Evaluating Fracture Risk in Metastatic Femoral Lesions
A recently published study demonstrated that CT-based structural rigidity analysis is superior to the traditional Mirels score in predicting which patients are at greatest risk for pathologic fracture.
Timothy B. Rapp, MD
Damron TA, Nazarian A, Entezari V, et al. CT-based structural rigidity analysis is more accurate than Mirels scoring for fracture prediction in metastatic femoral lesions. Clin Orthop Relat Res. 2016 Mar;474(3):643-51. doi: 10.1007/s11999-015-4453-0.
A major challenge for general orthopaedic and orthopaedic tumor surgeons is predicting a patient’s risk of a pathologic fracture. The patient’s bone quality, tumor morphology, activity level, and other factors have traditionally made this difficult. Treating patients before they sustain a fracture significantly improves outcome, but predicting who would benefit most from prophylactic fixation is an issue.
Traditionally, surgeons have used the scoring system proposed by Mirels. The problem with this system is how it was developed: The researchers relied on a small group of heterogeneous tumor types and a retrospective assessment of the risk of fracture.
The current paper from Damron et al – a multi-institutional prospective analysis – explores an interesting and exciting alternative: The use of quantitative CT scan to assess fracture risk.
Researchers at the 6 study centers enrolled 125 patients with metastatic femoral lesions that could be at risk for pathologic fracture. The patients were first given a radiograph-based Mirels score and then they underwent CT scans that were to be used for CT-based structural rigidity analysis (CTRA).
Risk for fracture was defined as:
- CTRA showing more than 35% reduction in axial, bending, or torsional rigidities at the lesion
- Mirels score of 9 or more
The patients and their oncologists determined whether they would undergo prophylactic fixation of the potential fracture site. More than half (62%) opted not to undergo treatment, and they were followed for 12 months to determine if they had sustained a fracture through the lesion.
The analysis showed the value of quantitative CT compared with the Mirels score in projecting which patients were at highest risk for a pathologic fracture. The CTRA demonstrated higher:
- Sensitivity (100% vs. 66.7%)
- Specificity (60.6% vs. 47.9%)
- Positive predictive value (17.6% vs. 9.8%)
- Negative predictive value (100% vs. 94.4%)
This is a very important study in the treatment of metastatic bone disease and has the potential to change treatment algorithms. Additional studies are underway to improve the power of this study and to assess the feasibility of the widespread use of quantitative CT to other institutions.
Timothy B. Rapp, MD, is Associate Professor and Chief of the Division of Orthopaedic Oncology, Department of Orthopaedic Surgery, NYU Langone Medical Center – Hospital for Joint Disease, New York, New York.