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Patients undergoing a total hip replacement have an elevated risk of stroke in the weeks following the operation, researchers found.

Danish patients who underwent the procedure over a 10-year period were more likely than those who had not received a hip or knee replacement to have an ischemic stroke (HR 4.69, 95% CI 3.12 to 7.06) or hemorrhagic stroke (HR 4.40, 95% CI 2.01 to 9.62) in the first 2 postoperative weeks, according to Frank de Vries, PharmD, PhD, of the Utrecht Institute of Pharmaceutical Sciences in the Netherlands, and colleagues.

The stroke risk declined rapidly thereafter, becoming comparable in the two groups after 6 to 12 weeks, the researchers reported online in Stroke: Journal of the American Heart Association.

"Risk assessment of stroke in individual patients undergoing total hip replacement (i.e., evaluate other risk factors for stroke) should be considered during the first 6 to 12 weeks," de Vries and colleagues wrote.

It is known that stroke is a serious complication from total hip replacements seen at a rate as high as 0.6%. Comparisons had not previously been made, however, between patients undergoing the operation and nonsurgical controls.

In the current study, the researchers retrospectively examined data from national registries in Denmark for 66,583 adult patients who had a primary total hip replacement from 1998 to 2007. Each patient was matched by age, sex, and geographical region to about three nonsurgical control patients, for a total of 199,995 controls.

The mean age of both groups was 72, and 36.9% were males.

Compared with the matched controls, those who underwent total hip replacements had higher rates of ischemic stroke (26 versus 5.6 per 1,000 person-years) and hemorrhagic stroke (6.7 versus 1.6 per 1,000 person-years) in the first 2 weeks after the operation, differences that remained significant after adjustment for disease history and drug use.

Similarly increased risks were seen for weeks 2 to 6 for both ischemic stroke (HR 2.12, 95% CI 1.53 to 2.93) and hemorrhagic stroke (HR 2.16, 95% CI 1.14 to 4.06). From postoperative weeks 6 to 12, the risk remained higher in the patients who underwent surgery for hemorrhagic stroke only (HR 2.17, 95% CI 1.32 to 3.57).

Beyond 12 weeks, the stroke risk was similar in both groups.

The use of antiplatelet therapy after discharge attenuated the surgery-associated risk of ischemic stroke in the first 6 postoperative weeks compared with non-use of antithrombotic agents, but the researchers said that "this seemingly protective effect should be interpreted with caution, given the observational design and the lack of information on inpatient antithrombotic use."

They noted that "the underlying mechanism for the increased risk of stroke shortly after total hip replacement is thought to be related to cerebral hypoperfusion and marrow embolization."

"Intraoperative hypotension may result in hypoperfusion, and the decreased blood flow may slow down the washout of embolic material in the cerebral blood vessels," they wrote. "Marrow embolization may be caused by surgical invasion of the medullary canal of the femur, as shown previously."

Alternately, they added, the elevated stroke risk could be related to intraoperative arrhythmias and the effects of anesthesia.

The researchers acknowledged that the study was limited by the lack of information on body mass index and the inhospital use of antithrombotic agents, as well as the inability to differentiate between lacunar and territorial infarctions.

Also, the controls were not chosen based on hospitalization or operations other than total hip replacements, so it is possible that the greater observed stroke risk could be applicable to other types of operations and hospitalizations.

From the American Heart Association:

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