What is the recommended approach for assessing and managing knee pain or dysfunction in patients of any age or medical history?

Knee Assessment: Recommended Approach

Begin with plain radiographs of the knee (anteroposterior, lateral, and tangential patellar views) as the initial imaging study for any patient ≥5 years old presenting with knee pain, followed by MRI without contrast if radiographs are normal or show only effusion and pain persists. 1

Initial Clinical Assessment Framework

Your clinical evaluation must systematically address these specific elements before imaging:

Physical Status Assessment

• Pain characteristics: Location (anterior, medial, lateral, posterior), onset, duration, quality, and aggravating factors 1, 2
• Mechanical symptoms: Locking, catching, giving way, or inability to bear weight 1, 3
• Joint examination: Palpable tenderness (fibular head, patella, joint line), effusion, crepitus, range of motion (ability to flex to 90°), and alignment (varus/valgus deformity) 1, 2
• Neurovascular status: Check all lower extremity pulses bilaterally and assess for femoral bruits 4
• Weight and comorbidities: Document BMI and relevant medical conditions 1

Critical Red Flags Requiring Urgent Evaluation

• Infection indicators: Fever, erythema, warmth, severe swelling with limited range of motion 3
• Acute trauma with: Severe pain, gross deformity, inability to bear weight, or inability to take 4 steps 1
• Vascular compromise: Diminished pulses, exercise-induced symptoms resolving with rest 4

Rule Out Referred Pain FIRST

This is a common pitfall that leads to misdiagnosis and unnecessary knee-focused workup. 5, 4

• Lumbar spine pathology: Perform straight leg raise test and examine for radicular symptoms, especially when knee radiographs are unremarkable 1, 5, 4
• Hip pathology: Assess hip range of motion and perform hip provocation tests, as hip disease commonly refers pain to the knee 1, 5, 6
• Vascular claudication: Evaluate for diminished pulses and exercise-induced symptoms in patients with numbness/tingling 4

Imaging Algorithm

Step 1: Plain Radiographs (Initial Study)

Obtain knee radiographs for all patients ≥5 years old with chronic knee pain or acute trauma meeting clinical criteria. 1

Required views: 1

• Anteroposterior or Rosenberg/tunnel view
• Lateral view (25-30° flexion)
• Tangential patellar view

Clinical decision rules for acute trauma (age 18+): 1

• Age ≥55 years (Ottawa) or >50 or <12 years (Pittsburgh)
• Isolated patellar tenderness
• Fibular head tenderness
• Cannot flex knee to 90°
• Cannot bear weight immediately post-injury or take 4 steps in emergency department

Bypass clinical rules and obtain radiographs for: Gross deformity, palpable mass, penetrating injury, prosthetic hardware, altered mental status, neuropathy, or multiple injuries 1

Step 2: MRI Without Contrast (When Radiographs Are Normal/Equivocal)

MRI is the next indicated examination when initial radiographs are normal or show only joint effusion but pain persists. 1, 6

MRI is specifically indicated for: 1

• Normal radiographs with persistent pain
• Joint effusion on radiographs without clear cause
• Suspected meniscal or ligamentous injury
• Osteochondritis dissecans, loose bodies, or history of cartilage repair
• Signs of prior osseous injury (Segond fracture, tibial spine avulsion)
• Suspected popliteal cyst or synovitis 6

MRI detects critical pathology missed by radiographs: 1, 5

• Subchondral insufficiency fractures (often initially radiograph-negative, especially medial femoral condyle in middle-aged/elderly females)
• Tibial stress fractures
• Bone marrow lesions (associated with increased pain, especially in males or those with family history of OA)
• Early cartilage abnormalities

Step 3: Alternative/Adjunctive Imaging

CT without contrast: May be appropriate for patellofemoral anatomy evaluation (subluxation, maltracking, trochlear morphology) or confirming prior osseous injury 1

Ultrasound: Useful for localizing suspected loose bodies in popliteal cyst, detecting effusions, and evaluating synovial pathology with power Doppler 1, 6

Joint aspiration (US or fluoroscopy-guided): Indicated when effusion present with concern for crystal disease or infection 1

Age-Specific Considerations and Common Pitfalls

Critical Interpretation Caveats

Not all imaging findings are symptomatic—this is a major source of overtreatment. 1, 5, 4

• Age >70 years: Majority have asymptomatic meniscal tears; bilateral structural abnormalities can exist with unilateral symptoms 1, 6
• Age 45-55 years: Likelihood of meniscal tear being present is not significantly different between painful and asymptomatic knees 1, 5
• Premature MRI: Approximately 20% of chronic knee pain patients undergo MRI without recent radiographs—this is inappropriate 5, 4, 6

Subchondral Insufficiency Fractures

Radiographs are often initially normal; MRI is required for early detection. 1, 5, 4 Later radiographs may show articular surface fragmentation, subchondral collapse, and progressive OA sometimes requiring total knee arthroplasty 1

Anatomic Location-Based Differential Diagnosis

Anterior Knee Pain 5

• Patellofemoral disorders (cartilage loss, subluxation/dislocation, friction syndrome)
• Patellar tendinopathy
• Fat pad impingement/Hoffa's disease (enhancing synovitis >2mm in Hoffa's fat)
• Deep infrapatellar bursitis
• Medial plicae
• Osteochondritis dissecans

Medial Knee Pain 5

• Medial compartment osteoarthritis

Lateral Knee Pain 5

• Iliotibial band syndrome
• Lateral compartment osteoarthritis

Posterior Knee Pain 5, 6

• Popliteal (Baker's) cysts (often communicate with joint)
• Hamstring tendinopathy

Management Framework for Osteoarthritis

When OA is confirmed, provide an individualized comprehensive package including all five core interventions: 1

1. Information and education about OA nature, causes, consequences, and prognosis 1
2. Activity maintenance and pacing strategies 1
3. Regular individualized exercise regimen 1
4. Weight loss if overweight/obese 1
5. Reduction of adverse mechanical factors (appropriate footwear, walking aids, assistive technology) 1

When conservative measures fail: Consider intra-articular corticosteroid injections, radiofrequency ablation of genicular nerves (conventional or cooled), or surgical options through multidisciplinary decision-making 7