Radiological Reversibility of Incomplete Atypical Femoral Fracture with Cessation of Bisphosphonate: Including an Early Stage of Incomplete Fracture.

Background: We found some important early findings in simple radiographs under the bisphosphonate (BP) treatment through a retrospective study. Here, we report the degree of reversibility of the early findings before overt fracture and analyze the factors affecting the differences through a retrospective case-control study. Methods: We retrospectively inspected the clinical charts of patients diagnosed with atypical femoral fracture (AFF) at our institute between March 2006 and September 2018. Among the 209 screened patients, 102 patients were ultimately divided into 3 categories: Category 1 was described as endosteal diffuse flaring (EDF, early IAFF); category 2 was typical IAFF, with a tiny/partial crack that was limited to less than half of the thickness of the cortex; and category 3 was IAFF with a crack through the entire cortex. Demographics, clinical factors, and three categories of incomplete atypical femoral fracture (IAFF) were analyzed to determine whether their radiological condition "improved" or "progressed" after cessation of BP via univariate and multivariate analyses. Results: Thirty-three, 53, and 16 were classified as categories 1, 2, and 3, respectively. Groups 1 and 2 consisted of 79 patients whose IAFF on the side of interest improved and 23 patients whose IAFF progressed, respectively. The uni/multivariate analyses of the groups demonstrated that the total period of BP (odds ratio [OR] = 1.49) and period of cessation of BP (OR = 0.24) were significant variables. In addition, prophylactic treatment for a contralateral IAFF was a strong factor for progression of the incomplete lesion on the side of interest (OR = 25.99). The rate of progression was significantly higher in patients with a mean treatment period of 43 months or longer, and in those with a mean cessation period shorter than 1.2 months. Conclusion: Early-stage IAFF was found to be a unique finding in simple radiographs before the typical features of AFF. This EDF (category 1) was definitively reversible to normal bone when administration of BP was stopped. In addition, a long period of BP treatment and recent cessation of BP adversely affected IAFF with respect to spontaneous healing. Level of Evidence: Level III, a retrospective case-control study.