**Core Concept**
Tom-Smith arthritis, also known as septic arthritis, is a joint infection caused by the direct spread of microorganisms from adjacent infected tissues or via hematogenous spread from a distant site. This condition requires prompt medical attention to prevent joint destruction and long-term sequelae.

**Why the Correct Answer is Right**
Septic arthritis typically results from the invasion of a joint space by pathogenic microorganisms, such as bacteria or fungi. In the case of Tom-Smith arthritis, the infection originates from a contiguous focus, often an osteomyelitis of the adjacent bone. The infection spreads to the joint through direct extension, leading to the characteristic symptoms of septic arthritis, including joint pain, swelling, and reduced mobility. The joint space is then invaded by polymorphonuclear leukocytes, leading to the release of pro-inflammatory cytokines and the subsequent destruction of joint tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the definition of Tom-Smith arthritis.
**Option B:** This option does not accurately describe the pathogenesis of Tom-Smith arthritis.
**Option C:** This option is incorrect as it refers to a different condition altogether.

**Clinical Pearl / High-Yield Fact**
Septic arthritis requires prompt recognition and treatment to prevent permanent joint damage and disability. A high index of suspicion and early imaging studies, such as ultrasound or MRI, are crucial in diagnosing this condition.

**Correct Answer: D.**