The ulnar greater sigmoid notch "coverage angle": Bone and cartilage contribution. Magnetic resonance imaging anatomic study on 78 elbows

Background: To study the degree of coverage provided by the greater sigmoid notch (GSN) to the humeral trochlea, as well as the contribution of the olecranon and coronoid process cartilage tips to this angle, and its variations. Methods: We recruited 39 healthy volunteers, comprising 19 women and 20 men, with a mean age of 28 years (range, 21-32 years). High-definition magnetic resonance images were obtained for the right and left elbows. Four angles were measured on the sagittal plane passing through the coronoid and olecranon tips: angle A, identified by 2 lines from the trochlea center to the olecranon bone-cartilage junction and olecranon cartilage tip; angle B, identified by 2 lines from the trochlea center to the olecranon and coronoid bone-cartilage junction; angle C, identified by 2 lines from the trochlea center to the coronoid bone-cartilage junction and coronoid cartilage tip; and GSN coverage angle (GSN-ca), defined as the sum of angles A, B, and C. Pearson correlation tests, t tests, and intraclass correlation coefficients were used for statistical analyses. Results: The mean angle A, angle B, and angle C values were 6° (range, 2°-12°), 182° (range, 153°-204°), and 9° (range, 2°-16°), respectively. No correlations were found between these 3 angles. The mean GSN-ca was 198° (range, 167°-222°), and the GSN-ca was less than 180° in 8% of the cases. No significant differences emerged for side or gender or for total length of the ulna. Conclusion: The GSN showed significantly different shapes on the sagittal plane that we defined as closed type when the GSN-ca was greater than 180° (92%) and as open type when the GSA-ca was less than 180° (8%). The cartilage tip contribution varied and was not correlated with that of bone.