**Core Concept**
Dactylitis refers to the inflammation of an entire digit, often seen in conditions like psoriatic arthritis, reactive arthritis, and sickle cell disease. It is characterized by swelling of the entire toe or finger due to inflammation of the soft tissues and bone.

**Why the Correct Answer is Right**
Dactylitis is typically seen in conditions that affect the entire digit, such as psoriatic arthritis and sickle cell disease. These conditions lead to inflammation of the soft tissues and bone, causing swelling of the entire toe or finger. In contrast, conditions that primarily affect the joints or bones, such as osteoarthritis, are less likely to cause dactylitis.

**Why Each Wrong Option is Incorrect**
**Option A:** Conditions like psoriatic arthritis often cause dactylitis due to inflammation of the soft tissues and bone.
**Option C:** Sickle cell disease can cause dactylitis due to the sickling of red blood cells within the small blood vessels of the affected digit.

**Clinical Pearl / High-Yield Fact**
Dactylitis is a characteristic feature of psoriatic arthritis, and its presence should prompt further investigation for this condition.

**Correct Answer: D. Osteoarthritis.**