Sagittal Fluid Sensitive MR slice showing large synovial popliteal (Baker’s) cyst (above top image) and large synovial effusion (above bottom image)
Note multiple patchy dark signal areas on both images, representing fibrinoid inflammatory depostits aka “rice bodies” a characteristic MRI feature of RA

Conservative management followed by operative care in complicated cases of tendon ruptures and joints dislocations
Supplemental reading:
Diagnosis and Management of Rheumatoid Arthritis – AAFP
https://www.aafp.org/afp/2011/1201/p1245.html

Septic arthritis – d/t bacterial or fungal contamination of the joint. SA may cause rapid joint destruction and requires prompt Dx and antibiotic administration
Joints affected: large joints with rich blood supply (knee 50%>

Initially non-specific ST/joint effusion, obscuration/distortion of fat planes. Because it takes 30% of compact and 50-75% trabecula bone to be destroyed before seen on x-rays, radiography is insensitive to some of the early changes. MR imaging is the preferred modality
If MRI is not available or contraindicated. Bone scintigraphy with Tc-99 MDT can help
In children US preferred to avoid ionizing radiation. In children US can be more sensitive than in adults due to lack of bone maturation

Early findings are unrewarding. Early features may include: joint widening d/t effusion. Soft tissue swelling and obscuration/displacement of fat planes
1-2 weeks: periarticular and adjacent osseous changes manifesting as patchy demineralization, moth-eaten, permeating bone destruction, loss and indistinctness of the epiphyseal “white cortical line” with increase in soft tissue swelling. MRI may be helpful with early Dx.
Late features: complete joint destruction and ankyloses
N.B. Septic arthritis may progress rapidly within days and requires early I.V. antibiotic to prevent major joint destruction

T1 (above left) and T2 fat-sat sagittal knee MRI slices reveal loss of normal marrow signal on T1 and increase on T2 due to septic edema. Bone sequestrum d/t osteomyelitis progressing into septic arthritis is noted. Marked joint effusion with adjacent soft tissue edema are seen. Dx: OSM and septic arthritis

Crystalline arthritis: a group of arthropathies resulting from crystal deposition in and around the joint.
2-m/c: Monosodium urate crystals (MSU) and Calcium Pyrophosphate Dehydrate crystals (CPPD) arthropathy
Gout: MSU deposition in and around joints and soft tissues. Elevated levels of seurm uric acid (UA) (>7mg/dL) causd by overproduction or under-excretion of uric acid
Once UA reached/exceeded 7mg/dL it will deposit in the peripheral tissues. Primary gout: disturbed metabolism of nucleic acids and purines breakdown. Secondary gout: increased cell turnover: Psoriasis, leukemia, multiple myeloma, hemolysis, chemotherapy etc.
Gout presents with 5-characteristic stages:
1)asymptomatic hyperuricemia (years/decades)
acute attacks of gouty arthritis (waxes and wanes and lasts for several years)
Interval phase between attacks
Chronic tophacious gout
Gouty nephropathy

Depends on stages
Acute attacks: acute joint pain “first and the worst” even painful to light touch
DDx: septic joint (both may co-exist) bursitis etc.
Gouty arthritis typically presents as monoarthropathy
Chronic tophacious stage: deposits in joints, ear pinna, ocular structures and other regions. Nephrolithiasis etc. Men>women. Obesity, diet, and age >50-60.
Radiography: early attacks are unremarkable and may present as non-specific joint effusion
Chronic tophacious gout radiography: punched out peri-articular, para-aticular and/or intraosseous erosions with overhanging edges. Characteristic rim of sclerosis and internal calcification, soft tissue tophi. Target sites: lower extremity m/c
Rx: allopurinol, colchicin (esp. preventing acute episodes and maintenance)

Synovial aspiration with polarized microscopy reveal negatively birefringent needle-shaped MSU crystals with large inflammatory PMN presence. DDx: positively birefringent rhomboid-shaped CPPD crystals (above bottom right) seen in Pseudogout and CPPD

Density and joint effusion puched out osseous erosion with overhanging margins, overall perservation of bone density, internal calcifications Dx: chronic tophacious gout

Erosions with overhanging margins, low signal on T1 and high on T2 and fat suppressed images. Peripheral contrast enhancement of tophacious deposits d/t granulation tissue
Dx: final Dx; synovial aspiration and polarized microscopy

Knee Arthritis: Diagnostic Imaging Approaches II | El Paso, TX.