CT-based Structural Rigidity Analysis Is More Accurate Than Mirels Scoring for Fracture Prediction in Metastatic Femoral Lesions

Abstract

Background Controversy continues regarding the appropriate assessment of fracture risk in long bone lesions affected by disseminated malignancy. Questions/purposes The purpose of this ongoing Musculoskeletal Tumor Society-sponsored, multi-institutional prospective cross-sectional clinical study is to compare CT-based structural rigidity analysis (CTRA) with physician-derived Mirels scoring for predicting pathologic fracture in femoral bone lesions. We hypothesized CTRA would be superior to Mirels in predicting fracture risk within the first year based on (1) sensitivity, specificity, positive predictive value, and negative predictive value; (2) receiver operator characteristic (ROC) analysis; and (3) fracture prediction after controlling for potential confounding variables such as age and lesion size. Methods Consented patients with femoral metastatic lesions were assigned Mirels scores by the individual enrolling orthopaedic oncologist based on plain radiographs and then underwent CT scans of both femurs with a phantom of known density. The CTRA was then performed. Between 2004 and 2008, six study centers performed CTRA on 125 patients. The general indications for this test were femoral metastatic lesions potentially at risk of fracture. The enrolling physician was allowed the choice of prophylactic stabilization or nonsurgical treatment, and the local treating oncology team along with the patient made this decision. Of those 125 patients, 78 (62%) did not undergo prophylactic stabilization and had followup sufficient for inclusion, which was fracture through the lesion within 12 months of CTRA, death within 12 months of CTRA, or 12-month survival after CTRA without fracture, whereas 15 (12%) were lost to followup and could not be studied here. The mean patient age was 61 years (SD, 14 years). There were 46 women. Sixtyfour of the lesions were located in the proximal femur, 13 Clin Orthop Relat Res (2016) 474:643-651 DOI 10.1007/s11999-015-4453-0 Clinical Orthopaedics and Related Research ® A Publication of The Association of Bone and Joint Surgeons®were in the diaphysis, and four were distal. Osteolytic lesions prevailed (48 lesions) over mixed (31 lesions) and osteoblastic (15 lesions). The most common primary cancers were breast (25 lesions), lung (14 lesions), and myeloma (11 lesions). CTRA was compared with Mirels based on sensitivity/specificity analysis, ROC, and fracture prediction by multivariate analysis. For the CTRA, reduction greater than 35% in axial, bending, or torsional rigidities at the lesion was considered at risk for fracture, whereas a Mirels score of 9 or above, as suggested in the original manuscript, was used as the definition of impending fracture. Results CTRA provided higher sensitivity (100% versus 66.7%), specificity (60.6% versus 47.9%), positive predictive value (17.6% versus 9.8%), and negative predictive value (100% versus 94.4%) compared with the classic Mirels definition of impending fracture (C 9), although there was considerable overlap in the confidence intervals. ...

Treatment of pathological fractures of the long bones

“…2). 13 Although the future of fracture risk analysis is CT-based, 14 the axial cortical involvement is the most practical tool to use if only conventional radiographs are available.…”

FDG PET/CT Assesses the Risk of Femoral Pathological Fractures in Patients With Metastatic Breast Cancer

“…We use quantitative measures of FDG avidity to identify subsequent fracture risk. For the most commonly used measure of FDG avidity, SUVmax, sensitivity and specificity of 58% and 85% were achieved, respectively, better than reported values for Mirel’s criteria [8–10]. For the volumetric measurement TLG, which accounts both for size and intensity of FDG-avidity, sensitivity and specificity were 85% and 80%.…”

“…Pathological fracture risk is often estimated using Mirel’s scoring [7], which combines the use of radiographs to grade size, location, and radiopacity of metastases, as well as the patient’s level of pain, to determine a composite score up to 12. Mirel’s scores of 9 or above suggested high fracture risk in initial reports [7], however subsequent evaluations found that the specificity of Mirel’s scoring is only 35–50% [8–10]. Accordingly, better prediction of pathological fracture risk is needed.…”

The Orthopedic Burden of U.S. Cancer Care

“…The orthopaedic surgeon must be able to decide whether or not to operate on a patient with metastatic disease without pathologic fracture. Several clinical scoring systems and imaging-based structural rigidity analyses have been developed to assist the orthopaedic practitioner predict the likelihood of fracture [19][20][21]. The wide range of surgical treatment options is beyond the scope of this conversation, but the goals of treatment should always focus on pain relief and functional optimization.…”