What is the cause of acute plantar fascia and bilateral knee pain in a patient with a 1-day history of symptoms?

Acute Plantar Fascia and Bilateral Knee Pain: Diagnostic Approach

The most likely diagnosis in a patient with acute onset (1-day history) of plantar fascia and bilateral knee pain is acute polyarticular gout or pseudogout, requiring immediate joint aspiration for synovial fluid crystal analysis to confirm the diagnosis and exclude septic arthritis. 1

Primary Diagnostic Considerations

Crystal Arthropathy (Most Likely)

• Acute gout classically presents with sudden onset pain, often beginning at night, and while typically monoarticular, can occur as polyarticular gout affecting multiple joints simultaneously, particularly in older patients 1
• The bilateral knee presentation with concurrent plantar fascia involvement suggests polyarticular crystal deposition disease 1
• Pseudogout (calcium pyrophosphate deposition disease) presents identically to gout with acute onset pain and requires synovial fluid analysis to differentiate, as both can affect the patellofemoral joint and other lower extremity joints 1
• Joint aspiration with synovial fluid analysis for crystal identification (monosodium urate for gout, calcium pyrophosphate for pseudogout), cell count, Gram stain, and culture is mandatory to confirm diagnosis and exclude infection 1

Septic Arthritis (Must Exclude)

• Bilateral simultaneous septic arthritis is rare but possible in immunocompromised patients and must be excluded in any acute oligoarticular arthritis 1
• The absence of fever or leukocytosis should not dissuade consideration of infection 2
• Synovial fluid white blood cell count >50,000 cells/μL with >90% neutrophils suggests septic arthritis 1

Initial Diagnostic Workup

Immediate Laboratory Studies

• Complete blood count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) to assess for infection or inflammatory arthritis 1
• Serum uric acid level (though normal levels do not exclude acute gout) 1
• Basic metabolic panel to assess renal function before NSAID use 1

Imaging Protocol

For bilateral knees:

• Obtain standing anteroposterior, lateral, tunnel, and tangential patellar radiographs bilaterally as initial imaging to exclude fracture, loose bodies, and identify chondrocalcinosis (which appears as linear calcification in cartilage, suggesting pseudogout) 2, 1
• Radiographs should be performed before any advanced imaging 3
• Chondrocalcinosis may be visible on radiographs in pseudogout, though absence does not exclude the diagnosis 1

For plantar fascia:

• Plain radiographs of the heel are not typically needed for acute plantar fasciitis diagnosis, which is primarily clinical 4, 5
• However, given the acute bilateral presentation with knee involvement, heel radiographs may help identify calcifications or other pathology 2

Ultrasound Assessment

• Assess for joint effusion clinically and with ultrasound if available 1, 3
• Ultrasound can detect synovial pathology, effusions, and demonstrate increased synovial blood flow associated with acute inflammation 3
• If effusion is present, perform arthrocentesis immediately for crystal analysis 1

Critical Differential Diagnoses to Consider

Reactive Arthritis

• Can present with acute oligoarticular arthritis affecting lower extremities 6
• History of recent gastrointestinal or genitourinary infection should be elicited 6

Subchondral Insufficiency Fracture

• Most commonly affects the medial femoral condyle in middle-aged to elderly females 1
• Bilateral simultaneous presentation would be extremely rare 1
• Radiographs are often initially normal; MRI without contrast is indicated if radiographs are normal but symptoms persist to evaluate for subchondral insufficiency fracture or bone marrow lesions 1, 3

Plantar Fasciitis Association

• Recent research demonstrates that plantar fasciitis is frequent in knee osteoarthritis patients (62% prevalence), with reduced ankle dorsiflexion being the main risk factor 7
• However, true plantar fasciitis typically presents with gradual onset pain, worst with first steps in the morning, not acute 1-day onset 4, 5
• The acute presentation makes isolated plantar fasciitis unlikely 4, 5

When Advanced Imaging is Indicated

• MRI without contrast should be obtained if radiographs are normal but symptoms persist after initial treatment, to evaluate for occult fracture, bone marrow edema, meniscal pathology, or cartilage lesions 1, 3
• MRI is not routinely used as initial imaging for acute knee trauma 2

Critical Pitfalls to Avoid

• Do not delay joint aspiration if effusion is present – this is the definitive diagnostic test and must be performed to exclude septic arthritis 1
• Hip pathology must be excluded when knee radiographs are unremarkable, as hip joint pathology (such as avascular necrosis or inflammatory arthritis) can refer pain to the knee 3
• Lumbar spine pathology can refer pain to the knee and foot, and should be considered if radiculopathy patterns are present 3
• NSAIDs should be used cautiously in elderly patients and avoided if renal insufficiency is present 1
• Do not assume bilateral presentation excludes infection – immunocompromised patients can develop bilateral septic arthritis 1

Treatment Algorithm Pending Diagnosis

If Crystal Arthropathy Confirmed

• NSAIDs (if no contraindications) or colchicine for acute gout 1
• Corticosteroid injection or systemic corticosteroids if NSAIDs contraindicated 1
• Avoid initiating urate-lowering therapy during acute attack 1

If Septic Arthritis Confirmed

• Urgent surgical consultation for drainage is required 2
• Empiric intravenous antibiotics should be started immediately after cultures obtained 2

Supportive Measures

• Rest and activity modification 4, 5
• Ice application to affected joints 4, 5
• Acetaminophen up to 4g/day in adults as first-line oral analgesic 3