What is the appropriate management for a patient presenting with a swollen and painful knee?

Management of Swollen Painful Knee

Begin with plain radiographs (anteroposterior, lateral, sunrise/Merchant, and tunnel views) and perform arthrocentesis with synovial fluid analysis immediately to exclude septic arthritis, crystal arthropathy, and fracture before initiating any treatment. 1, 2

Initial Diagnostic Workup

Mandatory First Steps

• Obtain four-view plain radiographs as the essential first imaging study to exclude fracture, osteoarthritis, osteochondritis dissecans, loose bodies, chondrocalcinosis, or tumor. 1, 3, 2

• Perform arthrocentesis with synovial fluid analysis to differentiate infectious arthritis, crystal-induced arthropathy (gout, CPPD), and inflammatory conditions—this is essential before any treatment decisions, particularly before administering corticosteroids. 2

• Assess for posterior knee swelling or palpable mass, and if present, obtain compression ultrasound of the proximal deep veins immediately to rule out popliteal vein thrombosis, which requires urgent anticoagulation. 3, 2

Critical Physical Examination Findings

• Document weight-bearing ability by having the patient take at least 4 steps, as inability to bear weight influences management decisions. 1

• Assess range of motion, specifically whether the patient can flex the knee to at least 90 degrees. 1

• Palpate for joint effusion, as it may indicate inflammatory processes, structural damage, or infection requiring immediate arthrocentesis. 1, 2

• Evaluate for signs of inflammation including warmth and erythema, which warrant immediate arthrocentesis to exclude septic arthritis before any corticosteroid administration. 2

Treatment Algorithm Based on Diagnosis

For Osteoarthritis with Effusion

• Initiate acetaminophen up to 4g/day as the first-line oral analgesic due to its safer profile for long-term use compared to NSAIDs. 4, 1

• Begin exercise therapy immediately, including regular progressive strengthening exercises directed at quadriceps and exercises to preserve normal knee mobility. 4, 1, 2

• Provide patient education explaining the nature of the condition and pain management strategies, addressing pain beliefs and behaviors that may affect recovery. 1

• Recommend weight reduction if the patient is obese, as it addresses a key risk factor for knee osteoarthritis. 1, 2

• Consider topical NSAIDs or capsaicin as second-line pharmacological options if acetaminophen is ineffective, due to their clinical efficacy and excellent safety profiles. 1

• Use oral NSAIDs with gastroprotection in patients unresponsive to acetaminophen, particularly if gastrointestinal risk factors exist. 4, 1, 2

• Administer intra-articular corticosteroid injection specifically for pain flares accompanied by effusion, but only after infection has been excluded by synovial fluid analysis. 4, 1, 2

For Crystal Arthropathy (CPPD Disease)

• Prescribe low-dose colchicine or NSAIDs combined with gastro-protective agents as first-line treatments for calcium pyrophosphate deposition disease with chronic inflammatory arthritis. 3, 2

For Suspected Septic Arthritis

• Never administer intra-articular corticosteroids before excluding infection—this can worsen septic arthritis and lead to joint destruction. 3

• In children with painful swollen knee, the likelihood of septic arthritis is >90% when both "age <5 years" and "CRP >2.0 mg/dl" are present, though in the absence of these factors, the risk remains over 15%, making aspiration the best next step. 5

Advanced Imaging Indications

When to Order MRI

• Reserve MRI for persistent symptoms despite 4-6 weeks of adequate conservative treatment with normal or non-diagnostic radiographs. 1, 2

• Order MRI when surgery is being considered, or when evaluating meniscal pathology, cartilage lesions, or bone marrow edema. 1

• Never perform MRI before plain radiographs—approximately 20% of patients with chronic knee pain inappropriately undergo MRI without recent radiographs. 3, 2

• If radiographs show only joint effusion or are normal, and ultrasound confirms Baker's cyst without DVT, MRI without and with IV contrast is the next appropriate study to evaluate for meniscal tears, articular cartilage damage, synovitis, or other intra-articular pathology. 3

Critical Pitfalls to Avoid

• Never delay compression ultrasound when posterior knee swelling is present—popliteal DVT requires immediate anticoagulation to prevent fatal pulmonary embolism. 3

• Do not withhold anticoagulation for confirmed popliteal DVT—the risk of fatal PE far outweighs bleeding risks. 3

• Avoid administering corticosteroids before arthrocentesis—septic arthritis must be excluded first to prevent catastrophic joint destruction. 3, 2

Surgical Referral Indications

• Consider joint replacement for refractory pain associated with disability and radiological deterioration after exhausting conservative options. 4

• Refer for surgery when there is radiographic evidence of osteoarthritis with refractory pain and disability despite conservative treatment, or when specific mechanical pathology is identified. 1

• For severe traumatic meniscal tears (eg, bucket-handle tears with displaced meniscal tissue), surgery is likely required, whereas degenerative meniscal tears should be managed conservatively with exercise therapy as first-line treatment. 6

Reassessment Timeline

• Reassess at 6 weeks if no favorable outcomes are observed, and consider MRI if not yet obtained and symptoms persist. 1