**Core Concept**
The patient's presentation of inflamed and painful joints, along with the presence of needle-shaped, negatively birefringent crystals, is indicative of a crystal-induced arthritis. This condition is characterized by the deposition of specific crystals within the joint space, leading to an inflammatory response.

**Why the Correct Answer is Right**
The presence of needle-shaped, negatively birefringent crystals is a hallmark of monosodium urate (MSU) crystals, which are commonly found in patients with gout. The pathophysiology of gout involves the deposition of MSU crystals within the joint space, leading to an intense inflammatory response. The negatively birefringent properties of MSU crystals are due to their unique crystal structure, which is composed of sodium urate molecules arranged in a hexagonal lattice.

**Why Each Wrong Option is Incorrect**
**Option A:** Calcium pyrophosphate dihydrate (CPPD) crystals are also found in joint fluid, but they are typically rhomboid or rod-shaped and have a positive birefringence. CPPD crystals are associated with pseudogout, a different type of crystal-induced arthritis.
**Option B:** Hydroxyapatite crystals are found in certain bone disorders, but they are not typically associated with joint inflammation or the presence of needle-shaped, negatively birefringent crystals.
**Option C:** Calcium oxalate crystals are found in kidney stones, but they are not typically associated with joint inflammation or the presence of needle-shaped, negatively birefringent crystals.

**Clinical Pearl / High-Yield Fact**
The presence of tophi ( deposits of MSU crystals) in the external ear, as seen in this patient, is a classic sign of chronic gout. Tophi can also be found in other areas of the body, including the hands and feet.

**Correct Answer:** C. Monosodium urate crystals.