The coronoid fossa is a depression on the anterior surface of the distal humerus that accommodates the coronoid process of the ulna during full elbow flexion. It lies immediately proximal to the medial part of the trochlea and lateral to the radial fossa which accommodates the radial head. Together the coronoid fossa and radial fossa allow unimpeded full elbow flexion by receiving the proximal ulna and radius respectively. The thin bony floor of the coronoid fossa is sometimes perforated, communicating directly with the olecranon fossa posteriorly.
Osteophytes arising from the rim of the coronoid fossa in elbow osteoarthritis impinge against the coronoid process during elbow flexion, causing a hard end-feel and painful terminal flexion deficit. Arthroscopic debridement of these osteophytes (arthroscopic elbow release) restores flexion in early osteoarthritis. In supracondylar fractures, the fracture line frequently passes through the thin floor of the coronoid fossa. Anterior elbow effusion is identified by soft-tissue fullness in the coronoid and radial fossae on lateral radiograph.
Osteophytes projecting from the coronoid fossa rim impinge against the coronoid tip during terminal elbow flexion in osteoarthritis, producing a hard mechanical block at 100-110 degrees that improves with arthroscopic debridement of both the coronoid tip and the fossa osteophytes.
The thin floor of the coronoid fossa provides a natural weakening plane through which supracondylar fractures propagate, creating the typical oblique fracture line crossing from the coronoid fossa to the olecranon fossa in the extension-type paediatric supracondylar humeral fracture.
