**Core Concept**
Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by inflammation of the synovial joints, leading to progressive joint destruction and disability. The key features of RA involve the synovial membrane, cartilage, and underlying bone.

**Why the Correct Answer is Right**
Osteosclerosis, which refers to an abnormal hardening or thickening of bone, is not typically seen in rheumatoid arthritis. In contrast, RA is associated with osteoporosis of the periarticular bone, particularly in the early stages, due to the inflammatory process and increased bone resorption. This is because the inflammatory cytokines and enzymes released in RA lead to the activation of osteoclasts, which break down bone tissue, resulting in bone loss and osteoporosis.

**Why Each Wrong Option is Incorrect**
**Option B:** Soft tissue swelling is indeed a characteristic feature of RA, as the inflammation of the synovial membrane leads to an accumulation of fluid and proliferation of synovial tissue, resulting in joint swelling.
**Option C:** Narrowing of joint space is also a hallmark of RA, as the inflammation and destruction of cartilage and bone lead to a reduction in joint space and eventual joint deformity.
**Option D:** Periarticular osteoporosis is a common feature of RA, as mentioned earlier, and is due to the inflammatory process and increased bone resorption.

**Clinical Pearl / High-Yield Fact**
In rheumatoid arthritis, the inflammation of the synovial membrane can lead to the formation of a pannus, a layer of granulation tissue that invades the joint space and contributes to cartilage and bone destruction. This is a critical factor in the progression of RA and is a target for therapeutic intervention.

**✓ Correct Answer: A. Osteosclerosis of joint**