What are the next steps for a patient with a knee injury who can bear weight but experiences worsening pain with extension?

Knee Injury with Weight-Bearing Ability and Pain Worse with Extension

For a patient who can bear weight but has worsening pain with knee extension after trauma, apply the Ottawa Knee Rules to determine if radiographs are needed, and if negative or unavailable, proceed with a focused physical examination to identify the specific injured structure—most commonly the anterior cruciate ligament, meniscus, or extensor mechanism.

Initial Assessment: Apply Clinical Decision Rules

The ability to bear weight is a critical discriminator in acute knee trauma management. The Ottawa Knee Rules provide validated criteria for determining when radiographs are necessary 1:

• Age ≥55 years
• Isolated patellar tenderness
• Tenderness at the head of the fibula
• Inability to flex knee to 90 degrees
• Inability to bear weight immediately after injury or take 4 steps in the emergency department

Since your patient can bear weight, they do not automatically meet Ottawa criteria unless other factors are present 1. The Pittsburgh Decision Rule similarly requires inability to take four weight-bearing steps, or age <12 or >50 years 1.

When to Obtain Radiographs

Obtain knee radiographs (minimum AP and lateral views) if the patient meets any Ottawa or Pittsburgh criteria 1. Application of these rules reduces unnecessary radiographs by 23-35% while maintaining 100% sensitivity for fractures 1.

Do NOT apply clinical decision rules and obtain radiographs regardless if the patient has 1:

• Gross deformity
• Palpable mass
• Penetrating injury
• Prosthetic hardware
• Altered mental status
• Neuropathy
• Multiple injuries affecting examination reliability

Physical Examination for Pain with Extension

Pain specifically worsening with extension suggests several possible injuries that require targeted examination 2, 3:

Anterior Cruciate Ligament (ACL) Injury

• Perform the Lachman test (more sensitive and specific than anterior drawer sign) 2, 3
• Physical examination for ACL tears: 74% sensitive, 95% specific 2
• Pain with extension may indicate ACL involvement, especially if combined with instability

Meniscal Injury

• Joint line tenderness: 75% sensitive but only 27% specific (high false positive rate) 2
• McMurray test (knee rotation with extension): 52% sensitive but 97% specific 2
• The combination of joint line tenderness (83% sensitive, 83% specific) with McMurray testing improves diagnostic accuracy 4, 2

Extensor Mechanism Injury

• Palpate the patella for tenderness (Ottawa criteria component) 1
• Assess ability to flex knee to 90 degrees (inability suggests extensor mechanism or severe injury) 1
• Evaluate for patellar instability or subluxation 1

Next Steps Algorithm

Step 1: Apply Ottawa/Pittsburgh rules

• If criteria met → Obtain AP and lateral knee radiographs 1
• If age 5-12 years → Consider radiographs (falls outside both rule age ranges) 1

Step 2: If radiographs negative or not indicated

• Perform focused ligamentous examination (Lachman for ACL, valgus/varus for collaterals) 2, 3
• Perform meniscal examination (McMurray test, joint line tenderness) 2, 3
• Physical examination has moderate sensitivity (87% for meniscus, 74% for ACL) and high specificity (92% for meniscus, 95% for ACL) 2

Step 3: Consider advanced imaging selectively

• MRI is NOT routinely indicated as initial imaging for acute knee trauma 1
• Reserve MRI for patients with persistent symptoms after initial management or when physical examination suggests ligamentous/meniscal injury requiring surgical planning 1

Common Pitfalls to Avoid

Do not reflexively order radiographs on all knee injuries—only 5.2% of acute knee injury radiographs show fractures 1. Validated clinical decision rules prevent unnecessary radiation exposure and costs 1.

Do not rely solely on joint line tenderness for meniscal diagnosis—it has poor specificity (27%) and will lead to overdiagnosis 2. Combine with McMurray testing for better accuracy 2.

Do not order MRI as first-line imaging—it is more sensitive but less specific than physical examination for ligamentous and meniscal injuries, leading to detection of clinically irrelevant findings 2. Physical examination should guide the need for MRI 2.

Recognize that pain with extension may indicate multiple pathologies—ACL tears, meniscal tears (especially posterior horn), and extensor mechanism injuries all can present this way 4, 2, 3. A systematic physical examination is essential to differentiate 3.

Initial Management Regardless of Diagnosis

While establishing the specific diagnosis:

• Recommend relative rest, ice, compression, and elevation (standard acute injury management)
• Analgesics as needed (acetaminophen/paracetamol first-line for pain control) 1
• Avoid complete immobilization—early mobilization improves outcomes without compromising stability 1