How should I evaluate and initially manage a knee injury?

Evaluation and Initial Management of Acute Knee Injury

Use the Ottawa Knee Rules to determine if radiographs are needed: obtain knee X-rays if the patient has focal bone tenderness (patella or fibular head), inability to bear weight for 4 steps, inability to flex to 90 degrees, or age >55 years. 1

Initial Clinical Assessment

History - Key Elements to Obtain

• Mechanism of injury: twisting injury, direct blow, hyperextension, or high-energy trauma (motor vehicle accident, knee dislocation) 1
• Immediate symptoms: audible "pop" (suggests ACL tear), immediate swelling within 2 hours (suggests hemarthrosis from ACL or fracture), delayed swelling (suggests meniscal injury) 2
• Ability to bear weight: inability to take 4 weight-bearing steps is a critical Ottawa rule criterion 1
• Locking or catching: suggests meniscal tear 2
• Instability or "giving way": suggests ligamentous injury 2

Physical Examination - Specific Maneuvers

Examine the uninjured knee first for comparison 2

• Inspection: Look for gross deformity, effusion, ecchymosis 1, 2
• Palpation: Assess for focal bone tenderness at patella, fibular head, joint line tenderness (meniscus) 1, 2
• Range of motion: Document flexion/extension, inability to flex to 90 degrees triggers Ottawa criteria 1
• Ligament stability testing:
  • Lachman test (most sensitive/specific for ACL): 74% sensitive, 95% specific 3
  • Valgus/varus stress for collateral ligaments 2
  • Posterior drawer and tibial sag for PCL 2
• Meniscal testing: McMurray test (97% specific but only 52% sensitive), joint line tenderness (75% sensitive but only 27% specific) 3

Note: Examination may be difficult acutely due to pain and swelling; repeat examination in 3-5 days if initial assessment is limited 4

Imaging Strategy

When to Order Initial Radiographs

Obtain AP and lateral knee radiographs if ANY Ottawa Knee Rule criteria are met 1:

• Age >55 years
• Isolated patellar tenderness (no other bone tenderness)
• Tenderness at head of fibula
• Inability to flex knee to 90 degrees
• Inability to bear weight for 4 steps (both immediately and in emergency department)

Also obtain radiographs regardless of Ottawa criteria if 1:

• Gross deformity
• Palpable mass
• Penetrating injury
• Prosthetic hardware present
• Altered mental status (head injury, intoxication, dementia)
• Neuropathy (paraplegia, diabetes)
• Multiple injuries limiting reliable examination

Standard Radiographic Views

• Minimum: AP and lateral views (lateral with knee at 25-30 degrees flexion) 1
• Add patellofemoral (sunrise) view if patellar fracture or dislocation suspected 1
• Cross-table lateral with horizontal beam to visualize lipohemarthrosis (indicates intra-articular fracture) 1

Advanced Imaging - When Radiographs Are Negative

If radiographs show no fracture but occult fracture or internal derangement (ligament/meniscus injury) is suspected, MRI without contrast is the next appropriate study 1:

• MRI is highly accurate for meniscal tears (87% sensitive, 92% specific), ACL tears (74% sensitive, 95% specific), and occult fractures 1, 3
• MRI is more sensitive than physical examination for ligamentous and meniscal damage but less specific 3
• MRI is NOT routinely obtained as initial imaging 1

CT without contrast may be used for better fracture characterization (tibial plateau fractures) but cannot evaluate soft tissues or ligaments as well as MRI 1

High-Energy Trauma or Suspected Knee Dislocation

For significant trauma (motor vehicle accident, suspected knee dislocation), obtain both radiographs AND CTA of lower extremity 1:

• Vascular injury occurs in ~30% of posterior knee dislocations and requires urgent surgical intervention 1
• CTA is less invasive than conventional angiography with similar accuracy 1

Initial Management

Immediate Treatment (First 24-72 Hours)

• RICE protocol: Rest, Ice, Compression, Elevation 5
• NSAIDs for pain and inflammation 5
• Aspiration of tense, painful effusion may be considered for symptom relief 1
• Weight-bearing status: As tolerated unless fracture or complete ligament disruption identified 6

Injuries That Can Be Managed Non-Operatively

• MCL sprains (most grades I-II, many grade III if isolated) 6, 4, 5
• PCL injuries (most isolated injuries) 4, 5
• Meniscal tears in patients <40 years: Recent evidence shows non-operative management can achieve outcomes equal to surgery at 1 year 6
• Patellar dislocations: Short period of bracing in extension with progression to weight-bearing as tolerated 6

Injuries Typically Requiring Surgical Referral

• ACL tears in active patients: Should be reconstructed as soon as possible when indicated, as risk of additional cartilage and meniscal injury increases within 3 months 1
• LCL injuries 4, 5
• Most meniscal tears requiring surgery (though many can be managed conservatively) 4
• Displaced fractures 1
• Knee dislocations with vascular injury 1

Critical Pitfalls to Avoid

• Don't skip radiographs in high-risk situations: Always obtain X-rays for gross deformity, altered mental status, or unreliable examination regardless of Ottawa criteria 1
• Don't order MRI as initial imaging: Radiographs first to rule out fracture 1
• Don't delay vascular assessment in high-energy trauma: CTA should be obtained urgently if knee dislocation suspected 1
• Don't rely solely on initial examination if limited by pain/swelling: Re-examine in 3-5 days 4
• Physician judgment supersedes clinical decision rules in all cases 1