Low Positive Predictive Value of Bone Scan to Predict Impending Complete Fracture among Incomplete Atypical Femoral Fracture

BACKGROUND: Although bone scan might be useful to detect incomplete atypical femoral fractures (AFFs) earlier than radiographs, there is no study on predicting further progression to a complete fracture among incomplete AFFs. Our purposes are to determine whether bone scan detects impending complete fracture among incomplete AFFs. METHODS: We reviewed 18 patients (20 AFFs) who underwent bone scan at the diagnosis of incomplete AFF and were not treated with prophylactic fixation. A diagnosis of impending complete fracture was made, when the femur completely fractured within 6 months after the scan. We correlated radioisotope uptake with the impending complete fracture to calculate sensitivity, specificity, positive predictive value and negative predictive value of bone scan. RESULTS: Thirteen AFFs (65%, 13/20) showed a positive uptake in bone scan. Among the 13, only one femur was completely fractured within 6 months. None of the 7 femurs without uptake in bone scan fractured. In diagnosing impending complete fracture, the sensitivity of bone scan was 100% and negative predictive value was 100%. However, the specificity (36.8%) and positive predictive value (7.7%) were quite low. CONCLUSION: Bone scan has no significant role in detecting the impending complete fracture, and a positive uptake does not mean the necessity of prophylactic fixation of incomplete AFF.