General principles of radiographic evaluation
Radiological evaluation of joints requires a systematic approach. When analyzing standard radiographs (CR), the physician sequentially examines a series of baseline parameters. First, the condition of the soft tissues is evaluated, as this is where the earliest signs of pathology (effusion, synovial hypertrophy) may appear. Next, the joint space width is studied in detail, the bone structure is assessed for osteopenia (osteopenia), and the presence of bone defects—erosions—is recorded. It is also important to check the tendon and ligament attachment sites (entheses) and the overall joint alignment (joint alignment).
The final conclusion is based on the distribution of the lesions: the specific joint groups involved provide critical information for the differential diagnosis.
Joint space and soft-tissue changes
Soft-tissue swelling (soft-tissue swelling) can manifest in various ways. In gout, it has an irregular, asymmetric, and "lumpy" appearance. In seronegative arthritides, the swelling can diffusely involve the entire finger, forming the characteristic sign of dactylitis (dactylitis).
Narrowing of the joint space directly indicates cartilage destruction:
- Inflammatory arthritides: narrowing is typically uniform throughout the affected joint.
- Osteoarthritis (OA): narrowing is more often asymmetric (e.g., affecting only the medial compartment of the knee joint).
- Gout and psoriatic arthropathy: a paradoxical situation where, despite pronounced bone destruction, the joint space width remains normal for a long time. Cartilage is destroyed only in late stages.
Bone changes: erosions and enthesitis
The presence of bone erosions (erosion) is a classic marker of an inflammatory process. Their location helps narrow down the differential diagnosis:
- Marginal erosions (marginal): occur at the boundary between the articular cartilage and the capsule. This is a hallmark of rheumatoid arthritis (RA).
- Central erosions: penetrate deep into the bone beneath the articular cartilage. Found in erosive osteoarthritis.
- Juxta-articular erosions: located at a distance from the joint, appearing as "punched-out" lesions with sharp, overhanging margins. Specific to gout.
In rheumatoid arthritis, erosions are usually not accompanied by new bone formation. In contrast, seronegative arthritides are characterized by active bone proliferation around the defects. Involvement of ligament attachment sites (enthesitis) is also typical for this group, accompanied by the growth of coarse bony outgrowths—enthesophytes (enthesophyte).
Damage patterns and differential diagnosis
The topography of hand and foot joint involvement plays a crucial role in the diagnosis of polyarthritides.
| Sign | Rheumatoid arthritis | Seronegative arthritides | Osteoarthritis |
|---|---|---|---|
| Localization | Symmetric, proximal (MCP, wrist) | Distal (interphalangeal joints) | Distal, asymmetric |
| Joint space narrowing | Panarticular, uniform | Often uniform, ankylosis possible | Asymmetric |
| Bone features | Periarticular osteopenia | Bone proliferation, enthesophytes | Osteophytes, subchondral sclerosis |
Systemic lupus erythematosus (SLE) deserves a separate mention. In this condition, tendon dysfunction leads to marked axis deviation (e.g., ulnar deviation of the fingers), but radiographs show no bone erosions or signs of cartilage loss.
Briefly: answers to topical questions
What specific radiological signs are characteristic of psoriatic arthritis?
Psoriatic arthritis is characterized by a set of radiological signs affecting the peripheral joints and the axial skeleton.
The hands and feet reveal:
- Joint space narrowing.
- Cyst-like radiolucencies in the bone tissue.
- Marginal erosions and marginal osteolysis.
- Resorption of the terminal phalanges and mutilating changes—"pencil-in-cup" deformity.
- Bone proliferations—marginal outgrowths that should be distinguished from osteophytes.
- Periosteal reactions.
- Enthesophytes at enthesis attachment sites, especially in the heel region.
- Bony ankylosis.
Sacroiliitis of various stages is detected in the sacroiliac joints; psoriatic spondylitis is characterized by asymmetric involvement of the sacroiliac joints. The spine may reveal marginal syndesmophytes, including "bridging" syndesmophytes, coarse paravertebral ossification, as well as involvement of the zygapophysial joints with joint space narrowing, erosions, and bony ankylosis. Spinal syndesmophytes in PsA are coarser and have a more horizontal orientation.
What radiological stages of rheumatoid arthritis are classified according to Steinbrocker?
The radiological stages of rheumatoid arthritis according to Steinbrocker (modified) include:
- Stage 1 — periarticular osteoporosis.
- Stage 2 — osteoporosis combined with joint space narrowing (single erosions may also be present).
- Stages 3 and 4 — late stages of joint involvement. At these stages, changes may begin to be detected in the distal interphalangeal joints of the hands and the proximal interphalangeal joints of the feet.
For patients with stages 3 and 4, the frequency of radiography is determined strictly by clinical indications, for example, when septic arthritis is suspected or in preparation for surgery.
Which specific hand joints are most frequently affected in osteoarthritis?
Primary osteoarthritis typically involves the interphalangeal joints of the hand, with the damage pattern usually being asymmetric.
The specific joints most commonly affected include:
- Distal interphalangeal joints — dense osteophytes form in this area, known as Heberden nodes (Heberden nodes).
- Proximal interphalangeal joints — Bouchard nodes (Bouchard nodes) form here, located on the lateral surfaces of the joint.
- First carpometacarpal joint of the thumb (thumb carpometacarpal joint) — involvement of the base of the thumb is characteristic.
- Scaphotrapezio-trapezoid joint (scaphotrapezio-trapezoid [STT] joint).
Metacarpophalangeal joints are involved significantly less frequently in osteoarthritis.
For quick memorization of erosion locations: Rheumatoid arthritis — Right by the joint (marginal), Gout — Punchout (punched-out juxta-articular), Seronegative arthritis — Swith bone proliferation.
Class and exam questions
How does joint space narrowing differ between inflammatory arthritis and osteoarthritis?
In inflammatory arthritis, cartilage destruction is diffuse, leading to uniform joint space narrowing. In osteoarthritis, mechanical wear predominates, so the narrowing is asymmetrical and accompanied by marginal osteophytes.
How to distinguish rheumatoid arthritis from systemic lupus erythematosus on a hand radiograph?
Both conditions can cause pronounced deformation (e.g., subluxations). However, in SLE, these deformations occur due to ligamentous dysfunction without bone destruction, so erosions and joint space narrowing are absent.
What is dactylitis on a radiograph?
This is massive, diffuse soft tissue swelling of the entire digit, giving it a "sausage" shape. It is a characteristic radiologic sign of seronegative inflammatory arthritides.
What else to study on this topic
- Formation of enthesophytes and the radiological pattern of entheseal pathology.
- Capabilities of MRI and ultrasound in detecting early synovitis and soft tissue edema.
- Biomechanical and genetic factors in the etiology of osteoarthritis.
- Terminal stages of joint diseases: development of bony ankylosis.
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