Lower Extremity Arterial Calcification: Association with Walking Impairment in Patients with Peripheral Arterial Disease

Introduction: Increasing prevalence of arterial calcium in the lower extremities of patients with peripheral arterial disease (PAD) is associated with worsening clinical outcomes. Calcium burden can be detected in patients using standard imaging methods. However, quantitative evaluation of calcium burden in specific arteries of the leg in PAD patients is uncommon in the clinical setting, and the association between quantified levels of vessel-specific calcium burden and functional capacity in PAD remains understudied. We hypothesized that x-ray computed tomography (CT) imaging could quantify calcium mass of the superficial femoral (SFA) and popliteal artery and CT-derived measures of calcium burden would be associated with walking impairment scores. Methods: Healthy controls (n=8) and patients with PAD (n=44) underwent CT imaging of the legs. Calcium mass was quantified from CT images by manual segmentation of the combined SFA and popliteal artery from axial images, with established calcium defined as arterial segments with CT image intensities >130 Hounsfield units. To assess functional capacity, the Walking Impairment Questionnaire (WIQ) was administered at the time of imaging. Univariate and multivariate analyses were performed to assess the association between calcium measures and walking impairment scores. Results: WIQ scores for distance, speed, and stairs significantly differed between healthy controls and PAD patients (all scores, p<0.0001). Calcium mass values for the SFA-popliteal artery were significantly higher in PAD patients versus healthy controls (p=0.0005). In univariate analysis, WIQ scores for distance (p=0.004), speed (p<0.001), and stairs (p=0.002) were significantly associated with calcium mass of the SFA-popliteal artery. Associations between WIQ scores and SFA-popliteal artery calcium mass remained significant after adjusting for age and body mass index in multivariate analyses. Conclusions: These results suggest that calcium burden above the knee is significantly associated with walking impairment. Implementation of arterial calcium scoring for the lower extremities in PAD patients may provide novel insight into the relationships between calcium burden, PAD symptoms, and functional limitations.