**Core Concept**
Psoriatic arthritis (PsA) is a chronic inflammatory condition that primarily affects the joints, characterized by the presence of psoriasis. It is a type of spondyloarthritis that involves the axial skeleton, peripheral joints, and entheses. The pathophysiology of PsA involves an interplay between genetic predisposition, immune dysregulation, and environmental triggers.

**Why the Correct Answer is Right**
PsA is classically associated with the involvement of the distal interphalangeal (DIP) joints. This is due to the characteristic "pencil-in-cup" deformity, which is a hallmark radiographic feature of PsA. The involvement of the DIP joints is thought to be related to the abnormal activation of osteoclasts and osteoblasts, leading to bone resorption and new bone formation. This process is mediated by various inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interleukin-17 (IL-17).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because PsA can also involve the proximal interphalangeal (PIP) joints, but the DIP joints are more characteristic.
**Option B:** This option is incorrect because rheumatoid arthritis (RA) typically involves the PIP and metacarpophalangeal (MCP) joints, with a predilection for the MCP joints.
**Option C:** This option is incorrect because osteoarthritis (OA) primarily affects the weight-bearing joints, such as the knees and hips, and is not associated with the characteristic "pencil-in-cup" deformity of PsA.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that PsA can present with a wide range of clinical manifestations, including skin lesions, joint inflammation, enthesitis, and axial involvement. A thorough physical examination and radiographic evaluation are necessary to diagnose PsA accurately.

**Correct Answer:** C.