**Core Concept**
The quadrangular space, also known as the quadrilateral space, is an anatomical region in the shoulder that provides a pathway for the axillary nerve and the posterior circumflex humeral artery. It is bounded by several muscles and bones.

**Why the Correct Answer is Right**
The quadrangular space is formed by the teres minor muscle, the teres major muscle, the long head of the triceps brachii muscle, and the surgical neck of the humerus. The border of the quadrangular space is critical for the passage of the axillary nerve and the posterior circumflex humeral artery, which can be compromised in cases of shoulder trauma or surgery.

**Why Each Wrong Option is Incorrect**
**Option A:** Teres minor muscle is one of the correct borders of the quadrangular space.
**Option B:** Teres major muscle is also a correct border of the quadrangular space.
**Option C:** Long head of the triceps brachii muscle is a correct border of the quadrangular space.
**Option D:** Supraspinatus tendon is not a border of the quadrangular space; it is actually a tendon of the supraspinatus muscle that forms the roof of the subacromial bursa.

**Clinical Pearl / High-Yield Fact**
The quadrangular space is an important landmark for shoulder surgeons and anatomists, as it provides a critical pathway for the axillary nerve and the posterior circumflex humeral artery.

**Correct Answer: D. Supraspinatus tendon.**