What is the appropriate history, physical examination, imaging studies, and initial management for a patient presenting with knee pain after a fall?

Examination and Management of Knee Pain After Fall

For patients ≥5 years presenting with knee pain after a fall, obtain plain radiographs (anteroposterior and lateral views) if any Ottawa Knee Rule criteria are met: age ≥55 years, isolated patellar tenderness, fibular head tenderness, inability to flex knee to 90°, or inability to bear weight for 4 steps immediately after injury or in the examination room. 1, 2, 3

History: Key Elements to Document

• Mechanism of injury: Determine if the fall involved direct impact to the knee, twisting motion, or landing on feet from height 1, 4
• Immediate symptoms: Ask specifically about an audible "pop" at time of injury, which suggests ligamentous or meniscal tear 2
• Weight-bearing ability: Document whether the patient could take 4 consecutive steps immediately after injury and currently in the examination room 2, 3
• Age: Patients ≥55 years have higher fracture risk and automatically meet imaging criteria 2, 3
• Red flag symptoms: Fever with joint swelling (septic arthritis), gross deformity, or palpable mass require immediate intervention 3, 4

Physical Examination: Systematic Approach

Initial Inspection and Palpation

• Observe gait pattern and document ability to bear weight for 4 consecutive steps 3
• Assess for gross deformity or palpable gap in tendon, which mandates immediate orthopedic referral 3
• Evaluate for joint effusion by inspecting for swelling and performing ballottement test 2, 3
• Palpate specific bony landmarks: isolated patellar tenderness and fibular head tenderness are Ottawa Rule criteria requiring radiographs 2, 3
• Check for joint line tenderness along medial and lateral compartments to assess for meniscal pathology 3

Range of Motion Assessment

• Test active and passive flexion/extension: Inability to flex knee to 90° is an Ottawa criterion requiring imaging 2, 3
• Perform bounce test to assess for mechanical block to full extension, suggesting meniscal tear 3

Ligamentous Stability Testing

• Lachman test (knee at 20-30° flexion) is the most sensitive and specific for ACL injury (sensitivity 74%, specificity 95%) 3
• Assess collateral ligaments with varus and valgus stress testing 2
• Important caveat: Excessive swelling and pain limit examination accuracy for up to 48 hours; re-examine at 3-5 days if initial assessment is limited 3

Imaging Strategy

Initial Radiographs: When to Order

Order knee radiographs immediately if ANY of the following Ottawa Knee Rule criteria are present: 1, 2, 3

• Age ≥55 years
• Isolated patellar tenderness on palpation
• Fibular head tenderness
• Inability to flex knee to 90°
• Inability to bear weight for 4 steps immediately after injury
• Inability to bear weight for 4 steps in the examination room

Also order radiographs regardless of Ottawa criteria if: 2

• Gross deformity present
• Palpable mass
• Penetrating injury
• Prosthetic hardware
• Altered mental status
• Neuropathy
• History suggesting increased fracture risk

Required Radiographic Views

• Minimum two views: anteroposterior and lateral (with knee at 25-30° flexion) 2, 3, 4
• Additional views to consider: patellofemoral view, cross-table lateral, internal and external oblique views based on clinical suspicion 2, 4

Advanced Imaging: MRI Without Contrast

MRI knee without IV contrast is the appropriate next study after negative radiographs when: 1, 2

• Persistent pain with suspected internal derangement (meniscal or ligamentous injury)
• Significant joint effusion persisting 5-7 days
• Inability to fully bear weight after 5-7 days
• Mechanical symptoms (locking, catching) suggesting meniscal tear
• Joint instability on examination suggesting ligamentous injury

Do not order MRI as initial imaging—radiographs must come first to exclude fracture 2

Do not add IV contrast routinely—it increases cost and risk without improving diagnostic yield for acute internal derangement 2

CT Imaging: Limited Role

• CT without IV contrast is appropriate only when occult fracture is specifically suspected (100% sensitivity for tibial plateau fractures vs. 83% for radiographs) 2
• CT has low sensitivity for soft-tissue injuries and should not be used to evaluate meniscal or ligamentous pathology 2

Initial Management

If Radiographs Are Negative

• Ability to bear weight rules out most fractures requiring surgical intervention, though soft-tissue injuries may still be present 2
• Conservative management: Rest, ice, compression, elevation with close follow-up 4
• Reassess clinically at 2 days post-injury, evaluating weight-bearing ability, range of motion, focal tenderness, effusion, and stability 2
• Consider MRI at 5-7 days only if concerning findings persist (significant effusion, inability to bear weight, mechanical symptoms, instability) 2

Red Flags Requiring Urgent Action

• Fever with joint effusion: Perform urgent joint aspiration to exclude septic arthritis 3, 4
• Gross deformity or palpable mass: Immediate orthopedic referral 3, 4
• Vascular compromise: In knee dislocation with suspected vascular injury, obtain CTA lower extremity (vascular injury occurs in ~30% of posterior knee dislocations) 2
• Inability to bear weight with large effusion: Joint aspiration to exclude septic arthritis 2

Special Population Considerations

• Adolescents with knee pain and inability to bear weight: Consider slipped capital femoral epiphysis (SCFE); perform hip examination and imaging 3
• Children <5 years with fever: Age <5 years plus C-reactive protein >2.0 mg/dL predicts >90% probability of septic arthritis 4
• Patients with pre-existing osteoarthritis: Negative radiographs exclude fractures requiring urgent intervention; MRI is indicated only for specific clinical concerns (persistent mechanical symptoms, instability), not patient request alone 2

Common Pitfalls to Avoid

• Do not skip radiographs and proceed directly to MRI—this violates evidence-based practice and may miss fractures 2
• Do not order MRI solely because the patient requests it or "to be thorough"—approximately 20% of patients inappropriately receive MRI without recent radiographs or clear indication 2
• Do not assume meniscal tears found on MRI are clinically significant in older adults—asymptomatic meniscal tears are highly prevalent in patients >70 years and often unrelated to acute trauma 2
• Do not rely on physical examination alone in the first 48 hours—swelling and pain limit accuracy; re-examine at 3-5 days if initial assessment is limited 3
• Do not order MR arthrography for acute trauma—it is reserved for chronic conditions and adds unnecessary cost and complexity 2