Radiographic Findings in Osteoarthritis of the Knee
The correct answer is (c): Decreased joint space, subchondral sclerosis, bone cysts, and osteophytes—these are the classic radiographic hallmarks of osteoarthritis.
Classic Radiographic Features of Osteoarthritis
The diagnosis of osteoarthritis relies on characteristic X-ray findings that reflect the degenerative process affecting the joint 1. The four cardinal radiographic features are:
- Decreased (narrowed) joint space - This is the most fundamental finding, reflecting cartilage loss
- Subchondral sclerosis - Increased bone density beneath the cartilage
- Bone cysts (subchondral cysts) - Fluid-filled cavities in the bone
- Osteophytes - Bony spurs at joint margins
These findings were explicitly described in multiple AAOS guidelines 2 documenting cases of knee osteoarthritis with "loss of joint space" and "osteophyte formation" as the defining radiographic characteristics.
Why the Other Options Are Incorrect
Options (a) and (b) - Increased joint space: This is anatomically implausible in osteoarthritis. OA is characterized by cartilage degradation, which causes joint space to narrow, not widen. Increased joint space would suggest joint effusion or other pathology, not the structural cartilage loss that defines OA.
Options (b) and (e) - Soft tissue swelling and periarticular osteopenia: These findings are characteristic of inflammatory arthritis (such as rheumatoid arthritis), not osteoarthritis 1. The ACR guidelines emphasize that OA must be differentiated from rheumatoid arthritis, which presents with soft tissue swelling and periarticular osteopenia on radiographs.
Option (d) - Normal X-ray: While early OA can present with normal radiographs 3, this 79-year-old woman has severe nighttime pain—a presentation suggesting advanced disease. Research demonstrates strong correlation between radiographic severity and pain symptoms 4. In symptomatic elderly patients, radiographic changes are typically evident.
Clinical Context
This patient's presentation is typical for osteoarthritis:
- Age 79 (OA prevalence exceeds 10% in those over 60) 5
- Severe nighttime pain (correlates with advanced radiographic disease) 4
- Female sex (women represent 78% of OA diagnoses) 5
The ACR Appropriateness Criteria 3 confirm that radiography is the appropriate initial imaging modality for chronic knee pain, with MRI reserved for cases where radiographs are normal or equivocal but symptoms persist.
Key Diagnostic Pitfall
Do not confuse osteoarthritis with inflammatory arthritis. The presence of subchondral sclerosis, osteophytes, and decreased joint space (without soft tissue swelling or periarticular osteopenia) distinguishes OA from rheumatoid arthritis and other inflammatory conditions 1.