How should severe knee pain be evaluated and managed acutely?

Evaluation and Management of Severe Knee Pain

Begin with plain radiographs (anteroposterior, lateral at 25-30° flexion, and tangential patellar views) as the mandatory first imaging study, then proceed to MRI without contrast only if radiographs are normal or show isolated effusion and pain persists beyond 5-7 days with concerning clinical features. 1, 2

Immediate Red Flags Requiring Urgent Action

Before any imaging, assess for emergent conditions that demand immediate orthopedic consultation:

• Septic arthritis indicators: Fever with systemic symptoms, recent bacteremia, inability to bear weight or move the joint, or significant effusion with inflammatory markers (CRP >2.0 mg/dL) 3
• Vascular compromise: Gross deformity, palpable mass, or signs of limb ischemia—particularly in posterior knee dislocations where vascular injury occurs in ~30% of cases 2
• Open injuries or penetrating trauma: Require immediate surgical evaluation 1, 2

If any red flag is present, obtain blood cultures, perform urgent joint aspiration with synovial fluid analysis, initiate empiric IV antibiotics after cultures, and admit for orthopedic management. 3

Initial Imaging: Plain Radiographs

Radiographs are the cornerstone of evaluation and must precede any advanced imaging. 1, 2

When to Order Radiographs

Apply the Ottawa Knee Rules for acute trauma—order radiographs if ANY criterion is met: 1, 2, 4, 5

• Age ≥55 years
• Isolated patellar tenderness (no other bony tenderness)
• Tenderness at the fibular head
• Inability to flex knee to 90°
• Inability to bear weight for 4 steps immediately after injury AND in the examination room

Clinical judgment supersedes these rules—always obtain radiographs if the patient has gross deformity, prosthetic hardware, altered mental status, neuropathy, or unreliable examination due to multiple injuries. 2, 4

Required Radiographic Views

Obtain a minimum three-view series: 1, 2, 4

• Anteroposterior (AP) view: Evaluates tibiofemoral joint, fractures, and alignment
• Lateral view: Must be obtained at 25-30° knee flexion to visualize joint effusion and patella in profile; a cross-table lateral with horizontal beam can demonstrate lipohemarthrosis (indicating intra-articular fracture)
• Tangential patellar view (sunrise/skyline): Assesses patellofemoral joint for subluxation, dislocation, or fracture

For chronic knee pain or suspected osteoarthritis, use weight-bearing views to improve diagnostic accuracy. 4

Critical Pitfall

Approximately 20% of patients with chronic knee pain inappropriately receive MRI without recent radiographs (within the prior year)—this violates evidence-based practice and increases costs without improving outcomes. 1, 2, 4

Differential Diagnosis Based on Clinical Features

Osteoarthritis (Most Common in Age ≥45 Years)

Clinical criteria are highly accurate: age >50 years, activity-related pain, morning stiffness <30 minutes, crepitus, or bony enlargement (89% sensitive, 88% specific). 6, 5 Radiographic confirmation shows joint space narrowing, osteophytes, subchondral sclerosis, and bone end deformities. 7

First-line management: Exercise therapy, weight loss if overweight, education/self-management programs, and topical or oral NSAIDs (if no contraindications). 6, 8 Intra-articular corticosteroid injections provide short-term relief; duloxetine has demonstrated efficacy. 8 Reserve total joint replacement for end-stage disease (minimal joint space, inability to cope with pain) after exhausting conservative options. 6, 8

Meniscal Tears

Acute traumatic tears (age <40 years): Twisting injury with joint line tenderness (83% sensitive, 83% specific) and positive McMurray test (61% sensitive, 84% specific for concurrent rotation and extension). 6, 5

Degenerative tears (age ≥40 years): Often asymptomatic—the majority of people >70 years have meniscal tears on imaging regardless of symptoms, and prevalence in painful versus painless knees is similar in ages 45-55. 1, 6 Physical examination (joint line tenderness 75% sensitive but only 27% specific; McMurray test 52% sensitive, 97% specific) is moderately accurate. 5

