Rheumatoid and inflammatory arthritis

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Intermediate

Inflammatory arthritides are driven by inflamed synovium (the joint lining) or by inflammation where tendons and ligaments attach to bone (entheses). On X-ray they share some features that set them apart from osteoarthritis, particularly erosions and uniform joint space loss, but each has its own distribution and texture. Rheumatoid arthritis (RA) is the classic synovial disease; psoriatic arthritis, ankylosing spondylitis and related conditions form the seronegative spondyloarthropathies, which add new bone formation and spine involvement. Early disease often has a normal X-ray, so imaging supports, but does not make, the diagnosis.

1. An approach to arthritis films

Work through the same five headings every time:

• Alignment: subluxations and deformities (for example ulnar deviation).
• Bone density: reduced around the joint (periarticular osteopenia) in RA; usually preserved in psoriatic arthritis, gout and OA.
• Cartilage: joint space narrowing, which is uniform in inflammatory disease and focal in OA; erosions and their position (marginal, central, juxta-articular).
• Distribution: which joints, symmetric or asymmetric, hands or feet, large joints, spine and sacroiliac joints.
• Soft tissues: swelling (fusiform around a joint, or a whole "sausage" digit), calcification, nodules.

Compare with osteoarthritis and gout and crystal arthritis as you go.

2. Rheumatoid arthritis

Signs, roughly in order of appearance

• Soft-tissue swelling around the joints, symmetrical and fusiform.
• Periarticular osteopenia: the bone next to the joint is less dense than the shaft.
• Marginal erosions at the "bare areas", the parts of the joint inside the capsule that are not covered by cartilage, where inflamed synovium touches bone directly.
• Symmetrical, uniform (concentric) joint space loss.
• No osteophytes, unless secondary OA develops later.
• Late deformities: ulnar deviation and subluxation at the MCP joints, swan-neck and boutonnière deformities, the "Z-thumb", and fusion (ankylosis) of the carpus.

Distribution

• Hands: MCP and PIP joints and the wrist, including the carpus and the ulnar styloid. The DIP joints are usually spared.
• Feet: the MTP joints, especially the fifth MTP, which is often the earliest site of erosion. Request foot films when assessing suspected RA.
• Large joints: concentric narrowing; at the hip this leads to axial migration and sometimes protrusio acetabuli.

3. RA and the cervical spine

RA can erode the ligaments that hold the dens (odontoid peg) against the front of C1, leading to atlanto-axial subluxation.

• Measure the predental (atlanto-dental) interval on the lateral view: the gap between the back of the anterior arch of C1 and the front of the dens. In adults it is normally 3 mm or less.
• Instability may only show on a flexion view. Flexion and extension views should only be done when clinically appropriate and under supervision; in a patient with neurological symptoms, MRI is the test.
• Instability matters before anaesthesia and intubation, when neck manipulation can compress the cord. Follow local pre-operative assessment protocols.
• Other patterns are vertical settling of the dens (basilar invagination) and subaxial subluxations ("staircase" alignment).

See also the cervical spine X-ray.

4. Psoriatic and reactive arthritis

Psoriatic arthritis

• DIP joint involvement, often asymmetric, sometimes along a single ray.
• Erosions with new bone formation: fluffy periosteal reaction and "whiskering" next to erosions. This mix of destruction and proliferation is characteristic.
• Pencil-in-cup deformity: one bone end whittled to a point inside a cupped neighbour.
• Dactylitis ("sausage digit"): diffuse swelling of a whole finger or toe.
• Acro-osteolysis (resorption of the terminal tufts) and the ivory phalanx (a dense distal phalanx).
• Bone density usually preserved.
• Severe disease: arthritis mutilans, with telescoping digits.
• Spine and sacroiliac joints: asymmetric sacroiliitis and bulky, asymmetric, non-marginal syndesmophytes.

Reactive arthritis

Mainly the lower limbs, especially the feet and heels, with fluffy new bone at entheses such as the plantar fascia insertion, and asymmetric sacroiliitis. Enteropathic arthritis (with inflammatory bowel disease) tends to cause symmetrical sacroiliitis, like ankylosing spondylitis.

