**Core Concept**
The spread of infection in the hand is influenced by the anatomic arrangement of the palmar fascia and the compartments of the hand. The thenar and hypothenar eminences are separated by the mid-palmar space, which is a potential pathway for infection spread.

**Why the Correct Answer is Right**
The thenar space, located on the radial (thumb) side of the hand, is a common site for the spread of infection from the index finger. This occurs due to the direct communication between the thenar space and the palmar fascia surrounding the index finger. The palmar fascia, a fibrous structure, provides a conduit for the spread of infection between the compartments of the hand. In the case of sepsis of the index finger, the infection can track along the palmar fascia and spread to the thenar space.

**Why Each Wrong Option is Incorrect**
**Option B:** The mid-palmar space is a potential pathway for infection spread, but it is not the most direct route for sepsis of the index finger to spread. The mid-palmar space is more commonly involved in infections of the middle finger.
**Option C:** The hypothenar space, located on the ulnar (little finger) side of the hand, is not directly connected to the palmar fascia surrounding the index finger, making it a less likely site for the spread of infection.
**Option D:** While all the options listed are potential pathways for infection spread, the thenar space is the most direct and common site for the spread of sepsis from the index finger.

**Clinical Pearl / High-Yield Fact**
In the context of hand infections, it is essential to remember that the anatomy of the hand is divided into several compartments, each with its own potential pathways for infection spread. Understanding these anatomic relationships is crucial for diagnosing and managing hand infections effectively.

✓ Correct Answer: A. Thenar