Determination of Sex from the Sternum and Fourth Rib Measurements (A Cross-Sectional Study Using Thoracic Computed Tomography (CT)

Background: Sex determination from skeletal elements is a cornerstone of forensic anthropology, especially in cases where the pelvis or skull is absent, fragmented, or unsuitable for analysis. The sternum and ribs, owing to their structural resilience and marked sexual dimorphism, have emerged as reliable alternatives. With the advent of multidetector computed tomography (MDCT), precise non-invasive morphometric analysis of thoracic bones has become feasible. Despite its potential, limited population-specific standards exist for the Indian demographic, necessitating further validation. Aim: To evaluate sexual dimorphism in sternal and fourth rib measurements using thoracic CT scans and to establish discriminant function models for reliable sex estimation in a contemporary Indian population. Materials and Methods: This cross-sectional study analyzed thoracic CT scans of 200 adult subjects (100 males and 100 females), aged 20–70 years, obtained retrospectively. Seven morphometric parameters were measured: manubrium length, mesosternum length, sternal body width, manubriosternal angle, xiphoid process length, and fourth rib anteroposterior (AP) breadth and superoinferior (SI) height. Statistical analyses included descriptive statistics, independent sample t-tests, discriminant function analysis (DFA), and reliability testing using intraclass correlation coefficients (ICC). Results: All measured parameters, except the manubriosternal angle, demonstrated significantly larger values in males compared to females (p < 0.001). Females exhibited a wider manubriosternal angle. Rib AP breadth emerged as the most discriminant variable (Wilks’ λ = 0.548), followed by xiphoid process length and manubrium length. DFA yielded an overall classification accuracy of 95.5% (96.0% for males and 94.9% for females), with cross-validation confirming robustness (95.0%). However, ICC values indicated variability in inter-observer reliability, suggesting the need for stricter standardization of measurement protocols. Conclusion: Thoracic CT-based measurements of the sternum and fourth rib reveal pronounced sexual dimorphism and provide a highly accurate method for sex estimation. The derived population-specific discriminant equations hold considerable promise for forensic anthropology and medicolegal investigations in the Indian context, especially where conventional skeletal markers are unavailable.