What is the appropriate management for a patient presenting with right knee pain, considering potential underlying causes and the need for a thorough medical evaluation?

Management of Right Knee Pain

Start with plain radiographs of the knee (anteroposterior, lateral, and tangential patellar views) as the initial imaging study for chronic knee pain, and proceed to MRI only if radiographs are normal or show effusion but pain persists despite conservative treatment. 1

Initial Clinical Evaluation

Critical first step: Rule out referred pain sources before focusing solely on the knee:

• Examine the hip if knee radiographs are unremarkable, as hip pathology commonly refers pain to the knee 1, 2
• Assess the lumbar spine for radicular symptoms or spinal pathology that may manifest as knee pain 1, 2
• Look for red flags requiring urgent referral: severe pain with inability to bear weight after acute trauma, fever with joint swelling/erythema/limited range of motion suggesting septic arthritis, or severe instability 3

Age-Specific Diagnostic Considerations

Pattern recognition by demographics improves diagnostic accuracy:

• Teenage girls and young women (<40 years): Consider patellofemoral pain syndrome (91% sensitive with anterior pain during squatting) or patellar subluxation 4, 5
• Teenage boys and young men: Evaluate for tibial apophysitis (Osgood-Schlatter) or patellar tendonitis 4
• Adults ≥45 years: Osteoarthritis is most likely if activity-related pain with <30 minutes morning stiffness (95% sensitivity, 69% specificity) 5
• Middle-aged to elderly females: Consider subchondral insufficiency fractures of medial femoral condyle, which are often initially normal on radiographs 1, 2

Imaging Algorithm

Follow this stepwise approach to avoid premature or unnecessary imaging:

Initial Imaging

• Obtain knee radiographs (anteroposterior/Rosenberg/tunnel view, tangential patellar view, lateral view) for chronic pain >6 weeks or acute trauma meeting evidence-based criteria 1, 6
• Avoid MRI without recent radiographs (within past year), as approximately 20% of chronic knee pain patients undergo premature MRI 1, 2

If Radiographs Are Normal or Show Effusion

• Proceed to MRI without IV contrast if pain persists, as it is more sensitive for detecting effusions, synovitis, popliteal cysts, subchondral cysts, articular cartilage abnormalities, and meniscal tears 1
• Important caveat: Meniscal tears are often incidental in patients >70 years (majority have asymptomatic tears), and likelihood of tears in painful vs. asymptomatic knees is similar in ages 45-55 1

If Radiographs Show Specific Findings

• For osteochondritis dissecans or loose bodies: Consider CT without contrast or MRI to evaluate fragment stability and guide treatment 1
• For patellofemoral subluxation/maltracking: CT or MRI can measure tibial tubercle-trochlear groove distance and trochlear morphology 1

Alternative Imaging Modalities

• Ultrasound is useful for detecting synovial pathology, effusions, Baker cysts, and meniscal extrusion 1, 6
• CT arthrography can substitute for MRI when evaluating menisci and articular cartilage if MRI is contraindicated 1

MRI Findings That Correlate With Pain

Not all MRI abnormalities cause symptoms—focus on these pain-associated findings:

• Bone marrow lesions (BML): New or increasing BMLs correlate with increased knee pain, especially in males or those with family history of osteoarthritis; decreasing BMLs correlate with reduced pain 1
• Synovitis/effusion: Systematic reviews confirm these indicate pain origin in osteoarthritis patients 1
• Subchondral insufficiency fractures: Appear as bone marrow edema on MRI before radiographic changes develop; may progress to articular collapse requiring arthroplasty 1, 2

Conservative Management Principles

First-line treatment for most knee pain conditions emphasizes non-surgical approaches:

• For osteoarthritis: Exercise therapy, weight loss if overweight, education, and self-management programs are first-line; reserve joint replacement for end-stage disease after exhausting conservative options 5
• For patellofemoral pain: Hip and knee strengthening exercises combined with foot orthoses or patellar taping; surgery is not indicated 5
• For meniscal tears: Exercise therapy for 4-6 weeks is first-line, even with mechanical symptoms (locking/catching); surgery only for severe traumatic bucket-handle tears with displaced tissue 5

Interventional Options

Consider joint aspiration and injection when appropriate:

• Aspiration indications: Perform US- or fluoroscopy-guided aspiration if effusion present with concern for crystal disease or infection 1
• Corticosteroid injection: Can reduce synovitis on MRI in two-thirds of patients for 1-2 weeks; inject deeply into gluteal muscle for systemic effect (40-80 mg range) or intra-articularly (2.5-15 mg depending on joint size) 7
• Injection technique: Ensure strict aseptic technique, avoid blood vessels, inject into tendon sheath (not substance) for tenosynovitis, and aspirate excessive synovial fluid before intra-articular injection 7

Critical Pitfalls to Avoid

• Do not overlook referred pain from hip or lumbar spine before attributing all symptoms to knee pathology 2, 8
• Do not rush to MRI before obtaining recent radiographs and completing thorough clinical examination 2, 8
• Do not assume all meniscal tears are symptomatic, particularly in patients >45 years where tears are common incidentally 1, 2
• Do not miss subchondral insufficiency fractures in middle-aged/elderly females with medial knee pain and initially normal radiographs 1, 2
• Do not interpret bilateral structural abnormalities on imaging as necessarily explaining unilateral symptoms, especially in patients >70 years 1