A large percentage of patients who suffer spinal-cord injury and become wheelchair users experience osteoporosis.
Osteoporosis after spinal-cord injury has been extensively studied and is known to appear soon after a spinal-cord lesion. The incidence of long bone fractures in the lower extremities has been estimated to be between four and seven percent of patients with spinal-cord injury.
When a patient has suffered spinal-cord injury and uses a wheelchair, little or no weight bearing activities occur – for example, using tilt tables or standing wheelchairs, or other means of weight bearing such as walking with callipers. In the uninjured person, bone mineral density is kept optimal by normal metabolism, proper intake of calcium and normal functioning of various hormones. Also important is sun exposure providing Vitamin D. The bone forming cells produce enough bony matrix to keep bones healthy and strong. There is a balance between bone formation (carried out by cells called osteoblasts) and bone resorption (done by cells called osteoclasts) and this balance tends to be negative with age, particularly in post-menopausal women, which can lead to a loss of bone mineralisation serious enough to cause fractures. This lack of bone mineralisation is called osteoporosis.
The spinal cord-injured person becomes osteoporotic for various reasons. Some of these are:
- After injury there is loss of the all-important weight bearing effect on healthy bone. The human skeleton requires the bones to be “stressed” in the form of the stresses of weight bearing and also the normal stresses that intact muscles and tendons have on bones. The effect of non-weight bearing or “disuse osteoporosis “was first noted in astronauts returning from space. Persons who are unable to weight bear and thus stress the bones become osteoporotic.
- It is believed that after injury there is a change in the functioning levels of hormones that normally control bone formation.
- There is a change in the fine balance between the cells producing bone and those that resorb bone, and it is thought that there is more resorption than formation, which then leads to osteoporosis.
- A lack of vitamin D, which is important in calcium absorption, is thought to exacerbate the bone mineral loss. Most of the human body’s vitamin D comes from exposure to the sun; insufficient exposure leads to low levels of vitamin D in the body (although small quantities of vitamin D are available from certain dietary sources).
These conditions occur in all spinal cord-injured persons who are wheelchair dependent, and they can become osteoporotic, which leads to a higher risk of fractures, especially in the lower limbs. A fracture can occur even when very little noticeable force is applied and often without the patient even noticing the incident. The first sign of trouble will often be swelling or a limb that shows some deformity.
Fractures can cause serious problems and may influence seating, can result in hyper-reflexia (over-responsive reflexes) and may increase spasms. If a fracture is suspected, please visit your doctor.
Dr Ed Baalbergen is the medical officer at the Vincent Pallotti Rehabilitation Centre (Cape Town) and is a member of the International Spinal Cord Society and the Southern African Neurological Rehabilitation Association. email: firstname.lastname@example.org