Radiographic patterns of large joints
Conventional radiography often does not correlate with pain intensity, but reliably demonstrates structural changes.
Knee joint: Extremely common. The main sign is asymmetrical narrowing of the joint space. The most typical pattern consists of narrowing of the medial compartment, which eventually leads to varus deformity (varus deformity). Involvement of the lateral or patellofemoral compartments is significantly less common. For adequate assessment of the knee joint, it is critically important to obtain weight-bearing (standing) radiographs.
Hip joint: Joint space narrowing is also asymmetrical. The superior aspect is most frequently affected, causing the femoral head to migrate superiorly. As progression occurs, subchondral cysts, sclerosis, and flattening of the femoral head appear. Atypical signs include the formation of a central osteophyte (displacing the femur laterally, making the joint space falsely appear preserved). A specific appearance is the bone hypertrophy of the femoral neck — buttressing (buttressing), manifested by thickening of the medial cortical layer.
Involvement of the hands, feet, and spine
In hand osteoarthritis, involvement is usually asymmetrical. The disease affects the interphalangeal joints with the formation of hard nodules (due to synovial hypertrophy or osteophytes): Heberden's nodes form on the distal joints, and Bouchard's nodes on the proximal ones. The metacarpophalangeal joints remain intact. In the wrist, the base of the thumb is frequently affected.
Degenerative changes of the spine are localized predominantly in the cervical and lower lumbar regions. The following abnormalities are detected:
- Discs: loss of height and the "vacuum phenomenon".
- Vertebrae: large anterior osteophytes, endplate sclerosis.
- Facet joints: bone hypertrophy. Together with ligamentum flavum thickening, this can cause spinal canal stenosis.
- Degenerative spondylolisthesis (anterior displacement of a vertebra due to disc and ligament degeneration) may occur.
Erosive osteoarthritis
Erosive (inflammatory) osteoarthritis is a specific subset of the disease characterized by pronounced destruction. It is more common in women, presents as polyarthritis of the small joints of the hands, and has a less favorable prognosis.
Unlike the classic form, radiographs here reveal central subchondral erosions, forming the characteristic "seagull wing" sign (seagull wing). Marginal erosions are rare. Furthermore, the erosive form can exhibit reparative processes leading to bony ankylosis, which is completely atypical for non-erosive osteoarthritis.
Role of ultrasound, MRI, and differential diagnosis
The modern concept views osteoarthritis as a disease of the entire joint, including ligaments, menisci, and periarticular tendons. Ultrasound and MRI allow visualization of what is hidden on radiographs:
- Synovitis: easily visualized on ultrasound (anechoic effusion) and MRI. It frequently acts as a predictor of pain.
- Subchondral bone: MRI excellently demonstrates cysts and a specific signal — bone marrow involvement (bone marrow lesion), previously erroneously referred to as true edema.
It is important to distinguish osteoarthritis from rheumatoid arthritis (RA). Unlike osteoarthritis, RA causes symmetrical polyarthritis with panarticular (diffuse) joint space narrowing. In RA, the distal interphalangeal joints are spared, and the main marker is marginal bone erosions (up to the "dotted line" sign of the cortical layer).
Briefly: answers to topical questions
What radiographic stages of osteoarthritis are distinguished according to the Kellgren-Lawrence classification?
According to the Kellgren and Lawrence (Kellgren-Lawrence) classification cited in the sources, stages I, II, III, and IV are identified.
- Stages I–II — early stages, for which conservative treatment is primarily indicated.
- Stages III–IV — later stages, for which surgical treatment is indicated; conservative treatment may be continued concurrently with surgery, or used when surgery is impossible or refused by the patient.
- In early stages, surgical treatment is possible if conservative therapy is ineffective and pain is severe and intractable.
What ultrasound features are characteristic of osteoarthritis?
Ultrasound in osteoarthritis may reveal signs of involvement in various joint components, although ultrasound cannot assess changes within the subchondral bone.
Characteristic ultrasound findings:
- Synovitis — easily detected on ultrasound; in knee OA, it can bulge around the medial meniscus and displace the medial collateral ligament.
- Joint effusion — for example, anechoic effusion can distend the suprapatellar pouch.
- Osteophytes — visualized on ultrasound; in the wrist joint, ultrasound is more sensitive for their detection compared to standard radiography.
- Ligamentous changes — belong to findings that can be identified by additional imaging modalities in OA.
What hyaline cartilage changes are detected in early stages of osteoarthritis by MRI?
According to MRI data in cartilage degeneration within the patellofemoral compartment, which frequently occurs in the setting of osteoarthritis, the following stages of cartilage damage are described:
- MR signal alteration — early injury.
- Surface irregularity.
- Partial loss of cartilage thickness.
- Full-thickness defect.
Subsequent stress loading on the subchondral bone can lead to bone marrow edema and the formation of subchondral cysts.
To remember hand nodules: Closer — Bouchard's (proximal joints), Deeper/distal — Heberden's (distal joints).
Class and exam questions
Why is axial loading necessary during knee radiography?
On non-weight-bearing (supine) images, joint spaces may appear normal. Weight-bearing views, especially with semi-flexion (30°), reliably reveal hidden compartment narrowing.
What is the difference between degenerative spondylolisthesis and spondylolysis?
In degenerative spondylolisthesis, the vertebra shifts forward entirely, narrowing the spinal canal. In true spondylolisthesis due to a pars defect, posterior elements remain in place, and the central canal is not deformed.
How does erosive osteoarthritis differ from rheumatoid arthritis on hand imaging?
In erosive osteoarthritis, distal joints are affected with the formation of central erosions ("seagull wing"). In RA, distal joints are spared, and erosions are marginal in nature.
What else to study on this topic
- Radiography of the patellofemoral joint in an axial projection (Skyline)
- Ultrasound diagnostics of synovitis and suprapatellar pouch effusion
- Specific hand deformations in rheumatoid arthritis (swan neck, boutonnière)
- Differential diagnosis of subchondral bone lesions on MRI
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