Drugs used to treat osteoporosis — the brittle bone disease — could make limbs easier to break if used for too long,new studies have found.
According to two studies — presented at the annual meeting of the American Academy of Orthopaedic Surgeons’ in New Orleans — overuse of the drugs upset the mineral and crystalline structure of bone,causing weaknesses that can lead to fractures.
A team of investigators from Columbia University Medical Center (CUMC) studied bone structure of 111 post-menopausal women with osteoporosis — 61 of whom had been taking the drugs for at least four years while remaining 50 were treated with calcium and vitamin D supplements.
The team found that bisphosphonates improved bone structure early on in treatment,but over time this benefit diminished.
Dr Melvin Rosenwasser,an orthopaedic surgeon at the CUMC,said: “In the early treatment period,patients using bisphosphonates experienced improvements in all parameters,including decreased buckling ratio and increased cross-sectional area.
“However,after four years of use,these trends reversed,revealing an association between prolonged therapy and declining cortical bone structural integrity,” Rosenwasser said.
The second study conducted at the Hospital for Special Surgery (HSS) evaluated the bone composition of 21 post-menopausal women treated for thigh fractures.
Of these 21 women,12 had a history of bisphosphonate treatment for an average of 8.5 years while nine had not been given bisphosphonates.
Researchers collected samples of bone from each patient’s thigh bone and analysed it. They observed less structural uniformity in the bone tissue from bisphosphonate-treated patients.
This could result in weakness and contribute to out-of-the-ordinary fractures,the researchers said.
“Patients who had been treated with bisphosphonates showed a reduction in tissue heterogeneity,specifically with mineral content and crystal size compared with the control group,” said researcher Brian Gladnick,from HSS.
“This tells us that there may be some measurable differences in bone quality parameters in patients on long-term bisphosphonate therapy,which might contribute to the development of atypical fractures,” Gladnick said.
The scientists believe bisphosphonates suppress the body’s natural ability to remodel bone,but say more research is needed to assess the long-term effectiveness of the drugs.