Equipment suppliers who are involved in the process of providing wheelchairs and seating components to individuals who have suffered a spinal cord injury (SCI) should understand the anatomy and physiology of SCI, as well as what to expect at each level of injury. As part of the central nervous system (CNS), the spinal cord (SC) is comprised of delicate tracts of nerve tissue originating in the brain. As it emerges from the base of the skull and extends down the back, it is encircled and protected by the bones (vertebrae) of the spinal column.
The SC and spinal column are divided into four sections; cervical (neck), thoracic (mid back), lumbar (low back) and sacral. As the SC descends, it sends out nerve roots through the spaces between each vertebra. These roots then branch to form the peripheral nerves that go to and from the muscles and organs of the body. The peripheral nerves control (innervate) specific areas of the body. Those that come from the cervical roots innervate the neck and upper extremities (UEs), those that branch from the thoracic roots innervate the trunk, those from the lumbar roots innervate the lower extremities (LEs) and those from the sacral roots control bowel and bladder function. The function of the SC is to carry messages between the brain and the body via motor and sensory nerves. Motor nerves send messages from the brain to the muscles to cause them to contract or relax. Sensory nerves take messages from sensory receptors in the muscles and joints and carry them to the brain to provide information regarding temperature, pain, touch, position in space and other sensory data.
The mechanism for SCI can vary. Some occur when something presses into the delicate nerve tissue, such as a dislocated vertebra, fragments from a fractured vertebra, a tumor or some other growth. Others are caused by a compressive or explosive force, such as that from a gunshot or a forceful blow, or a result of disease, such as transverse myelitis or the polio virus. Most injuries are due to impingement into the tissue by an external force or object, followed by swelling and bleeding, all of which causes an interruption in transmission of the nerve impulses at and below the level of injury (LOI). The effects of SCI can include mild to severe deficits in muscle strength, muscle tone, coordination, sensation and/or balance. The extent of the impairments depend on where the injury occurs and the extent of the tissue damage. Cervical injuries affect some or all of the muscles of the upper and lower extremities and trunk (quadriplegia).
Thoracic injuries affect some or all of the trunk and lower extremity muscles, and lumbar injuries affect some or all of the lower extremity muscles (paraplegia). In the most severe cases there is no motor or sensory function below the LOI. In other cases, some nerve impulses get past the damaged area, allowing some movement and/or sensation below the LOI, although this may or may not be functional. In best case scenarios, there is minimal damage and few residual effects or even complete recovery. Secondary complications with SCI can include respiratory and/or circulatory compromise, loss of bowel and/or bladder control, seizures, inability to control body temperature, postural hypotension, autonomic dysreflexia and heterotopic ossification. Communication and cognition are typically not affected.
We name the SCI according to lowest level of the spinal cord at which messages are still being transmitted to enable muscle function. This is identified by testing muscle strength. It is not necessary to test the strength of every single muscle to determine this. Although most muscles are innervated by more than one nerve root (level of the SC), certain key muscles receive most of their innervation from one particular level. If key muscles have functional strength, this is an indication that the messages from their nerve root are getting through. Key muscles and their primary level of innervation are listed in the above chart. Using the key muscles, we can name the SCI by the lowest level at which a key muscle and all key muscles above are at least functional in strength. For example, if the diaphragm and shoulder elevators (C4), shoulder flexors, shoulder abductors and elbow flexors (C5) and wrist extensors (C6) are all functional, we would call this a C6 SCI. If the hip flexors (L1) and all key muscles above are functional, we would call this an L1 SCI. SCI is also classified as complete or incomplete. In complete injuries there are no key muscles or sensation functioning below the LOI. With incomplete injuries, there is some strength in one or more key muscles and/or sensation below the LOI, although the strength might/might not be functional. Although SCI itself is a non-progressive condition, some recovery in function can occur following initial injury.
Once the bleeding and swelling subside, some nerve impulses might bypass the damaged area. Treatment and rehabilitation can affect changes in muscle strength, muscle tone, how the muscles are used, balance, mobility, transfers, weight shifts and independence in ADLs. Changes in body dimensions due to weight gains/losses and muscle atrophy can also affect function. Therefore, we must consider—when working with new injuries—that what is appropriate at the time of discharge may not be appropriate in a year or two. It is important to choose equipment that can be modified and reconfigured and to establish a regular schedule for follow-up. Typically, function will stabilize within a year or so after a SCI. Years later, however, functional and medical changes can occur due to the normal aging process. For someone with an older injury, what has worked for many years may no longer be appropriate. With these individuals, we must be aware of changes in function and medical status and choose equipment that will match any new needs.
