Osteoporosis is a deterioration of bone. Healthy bone goes through a natural cycle that balances the breakdown of old bone tissue and the manufacture of new bone. The breakdown occurs more quickly in osteoporosis, resulting in weak and brittle bones. Several studies have shown that regional osteoporosis of a limb paralyzed by stroke occurs rapidly after immobilization. More widespread osteoporosis occurs later.
"Osteoporosis is a significant complication of stroke," says Kenneth Poole, BM, MRCP, Stroke Registrar and clinical fellow at the Medical Research Council in the United Kingdom. "When someone is put to bed and has an immobilized limb, the cells that break down bone are overactive."
In a review of several studies on osteoporosis and hip fracture after stroke, Poole and his colleagues report that one Swedish study shows hip fracture was two to four times more likely in stroke patients than in an age-matched reference population. Another study reported a more than four-fold increased risk of hip fracture for stroke survivors in the immediate post stroke period compared with the general Swedish population.
In Poole’s report, researchers who investigated the mechanisms of osteoporotic fracture in older people found that most fractures in stroke patients occur on the side paralyzed by stroke. The fractures are usually caused by accidental falls. One study shows that 73 percent of 108 patients studied had fallen in the six months after suffering a stroke. Research has shown that stroke patients fall to the side of the paralysis and are less able to stretch out an arm on that side to cushion the fall. Lower limb dysfunction and visual impairment also make them more likely to fall.
Stroke patients who break their hips also have a higher mortality and morbidity rate than age-matched individuals who have not had a stroke. Moreover, more than half of all strokes occur in people over age 70, says Poole. "They are already at risk for osteoporosis because of their age – they can ill afford to lose further bone."
The researchers say prescribing biophosphonates, drugs that prevent bone loss associated with osteoporosis, is an important way to help prevent hip fractures in stroke patients. Poole says the drugs may be most helpful if administered early in rehabilitation. Bisphosphonates inhibit cells in the bone – called osteoclasts – from breaking down bone tissue. The drugs, given intravenously or taken orally, have been used to treat osteoporosis in postmenopausal women.
Poole says the intravenous form of the drug would most likely have to be used in stroke patients because the oral form requires standing or sitting for 30 minutes before and after swallowing it. "Many stroke patients often can’t walk, sit up or swallow immediately after their stroke," he says. "So it is unlikely that the pill form could be used early on."
Other potential interventions include mechanical hip protectors in stroke survivors with a high risk of bone mineral loss. Vitamin D and calcium supplements may also be helpful, he says.
The researchers say treating stroke victims for osteoporosis is an important area for further study. Preventing osteoporosis also should be a priority in managing patients with stroke, says Poole.
"Measures to prevent bone loss have not been a part of stroke management thus far," he says. "Our review makes a good case for a trial of intravenous biphosphonates after stroke."
NR02 – 1072 (Stroke/Poole)
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