Prediction of pathological fracture in patients with lower limb bone metastasis using computed tomography imaging

Lower limb pathological fractures caused by bone metastases can severely impair activities of daily living, so recognizing fracture risk is essential. Medial cortical involvement (MCI) in the proximal femur has been demonstrated to affect bone strength in biomechanical studies, but it has not been investigated in real patients. Between 2012 and 2019, 161 bone metastases with computed tomography (CT) images were retrospectively examined. Twenty-nine fractures were observed including 14 metastases with pathological fractures at the first examination, and prophylactic surgery was performed for 50 metastases. We extracted clinicopathological data using CT images, including patient's background, MCI in the proximal femur, site, size, circumferential cortical involvement (CCI), pain, and nature of metastasis. Cox proportional hazard regression analyses were performed, and we created integer scores for predicting fractures. We revealed that MCI, CCI, lytic dominant lesion, and pain were significant factors by univariate analyses. By multivariable analysis, MCI and each 25% CCI were significant and integer score 1 was assigned based on hazard ratio. The full score was four points, with MCI in the proximal femur (one point) and ≥ 75% CCI (three points). With integer score two, sensitivity was 88.9% and specificity was 81.2% for predicting fracture within 60 days. In conclusion, MCI and CCI examined by CT images were the risk factors for pathological fracture. CCI ≥ 50% is a widely known risk factor, but in addition, it may be better to consider surgery if MCI in the proximal femur is observed in metastasis with 25-50% CCI.