**Core Concept**
Osteoarthritis (OA) is a degenerative joint disease characterized by progressive wear and tear of articular cartilage, leading to joint pain, stiffness, and limited mobility. It involves an interplay of mechanical, biochemical, and inflammatory factors that contribute to cartilage degradation and joint damage.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of osteoarthritis, which involves the breakdown of articular cartilage due to the imbalance between the production and degradation of cartilage matrix components. This process is influenced by various factors, including mechanical stress, inflammation, and biochemical changes. The breakdown of cartilage leads to the exposure of underlying bone, which can cause pain and further joint damage.

**Why Each Wrong Option is Incorrect**
**Option A:** Wear and tear of articular cartilage is a hallmark of osteoarthritis, making this option correct and not the answer we're looking for.
**Option B:** Inflammation is a key component of osteoarthritis, contributing to joint pain and damage, so this option is also incorrect.
**Option C:** Joint instability and mechanical stress are risk factors for osteoarthritis, as they can lead to increased wear and tear on the joint, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
Osteoarthritis is a leading cause of disability worldwide, affecting millions of people. It is characterized by a gradual loss of joint function and mobility, making early diagnosis and treatment crucial to prevent further joint damage and improve quality of life.

**Correct Answer: D.**