5. Ankylosing spondylitis and axial spondyloarthritis

Sacroiliac joints

• Bilateral and symmetrical sacroiliitis.
• Sequence: erosions on the iliac side first, causing apparent widening ("pseudo-widening"), then sclerosis, then fusion (ankylosis).
• The modified New York criteria grade sacroiliitis on X-ray from 0 to 4.
• Early disease can be invisible on X-ray. MRI shows active inflammation (bone marrow oedema) in non-radiographic axial spondyloarthritis (ASAS criteria).

Spine

• Romanus lesions ("shiny corners"): sclerosis at the corners of the vertebral bodies.
• Squaring of the vertebral bodies.
• Thin, vertical, marginal syndesmophytes bridging the vertebrae, eventually forming a bamboo spine.
• The dagger sign (a central line of ossified interspinous and supraspinous ligaments) and the trolley-track sign (three parallel lines from that ligament and the ossified facet joint capsules).

6. Side-by-side comparison

Feature	RA	Psoriatic	OA	Gout
Bone density	Periarticular osteopenia	Preserved	Preserved or sclerotic	Preserved
Joint space	Uniform loss	Variable; may widen with erosion	Focal loss	Preserved until late
Erosions	Marginal, no new bone	Marginal with fluffy new bone	None (central in erosive OA)	Punched-out with overhanging edges
Typical hand joints	MCP, PIP, wrist	DIP, asymmetric	DIP, PIP, 1st CMC	Any; 1st MTP in the foot
Symmetry	Symmetrical	Asymmetric	Variable	Asymmetric

7. Pitfalls and mimics

• DISH (diffuse idiopathic skeletal hyperostosis) mimics ankylosing spondylitis. It produces flowing ossification along the anterolateral aspect of at least four contiguous vertebral bodies, typically on the right of the thoracic spine, with preserved disc heights and normal sacroiliac joints (Resnick criteria). AS syndesmophytes are thin and marginal, and AS involves the SI joints.
• A normal X-ray does not exclude early inflammatory arthritis. Ultrasound and MRI detect synovitis and early erosions; clinical assessment and serology drive referral.
• Erosive OA mimics psoriatic arthritis in the DIP joints; look for central erosions with osteophytes ("gull-wing") rather than marginal erosions with periostitis.
• Secondary OA in long-standing RA adds osteophytes, which can confuse the pattern.
• Septic arthritis can complicate RA, particularly with immunosuppression. A single joint that flares out of step with the others needs aspiration.
• Hyperparathyroidism causes subperiosteal resorption that can mimic erosions (see metabolic bone disease).

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	RA signs and distribution, the difference from OA, pencil-in-cup and bamboo spine.
Nurse / practitioner	Neck precautions and anaesthetic alerts in RA; spinal immobilisation for any fall in a patient with AS.
Junior doctor	Request hands and feet for suspected RA, know that early films can be normal, and image the AS spine with CT after trauma.
Radiographer	Standard hand and foot series with good detail for erosions; careful handling of the rigid spine in AS.
Advanced / FRCR	Distribution analysis, DISH versus AS, subtle sacroiliitis and RA cervical instability patterns.

Practise on bone and joint X-rays →

References

1. Radiopaedia. Rheumatoid arthritis. radiopaedia.org
2. Radiopaedia. Ankylosing spondylitis. radiopaedia.org
3. Radiology Masterclass. Arthritis gallery. radiologymasterclass.co.uk
4. van der Linden S, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis: a proposal for modification of the New York criteria. Arthritis Rheum 1984;27(4):361–368.
5. Resnick D, Niwayama G. Radiographic and pathologic features of spinal involvement in diffuse idiopathic skeletal hyperostosis (DISH). Radiology 1976;119(3):559–568.
6. National Institute for Health and Care Excellence. Rheumatoid arthritis in adults: management (NG100). nice.org.uk

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