Bisphosphonates have shown robust efficacy in preventing fractures and are widely prescribed for patients with osteoporosis, a musculoskeletal disease characterized by low bone mass [[1], [2], [3]]. Approximately 12.8 million Japanese individuals have osteoporosis, and 30–50% of American women with osteoporosis are affected by fragility fractures [4,5]. Several studies have revealed an association between bisphosphonate use and atypical fractures of the femoral shaft or subtrochanteric region [[6], [7], [8]]. It has been shown that long-term suppression of bone turnover and suppressed bone remodeling from prolonged exposure to bisphosphonates may lead to an accumulation of microdamage [6,9].

A previous systematic review investigated the predisposing factors associated with atypical ulnar fractures (n = 8), including older age, female sex, and long-term bisphosphonate use [10]. According to a recent case report, bilateral atypical ulnar fractures might occur even after the 2-year use of teriparatide following long-term treatment with bisphosphonate [11].

The tensile stress caused by axis loading is a biomechanical factor for fractures [12]. The interosseous membrane of the forearm plays an important role as a longitudinal stabilizer of the forearm, maintaining its function, and acts as a load transmitter between the radius and ulna [13]. However, the precise mechanisms and characteristics associated with atypical ulnar fractures are unclear because of their low incidence. The purpose of this study was to examine the relationship between the site of atypical ulnar fractures and the anatomy of the forearm using finite element (FE) analysis to elucidate the mechanisms underlying these fractures.