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Abstract
Background and purpose The risk of atypical fracture of the femur is associated with bisphosphonate use. While characterizing atypical fractures from a previous nationwide study in radiographic detail, we had the impression that the fractures were located either in the subtrochanteric region or in the shaft. We determined whether there is a dichotomy in this respect.
Patients and methods The distance between the atypical fractures and the lesser trochanter was measured on plain radiographs from 129 of 160 patients with atypical fractures, taken from 2008 through 2010. Analysis of the distances measured showed 2 clusters, which were then analyzed with regard to bisphosphonate use and age.
Results The distribution of the distances would be best described as 2 clusters, with a dichotomy at 8 cm. The proximal (subtrochanteric) cluster comprised 25 patients who were generally younger (median 71 years) than the 104 patients in the cluster with shaft fractures (median 80 years). The 95% CI for the difference between medians was 4–11 years. Of the patients with subtrochanteric fractures, 18 of 25 used bisphosphonates as compared to 89 of 104 with shaft fractures.
Interpretation The younger age and possibly smaller proportion of bisphosphonate users in the subtrochanteric cluster may be compatible with a greater influence of mechanical stress in the underlying pathophysiology of proximal fractures.
VK contributed to the evaluation of radiographs, analysis, interpretation of data, and drafting of the article. JS collected all the radiographs and helped revise the article. PA contributed to interpretation of the data, and to drafting and revision of the article.
We thank Thomas Annerholm for his technical support using the PACS and Philippe Wagner for helping us to get started with R. The study was funded by the Swedish Research Council (VR 02031-47-5), Linköping University, Östergötland County Council, and the King Gustaf V and Queen Victoria Free Mason Foundation.
PA has a patent on a process for coating metal implants with bisphosphonates, and has shares in a company that is trying to commercialize the principle (Addbio AB). PA has also received consulting reimbursement and grants from Eli Lilly & Co. VK and JS have no competing interests to declare.