Sudden bone breaks have been reported in patients taking the popular osteoporosis drug, Fosamax.

Although the active ingredient is supposed to make bones stronger, some doctors believe it is responsible for many spontaneous fractures and breaks.

A news station in Charleston S.C. reported on a woman whose leg snapped while she was walking. A clean break through the middle of her thigh bone was illustrated on X-rays - an extremely rare type of fracture and coupled with the fact that she neither tripped nor fell prior to the break has made doctors curious.

Furthermore, it's not a typical break for a person with osteoporosis.

Fosamax is designed to stop osteoclasts - cells that re-absorb bone in the body. To prevent osteoporosis, osteoblasts, the cells that produce bone, are supposed to keep working. However, tests have revealed that both sets of cells have ceased function in patients who have suffered from these sudden fractures.

The rare fractures have been dubbed "frozen bone" by Dr. Robert Bunning, a lead rheumatologist at the National Rehabilitation Hospital. Most patients are unaware of any problems, experiencing vague thigh pain before the fracture, however the brittle bone is very susceptible to breaks.

Merck and Co Inc, the makers of the drug, has denied a link between the drug and the fractures. Osteoporosis has been blamed for many of the breaks, although doctors have been quick to point out that most osteoporosis breaks occur in the hip area and usually occur after a fall.

The U.S. Food and Drug Administration is currently researching the situation as allegations mount against the medication. Fosamax, however, has been linked to additional harmful side effects.

The drug has been shown to cause a painful medical condition called osteonecrosis (ONJ), or "dead jaw." Osteonecrosis is a slow death of bone tissue in the jaw that occurs because of poor blood supply to the bone. Side effects of ONJ include mouth swelling, loosening of teeth and exposed bone.

A New York federal judge refused to dismiss the lawsuits against Merck in early 2010 alleging the drug caused ONJ in an Indiana woman who took the medication for close to eight years. Close to 900 Fosamax lawsuits have been filed nationwide.

Merck will defend the drug during the April 2010 trial, claiming other factors contributed to the patients' jaw problems. Fosamax generated close to $3 billion annually until generic versions of the drug hit the market.