Where is the inflammation typically located in a patient with gout in the knees?

Location of Inflammation in Knee Gout

In gout affecting the knee, inflammation is located within the synovial membrane (synovitis), the joint space where monosodium urate crystals deposit, and can extend to surrounding periarticular structures including bursae, with crystal deposits visible throughout the articular surfaces, menisci, ligaments, and synovial tissue. 1

Primary Sites of Inflammation

Intra-articular Involvement

• The synovial membrane develops marked inflammatory reaction in response to monosodium urate crystal deposition, which directly stimulates the inflammasome in leukocytes causing acute inflammatory attacks 1
• Crystal deposits accumulate throughout the articular cartilage surfaces, partially covering the synovial tissue, anterior cruciate ligament, and menisci 2
• The joint space itself becomes the primary site where MSU crystals precipitate and trigger the inflammatory cascade 3
• Synovial fluid analysis from inflamed knees reveals MSU crystals in approximately 70% of patients even during asymptomatic intercritical periods 1

Periarticular and Soft Tissue Involvement

• MSU crystals aggregate in extra-articular regions including tendons, bursae (particularly prepatellar and infrapatellar), bone, and other soft tissues to form tophi 1
• Bursal inflammation due to gout (especially prepatellar or olecranon bursa) follows comparable inflammatory patterns to joint involvement 1
• Monosodium urate crystals accumulate in joints and other tissues, creating inflammatory responses wherever they deposit 4

Characteristic Inflammatory Features

Clinical Presentation

• Inflammation presents with joint swelling, pain, and overlying erythema that reaches maximum intensity within 6-12 hours 4
• The knee demonstrates synovial hypertrophy with increased blood flow detectable on color Doppler ultrasonography 1
• Chronic inflammation can lead to chondropathy (cartilage damage) of the medial and lateral femoral condyles 2

Structural Changes

• Cortical erosions develop at sites of persistent crystal deposition and inflammation 1
• The inflammatory process causes ulceration of joint cartilage, marginal osteophytosis, geodic and erosive lesions defining chronic urate joint disease 5
• Permanent tissue damage results from chronic synovial membrane inflammation 5

Diagnostic Imaging Findings

Ultrasound Detection

• Double contour sign (hyperechoic enhancement over articular cartilage) indicates MSU crystal deposition on the cartilage surface with 74% sensitivity and 88% specificity 1
• Tophi appear as hyperechoic masses with a "wet clumps of sugar" appearance, detected with 65% sensitivity and 80% specificity 4
• Intra-articular microtophi and echogenic synovial hypertrophy are characteristic findings 1

Advanced Imaging

• Dual-energy CT demonstrates MSU crystal deposits throughout the knee with 85-100% sensitivity and 83-92% specificity, providing color-coded visualization 1, 4
• MRI with gadolinium shows synovial hypertrophy, soft tissue abnormalities, and increased fluid signal in bone marrow subjacent to inflammatory sites 1

Critical Clinical Pitfall

Even when MSU crystals are confirmed, septic arthritis must be excluded through Gram stain and culture, as gout and infection can coexist in the same joint with potentially devastating consequences including joint destruction, amputation, and death 1, 4. The discriminative value of synovial fluid culture between septic arthritis and gout shows 76% sensitivity and 96% specificity 1.