What would an X-ray picture of osteoarthritis typically show in a patient with a history of sacroiliitis, rheumatoid arthritis, avascular necrosis, and impaired renal function, with glucocorticoid exposure?

X-ray Findings in Osteoarthritis

Plain radiographs should be obtained as the first-line imaging modality for suspected osteoarthritis, showing characteristic features of joint space narrowing, subchondral sclerosis, osteophytes, and subchondral cysts—distinctly different from the marginal erosions and periarticular osteopenia seen in rheumatoid arthritis or the erosions with eventual ankylosis seen in inflammatory sacroiliitis. 1

Classic Radiographic Features of Osteoarthritis

The hallmark radiographic findings that distinguish osteoarthritis from inflammatory arthropathies include:

• Joint space narrowing - typically non-uniform, affecting weight-bearing surfaces preferentially 1, 2
• Subchondral sclerosis - increased bone density beneath the articular cartilage, particularly prominent in osteoarthritis compared to the periarticular osteopenia of rheumatoid arthritis 1, 2
• Osteophytes - bony spurs at joint margins, a defining feature of osteoarthritis not seen in inflammatory arthritis 1, 2
• Subchondral cysts - fluid-filled lesions in the subchondral bone 2

Critical Distinctions from Inflammatory Arthropathies

Rheumatoid Arthritis vs. Osteoarthritis

Rheumatoid arthritis demonstrates marginal erosions at joint margins with periarticular osteopenia, contrasting sharply with the subchondral sclerosis and osteophytes characteristic of osteoarthritis 1. In RA, erosions occur at the "bare areas" of joints where synovium directly contacts bone, whereas osteoarthritis shows central joint involvement with productive bone changes 3.

Sacroiliitis vs. Osteoarthritis

Inflammatory sacroiliitis shows erosions, initial joint space widening, and eventual ankylosis—distinctly different from osteoarthritis 1. Plain radiographs have low sensitivity (19-72%) for early inflammatory sacroiliitis, often requiring 7 or more years for radiographic changes to appear 3. In contrast, degenerative changes in the sacroiliac joints show subchondral sclerosis without the bilateral symmetric erosions and ankylosis of inflammatory disease 4, 5.

Special Considerations in Your Patient Context

Impaired Renal Function

Avoid gadolinium-based MRI contrast in patients with impaired renal function due to nephrogenic systemic fibrosis risk 1. If advanced imaging beyond plain radiographs is needed, non-contrast MRI with STIR or T2 fat-saturated sequences is sufficient for detecting inflammation and avascular necrosis 1.

Glucocorticoid Exposure and Avascular Necrosis

In patients with glucocorticoid exposure and avascular necrosis, plain radiographs may show subchondral collapse, crescent sign, or secondary osteoarthritic changes 1. However, early AVN may not be visible on radiographs and would require MRI if clinically suspected.

Distinguishing Degenerative from Inflammatory Sacroiliac Changes

Radiographic changes of the sacroiliac joints in rheumatoid arthritis are mostly degenerative in nature, not differing significantly from osteoarthritis 5. In asymptomatic patients over age 30, asymmetry (77%) and focal joint space narrowing (74%) are common normal variants 4. True inflammatory sacroiliitis indicators include bilateral uniform joint space less than 2mm, erosions, and intraarticular ankylosis 4.

Imaging Algorithm

Start with plain radiographs of the symptomatic joint(s) 1:

• For peripheral joints: standard views showing joint space, subchondral bone, and margins 3
• For sacroiliac joints: anteroposterior pelvis view (oblique views add no diagnostic benefit) 3

If radiographs are negative or equivocal and inflammatory disease is suspected, proceed to MRI without gadolinium given the renal impairment 3, 1. CT can identify subtle erosions and structural changes better than radiographs but cannot detect active inflammation 3.

Common Pitfalls

• Do not mistake age-related degenerative changes for inflammatory disease: nonuniform iliac sclerosis (83% of normal patients) and focal joint space narrowing in patients over 30 (74%) are common normal findings 4
• Do not rely solely on radiographs for early inflammatory disease: structural changes lag clinical symptoms by 7+ years in axial spondyloarthropathy 3
• Do not use gadolinium contrast in renal impairment: non-contrast fluid-sensitive sequences are adequate 1