Equipment Selection for Each Injury Level
Brain Stem, C1, C2, C3 SCI—At these levels of SCI there is no function in the arms, legs or trunk. These individuals are dependent in all activities of daily living (ADLs) and will need a power wheelchair with an alternative drive control, power tilt and/or recline and full postural support. The seating materials and shape should provide skin protection. Because the diaphragm is also nonfunctional, these individuals will require ventilator support. Operation of a computer and electronic aids to daily living (EADLs) might be possible through wireless control using the power wheelchair electronics, voice activation, eye gaze or facial muscle contraction. Limited operation might be achieved using a mouth or head stick.
C4 SCI—At a C4 level, the diaphragm and the shoulder elevators are functioning to enable independent respiration without ventilator support, however the respiratory status may still be fragile. Seating, mobility and assistive technology needs will be similar to that required at the C1-C3 levels.
C5 SCI—With the addition of the shoulder flexors, shoulder abductors and elbow flexors, many individuals with a C5 SCI can drive a power wheelchair with a standard joystick, although an alternative handle, a wrist brace and/or an external support for the hand and forearm may be necessary. Most individuals will require power seating for weight shifts and all will require skin protection and positioning through use of appropriate materials and contours in the seat cushion and back support. Some independence in ADLs may be achieved after assistance for setup. Operation of a computer and an EADL might be achieved through the power wheelchair electronics, voice control or adapted remotes/keyboards with a wrist orthosis.
C6 SCI—The wrist extensors that are functional with a C6 SCI provide some stability to the wrist and enable an action called tenodesis, in which the fingers automatically curl into flexion when the wrist is bent back. Tenodesis provides these individuals with a mild grip to further increase independence in performing ADLs with setup assistance, adapted devices and utensils, and possibly a hand orthotic. The type of mobility device required and the level of independence in functional activities will depend on the individual’s strength, endurance, joint integrity, overall medical status and even age. Some may be able to propel an ultralightweight manual wheelchair, others may require a push-rim power assist, while others will need a power wheelchair with a standard joystick and possibly power seating. Some may be able to perform independent sliding board transfers and side-to-side or forward weight shifts. Contour and skin protection materials will still be needed in the cushion and/or back support. Computer access and EADL operation might be achieved through the power wheelchair electronics, voice control or an adapted remote with/without a hand orthosis.
C7 SCI—The addition of the triceps at C7 is often called the “key to independence,” because being able to extend the elbow against gravity significantly increases functional use of the arm. These individuals should be independent in most ADLs with some adapted devices/utensils. Independent mobility is achieved using an ultralightweight manual wheelchair. In some cases, a push-rim power assist might be appropriate. Contour in the seat along with skin protection materials is still important to maintain posture and skin integrity. Tight-back upholstery may suffice, although many would benefit from a simple solid back support. Independence in weight shifts should be possible by lifting or leaning side to side. Computer access and EADL operation are the same as at a C6 LOI.
C8, T1 – T12 SCI—The finger muscles are added at C8, upper trunk muscles are added at T1 – T6 and lower trunk muscles are added at T6 – T12. Individuals at any of these levels should be independent in all ADLs and in computer and EADL operation using a standard keyboard, mouse and remote. An ultralightweight manual wheelchair should enable independent mobility in all environments. The amount of postural support needed in the seating will decrease as the level of injury descends, particularly as the lower trunk muscles are added. Using appropriate materials for skin protection will still be important.
L1, L2 SCI—The addition of the hip flexors at L1 and L2 may allow some ability to ambulate very short distances with forearm crutches and long leg braces. However, the effort required for this is high and an ultralightweight manual wheelchair with minimal seating supports will most likely be used for mobility. Independence in all ADLS should be achievable with few adaptive devices.
L3, L4, L5, S1, S2 SCI—Individuals with injuries at L3, L4 and L5 should be independent ambulators for most/all mobility with the addition of knee extensors, ankle dorsiflexors and toe extensors. At L3, an ankle-foot-orthoses (AFOs) and possibly crutches or canes will be needed for balance and gait. In some cases, an ultralightweight manual wheelchair may be needed for long distance mobility. Some L4 or L5 SCI will ambulate without a device, while others may need a cane. Independent bowel and bladder control is achieved at S1-S2.
We cannot base our equipment solutions solely on the level of injury, because each person responds differently. We must consider other contributing factors that could result in significant variations in function, even among individuals with the same level of injury. Consider age, medical issues, individual’s support system and motivation/outlook. A thorough clinical evaluation and analysis of the results can determine current needs. Regular follow-up is crucial to assess any changes in function and satisfaction. We must verify that the equipment continues to meet daily needs, prevent skin breakdown, promote optimal posture, fit anatomical shape/dimensions, promote maximum function and provide comfort.
