A 69-year-old woman was referred to radiology clinic for a magnetic resonance imaging (MRI) due to acute left thigh pain. Her medical history was significant for osteoporosis and she was having biphosphonate (BP) treatment. She had no history of significant trauma or other known chronic illnesses.
Anteroposterior and lateral radiographs of the left femur and hip-joint showed an incomplete, lucent fracture line on the lateral cortex of femoral diaphysis, and associated solid periosteal reaction. MRI of thigh confirmed the fracture line and demonstrated the accompanying bone-marrow oedema surrounding the fracture in this location as well as the cortical thickening due to periosteal reaction.
Biphosphonates are a group of drugs prescribed for the treatment of metabolic bone diseases, mostly for osteoporosis to prevent bone loss and reduce osteoporotic bone fractures [1-3]. Nevertheless, long term use of BP may occasionally lead to some adverse effects including atypical femoral fractures and osteonecrosis. Classical osteoporotic femur fractures involve the weakest and most weight-bearing parts of femur such as femoral neck and intertrochanteric area. According to reports published by American Society for Bone and Mineral Research (ASBMR) in 2013, atypical femoral fractures are defined as fractures involving subtrochanteric region down to supracondylar line, excluding pathologic fractures due to malignancy, peri-prosthetic fractures and trauma related fractures. Atypical femoral fractures typically start with cortical thickening of lateral side, then an incomplete lucent fracture line appears and it progresses to a complete fracture by reaching medial cortex [1, 2]. The geometrical shape of femur determines the load on lateral cortex, therefore bowing deformity of femur increases burden of the bone, causing mechanical stress. Bowing deformity was found to be correlated with increased fracture risk in patients receiving BP [4]. In our case, the typical location of the fracture line at the lateral cortex, the absence of trauma history, and the presence of localised periosteal thickening at the fracture site fulfill all of the major criteria according to ASBM Task Force 2013 Revised Case Definition of AFFS. In conclusion, the sudden onset of hip or thigh pain in an osteoporotic patient under BP treatment may indicate an atypical fracture related to therapy. In patients with the suspicion of atypical femur fracture, following a careful evaluation of radiographs, MR imaging, showing bone marrow oedema, can be helpful in early diagnosis of an incomplete fracture before it evolves to a full thickness one. Nuclear bone scans can also be helpful for early diagnosis, demonstrating metabolic changes as hotspots associated with increased bone turnover. For the treatment, surgical fixation and withdrawal of the BP therapy are recommended [1,5]. The differential diagnosis of femoral shaft fractures involves stress and osteoporotic fractures, pathological fractures and pseudofractures. Subtrochanteric diaphysis is the strongest part of the femur, so stress and osteoporotic fractures are unexpected in this part of the bone. Additionally, medial cortical involvement in stress fractures and pseudofractures is a useful finding to distinguish them from BP related fractures. Pathologic fractures are usually associated with an underlying bone lesion and have poor margins at the fracture site [1,5]. Written informed patient consent for publication has been obtained.
BP related atypical femur fracture
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
From the patient’s bilateral hip and femoral X-ray images, localized thickening of the lateral cortex in the proximal mid-shaft of the left femur can be observed, with a suspicious incomplete linear radiolucent area at the lateral cortex. There is no obvious mass or destructive lesion in the surrounding soft tissue. MRI sequences (including coronal and axial T1, T2, and fat-suppression sequences) show a linear low signal beneath the lateral cortex of the left femur, with a thin line of bone marrow edema signal surrounding it, suggesting a microfracture or discontinuity of the cortical bone. In addition, local periosteal reaction and mild cortical thickening of the lateral cortex are noted, while signal changes in the soft tissues primarily manifest as edema or inflammatory exudation corresponding to the fracture site.
Combined with clinical information, the patient’s long-term bisphosphonate (BP) therapy history aligns with these imaging findings.
Based on the imaging findings and the patient’s history, the following diagnoses or differential diagnoses are considered:
Considering the patient is a 69-year-old female with a long-term bisphosphonate therapy history, no significant trauma history, and imaging findings of an incomplete lateral cortical fracture line accompanied by soft tissue and bone marrow edema, these features strongly suggest a bisphosphonate-related atypical femoral fracture (AFF).
If any doubt remains, a bone scan (nuclear medicine bone scintigraphy) or CT three-dimensional reconstruction can be performed to further clarify the fracture extent and bone quality.
1. Treatment Strategies
2. Rehabilitation and Exercise Prescription
During the acute phase or postoperative rehabilitation, it is important to balance low bone strength and pain control, following a gradual, individualized exercise regimen:
Throughout this process, closely monitor the degree of muscle fatigue and any local pain in the fracture area. If the patient experiences significantly increased pain or discomfort, stop or reduce the activity and consult a specialist promptly.
Disclaimer: This report is a reference analysis based on the information currently provided and does not replace an in-person consultation or professional medical advice. If you have any questions about the diagnosis or treatment, please consult an orthopedic specialist or undergo further medical examinations in a timely manner.
BP related atypical femur fracture
