Isolated Atypical Pedicle Stress Fractures in Patients on Prolonged Bisphosphonate Therapy: Report of Two Cases and a Literature-Based Proposal for Diagnostic Criteria

Background/Objectives: Long-term bisphosphonate (BP) therapy is an effective treatment for osteoporosis but has been associated with rare complications such as atypical femoral fractures (AFFs). Emerging reports suggest that similar insufficiency fractures may also occur in other skeletal sites, including the lumbar pedicles. This study reports two rare cases of isolated bilateral lumbar pedicle stress fractures in patients on prolonged BP therapy. Along with a structured literature review, the objective was to evaluate whether diagnostic criteria derived from those used for AFFs may apply to these atypical vertebral fractures. Methods: Two patients with osteoporosis and on long-term BP therapy diagnosed with isolated lumbar pedicle stress fractures were retrospectively analyzed. A structured literature review identified similar reported cases. All cases were evaluated using the 2010 American Society for Bone and Mineral Research AFF criteria to assess applicability to isolated pedicle stress fractures. Results: Both patients demonstrated bilateral lumbar pedicle fractures without vertebral body involvement. One was treated conservatively; the other underwent robotic-assisted percutaneous pedicle screw fixation with documented fracture healing at six months. The literature review identified eight similar cases of isolated pedicle fractures in patients on prolonged BP therapy. Clinical course and imaging findings demonstrated stress-type features analogous to AFFs. The proposed AFF-based diagnostic criteria for pedicular insufficiency fractures were found to be applicable to all ten patients. Conclusions: Isolated bilateral pedicle stress fractures may represent a spinal analog of AFFs. Based on shared clinical and imaging features, we propose preliminary diagnostic criteria for atypical pedicular insufficiency fractures. Increased awareness and standardized criteria may aid in early diagnosis and reporting, encouraging further studies on this rare spinal entity.