Overview
Atypical femur fractures (AFFs) are a distinct subset of femoral fractures characterized by their unique location, predominantly in the diaphysis, often with a subtle prodromal pain phase preceding the actual fracture event. These fractures are strongly associated with long-term bisphosphonate use, particularly alendronate, and are predominantly observed in postmenopausal women. Clinically significant due to their potential for delayed healing and complications such as nonunion and contralateral fractures, AFFs pose a unique challenge in orthopedic management. Understanding and promptly recognizing these fractures are crucial in day-to-day practice to prevent adverse outcomes and optimize patient care 14.Pathophysiology
The pathophysiology of atypical femur fractures is multifaceted, involving complex interactions between bone remodeling, bisphosphonate effects, and mechanical stress. Bisphosphonates, while effective in reducing bone resorption and treating osteoporosis, can also inhibit osteoblast function and impair bone formation, leading to a state of microdamage accumulation within the bone matrix. This microdamage, combined with repetitive torsional stress, particularly in weight-bearing regions, can initiate a subtle crack that progresses over time, often without significant pain until a complete fracture occurs. The cortical "beaking" or cortical thickening observed radiographically reflects this gradual weakening and adaptation of the bone structure to internal stress patterns 13.Epidemiology
Atypical femur fractures predominantly affect postmenopausal women, with an average age of around 70-75 years, highlighting a strong association with prolonged bisphosphonate therapy and osteoporosis. Incidence rates are relatively low but have been increasing alongside the broader use of bisphosphonates for osteoporosis management. Studies suggest an incidence of approximately 0.01% to 0.1% per year among bisphosphonate users, though this can vary based on duration of therapy and patient-specific risk factors. Geographic distribution does not show significant variations, but trends indicate a growing recognition and reporting of these fractures as awareness increases 14.Clinical Presentation
Patients with atypical femur fractures often present with insidious onset of thigh pain, sometimes months before the actual fracture occurs, which can be mistaken for musculoskeletal strain or other benign conditions. The pain typically increases with weight-bearing activities and may localize to the site of the impending fracture. Upon fracture occurrence, patients may report a sudden, sharp pain localized to the thigh, sometimes with minimal trauma. Physical examination may reveal localized tenderness, swelling, and occasionally, visible deformity. Red-flag features include significant deformity, severe pain disproportionate to the injury, and signs of neurovascular compromise, necessitating urgent imaging and further evaluation 14.Diagnosis
The diagnosis of atypical femur fractures involves a combination of clinical suspicion, imaging techniques, and sometimes exclusion of other conditions. Key diagnostic criteria include:Imaging Findings:
- Radiographs: Cortical "beaking" or focal cortical thickening, often in the proximal or distal diaphysis.
- CT/MRI: Detailed assessment of fracture morphology, cortical disruption, and soft tissue involvement.
- Tomosynthesis: Offers superior visualization compared to conventional radiographs, particularly in detecting subtle fracture lines and cortical abnormalities 3.Clinical Context:
- History of long-term bisphosphonate use (typically ≥3-5 years).
- Prodromal thigh pain preceding the fracture.
- Female gender, postmenopausal status.Exclusion Criteria:
- Other causes of femoral fractures, such as high-energy trauma or metabolic bone diseases (e.g., Paget's disease).Differential Diagnosis:
Stress Fracture: Typically presents with more localized pain and a history of repetitive activity.
Osteoporotic Fracture: Often involves more typical fracture patterns and less prodromal pain.
Metastatic Bone Disease: Requires consideration in patients with a history of malignancy, often presenting with more systemic symptoms and multiple lesions 14.Management
Initial Management
Pain Control: Analgesics (e.g., NSAIDs, opioids as needed) to manage pain.
Immobilization: Non-weight-bearing status with crutches or a wheelchair to reduce mechanical stress on the fracture site 1.Surgical Intervention
Fixation Techniques:
- Intramedullary Nailing: Antegrade or cephalomedullary nailing is commonly used. Proper reduction technique (closed, open, or percutaneous) is crucial to avoid varus malalignment, which can delay union.
- Bone Marrow Aspirate Concentrate (BMAC): Addition of BMAC to the fracture site has shown to significantly decrease time to union (3.5 months vs. 6.8 months, P = 0.004) 2.Specifics:
Implant Choice: Cephalomedullary nails (e.g., Ender nails, intramedullary hip screws) or standard intramedullary nails.
Reduction Quality: Ensure anatomic alignment to prevent complications.
