**Core Concept**
Long flexor tendons are fibrous cords that connect the flexor muscles to their respective bones, enabling finger and wrist movement. They play a crucial role in flexion, rotation, and stabilization of the hand. Long flexor tendons, particularly those in the hand, are prone to injury and conditions like flexor tenosynovitis.

**Why the Correct Answer is Right**
Long flexor tendons are indeed surrounded by a synovial sheath, which contains synovial fluid that reduces friction between the tendon and its surrounding tissues. This synovial sheath is essential for maintaining tendon health and preventing conditions like tenosynovitis. The long flexor tendons also have a specific anatomical arrangement, where they pass through a fibro-osseous tunnel, the flexor tendon sheath, which provides additional support and protection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a characteristic of long flexor tendons.
**Option B:** This option is incorrect as it does not accurately describe the anatomy of long flexor tendons.
**Option C:** This option is incorrect as it does not provide a true statement about long flexor tendons.

**Clinical Pearl / High-Yield Fact**
Long flexor tendons are prone to conditions like flexor tenosynovitis, which can be caused by repetitive strain, trauma, or infection. Early recognition and treatment of these conditions are essential to prevent long-term damage and disability.

**Correct Answer: D.