What should be done for a female patient who heard an audible pop while playing basketball and now has severe pain and tenderness to palpation over the left lateral knee?

Initial Management: Obtain Knee Radiographs Immediately

This patient meets Ottawa Knee Rule criteria (focal lateral tenderness and likely inability to bear weight given severe pain), making plain radiographs the mandatory first imaging study 1.

Immediate Diagnostic Workup

Clinical Assessment Priority

The audible "pop" during basketball with severe lateral knee pain and tenderness to palpation suggests:

• Most likely: ACL tear (often with lateral compartment bone bruising)
• Also consider: Lateral meniscus tear, lateral collateral ligament injury, or less commonly, popliteus tendon pathology

The lateral location is somewhat atypical for isolated ACL tears (which typically cause medial or diffuse pain), so maintain suspicion for combined injuries.

Initial Imaging Algorithm

Step 1: Plain Radiographs (AP and Lateral views minimum)

• Obtain at least two views: anteroposterior and lateral 1
• The lateral view should be at 25-30 degrees flexion to visualize joint effusion and lipohemarthrosis 1
• Add patellofemoral view if any patellar involvement suspected 1
• This rules out fractures, avulsions, and gross deformity

Step 2: If Radiographs Are Normal → MRI Without Contrast

• MRI is the definitive next study for suspected internal derangement 1
• MRI has superior sensitivity for ACL tears, meniscal injuries, bone contusions, and other soft tissue pathology
• Do not delay MRI if clinical suspicion is high and radiographs are negative 1

Physical Examination Specifics to Perform

While awaiting imaging:

• Lachman test: Most sensitive for ACL injury (check for anterior tibial translation with knee at 20-30° flexion) 2
• Joint effusion: Ballottement of patella suggests hemarthrosis (highly suggestive of ACL tear or fracture) 2
• Range of motion: Document any mechanical blocks suggesting meniscal tear
• Varus stress test: Assess lateral collateral ligament integrity given lateral pain location
• Neurovascular exam: Essential to rule out popliteal artery injury (though less likely without dislocation)

Critical Pitfalls to Avoid

1. Do not skip radiographs and go straight to MRI - This violates ACR appropriateness criteria and may miss fractures requiring immediate different management 1

2. Do not dismiss lateral-sided symptoms - While ACL tears classically present with medial or central symptoms, lateral pain may indicate:

   • Segond fracture (lateral capsular avulsion, pathognomonic for ACL tear)
   • Lateral meniscus tear (more common in females)
   • Rare snapping popliteus tendon (though this typically has chronic, not acute traumatic onset) 3, 4, 5

3. Do not assume ability to walk rules out serious injury - Many ACL tears can still ambulate initially before swelling peaks

Subsequent Management Framework

If MRI Confirms ACL Tear:

The 2016 AAOS guidelines indicate that for a young, active female athlete participating in basketball (a cutting/pivoting sport) 2:

Appropriate treatment options (rated 7-9/9):

• ACL reconstruction with autograft (rated 8/9) - preferred for this demographic
• ACL reconstruction with allograft (rated 7/9)
• Activity modification without reconstruction (rated 7/9) - not realistic for competitive athlete

Key reasoning: Young athletes in pivoting sports have very high risk of recurrent instability, subsequent meniscal tears, and early osteoarthritis without reconstruction 2. The evidence strongly favors surgical reconstruction to prevent progressive cartilage and meniscal damage.

Acute Phase Management (Before Definitive Treatment):

• Ice, elevation, compression
• Crutches with protected weight-bearing as tolerated
• NSAIDs for pain control
• Knee immobilizer if significant instability
• Urgent orthopedic referral (within 1-2 weeks)

The immediate priority is obtaining plain radiographs now, followed by MRI if radiographs are negative, to establish the diagnosis and guide definitive treatment planning.