A 28-year-old male footballer presents to the emergency department with acute onset severe pain and swelling in the right knee following a non-contact injury during a match. He describes a 'popping' sensation at the moment of injury. On examination, there is significant effusion, restricted range of motion, and a positive anterior drawer test. He is unable to bear weight. What is the most appropriate next step in management?

Explanation

## Initial Management of Acute Knee Injury ### Clinical Context This patient presents with classic signs of acute anterior cruciate ligament (ACL) tear: non-contact mechanism, 'popping' sensation, positive anterior drawer test, and acute effusion. The next step must establish baseline imaging and rule out fractures before proceeding to advanced imaging or intervention. ### Why Plain Radiographs First? **Key Point:** Plain radiographs (AP, lateral, and skyline views) are the standard initial imaging modality for all acute knee injuries. They serve to: 1. Rule out fractures (tibial plateau, femoral condyle, patella) 2. Detect loose bodies 3. Assess alignment and joint congruity 4. Guide further investigation decisions **High-Yield:** In acute knee trauma with effusion and restricted motion, plain X-rays must precede MRI. This is the standard protocol in emergency medicine and orthopedic practice [cite:Apley's System of Orthopaedics Ch 16]. ### Management Algorithm ```mermaid flowchart TD A[Acute knee injury with effusion]:::outcome --> B[Plain radiographs AP/Lateral/Skyline]:::action B --> C{Fracture present?}:::decision C -->|Yes| D[Orthopedic consultation + CT if needed]:::action C -->|No| E[Proceed to MRI for soft tissue assessment]:::action E --> F[ACL tear confirmed]:::outcome F --> G[Surgical planning with orthopedics]:::action ``` ### Timing Considerations | Modality | Timing | Purpose | In This Case | |----------|--------|---------|---------------| | **Plain X-ray** | Immediate | Rule out fracture | **FIRST** | | **MRI** | Within 48–72 hrs | Soft tissue detail (ACL, menisci) | After X-ray | | **Arthroscopy** | Elective (1–2 weeks) | Therapeutic, not diagnostic | Not immediate | **Clinical Pearl:** The acute effusion and inability to bear weight do not mandate emergency surgery. Acute ACL tears are managed conservatively initially (RICE protocol) with definitive imaging and surgical planning once fractures are excluded. **Warning:** Do NOT proceed to MRI or arthroscopy without first ruling out fractures on plain films. Missed fractures can lead to complications and delayed treatment. ### Why Not the Other Options? - **MRI immediately:** Appropriate after X-rays confirm no fracture, but not the first step. - **RICE + reassessment:** Reasonable for conservative management but does not address the need for baseline imaging. - **Arthroscopy immediately:** Diagnostic arthroscopy is not indicated; MRI is the gold standard for soft tissue diagnosis in the acute setting.