A Displaced Atypical Femoral Fracture Healed Without Anti-osteoporotic Agents in a Case of Ankylosing Spondylitis.

Bone loss leading to osteoporosis is a well-known feature in patients with ankylosing spondylitis (AS), with the prevalence of osteoporosis varying widely across different studies. However, there is still no consensus on the treatment of osteoporosis in AS patients. A 67-year-old male, a case of AS under medication control, had taken oral bisphosphonate for about seven years for suspected osteoporosis due to compression fracture at T12 and discontinued for disproportionately high dual-energy X-ray absorptiometry T-score (11.0 SD). He had been well until his right hip painful disability developed after a fall at home with a resultant right subtrochanteric transverse fracture with medial cortical spike, fulfilling features of atypical femoral fractures five months later. Open reduction and internal fixation with a cephalomedullary femoral nail were performed smoothly on the same day, and the fracture healed slowly and eventually one year later with only supplementation of calcium with vitamin D.