Question

Extension (or straightening) of the elbow stops when the proximal end of the ulna engages the ________. trochlea of the humerus olecranon fossa of the humerus coronoid fossa of the humerus medial epicondyle of the humerus.

Answer 1

Extension or straightening of the elbow stops when the proximal end of the ulna engages the olecranon fossa of the humerus.

Explanation:

Extension of the elbow is the straightening of the forearm or bringing it back to its anatomical position by the triceps brachii and the anconeus muscles.

The elbow joint, a hinge type of joint, is formed at the conjunction of humeral distal end with the ulnar proximal end.

Olecranon process is a structure at the ulnar distal end which fits exactly into the olecranon process at the humeral proximal head with the arm in extended position.

Olecranon fossa is a triangular depression or fossa which is deep in the posterior humerus. So the range of motion due to extension of forearm terminates or limits at the contact of the ulnar olecranon process with that of the humeral olecranon process at the olecranon fossa.