The relationship between the 2nd metacarpal index and bone mineral density for osteopenia/osteoporosis screening: a systematic review

Abstract

Osteoporosis screening is essential for early intervention and fracture prevention. While dual-energy X-ray absorptiometry (DXA) remains the gold standard for bone mineral density (BMD) assessment, alternative, cost-effective methods are being explored. Radiogrammetry (DXR) has shown promising results; however, it needs specialized computer software. Hand radiographs, particularly the second metacarpal cortical index (2MCI), have shown promise in BMD evaluation. This study aims to systematically review the evidence on the diagnostic accuracy of the 2nd MCI in assessing BMD. A systematic search of PubMed, Scopus, and EMBASE databases was conducted on May 6, 2025, to identify observational and diagnostic accuracy studies evaluating the relationship between the 2MCI and BMD in adults aged 50 years and older. Case reports and non-English studies were excluded. Data extraction followed PRISMA guidelines, and study quality was assessed using QUADAS-2. Due to heterogeneity in study designs, a narrative synthesis was performed. Six studies with a total of 1028 participants were included. Findings consistently demonstrated that 2MCI radiographs correlate with BMD. In addition, machine learning models enhanced the predictive performance of the 2MCI. However, accuracy of findings particularly sensitivity and specificity remains variable in identifying osteopenia or osteoporosis. This study highlights the importance of adhering to standardized protocols and continuously refining measurement approaches to enhance reliability of 2MCI as screening tool for either osteopenia or osteoporosis. With improved study designs, it further strengthens the clinical applicability of these findings.