How should I evaluate and manage pain behind my knee?

Evaluation and Management of Pain Behind the Knee

Begin with plain radiographs (anteroposterior, lateral, and tangential patellar views) to exclude fracture, osteoarthritis, and effusion, then proceed to MRI without contrast only if radiographs are normal or show isolated effusion and pain persists despite 4-6 weeks of conservative treatment. 1, 2, 3

Initial Clinical Assessment

Key Historical Features to Elicit

• Age and activity level: Osteoarthritis is most likely in patients ≥45 years with activity-related pain and <30 minutes of morning stiffness (95% sensitivity, 69% specificity), while patellofemoral pain typically affects physically active individuals <40 years with 25% lifetime prevalence 4
• Mechanism of injury: Acute twisting injury in patients <40 years suggests traumatic meniscal tear, whereas degenerative tears occur in patients ≥40 years with concurrent osteoarthritis 4
• Pain location and pattern: Posterior knee pain may indicate Baker cyst, popliteal pathology, or referred pain from hip/lumbar spine 1
• Functional impact: Document inability to work, participate in sports/hobbies, and specific activities that provoke symptoms 5

Physical Examination Maneuvers

• McMurray test: Perform concurrent knee rotation (internal for lateral meniscus, external for medial meniscus) with extension (61% sensitivity, 84% specificity for meniscal tears) 4
• Joint line tenderness: 83% sensitivity and 83% specificity for meniscal tears 4
• Valgus stress testing: Apply at full extension and 30° flexion to evaluate medial collateral ligament integrity 6
• Palpation of posterior structures: Assess for Baker cyst, popliteal masses, and effusion 1
• Hip and lumbar spine examination: Essential if knee radiographs are normal, as referred pain is common 1, 2

Diagnostic Imaging Algorithm

Step 1: Initial Radiographs (Always First)

• Order three-view series: Anteroposterior, lateral, and tangential patellar (skyline) views to evaluate all joint compartments 2, 3
• Avoid the 20% error: Never order MRI without recent radiographs (within past year), as this represents inappropriate utilization 1, 2
• Document laterality: Use specific ICD-10 codes (M25.561/M25.562 for right/left knee pain; M25.461/M25.462 for effusion) rather than "unspecified" codes 1, 2

Step 2: Advanced Imaging (Selective Use)

• MRI without contrast: Indicated when radiographs are normal or show only effusion AND pain persists despite adequate conservative treatment, or when surgery is being considered 1, 3
• Ultrasound: Useful for confirming effusion, guiding aspiration, evaluating Baker cysts, popliteal masses, and medial plica 1, 3
• Consider referred sources: If knee radiographs are unremarkable, obtain hip (M25.551/M25.552) or lumbar spine (M54.5) imaging based on clinical suspicion 1, 2

Conservative Management (First-Line for Most Conditions)

Exercise Therapy Protocol

• Knee-targeted exercises: Initiate quadriceps and knee strengthening as primary intervention when weakness is identified on examination 5
• Hip-and-knee combined therapy: Add hip strengthening exercises for patients with poor tolerance to loaded knee flexion or when hip weakness is present 5
• Progression strategy: Modify task, load, intensity, and frequency based on symptom severity and irritability 5
• Duration: Implement 4-6 weeks of structured exercise therapy before considering surgical referral 4

Supporting Interventions (Evidence-Based Adjuncts)

• Prefabricated foot orthoses: Prescribe when treatment direction tests show favorable response; customize for comfort by modifying density and geometry (most beneficial short-term) 5
• Patellar taping: Consider when rehabilitation is hindered by elevated symptom severity and irritability; discontinue if no favorable outcomes after realistic trial period 5
• Movement retraining: For runners with low cadence or narrow step width, consider cadence increase or step-width modification 5

Patient Education (Underpins All Interventions)

• Challenge inaccurate beliefs: Address misconceptions about pain equating to tissue damage, particularly in chronic presentations 5
• Set realistic expectations: Discuss recovery timeframes, expected outcomes relative to presentation, and the concept of building tissue tolerance to load 5
• Promote autonomy: Develop self-management skills, load management strategies, and reduce fear-avoidance behaviors 5

Common Pitfalls to Avoid

• Premature MRI ordering: Approximately 20% of patients inappropriately receive MRI without prior radiographs, leading to unnecessary costs and potential overdiagnosis 1, 2
• Missing referred pain: Always examine hip and lumbar spine when knee imaging is unremarkable, as posterior knee pain may originate from these sources 1, 2
• Inappropriate surgical referral: For degenerative meniscal tears, exercise therapy is first-line even with mechanical symptoms (locking, catching); surgery is not indicated 4
• Neglecting conservative management duration: Most conditions require 4-6 weeks of adequate conservative treatment before advanced imaging or surgical consideration 3, 4

Surgical Considerations (Highly Selective)

• Severe traumatic meniscal tears: Bucket-handle tears with displaced meniscal tissue likely require surgery 4
• End-stage osteoarthritis: Consider joint replacement only after exhausting all appropriate conservative options in patients with minimal joint space and inability to cope with pain 4
• Infrapatellar plica syndrome: Arthroscopic release or resection of the ligamentum mucosum may relieve anterior knee pain by untethering the fat pad in refractory cases 7