A new study finds that long-term use of already widely used anti-osteoporosis drugs such as Fosamax and Actonel significantly increases the risk of a rare and critical type of femur fracture. To prevent hip, spine and wrist fractures due to osteoporosis, some women over 50 years of age take these drugs for years. However, a small number of these patients have suffered thigh fractures simply from everyday actions such as crossing obstacles, which begs the question of whether osteoporosis treatment is relevant. The Archives of Internal Medicine, a journal published by the American Medical Association, published a new study online Monday that suggests a link between the drugs and so-called atypical femur fractures. The researchers noted that the findings support the overall effectiveness of anti-osteoporosis drugs in preventing fractures, even after taking these drugs for only a few years. At the same time, they claim that such fractures are very rare. But at the same time, they said, the new findings make it even more clear that patients should consider whether to continue taking the drugs after three to five years. The drugs are a class of bisphosphonates. These drugs sold $4.2 billion in the U.S. last year, according to data provider IMS Health. In 2010, the Food and Drug Administration had notified that the labels of such drugs should be labeled as having the potential to cause rare femur fractures. Although experts convened by the agency decided last year not to place restrictions on the drug’s use anymore, they still expressed concern about atypical fractures. Merck & Co. Technologies LLC, which sells Fosamax, faces more than 3,100 product lawsuits, 1,200 of which claim the drug causes jawbone degeneration in patients, according to a recently announced Securities and Exchange Commission filing. A spokesman for Merck said the company advises patients to consult with their doctors about the pros and cons of taking Fosamax. the maker of Actonel, Warner Chilcott AG, did not respond to comments. The study, conducted by physicians at the University Hospital of Geneva in Switzerland, looked at 477 patients aged 50 years or older admitted to the hospital between 1999 and 2010 with specific types of femur fractures. Of these, 438 patients had a typical fracture caused by a fall or other trauma. However, 39 patients suffered uncommon femur fractures with minimal or no trauma. Of these, 32 were on bisphosphonates and 11 were bilateral lesions. Robin Peter, an orthopedic surgeon at Swiss Hospital who helped write the article, said the data show that atypical fractures are associated with drug use. Dr. Peter said that given the increased probability of fractures over time, doctors should re-examine patients after three to five years on the drugs to determine whether to continue taking them. Otherwise, continuing to take the medication may do more harm than good. Dr. Peter also said that, overall, studies have shown that the drugs are effective in avoiding fractures for all patients with fractures. Given these benefits, physicians should focus on determining the population at risk for atypical fractures. Douglas Bauer, an internist from the University of California, San Francisco, has a long history of research on bisphosphonates. He writes in a commentary accompanying the journal that he will evaluate patients after they have been on the drug for three to five years to determine whether they will continue to benefit from it. Dr. Bauer said he will examine the patient’s bone density and history of fractures. And Dr. Peter suggests that when a patient has an abnormal fracture of one femur and complains of pain in the other thigh, the doctor should consider stopping treatment.