**Core Concept**
Osteoarthritis (OA) is a degenerative joint disease characterized by progressive loss of articular cartilage, leading to joint pain, stiffness, and limited mobility. The pathophysiology of OA involves a combination of mechanical, biochemical, and genetic factors that contribute to cartilage degradation and joint damage.

**Why the Correct Answer is Right**
Osteoarthritis is associated with various factors, including age-related wear and tear, joint trauma, obesity, and genetic predisposition. The joint cartilage is composed of chondrocytes, collagen fibers, and proteoglycans, which work together to provide mechanical support and cushioning. In OA, the cartilage matrix is degraded by enzymes such as matrix metalloproteinases (MMPs) and aggrecanases, leading to cartilage breakdown and joint damage. The subchondral bone also undergoes changes, including sclerosis and cyst formation.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because OA is indeed associated with age-related wear and tear, making it a common condition in older adults.
**Option B:** This is incorrect because joint trauma, such as a fracture or ligament sprain, can lead to OA by causing cartilage damage and joint instability.
**Option C:** This is incorrect because obesity is a risk factor for OA, particularly in weight-bearing joints such as the knee and hip.

**Clinical Pearl / High-Yield Fact**
OA is the most common type of arthritis, affecting over 30 million adults in the United States alone. It is a leading cause of disability and reduces quality of life, making early diagnosis and treatment crucial for managing symptoms and slowing disease progression.

**Correct Answer:** D