The trochlear notch (semilunar notch) of the ulna is the large C-shaped articular surface of the proximal ulna that wraps around the trochlea of the humerus to form the humeroulnar joint. It is bounded proximally by the olecranon and distally by the coronoid process, with its articular cartilage interrupted by a transverse non-articular ridge at its midpoint.
| Articulations | |
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| Landmarks |
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| Ossification | The trochlear notch is formed by the primary ulnar ossification centre, present from the 7th fetal week. The olecranon secondary centre appears at puberty and fuses at 14-16 years. |
The trochlear notch is the site of olecranon fractures (proximal component) and coronoid fractures (distal component). Comminuted fractures spanning the entire notch (trans-olecranon fracture-dislocation) require careful reconstruction of the articular surface to restore elbow congruence. The non-articular transverse ridge is a normal anatomical variant and must not be confused with an articular surface fracture on imaging. Cubitus varus and valgus deformities alter trochlear notch tracking.
Fractures through the trochlear notch disrupt the ulnohumeral articulation and the triceps mechanism.
Loss of congruity between the trochlear notch and the humeral trochlea, usually posterior.
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