What is the appropriate initial management for a 19‑year‑old who heard a pop in his knee while playing soccer and now has pain?

Initial Management of Acute Knee Injury with Audible Pop in a 19-Year-Old Soccer Player

Obtain plain radiographs (anteroposterior and lateral views) of the knee immediately if the patient meets any Ottawa Knee Rule criteria: focal tenderness at the patella or fibular head, inability to bear weight for 4 steps, or inability to flex the knee to 90 degrees. 1

Immediate Clinical Assessment

Evaluate for the following Ottawa Knee Rule criteria that mandate radiography: 1

• Focal bony tenderness at the patella or fibular head
• Inability to bear weight for 4 steps both immediately after injury and in the examination room
• Inability to flex knee to 90 degrees
• Age ≥55 years (not applicable to this patient)

Additionally, obtain radiographs regardless of Ottawa criteria if any of these red flags are present: 1

• Gross deformity
• Palpable mass
• Penetrating injury
• Altered mental status
• Neuropathy

Required Radiographic Views

Order a minimum of two standard views: 1

• Anteroposterior (AP) view
• Lateral view with knee at 25-30 degrees of flexion in lateral decubitus position

Consider additional views based on clinical findings: 1

• Cross-table lateral view with horizontal beam to visualize lipohemarthrosis (suggests intra-articular fracture)
• Patellofemoral view if anterior knee pain or patellar tenderness is present
• Internal and external oblique views for complex injury patterns

Management Based on Radiographic Results

If Radiographs Are Negative

Order MRI of the knee without IV contrast if clinical suspicion remains high for internal derangement (meniscal tear, ACL rupture, or other ligamentous injury), particularly given the audible pop and mechanism of injury. 1, 2

The American College of Radiology classifies MRI without contrast as "usually appropriate" (highest rating) for this exact scenario. 2

Timing of MRI: 2, 3

• Can be ordered immediately if significant joint effusion, mechanical symptoms (locking, catching), or joint instability are present
• If patient can bear weight and symptoms are mild, consider conservative management with re-evaluation at 5-7 days; order MRI if symptoms persist or worsen

If Radiographs Show Fracture

Obtain orthopedic consultation for fracture management. 3

Consider CT without IV contrast for better characterization of complex fractures, particularly tibial plateau fractures (CT has 100% sensitivity vs. 83% for radiographs). 1, 2

Conservative Management During Evaluation Period

While awaiting imaging or specialist evaluation: 4

• Pain management with NSAIDs or analgesics
• Minimize knee swelling with rest, ice, compression, elevation (RICE protocol)
• Maintain range of motion with gentle exercises as tolerated
• Preserve quadriceps activation to prevent atrophy
• Protected weight-bearing with crutches if needed

Common Pitfalls to Avoid

Do not order MRI as the initial imaging study—plain radiographs must be obtained first to exclude fracture and comply with evidence-based guidelines. 1, 2

Do not add IV contrast to routine knee MRI for acute trauma—it increases cost and risk without improving diagnostic yield for meniscal or ligamentous injuries. 2

Do not order MR arthrography for acute injuries—this is reserved for chronic conditions requiring detailed cartilage assessment. 2

Do not dismiss the injury if radiographs are negative—an audible pop during twisting injury in a young athlete has high probability of ACL tear or meniscal injury, which requires MRI for diagnosis. 5, 4

Physician judgment supersedes clinical decision rules—if clinical suspicion is high despite negative Ottawa criteria, obtain radiographs. 1

Expected Outcomes and Referral Indications

Most meniscal injuries, ACL tears, and lateral collateral ligament injuries require surgical management and orthopedic referral. 4

Medial collateral ligament injuries and some small meniscal tears can be managed conservatively with physiotherapy. 4

With appropriate combined treatment (surgery when indicated plus intensive physiotherapy), athletes typically return to pre-injury level within 4.5 months. 6

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