What are the manifestations of osteoarthritis (OA) on knee echography?

Ultrasound Manifestations of Knee Osteoarthritis

Knee ultrasound in osteoarthritis detects cartilage thinning/lesions, osteophytes, joint effusion, synovial proliferation, loose bodies, and Baker's cysts, though it is not recommended as a comprehensive screening examination. 1

Primary Ultrasound-Detectable Features

Cartilage Changes

• Cartilage thinning and cartilage lesions are directly visualizable on ultrasound examination of the knee 1
• The suprapatellar transverse scan in maximal flexion allows visualization of femoral articular cartilage 1

Bony Abnormalities

• Osteophytes appear as bony protrusions at joint margins and represent a cardinal feature of osteoarthritis on ultrasound 1
• Irregular bone surface and changes in bone profile are detectable 1
• Erosions may be identified, though these are more characteristic of inflammatory arthropathies 1

Soft Tissue Findings

• Joint effusion can be detected even in small amounts, particularly in the suprapatellar pouch using longitudinal and transverse scans with quadriceps muscle tightening 1
• Synovial proliferation may be present, though distinguishing between effusion and synovitis can be challenging without Doppler or contrast 1
• Baker's cysts (popliteal cysts) appear as comma-shaped fluid collections between the medial gastrocnemius head and semimembranosus tendon on posterior transverse scans 1
• Cyst rupture is readily identified by ultrasound and may clinically mimic deep vein thrombosis 1

Additional Pathology

• Loose joint bodies can be detected in the suprapatellar pouch, infrapatellar region, and popliteal areas, though failure to detect them does not exclude their presence 1
• Calcifications within periarticular tissues may be visualized 1

Clinical Utility and Limitations

Appropriate Indications

• Ultrasound is most appropriate for confirming suspected effusion and guiding aspiration rather than serving as a comprehensive diagnostic examination 1
• US demonstrates accuracy comparable to MRI for diagnosing popliteal cysts and detecting cyst rupture 1
• Evaluation of medial plicae and following iliotibial band syndrome are additional appropriate uses 1

Key Limitations

• Ultrasound is not useful as a screening test or comprehensive examination for knee osteoarthritis 1
• The modality cannot adequately assess subchondral bone marrow lesions, which correlate with pain in osteoarthritis 1
• Deep intra-articular structures may be difficult to visualize completely 1

Comparison with Other Imaging Modalities

When Radiography is Preferred

• Plain radiography should be used before other modalities and remains the gold standard for morphological assessment, showing joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts 1, 2
• Weightbearing and patellofemoral views are specifically recommended for optimal detection of knee OA features 1

When MRI is Superior

• MRI better detects cartilage abnormalities, bone marrow lesions, and early structural changes before radiographic manifestations appear 1, 3
• Bone marrow lesions and synovitis/effusion on MRI correlate with pain origin in osteoarthritis patients 1

Practical Scanning Technique

Standard Scanning Positions

• Suprapatellar longitudinal and transverse scans in neutral position with pressure on the suprapatellar and parapatellar pouches 1
• Suprapatellar transverse scan in maximal flexion for cartilage visualization 1
• Posterior transverse scan for popliteal region assessment 1

Common Pitfalls

• Very small effusions or early synovitic proliferations missed on clinical examination can often be demonstrated by ultrasound, but the operator must use appropriate technique with quadriceps tightening 1
• Failure to examine the popliteal region may miss Baker's cysts, which frequently communicate with the joint space 1
• The inability to detect a loose body on ultrasound never rules out its presence elsewhere in the joint 1