Imaging of Musculoskeletal Disorders Rheumatoid arthritis
Key features
Erosions
Synovitis/pannus
Deformity
Symmetrical pattern
Rheumatoid arthritis manifests as a symmetrical arthritis, most commonly affecting the hands. If the pattern of disease is not symmetrical, then a different diagnosis should be considered.
In early rheumatoid there may be no changes visible on an X-ray. Ultrasound can be used to look for erosions, synovitis, and tenosynovitis.
In rheumatoid arthritis the synovium of a joint proliferates and becomes thickened. This synovial proliferation is also known as pannus. Increased blood flow seen on Doppler Ultrasound indicates active inflammation.
Large erosions have formed at the margins of the thumb metacarpophalangeal joint
The marginal erosions seen in rheumatoid arthritis differ from the sub-cortical cysts seen in osteoarthritis which are located deep to the articular surfaces of joints
As the disease progresses further the joints become unstable and sublux (partially dislocate). ‘Ulnar deviation’ is a characteristic feature of rheumatoid arthritis in the hands; this is the phenomenon of subluxation of the proximal phalanges at the metacarpophalangeal joints with deviation of the fingers towards the ulnar side.
The joint spaces of the wrist are narrowed and there is severe erosion of the carpal bones
At the metacarpophalangeal joints the tendons of the hand pull the subluxed fingers towards the ulnar side – this correlates with the clinical sign of ulnar deviation
Rheumatoid arthritis may also affect the large joints of the body such as the hip, knee, and shoulder.
Large peri-articular erosions have formed around the humeral head
Erosion of the distal clavicle – a classic feature of advanced rheumatoid arthritis affecting the shoulder – causes widening of the acromioclavicular joint (asterisk)
The acetabulum is eroded such that the femoral head (red line) encroaches medial to the inner rim of the pelvis (green line) – compare to the normal position of the right femoral head (white line)
‘Protrusio acetabuli’ – protrusion of the femoral head medially through the acetabulum – is a classic feature of advanced rheumatoid arthritis affecting the hip
Rheumatoid arthritis can result in erosion of the odontoid peg in the cervical spine
The odontoid peg becomes more pointed than normal due to erosion resulting in a ‘candy-licked’ appearance
These lateral images of the cervical spine taken with the neck in flexion and extension show a large gap forming between the odontoid peg and the anterior arch of the atlas on flexion
This gap indicates that the stabilising ligaments of the anterior atlanto-axial joint are no longer intact
