**Core Concept**
The 1987 modified American Rheumatism Association (ARA) criteria for rheumatoid arthritis (RA) emphasize the involvement of specific joints to establish the diagnosis. RA typically affects small joints of the hands and feet, as well as larger joints like the knees and elbows. The criteria categorize joint involvement into different groups, including the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints, proximal interphalangeal (PIP) joints, and other larger joints.

**Why the Correct Answer is Right**
The tarsometatarsal joint is not included in the 1987 modified ARA criteria for RA. This is because RA primarily affects smaller joints, such as those in the hands and feet, whereas the tarsometatarsal joint is a larger joint in the foot. The involvement of larger joints like the tarsometatarsal joint is more characteristic of other conditions, such as osteoarthritis or inflammatory arthritis like psoriatic arthritis.

**Why Each Wrong Option is Incorrect**
**Option A:** Knee - The knee joint is indeed involved in RA, and its involvement is one of the criteria for diagnosing the disease.
**Option B:** Ankle - While not specifically listed in the 1987 criteria, ankle joint involvement can occur in RA, particularly in more advanced cases.
**Option D:** Metatarsophalangeal - The MTP joints are actually included in the 1987 modified ARA criteria for RA, as they are a common site of involvement.

**Clinical Pearl / High-Yield Fact**
When considering the diagnosis of RA, remember that the 1987 modified ARA criteria emphasize the involvement of small joints, such as the MCP, PIP, and MTP joints. Involvement of larger joints, like the tarsometatarsal joint, suggests alternative diagnoses.

**✓ Correct Answer: C. Tarsometatarsal.**