Inter- and intra-observer variability associated with the use of the Mirels' scoring system for metastatic bone lesions.

Metastatic bone disease is increasing in association with ever-improving medical management of osteophylic malignant conditions. The precise timing of surgical intervention for secondary lesions in long bones can be difficult to determine. This paper aims to evaluate a classic scoring system. All radiographs were examined twice by three orthopaedic oncologists and scored according to the Mirels' scoring system. The Kappa statistic was used for the purpose of statistical analysis. The results show agreement between observers (κ = 0.35-0.61) for overall scores at the two time intervals. Inter-observer agreement was also seen with subset analysis of size (κ = 0.27-0.60), site (κ = 0.77-1.0) and nature of the lesion (κ = 0.55-0.81). Similarly, low levels of intra-observer variability were noted for each of the three surgeons (κ= 0.34, 0.39, and 0.78, respectively). These results indicate a reliable, repeatable assessment of bony metastases. We continue to advocate its use in the management of patients with long bone metastases.