Rheumatoid Arthritis

For Medical Students

What It Shows

Rheumatoid arthritis is a symmetrical inflammatory arthropathy with uniform synovial involvement and erosion of bone. 5.5.11 covers the synovium.

In the knee it shows uniform synovial thickening, an effusion, erosion at the bare areas and symmetrical cartilage loss. 5.3.17 covers joint space narrowing.

It matters because the diagnosis is made clinically and serologically, so imaging of the knee stages damage rather than identifying disease. 5.1.2 covers clinical examination versus imaging.

How It Is Acquired

Start with radiographs for the joint space, the erosions and the alignment. 5.3.1 covers the AP view.

Add a skyline view, since the patellofemoral joint is involved and is otherwise hidden. 5.3.3 covers the skyline view.

Use magnetic resonance imaging when the question is synovial extent or early erosion. 5.5.11 covers the synovium.

Assess all three compartments, because loss is symmetrical rather than confined. 5.3.17 covers joint space narrowing.

Assess the bone stock, because it decides what any operation can hold. 5.3.19 covers subchondral sclerosis.

What Normal Looks Like

Uniform joint space across all three compartments. 5.3.17 covers joint space narrowing.

No erosion at the bare areas inside the capsule. 5.5.6 covers the bones.

Bone density appropriate to age. 5.3.19 covers subchondral sclerosis.

A thin synovial lining with physiological fluid. 5.5.11 covers the synovium.

What Abnormal Looks Like

Symmetrical joint space loss across the compartments, without the compartment pattern of osteoarthritis. 5.20.6 covers reporting osteoarthritis.

Erosion at the bare areas where synovium meets bone inside the capsule. 5.5.6 covers the bones.

Uniform synovial thickening rather than nodular. 5.14.1 covers synovitis.

Reduced bone density around the joint. 5.3.19 covers subchondral sclerosis.

Absent or minimal osteophyte, which separates this from osteoarthritis. 5.3.18 covers osteophytes.

MRCS Level

How It Is Acquired

In a viva the expected answer separates this from osteoarthritis on pattern.

The expected points are the radiographs, the skyline view, the symmetrical loss, the erosions, and the bone stock.

Say that the pattern rather than the severity makes the distinction. 5.20.6 covers reporting osteoarthritis.

Say that the absence of osteophyte is as informative as the erosion. 5.3.18 covers osteophytes.

Say that the imaging stages damage and does not make the diagnosis. 5.1.2 covers clinical examination versus imaging.

What Abnormal Looks Like

The reasoning expected is that the disease acts through the synovium, so it damages every surface the synovium touches, which produces symmetry where a mechanical disease produces a compartment pattern. 5.5.11 covers the synovium.

Erosion happens where bone inside the capsule is not covered by cartilage, which is why the bare areas are the sites to look at. 5.5.6 covers the bones.

Reduced bone density belongs to the disease and its treatment together, and it determines what fixation or implant will hold. 5.17.8 covers the total knee replacement.

Effective treatment has changed the appearance, so the florid textbook knee is becoming a historical picture. 5.1.7 covers evidence-based imaging.

How Good It Is

Radiography is the best available record of the damage and magnetic resonance imaging the best available measure of the synovium, and neither diagnoses the disease.

Its best contribution is the compartment pattern, the erosions and the bone stock, which is what a surgical decision needs. 5.3.17 covers joint space narrowing.

It is limited because the appearance overlaps other inflammatory arthropathies and because treatment alters it. 5.14.3 covers psoriatic arthritis.

No figures appear for accuracy on this page, under decision 028, and no erosion scores or joint space measurements appear either: those are published quantities from particular scoring systems and this environment cannot check them.

FRCS Level

How Good It Is

At decision level the imaging answers whether a replacement is needed and what it will have to cope with. 5.17.8 covers the total knee replacement.

Bone stock, deformity and soft tissue quality are the three answers wanted, and the films carry two of them. 5.3.19 covers subchondral sclerosis.

Symmetrical loss removes a partial replacement from the options. 5.3.17 covers joint space narrowing.

The cervical spine and the other joints belong in the plan rather than in the history, and neither is knee imaging. 5.1.3 covers choosing the correct investigation.

Active synovitis on a scan is a rheumatological finding before it is a surgical one. 5.14.1 covers synovitis.

Where It Misleads

The commonest error is reading symmetrical loss as advanced osteoarthritis. 5.20.6 covers reporting osteoarthritis.

Erosion is read as a cyst. 5.5.6 covers the bones.

Synovial thickening is read as disease activity when it may be treated residue. 5.14.1 covers synovitis.

Reduced bone density is read as a technical factor on the radiograph. 5.3.19 covers subchondral sclerosis.

A superimposed infection is missed because the knee was expected to be inflamed. 5.14.7 covers septic arthritis.

Fellowship Level

Where It Misleads

At fellowship level these knees come with long histories, altered appearances and several previous operations. 5.20.7 covers reporting the post-operative knee.

The imaging describes a joint shaped by decades of treatment, so a textbook comparison is the wrong reference. 5.1.7 covers evidence-based imaging.

Bone stock is the finding that decides the operation and the hardest to judge from a scan near metal. 5.17.9 covers the revision arthroplasty.

A painful knee in this population carries a higher prior probability of infection, and imaging does not settle it. 5.14.7 covers septic arthritis.

Serial radiographs in a consistent projection remain the best record of progression. 5.3.1 covers the AP view.

The useful report gives the compartment pattern, the erosions, the bone stock, the alignment and the soft tissue, and leaves disease activity to the clinician. 5.20.1 covers structured reporting.