What is the medial border of the Quadrilateral Space?

• A. Teres Major
• B. Humeral Shaft
• C. Long Head of Triceps
• D. Deltoid Muscle

Answer: (C)

The medial border of the quadrilateral space is identified by the long head of the triceps muscle. The quadrilateral space is an anatomical region located in the posterior shoulder area, bordered by important structures that facilitate the passage of nerves and blood vessels.

The significance of the long head of the triceps lies in its anatomical position; it runs along the medial aspect of the space, marking its boundary. This detail is critical when considering the neurovascular contents that traverse this region—specifically, the axillary nerve and the posterior circumflex humeral artery, which are vital for shoulder function and stability.

Recognizing the positioning of surrounding structures, like the teres major, humeral shaft, and deltoid muscle, is important for a comprehensive understanding, but these do not define the medial border of the quadrilateral space as precisely as the long head of the triceps does. Thus, understanding these anatomical landmarks provides clarity on the relevance of each in relation to the quadrilateral space and its clinical significance.