**Core Concept**
A diarthrosis, also known as a synovial joint, is a type of joint that allows for a wide range of motion and is characterized by a space between the articulating bones that contains synovial fluid. This fluid reduces friction and allows for smooth movement. Diarthroses are classified into six types based on the shape and structure of the bones and the ligaments surrounding them.

**Why the Correct Answer is Right**
Skull sutures are fibrous joints that connect the bones of the skull together. Unlike diarthroses, they do not have a space between the bones or synovial fluid. Instead, the bones are held together by dense connective tissue that allows for some flexibility, but not the same range of motion as diarthroses. The fibrous joints of the skull provide stability and protection for the brain, while also allowing for some degree of movement and flexibility.

**Why Each Wrong Option is Incorrect**
**Option A:** The elbow joint is an example of a hinge synovial joint, which is a type of diarthrosis. It allows for flexion and extension of the forearm.
**Option B:** Interphalangeal joints are also synovial joints, specifically hinge joints, that connect the phalanges of the fingers and toes. They are a type of diarthrosis.
**Option D:** The hip joint is a ball-and-socket synovial joint, which is another type of diarthrosis. It allows for a wide range of motion in three planes.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the classification of joints into diarthroses, amphiarthroses, and synarthroses is based on the type of joint and its function. Understanding the characteristics of each type of joint is crucial in orthopedic and trauma surgery.

**✓ Correct Answer: C. Skull sutures**