**Core Concept:** Gout is a common form of inflammatory arthritis caused by the buildup of uric acid crystals in the joints, leading to pain, inflammation, and swelling. Tophi are urate crystal deposits that can form outside the joints, often in soft tissues.

**Why the Correct Answer is Right:** Tophi in gout are primarily found in areas with soft tissue, such as the synovial membrane (lining of joints), joint capsule (enclosing joint space), and articular cartilage (surface of joint). The correct answer is excluded because tophi are not typically found in the skin or muscles.

**Why Each Wrong Option is Incorrect:**

A. Joint capsule: Tophi can form within the joint capsule, so this is incorrect.
B. Skin: While tophi can involve the skin, the correct answer excludes this option because tophi are also found in other regions.
C. Muscle: Tophi can infiltrate muscles, but excluding this option is based on the fact that tophi are more commonly seen in other regions as well.
D. Articular cartilage: Tophi in gout can affect articular cartilage, making this option incorrect as well.

**Clinical Pearl:** Tophi in gout may present as hard, subcutaneous nodules, and their presence indicates a chronic, untreated gout condition. Early diagnosis and management are crucial to prevent joint damage and long-term complications.

**Correct Answer:** D. Articular cartilage (synovial membrane, joint capsule, and muscles are correct options)