Management: Conservative treatment (exercise therapy for 4-6 weeks) is first-line for both traumatic and degenerative tears. 6 Surgery is indicated only for severe traumatic bucket-handle tears with displaced tissue; degenerative tears should not undergo surgery even with mechanical symptoms (locking, catching). 6

Ligamentous Injuries

Physical examination is moderately sensitive and highly specific: 5

• Anterior cruciate ligament: Lachman test (74% sensitive, 95% specific)—more accurate than drawer sign
• Posterior cruciate ligament: 81% sensitive, 95% specific
• Collateral ligaments: Assess joint stability with varus/valgus stress

Patellofemoral Pain (Age <40 Years, Physically Active)

Anterior knee pain during squatting (91% sensitive, 50% specific). 6 Lifetime prevalence ~25%. 6

Management: Hip and knee strengthening exercises combined with foot orthoses or patellar taping; no indication for surgery. 6

Advanced Imaging: When and What to Order

MRI Without Contrast

Indications after negative radiographs: 1, 2, 9

• Persistent pain beyond 5-7 days despite conservative management
• Significant joint effusion with suspected internal derangement
• Mechanical symptoms (locking, catching, giving way)
• Joint instability suggesting ligamentous injury
• Inability to fully bear weight after initial period

Protocol: Standard non-contrast knee MRI includes coronal, sagittal, and axial planes with T1-weighted, T2-weighted, proton-density, and fat-suppressed sequences—sufficient to evaluate menisci, cruciate/collateral ligaments, cartilage, and bone-marrow edema without IV contrast. 2

Diagnostic accuracy: MRI is more sensitive than physical examination for meniscal (87% vs. MRI higher) and ligamentous injuries but less specific. 5 However, in older adults, meniscal tears are frequently incidental findings unrelated to symptoms. 1, 2

Critical pitfall: Do not order MRI as initial imaging, do not add IV contrast routinely (increases cost and risk without improving diagnostic yield for acute internal derangement), and do not order MR arthrography for acute injuries (reserved for chronic cartilage/labral assessment). 2

CT Without Contrast

Indications: 2, 9

• High clinical suspicion for occult fracture (e.g., tibial plateau fracture)—CT achieves 100% sensitivity versus 83% for radiographs
• Evaluation of patellofemoral anatomy in chronic pain with repetitive subluxation or maltracking
• Better characterization of complex fractures

Limitation: Low sensitivity for soft-tissue injuries (menisci, ligaments). 2

CT Angiography

Indication: Suspected vascular injury in knee dislocation (occurs in ~30% of posterior dislocations). 2

Referred Pain Considerations

If knee radiographs are unremarkable and pain persists, consider: 1, 2

• Hip pathology: Obtain hip radiographs—hip disease commonly refers pain to the knee, especially with pain on internal hip rotation
• Lumbar spine pathology: Obtain lumbar spine radiographs if clinical evidence suggests radicular origin

Conservative Management Algorithm

For non-emergent severe knee pain after excluding fracture and infection: 3, 6, 8

1. Initial 5-7 days: Rest, ice, NSAIDs (if no contraindications), activity modification
2. Reassess at 2 days: Evaluate weight-bearing ability, range of motion, focal tenderness, effusion, and stability 2
3. If improving: Continue conservative management with progressive exercise therapy
4. If not improving or mechanical symptoms develop: Proceed to MRI without contrast 2, 3
5. Large effusion with inability to bear weight: Perform joint aspiration to exclude septic arthritis 3

Common Pitfalls to Avoid

• Never skip radiographs even when effusion is clinically obvious—plain films are essential to rule out fractures and chronic changes before advanced imaging. 2, 4
• Do not order MRI based solely on patient request or "to be thorough"—this does not align with evidence-based practice. 2
• Do not assume a fall in a patient with known osteoarthritis requires MRI—negative radiographs exclude fractures needing urgent intervention, and MRI findings (meniscal tears, cartilage loss) are often chronic and unrelated to the acute event. 2
• Avoid opiates for osteoarthritis pain management. 8
• Do not perform arthroscopic surgery for degenerative meniscal tears—exercise therapy is first-line even with mechanical symptoms. 6