## Core Concept
The articular cartilage undergoes significant changes with aging, affecting its structure and function. These changes include alterations in the composition and organization of the cartilage matrix, leading to reduced cartilage thickness and integrity. The aging process impacts the chondrocytes' ability to maintain and repair the cartilage.

## Why the Correct Answer is Right
The correct statement regarding the effect of aging on articular cartilage involves understanding that aging leads to decreased water content, reduced proteoglycan synthesis, and an increase in cartilage degradation. This results in a loss of cartilage elasticity and resilience, making it more susceptible to injury. The changes in articular cartilage with aging are a key factor in the development of osteoarthritis.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, aging leads to a decrease in the thickness and an increase in the fibrillation of articular cartilage. If option A states that aging increases articular cartilage thickness, it would be incorrect because the opposite occurs.
- **Option B:** If option B mentions that aging leads to an increase in proteoglycan synthesis in articular cartilage, it would be incorrect because aging actually results in decreased proteoglycan synthesis.
- **Option C:** Without specific details on option C, a general assumption can be made that if it inaccurately describes a known effect of aging on articular cartilage (such as increased degradation, decreased water content, or reduced chondrocyte function), it would be considered incorrect based on the established understanding of cartilage aging.
- **Option D:** Similarly, if option D inaccurately represents a change associated with aging articular cartilage, it would be deemed incorrect.

## Clinical Pearl / High-Yield Fact
A key clinical pearl related to the aging of articular cartilage is that **osteoarthritis**, a condition closely associated with aging cartilage changes, often presents with joint pain and stiffness, particularly after periods of rest. Early recognition and management can help mitigate symptoms and slow disease progression.

## Correct Answer: D.