunk over a stable pelvis allows better upper extremity reach, head control, and visual field. However, in the sitting position, the pelvis tends to roll back into a posterior tilt because the hips are flexed and the hamstrings pull the pelvis back; the tilt is accentuated when the knees are extended.⁵⁰ The line of gravity is posterior to the ischial tuberosities. This posture is adopted as a position of rest by an able-bodied person and as a position of stability by a wheelchair user with tetraplegia. The second sitting position is achieved by activating the back extensors to tilt the pelvis anteriorly into lumbar lordosis. As the pelvis rolls anteriorly, the line of gravity falls directly through the ischial tuberosities.¹⁵ This posture usually is assumed by a person with muscular disease as it is functionally advantageous because of weakness that is greater proximally than distally.¹⁶ The third seated posture is a forward sitting posture that has been described by Kangas²⁵ and Adrian and Cooper¹ as a functional task position or position of readiness. In this position, the trunk is forward and the line of gravity shifts toward the direction of activity. The trunk flexes forward in a position of anticipation. The arms and trunk are naturally brought forward into the visual field, and the feet are shifted backward behind the knees and bear more weight.

Fig. 44-2 Three dynamic postures of sitting: upright with slight anterior pelvis, posterior pelvis, and forward trunk or position of readiness.

Outcome studies of seating and positioning for function

A number of studies reported on how seating affects functional activities, upper extremity function, head control, and visual field.^24,33,36 The components of a seating system can provide support to align the body, normalize tone, prevent deformities, and clearly influence upper extremity movement. In one study, the sitting surface was explored to better determine the capacity to maintain balance and posture as a prerequisite for activities of daily living. The center of pressure of reaching was determined to be significantly greater on a generically contoured sitting surface than on a flat foam surface or a 3-inch Roho seat cushion.² The effect of different backrest heights and types of cushions were investigated in the SCI population to determine the relationship between posture and upper extremity reaching. The posture adopted by the user and the American Spinal Injury Association (ASIA) score were significant, and no evidence indicated that the type of cushion or back height affected reach.⁴⁸

Improvements in autonomic functioning, including respiratory, oral intake and digestion in children with cerebral palsy was found following adjustments in seating systems with improvement of the trunk, neck and head alignment.⁷ Hulme²³ found positive perceived changes in social interaction, positioning, tracking, grasping, and self-feeding skills. Nwaobi³⁷ found that the vital capacity in children with cerebral palsy improved with positioning in a seating system versus a sling type wheelchair. Improvements in speech intelligibility were documented in children with cerebral palsy using adapted seating versus without.³⁴

Reports on the effects of seating on upper extremity function are conflicting. In a 1986 study of children with cerebral palsy, different amounts of hip flexion were found to affect upper extremity function.³⁶ Another study found that children with cerebral palsy were able to activate and release a switch the fastest when they were in an anterior 15-degree tilt or in the position of readiness versus 0, 15, or 30 degrees of tilt back.³⁵ However, McPherson et al.³¹ found no significant differences in the quality of upper extremity movement in subjects with cerebral palsy in four different positions. Seeger et al.⁴⁵ also did not find any improvement (Fig. 44-3).

Fig. 44-3 Outcomes of studies of seating and positioning.

Seating assessment

Hands-on evaluation should be performed with the person either sitting or supine on the mat. Critical assessment of whether deformities are dynamic or fixed is more accurate when the patient is supine. Depending on the person’s disability, a mat assessment is not always mandatory. The three main determinations of the hands-on evaluation are as follows:

Classifications and description of sitting ability

The ability to sit independently is one factor that determines the type or amount of seating support needed. Hoffer²¹ classified a person’s ability to sit according to the amount of trunk control present. His classifications were modified by Tredwell and Roxborough in 1991 to include generalizations regarding the type of seating needed (Fig 44-4):

Fig. 44-4 Classification of sitting ability grouped according to the amount of trunk control present and the amount of support needed in a seating system.

Hands-Free Sitting Ability: Maintains independent sitting for long periods without using hands for support. Demonstrates good trunk balance and the ability to weight shift. In general, a person needs a simple seating system designed primarily for pelvic stability, comfort, and mobility (e.g., person with paraplegia).

Hand-Dependent Sitting Ability: Requires either one or both hands for support. Trunk control and balance are generally poor. Trunk supports are needed to allow use of hands for functional activities. Providing a more stable base of pelvic support may change a hand-dependent sitter to a hand-free sitter.

Propped Sitting Ability: Because of severe physical involvement or structural deformity, the person is unable to sit without total body support. Trunk and head control are very limited. Total support of the trunk, head, and extremities is needed, as for a person who demonstrates total body involvement with cerebral palsy, has a severe muscle disease, or has a high-level tetraplegia.