How does osteoarthritis (OA) of the metacarpophalangeal (MCP) joint appear on X-ray?

Radiographic Features of Osteoarthritis in the MCP Joint

Osteoarthritis of the metacarpophalangeal (MCP) joint is less common than in other hand joints, but when present, it typically demonstrates joint space narrowing, marginal osteophytes, subchondral sclerosis, and occasionally subchondral cysts on X-ray.

Prevalence and Distribution

• MCP joint OA occurs in approximately 32.5% of patients with hand osteoarthritis 1
• More frequently affects the first and second MCP joints 1
• More common in the dominant hand, suggesting mechanical factors play a role 1
• Less common and typically less severe than OA in interphalangeal joints 2

Characteristic Radiographic Features

Primary Features

• Joint space narrowing (JSN)

  • Sensitivity of 0.75-1.0 and specificity of 0.18-0.71 for diagnosing OA 3
  • Likelihood ratio of 1.60 (95% CI 1.29-1.99) 3
  • Typically less severe than in interphalangeal joints 2

• Marginal osteophytes

  • Most sensitive radiographic feature for detecting articular cartilage degeneration 4
  • Likelihood ratio of 1.61 (95% CI 1.12-2.33) 3
  • Size of osteophytes correlates with functional limitations 5

Secondary Features

• Subchondral sclerosis

  • High specificity (100%) but very low sensitivity (4%) 4
  • Significantly related to self-reported pain in hand OA 6

• Subchondral cysts

  • Highly specific (100%) but extremely insensitive (0%) 4
  • Rarely seen in isolation without other radiographic features 4

Differential Diagnosis

The radiographic appearance of MCP joint OA must be distinguished from other conditions that can affect these joints:

• Rheumatoid arthritis - primarily targets MCPJs and PIPJs with non-proliferative marginal erosions 2
• Psoriatic arthritis - may affect just one ray or target DIPJs 2
• Gout - can superimpose on pre-existing OA with periarticular erosions 2
• Hemochromatosis - mainly targets MCPJs and wrists 2

Clinical Correlation

• Radiographic findings may not correlate well with pain or functional limitations 5
• The presence of subchondral sclerosis has been shown to have an independent influence on pain compared to other radiographic features 6
• Risk factors for MCP joint OA include older age, manual occupation, and scaphotrapezial OA 1

Imaging Recommendations

• Standard posteroanterior radiograph of both hands on a single film is adequate for initial assessment 3
• Multiple views (posteroanterior, oblique, lateral, semisupinated) improve erosion identification 2
• When radiographs are equivocal, advanced imaging such as MRI or ultrasound may be considered to assess soft tissue involvement 2

Pitfalls and Caveats

• Radiographic findings alone have limitations in diagnosing OA; clinical correlation is essential
• Joint space narrowing, subchondral sclerosis, and subchondral cysts rarely occur without associated osteophyte formation 4
• The Kellgren-Lawrence classification system may not adequately categorize all radiographic presentations of hand OA 6
• Experience improves reliability of radiographic assessment, with experienced readers achieving better consistency 3