Which structure forms the lateral boundary of the quadrangular space?

Which structure forms the lateral boundary of the quadrangular space?

• A. Surgical neck of humerus
• B. Coracoid process
• C. Greater tubercle
• D. Head of humerus

Answer: (A)

The space in question is defined by four borders, forming a hollow passage for important neurovascular structures. Its lateral edge is the surgical neck of the humerus, which sits where the space opens toward the lateral upper arm. This boundary helps explain why the axillary nerve and posterior circumflex humeral vessels—traveling through this space—are positioned to come out around the deltoid region after passing the humerus at that level. The other structures listed don’t form this lateral boundary. The coracoid process sits on the anterior scapula and isn’t part of the posterior shoulder space’s lateral edge. The greater tubercle and the head of the humerus are features on the humeral proximal end, but they do not define the lateral border of the quadrangular space.

The space in question is defined by four borders, forming a hollow passage for important neurovascular structures. Its lateral edge is the surgical neck of the humerus, which sits where the space opens toward the lateral upper arm. This boundary helps explain why the axillary nerve and posterior circumflex humeral vessels—traveling through this space—are positioned to come out around the deltoid region after passing the humerus at that level.

The other structures listed don’t form this lateral boundary. The coracoid process sits on the anterior scapula and isn’t part of the posterior shoulder space’s lateral edge. The greater tubercle and the head of the humerus are features on the humeral proximal end, but they do not define the lateral border of the quadrangular space.