As stated earlier, overuse injuries can occur in non-athletes, but may take longer to develop. This section will list the cause(s) of common injuries and prevention methods for blisters, abrasions and lacerations; carpal tunnel syndrome; and shoulder pain (rotator cuff strain and impingement syndrome).
Blisters, Abrasions, & Lacerations
Although blisters, abrasions, and lacerations are not typically classified as overuse injuries, but occur frequently enough with wheelchair users (18%) to be included. Blisters usually occur when the skin comes in repeated contact with wheelchair parts. This continuous rubbing causes a collection of fluid below or within the epidermal layer of skin. Signs and symptoms include the area feeling hot, pain, and/or a burning sensation. The fluid within the blister may be clear (superficial) or may contain blood indicating that deeper tissue has been disrupted.
To prevent blisters, talcum powder or petroleum jelly can protect the skin from abnormal friction. Also, wearing gloves that fit well can help reduce the likelihood of blisters.
Abrasions are caused when the skin is scraped against a rough surface wearing away the epidermis and dermis. Numerous blood capillaries are exposed. Lacerations are wounds where the skin has been irregularly torn. Abrasions and lacerations can be prevented by wearing gloves or using plastic wheel-guard covers on wheelchairs. The use of armrests and changing the camber of the wheels can also help prevent abrasions and lacerations caused by getting fingers caught in the spokes of wheels. Always seek medical attention if injuries do not heal or there are signs of infection.
Carpal Tunnel Syndrome
People with spinal cord injuries place an inordinate amount of weight bearing stress on the upper extremities. This increases the prevalence of carpal tunnel syndrome in this population. The prevalence of carpal tunnel syndrome has been found to increase with the length of time after the injury. Transfers, propelling a wheelchair, and unweighting the sacrum with the upper extremity adducted against the body, the wrist in maximum extension, and the forearm in supination, is the proposed position in which a traumatic event produces carpal instability.
The carpal tunnel is bordered medially by the pisiform bone and the hook of the hamate, and laterally by the crest of the trapezium and the tuberosity of the scaphoid. The floor comprises the lunate and the capitate bones. The transverse carpal ligament forms the roof. The median nerve, along with all the flexor tendons, lies within this anatomical tunnel. Thus, it is easy to see that even the slightest trauma that produces swelling will compress the median nerve.
Compression of the median nerve produces tingling, numbness, and paresthesia over the thumb, index and middle fingers, and the palm of the hand . Pain often occurs at night due to impeded venous return. The thenar muscles (located at the pad of the base of the thumb) may be atrophied, and grip strength may be decreased on the affected side.
Treatment of carpal tunnel syndrome is usually conservative, involving rest, immobilization, and nonsteroidal anti-inflammatories. Most wheelchair users will not undergo any of these treatments due to loss of independence and mobility. Usually the condition worsens to the point where surgery is necessary to release the transverse carpal ligament. Again, wheelchair users are reluctant to undergo surgery due to loss of independence.
In a study by Aljure et. al, the incidence of carpal tunnel syndrome is 27% 1 - 10 years from injury onset; 54% 11 - 20 years from injury onset; around 54% 21 - 30 years from injury onset; and then a significant increase to 90% 31+ years from injury onset. This study suggests median and ulnar nerve functional testing within 5 years of injury even if the person is asymptomatic with periodic re-evaluations after that. The best treatment for carpal tunnel becomes prevention.
Rodgers et al. suggest that carpal tunnel syndrome can occur from fatigue or inappropriate wheelchair use, design and/or prescription. Proper biomechanics will help prevent carpal tunnel syndrome, but further studies to determine proper technique are needed. Wearing padded gloves, similar to cycling gloves, was suggested by Bloomquist because the pressure put on the hands is similar to that of cycling. In his article, he also suggests muscle strengthening, good body mechanics, proper maintenance of wheelchair and equipment, and padding pushrims.
Other preventative measures include applying ice to the wrists for 20 minutes at the end of each day, and adding a flexibility/strengthening program for wrist flexion/extension. There have been no studies showing whether any of these prevention measures will prevent or retard the onset of carpal tunnel syndrome, but these measures will do no harm.
Wrist flexibility and strengthening programs begin with few repetitions and light weights. If nerve/motor involvement prevents holding a weight, use wraparound weights. If hand weights are not available, use household items for weights, such as a 12-oz. soup can.
Rotator Cuff Strain/Shoulder Impingement
The glenohumeral joint (shoulder) is the most mobile joint in the body. This mobility predisposes it to injury from overuse, especially in the absence of protective mechanisms of pain and proprioception. The shoulder joint of the wheelchair user is the primary joint for transfer and propulsion. It is subject to overuse with resultant functional impairment. Even a minor injury to the shoulder can impair a person's ability to achieve independence . Frequent overuse injuries include muscle strain, rotator cuff tears, and impingement.
The rotator cuff is the common site of trauma among non-athletic wheelchair users. Most rotator cuff injuries are due to muscle imbalances of the shoulder. Biomechanically, any factors that preserve the acromiohumeral space could minimize the pressure on the rotator cuff.
The deltoid muscle pulls the humeral head upward when acting alone encroaching on the acromiohumeral space. Normally, this force is counterbalanced by the downward pull provided by the rotator cuff muscles: subscapularis, infraspinatus, and teres minor. A shoulder strength imbalance could allow impingement on the soft tissue structures of the acromiohumeral space which includes the rotator cuff muscle tendons.
In the study by Burnham et. al, they found that the pattern of imbalance was difference from swimmers and baseball pitchers. There was weakness of the shoulder adductors in people with paraplegia. This weakness could be a cause for the development or rotator cuff impingement syndrome. People with paraplegia also demonstrated a significant weakness of external and internal rotation. Strengthening of shoulder internal and external rotators as well as the adductors is recommended. These exercises are easy to perform.
The sitting position requires frequent and often prolonged overhead reaching for day-to-day and vocational tasks. This association with impingement has been described in able-bodied laborers and athletes, but has not been studied in wheelchair users. The overhead motion drives the humeral head into the acromiohumeral space. The biomechanics of wheelchair propulsion also drives the humeral head into the acromiohumeral space. This pressure is 2.5 times higher for non-wheelchair users. Proper biomechanics for wheelchair use is essential for preventing shoulder impingement.
It is important to look specifically at the kinds of injuries sustained in order to prevent their recurrence. Health professionals (physicians, physical therapists, athletic trainers, etc.) must be aware that the disability itself may mask the injury and thereby prevent the realization that an injury exists. Most studies the deal with overuse injuries look at able-bodied individuals; few studies have been conducted with wheelchair users. More research is needed in this area, ranging from proper biomechanics in wheelchair propulsion, wheelchair design, biomechanics for activities of daily living and transfers, and response to prevention measures. The prevention methods presented are those used for persons who are able-bodied, unless otherwise noted. Prevention is key for the treatment of overuse injuries because wheelchair users cannot afford to lose their independence.