Rheumatoid arthritis (musculoskeletal manifestations)

Rheumatoid arthritis (RA) is a chronic multisystem disease with predominant musculoskeletal manifestations. It is a disease that primarily affects synovial tissues, i.e. 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 and/or cardiac manifestations.

Radiographic features

Regarding disease detection, as the early rheumatoid arthritis manifestations are non-osseous in nature, ultrasound and MRI have been shown to be superior to radiographs and CT. Plain radiography, however, remains the mainstay of imaging in the diagnosis and follow-up of rheumatoid arthritis ². 

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 ⁴.

The radiographic hallmarks of rheumatoid arthritis are:

• marginal erosions; important early finding, in the “bare areas”, frequently in the radial side of the metacarpophalangeal (MCP) joints ⁷

• soft tissue swelling

  • fusiform and periarticular; it represents a combination of joint effusion, edema and tenosynovitis ⁵

  • 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, uniform

Hands and wrists

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

Rheumatoid arthritis is a synovial-based process, with a predilection for the:

• proximal interphalangeal and metacarpophalangeal joints (especially those of the index and middle fingers)

• ulnar styloid

• triquetrum

As a rule, the distal interphalangeal joints are spared.

Late changes include:

• subchondral cyst formation: the destruction of cartilage presses synovial fluid into the bone

• subluxation causing:

  • ulnar deviation of the metacarpophalangeal joints

  • boutonniere and swan neck deformities

• hitchhiker’s thumb deformity

• carpal instability: scapholunate dissociation, ulnar translocation

• ankylosis

• scallop sign: erosion of the ulnar aspect of the distal radius which may be predictive of extensor tendon rupture (Vaughan-Jackson syndrome)

• pencil-in-cup deformity: classically psoriatic arthropathy but well-recognized in rheumatoid arthritis

Elbow

• joint effusion (elevated fat pads) 

• joint space narrowing

• periarticular erosions 

• cystic changes

Feet

• similar to the hands, there is a predilection for the proximal interphalangeal and metatarsophalangeal joints (especially of the fourth and fifth toes)

• subtalar joint involvement

• posterior calcaneal tubercle erosion

• hammer toe deformity

• hallux valgus

Shoulder

• erosion of the distal clavicle

• marginal erosions of the humeral head: the superolateral aspect is a typical location ²

• reduction in the acromiohumeral distance: "high-riding shoulder" due to subacromial-subdeltoid bursitis and high incidence of rotator cuff tear

Hip

• concentric loss of joint space, compared with osteoarthritis (OA) where there is a tendency for superior loss of joint space

• acetabular protrusion

Knee

• 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 osteoarthritis

• prepatellar bursitis

Spine

The cervical spine is frequently involved in rheumatoid arthritis (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

Ultrasound

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

• synovial proliferation and inflammation of the superficial joints, which is often evident before bone changes are visible on radiographs

• tenosynovitis: extensor carpi ulnaris tendon involvement is common in early disease and may lead to erosion of the ulnar styloid ²

• bursitis

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

CT

CT is not routinely used in the evaluation of peripheral rheumatoid arthritis. It has applications in imaging of the spine, and peri-operative assessment ².

MRI

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

Commonly used sequences include T1-weighted contrast-enhanced spin-echo with fat saturation and T2-weighted spin-echo or gradient-echo sequences ².

Features of rheumatoid arthritis best demonstrated with MRI include ²:

• 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 rheumatoid arthritis 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 rheumatoid arthritis includes:

• degenerative osteoarthritis

  • involves the proximal and distal interphalangeal joints, and the thumb carpometacarpal joint

  • non-uniform joint space loss, subchondral sclerosis, and osteophytes

  • soft tissue swelling: Heberden nodes at distal interphalangeal joints, and Bouchard nodes at proximal interphalangeal joints

  • no erosions and no ankylosis

• erosive osteoarthritis

  • clinically acute inflammatory attacks (swelling, erythema, pain) in postmenopausal women

  • typically involves the proximal and distal interphalangeal joints and the thumb carpometacarpal joint ⁶, but not metacarpophalangeal joints or large joints

  • classic central erosions, possible ankylosis

• psoriatic arthritis (PsA)

  • commonly involves the hands and there is an interphalangeal predominant distribution in psoriatic arthritis compared to metacarpophalangeal joint predominance in rheumatoid arthritis

  • 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 rheumatoid arthritis)

  • osteoporosis not a feature in psoriatic arthritis

  • MRI dynamic enhancement pattern may differentiate psoriatic arthritis from rheumatoid arthritis at 15 minutes

• reactive arthritis

  • 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 metacarpophalangeal and proximal interphalangeal joints 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 metacarpophalangeal joints: symmetric joint space narrowing, subchondral cysts, and osteophytes

  • unlike rheumatoid arthritis: 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 metatarsophalangeal joint of the hallux (which is known as podagra)

Site-specific differential diagnosis: 

• distal clavicular erosion

• erosion of the odontoid process