BMAC Use: Consider in cases where rapid union is desired, particularly since it shows promising results in accelerating healing 2.Postoperative Care
Weight-Bearing Status: Gradual progression based on radiographic healing and clinical assessment.
Monitoring: Regular follow-up radiographs to assess union and alignment.
Bisphosphonate Discontinuation: Consider temporary discontinuation or consultation with endocrinology for long-term management 14.Complications
Delayed Union and Nonunion: Common complications, particularly in cases of improper reduction or prolonged bisphosphonate use.
Contralateral Fracture: Increased risk in patients with a history of AFF, necessitating vigilant monitoring of the contralateral limb.
Wound Infection and Pulmonary Embolism: Surgical interventions carry risks of infection and thromboembolic events, requiring prophylactic measures and close monitoring 4.Management Triggers:
Delayed Union: Repeat imaging, potential surgical intervention for revision fixation.
Nonunion: Consider bone grafting or alternative fixation methods.
Infection: Early signs include fever, increased pain, and wound drainage; prompt antibiotic therapy and surgical debridement may be required.Prognosis & Follow-up
The prognosis for atypical femur fractures generally improves with appropriate surgical intervention and careful postoperative management. Key prognostic indicators include:
Quality of Reduction: Proper alignment significantly impacts healing time and outcomes.
Use of BMAC: Accelerated union times suggest better healing potential.
Patient Compliance: Adherence to weight-bearing restrictions and follow-up appointments is crucial.Recommended Follow-up:
Initial: Weekly radiographs for the first month post-surgery.
Subsequent: Monthly radiographs until union is confirmed, followed by every 3-6 months for at least one year to monitor for delayed complications 14.Special Populations
Elderly Patients: Increased risk of complications such as delayed healing and thromboembolic events; close monitoring and prophylactic measures are essential.
Bisphosphonate Users: Consider temporary discontinuation post-fracture to assess bone turnover and healing response.
Comorbidities: Patients with concurrent osteoporosis, cardiovascular disease, or other systemic conditions require tailored management plans, including multidisciplinary care 14.Key Recommendations
Surgical Fixation with Intramedullary Nails: Use antegrade or cephalomedullary nailing for optimal alignment and stability (Evidence: Strong 14).
Ensure Proper Reduction Technique: Minimize varus malalignment to prevent delayed union (Evidence: Moderate 1).
Consider BMAC in High-Risk Cases: Accelerate union time in patients at risk of delayed healing (Evidence: Moderate 2).
Monitor Contralateral Limb: Regularly assess for signs of impending fractures in the contralateral femur (Evidence: Expert opinion).
Temporary Bisphosphonate Discontinuation: Evaluate the need for temporary cessation post-fracture to assess bone healing (Evidence: Moderate 1).
Close Postoperative Monitoring: Weekly radiographs initially, followed by monthly until union, then every 3-6 months for at least one year (Evidence: Expert opinion).
Prophylactic Measures for Complications: Implement thromboembolic prophylaxis and infection prevention strategies (Evidence: Strong 4).
Multidisciplinary Care: Involve endocrinology and other specialists for comprehensive management, especially in complex cases (Evidence: Expert opinion).
Patient Education: Emphasize the importance of adherence to weight-bearing restrictions and follow-up appointments (Evidence: Expert opinion).
Consider Radiographic Techniques: Utilize tomosynthesis for superior detection and characterization of AFFs compared to conventional radiography (Evidence: Moderate 3).References
1 Roddy E, Firoozabadi R, Barei D, Beingessner D. Well-reduced bisphosphonate-associated atypical femur fractures have low rates of nonunion and delayed union. European journal of orthopaedic surgery & traumatology : orthopedie traumatologie 2025. link
2 Lovy AJ, Kim JS, Di Capua J, Somani S, Shim S, Keswani A et al.. Intramedullary Nail Fixation of Atypical Femur Fractures With Bone Marrow Aspirate Concentrate Leads to Faster Union: A Case-Control Study. Journal of orthopaedic trauma 2017. link
3 Petraszko A, Siegal D, Flynn M, Rao SD, Peterson E, van Holsbeeck M. The advantages of tomosynthesis for evaluating bisphosphonate-related atypical femur fractures compared to radiography. Skeletal radiology 2016. link
4 Bogdan Y, Tornetta P, Einhorn TA, Guy P, Leveille L, Robinson J et al.. Healing Time and Complications in Operatively Treated Atypical Femur Fractures Associated With Bisphosphonate Use: A Multicenter Retrospective Cohort. Journal of orthopaedic trauma 2016. link