Fracture risk in unicameral bone cyst. Is magnetic resonance imaging a better predictor than plain radiography ?

The classical indication for treating a simple bone cyst is usually the risk of fracture, which can be predicted based on three parameters : the bone cyst index, the bone cyst diameter, and the minimal cortical thickness. A retrospective review was carried out based on imaging of 35 simple bone cysts (30 humeral and 5 femoral). The three parameters were measured on standard radiographs, and on T1-weighted and T2-weighted MRI. The measurements were performed by two independent reviewers, and twice by the same reviewer. Kappa values and binary logistic regression were used to assess the ability of the parameters to predict the fracture risk. Inter- and intra-observer agreement was measured. T1-weighted MRI was found to have the best inter- and intra-observer repeatability. The bone cyst index was found to be the best predictor for the risk of fracture.