Comment on Compston: pathophysiology of atypical femoral fractures and osteonecrosis of the jaw

Atypical fractures, a biased perspective

When stress fractures started to show up in the femurs of elderly ladies, it was soon evident that bisphosphonate use lay behind, and the absolute risk increase due to bisphosphonate use was reasonably well estimated already in 2008. Thereafter followed a period of confusion: the term atypical fracture was introduced, with a definition so vague that the true stress fractures tended to disappear in a cloud of ambiguity. This cast doubt on the association with bisphosphonates. The association was then re-established by large epidemiological studies based on radiographic adjudication. Atypical fractures are largely caused by bisphosphonates. With a correct indication, bisphosphonates prevent many more fractures than they cause, at least during the first years of use. With an incorrect indication they are likely to cause more harm than good.

Atypical femoral fractures, bisphosphonates, and mechanical stress

Atypical fractures are stress fractures occurring in the femoral shaft and closely related to bisphosphonate use. We here discuss their radiographic definition and different putative etiologies, apart from mechanical stress. Long time reduction of skeletal remodeling because of bisphosphonate use is thought to allow time for the bone to deteriorate mechanically, resulting in reduced toughness. However, the risk of atypical fracture diminishes rapidly after cessation of treatment, which suggests more acute effects of bisphosphonate use. Microdamage normally accumulates at areas of high stress. Possibly, ongoing bisphosphonate use reduces the ability to resorb and replace areas of microdamage by targeted remodeling. This could lead to crack propagation beyond a point of no return, ending in macroscopic stress fracture.

Fracture risk assessment: state of the art, methodologically unsound, or poorly reported?

Osteoporotic fractures, including hip fractures, are a global health concern associated with significant morbidity and mortality as well as a major economic burden. Identifying individuals who are at an increased risk of osteoporotic fracture is an important challenge to be resolved. Recently, multivariable prediction tools have been developed to assist clinicians in the management of their patients by calculating their 10-year risk of fracture (FRAX, QFracture, Garvan) using a combination of known risk factors. These prediction models have revolutionized the way clinicians assess the risk of fracture. Studies evaluating the performance of prediction models in this and other areas of medicine have, however, been characterized by poor design, methodological conduct, and reporting. We examine recently developed fracture prediction models and critically discuss issues in their design, validation, and transparency.