Morphometrics of the coronoid process and the radial notch of the ulna: implications for fracture assessment

PURPOSE: A comprehensive analysis of the morphology of fractures of the coronoid process (CP) can aid diagnosis and guide treatment. The involvement of the radial notch of the ulna (RN)—e.g., in anterolateral facet fractures and transverse fractures of the CP—may influence the biomechanical conditions of the proximal radioulnar joint. However, the morphometric relation between the CP and the RN and the extent to what the proximal radioulnar joint can be affected in these types of fractures is unknown. METHODS: A total of 113 embalmed, cadaveric ulnae were dissected. All soft tissue was removed. Strictly lateral, high-resolution photographs were taken and digitally analyzed. The height of the CP and its relation to the RN was measured. Sex differences and correlations between measured parameters were calculated. RESULTS: Mean height of the CP was 16 mm (range: 12–23 mm; SD: 2). Mean height of the RN was 16 mm (11–25 mm; 2.2). The 50% mark of the CP corresponded to 18% (0–56%; 11.2) of the height of the RN. No significant differences were found between male and female specimens. CONCLUSION: The RN of the ulna extends only to a small part to the CP. Transverse or anterolateral fractures of less than 50% of the coronoid process may involve only a small portion of the proximal radioulnar joint.