Rheumatoid arthritis (musculoskeletal manifestations)

Rheumatoid arthritis (RA) is a chronic multi-system disease with predominant musculoskeletal manifestations. Being a disease that primarily attacks synovial tissues, RA affects synovial joints, tendons, and bursae.

Refer to the related articles for a general discussion of rheumatoid arthritis and for the particular discussion of its respiratory manifestations.

Radiographic features

Regarding disease detection, as the early RA manifestations are non-osseous in nature, ultrasound and MRI have shown to be superior to radiographs and CT. Plain radiography, however, remains the mainstay of imaging in the diagnosis and follow-up of RA .

Plain radiograph

One large cohort study showed that radiographically demonstrable erosions were present in 30% of patients at diagnosis, and in 70% three years later .

The radiographic hallmarks of rheumatoid arthritis are:

  • erosions; important early finding, in the “bare areas”, frequently in the radial side of the metacarpophalangeal (MCP) joints
  • soft tissue swelling
    • fusiform and periarticular; it represents a combination of joint effusion, edema and tenosynovitis 
    • this can be an early/only radiographic finding
  • osteoporosis: initially juxta-articular, and later generalized; compounded by corticosteroid therapy and disuse
  • joint space narrowing: symmetrical or concentric
Hands and wrists

Diagnosis and follow-up of patients with RA commonly involve imaging of the hands and wrists. The disease tends to affect the proximal joints in a bilaterally symmetrical distribution.

RA is a synovial based process, with a predilection for:

  • PIP and MCP joints (especially 2 and 3 MCP)
  • ulnar styloid
  • triquetrum

As a rule, the DIP joints are spared.

Late changes include:

  • joint effusion (elevated fat pads) 
  • joint space narrowing
  • periarticular erosions 
  • cystic changes
  • similar to the hands, there is a predilection for the PIP and MTP joints (especially 4and 5 MTP)
  • involvement of subtalar joint
  • posterior calcaneal tubercle erosion
  • hammertoe deformity
  • hallux valgus
  • concentric loss of joint space, compared with osteoarthritis (OA) where there is a tendency for superior loss of joint space
  • acetabular protrusio
  • joint effusion
  • typically involves the lateral or non-weight bearing portion of the joint
  • loss of joint space involving all three compartments
  • lack of subchondral sclerosis and osteophytes, compared with OA
  • prepatellar bursitis

The cervical spine is frequently involved in RA (in approximately 50% of patients), whereas thoracic and lumbar involvement is rare. Findings include:

  • erosion of the dens
  • atlantoaxial subluxation
    • atlantoaxial distance is more than 3 mm on a flexion radiograph
  • atlantoaxial impaction (cranial settling): cephalad migration of C2
  • erosion and fusion of uncovertebral (apophyseal joints ) and facet joints
  • osteoporosis and osteoporotic fractures
  • erosion of spinous processes

Sonography can assess the soft tissue manifestations of RA. In particular:

  • synovial proliferation and inflammation of the superficial joints
  • tenosynovitis: extensor carpi ulnaris tendon involvement is common in early disease and may lead to erosion of the ulnar styloid
  • bursitis

Ultrasound also has a role in guiding corticosteroid injections in this setting.


CT is not routinely used in the evaluation of peripheral RA. It has applications in imaging of the spine, and peri-operative assessment .


MRI is particularly sensitive to the early and subtle features of RA.

Commonly used sequences include T1-weighted contrast-enhanced spin-echo with fat saturation and T2-weighted spin-echo or gradient-echo sequences .

Features of RA best demonstrated with MRI include :

  • synovial hyperemia: an indication of acute inflammation
  • synovial hyperplasia (rice bodies)
  • pannus formation
  • decreased thickness of cartilage
  • subchondral cysts and erosions:
    • MRI is much more sensitive than radiography
    • it is thought that subchondral cysts in RA eventually progress to erosions (i.e. constitute "pre-erosions")
    • contrast enhancement may distinguish erosions or pre-erosions from degenerative subchondral cysts
  • juxta-articular bone marrow edema
  • joint effusions

Differential diagnosis

The differential for the skeletal manifestations of RA includes:

  • degenerative osteoarthritis
    • involves the: DIPs, PIPs, 1CMC joints
    • non-uniform joint space loss, subchondral sclerosis, and osteophytes
    • soft tissue swelling: Heberden node (DIPs) and Bouchard node (PIPs)
    • no erosions and no ankylosis
  • erosive osteoarthritis
    • clinically acute inflammatory attacks (swelling, erythema, pain) in postmenopausal women
    • typically involves the DIPs, PIPs, 1CMC joint , but not MCP joints or large joints
    • classic central erosions, possible ankylosis
  • psoriatic arthritis (PsA)
    • commonly involves the hands and there is an interphalangeal predominant distribution in PsA compared to MCP joint predominance in rheumatoid arthritis (RA)
    • starts with erosions in the margins and eventually involves the
      whole joint, the classic changes being the pencil-in-cup deformity and bone proliferation (unlike RA)
    • osteoporosis not a feature in PsA
    • MRI dynamic enhancement pattern may differentiate PsA from RA at 15 minutes
  • reactive arthritis (Reiter syndrome)
    • a predilection for the lower limb
    • osteopenia and then osteoporosis, uniform joint space loss, subchondral cyst formation, subluxations, marginal erosions but no bone formation
    • symmetrical involvement of the: PIPs, MCPs, and carpal bones
  • systemic lupus erythematosus (SLE)/Jaccoud arthropathy
    • joint space loss, subchondral sclerosis, osteophyte, and ulnar deviation of the phalanges without erosions
  • calcium pyrophosphate dihydrate (CPPD) arthropathy
    • usually only affects the MCPs: symmetric joint space narrowing, subchondral cysts, and osteophytes
    • unlike RA: chondrocalcinosis and no erosions 
  • gout
    • usually in older men
    • punched out erosions usually with a sclerotic border and overhanging edges, tophi most commonly involves the 1 MTP (which is known as podagra)

Site-specific differential diagnosis: