Bisphosphonates are a class of drugs used to treat osteoporosis, the disease of thinning bone structure. People taking the drugs can experience unusual fractures in the femur bone of the leg. Breaks can happen in ways in which the leg does not usually break.
Recently, HSS doctors compared surgical repairs of these kinds of femur fractures in two groups of patients – those who were taking bisphosphonates and those who were not. They found that the group taking the bisphosphonates had significantly more surgical complications than the patients who were not taking the drugs.
A retrospective review compared 43 patients who had been taking bisphosphonates who experienced the kind of femoral shaft fractures associated with the drugs to a group of 20 patients with similar fractures who were not being treated with bisphosphonates. The patients were all treated surgically to repair their fractures over a period of time from 2002 to 2008.
Before surgery, 24% of the bisphosphonate-taking group had a confirmed diagnosis of osteoporosis. In the non-bisphospohate group, osteoporosis was diagnosed in only 5%.
The patients all received similar surgical implants during the operations to repair their broken legs, but a greater number of biological adjuvant treatments had to be used to repair the breaks in the bisphosphonate group.
During the repair surgeries, 21% of the patients who had been taking bisphosphonates experienced further fracturing during the necessary bone-affecting procedures and implants of the repair operations. None of the group who had not taken the drugs did. After the surgeries, 30% of the bisphosphonate-taking group experienced postoperative plate failures. Again, none of the group who had not taken the drugs did.
The natural process of how the body develops new bone involves a delicate balancing act of old bone cells being cleared away and healthy new bone cells developing.
Specialized cells called osteoclasts break down the old bone, releasing its mineral content, in a process called resorption. Other specialized cells called osteoblasts develop into new bone. Old bone leaves, new bone develops, in balance, structural integrity of the skeleton is maintained.
In osteoporosis, resorption continues, but not enough new bone develops. Old bone leaves, not enough new bone replaces it, structural integrity of the skeleton is not maintained, and bone density thins.
Bisphosphonates inhibit osteoclasts from resorption, which keeps the old bone cells from leaving. With old bone cells staying in the skeleton, the bone is less thin, but it is not the same quality as new bone. It cannot remodel or repair microdamage in the same way.
This study demonstrates how bisphosphonate treatment can affect fracture repair. Despite low rates of other risk factors and ample use of biologic adjuvants, patients treated with bisphosphonates who have femur fractures experience significantly more complications when surgical repair is needed.
Mark L. Prasarn MD
Attending Orthopaedic Trauma & Spine Surgeon, Assistant Clinical Professor of Orthopaedic Surgery, University of Texas Health, Science Center at Houston, Memorial Hermann Hospital, Houston, TX
Jaimo Ahn MD, PhD
Orthopaedic Trauma Surgeon, Assistant Professor, Penn Orthopaedic Trauma & Fracture Service, Department of Orthopaedic Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA
Dean G. Lorich, MD
Associate Director of Orthopaedic Trauma Service, Hospital for Special Surgery
Associate Professor of Orthopaedic Surgery, Weill Cornell Medical College