**Core Concept**
The interphalangeal joints of the fingers and toes are synovial joints that allow for flexion and extension movements. The joint capsule is a fibrous structure that surrounds the joint, providing stability and support. However, there are variations in the joint capsule across different joints.

**Why the Correct Answer is Right**
The interphalangeal joint of the thumb (1st carpometacarpal joint) is a saddle joint, allowing for opposition movements of the thumb. However, the interphalangeal joints of the fingers, except for the DIP joint, have an absent or reduced capsule. This is due to the need for greater mobility in these joints, particularly in the proximal interphalangeal joints (PIP), which allow for flexion and extension movements. The absence of the capsule in these joints is compensated by the presence of strong ligaments, such as the collateral ligaments, which provide stability.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as the joint capsule is not absent in the PIP joint.
* **Option B:** This option is incorrect as the joint capsule is not absent in the DIP joint, although it is reduced.
* **Option C:** This option is incorrect as the joint capsule is not absent in the metacarpophalangeal joint.

**Clinical Pearl / High-Yield Fact**
The absence of the joint capsule in the interphalangeal joints of the fingers, except for the DIP joint, is a key anatomical feature that allows for greater mobility in these joints. This is particularly important in the PIP joints, which require a wide range of motion for flexion and extension movements.

**Correct Answer:** D