Purpose: To address the primary null hypothesis that there is no difference in the articular surface area of the lesser sigmoid notch involved among Mayo classes. Second, we analyzed the fracture line location and the pattern of lesser sigmoid notch articular surface involvement among Mayo classes. Methods: Using quantitative 3-dimentional computed tomography, we reconstructed and analyzed fractures involving the lesser sigmoid notch articular surface in 52 patients. Furthermore, we assessed the surface area involved in the fracture, the number of fracture fragments, and the location and direction of the fracture lines. Coronoid fractures were classified according to Mayo types. Results: There was no significant difference between Mayo types 1 and 2 in any characteristic of the involvement of the lesser sigmoid notch articular surface, whereas Mayo type 3 was significantly different from both Mayo types 1 and 2 in the area involved in the fracture (42% in Mayo type III vs 9% in Mayo types I and II), the number of articular fragments (>3 fragments in type III vs 2 fragments in types I and II), and the direction of fracture line (both horizontal and vertical lines in type III vs only horizontal line in types I and II). Conclusion: Mayo type III results in a more complex fracture, which might need to be addressed directly or indirectly during open reduction internal fixation of the olecranon fracture dislocations because changes in the geometry of lesser sigmoid notch may affect the radioulnar joint if it remains incongruent.