3D Quantitative Measurement of the Coronoid Process and Proximal Ulna: A Chinese Adults-Based Morphometric Study

Purpose: To perform quantitative measurements of anatomic morphology of the proximal ulna and coronoid process and establish the morphologic references based on Chinese for the surgical protocol and implant design. Methods: The computed tomography data of 156 upper extremities were involved in this study. The ulna model was reconstructed in Mimics. Ten distance and 6 angle parameters were measured by 4 independent investigators with a new 3D quantitative measurement method. The intraclass correlation coefficient was used to evaluate the measuring reliability. Gender and side differences of measured parameters were evaluated. Results: Measurements showed a mean coronoid height of 15 mm, which was 42% of ulnar height with gender-specific differences (mean, 16 mm in men and 14 mm in women, p<0.001). A mean unsupported anteromedial facet width of 8 mm was 61% of coronoid anteromedial facet. A larger opening angle correlates to a larger olecranon-diaphysis angle (p<0.001) and larger coronoid height (p=0.001). A mean proximal ulna dorsal angulation of 4.7° is present in 80% of models at an average of 52 mm distal to olecranon tip. The average proximal ulna varus angulation was 16° at a mean of 74 mm distal to olecranon tip. Morphological features between the left and right sides were highly consistent. The high correlation between coronoid anatomic parameters, poor correlation among proximal ulnar parameters, and poor relevance between both was also found. The ICC was between 0.789 and 0.978 for inter-observer and between 0.696 and 0.997 for intra-observer reliability. Conclusions: The proximal ulna features variable morphology and poor correlation with coronoid. Over half of the anteromedial facet was not supported by the proximal ulnar diaphysis, making the coronoid vulnerable to elbow trauma. Surgeons should pay more attention to the effect of gender difference and sides consistency of proximal ulna morphology on the treatment of fractures.