What is the best approach to manage a suspected anterior cruciate ligament (ACL) tear in the emergency department (ED)?

Emergency Department Management of Suspected ACL Tear

Immobilize the knee with a rigid brace or splint for up to 10 days maximum, aspirate painful tense effusions for immediate symptom relief, obtain plain radiographs first to rule out fracture, and arrange urgent orthopedic follow-up within 1-2 weeks for definitive MRI and surgical planning—because early reconstruction within 3 months significantly reduces the risk of secondary meniscal and cartilage damage. 1, 2

Immediate ED Assessment and Intervention

Clinical Examination

• Perform the Lachman test as your primary diagnostic maneuver—it is over 80% sensitive for ACL tears and more accurate than other physical examination techniques 3
• Look for the classic presentation: non-contact twisting mechanism, audible "pop" at time of injury, rapid onset of knee effusion (within hours), and immediate inability to continue activity 4
• Document any associated injuries including collateral ligament tenderness, joint line pain suggesting meniscal pathology, or posterior cruciate ligament laxity 1

Effusion Management

• Aspirate painful, tense effusions immediately using sterile technique—this provides significant symptom relief and is specifically recommended by the American Academy of Orthopaedic Surgeons for confirmed or suspected ACL tears 2
• The presence of hemarthrosis strongly suggests internal derangement and supports the diagnosis 2

Initial Imaging

• Order plain radiographs first (AP, lateral, and sunrise views) to exclude fractures per Ottawa knee rules—radiographs are highly specific for ruling out bony injuries and may show avulsion fractures 1, 5
• Do not order MRI from the ED unless your institution has a specific acute sports injury protocol—MRI is the definitive study but should be coordinated through orthopedics 1

Immobilization and Pain Control

Bracing Strategy

• Apply a rigid knee brace or immobilizer for up to 10 days maximum to reduce initial pain and swelling 5
• Avoid prolonged immobilization beyond 10 days as this delays rehabilitation and muscle reactivation 5
• Allow immediate weight-bearing as tolerated with crutches if the patient can maintain a correct gait pattern without pain or increased effusion 1

Pain Management

• Apply cryotherapy (ice) for the first week to reduce pain—this is effective immediately post-injury through the first postoperative week 1
• Prescribe NSAIDs or acetaminophen for pain control as needed 3

Disposition and Follow-Up

Urgent Orthopedic Referral

• Arrange orthopedic follow-up within 1-2 weeks for definitive diagnosis and surgical planning 1, 2
• Emphasize to the patient that early reconstruction within 3 months is strongly recommended because the risk of additional cartilage and meniscal injury begins to increase significantly after this timeframe 1, 2
• This is a strong recommendation from the American Academy of Orthopaedic Surgeons, meaning it should be followed unless compelling contraindications exist 1

MRI Coordination

• The orthopedic surgeon will order MRI (1.5T or 3T are equivalent for ACL evaluation) to confirm the diagnosis and identify concomitant injuries including meniscal tears, collateral ligament injuries, bone contusions, and cartilage damage 1
• MRI has 96-97% sensitivity and specificity for ACL and meniscal tears and is superior to CT for soft tissue evaluation 1

Patient Education and Expectations

Activity Modification

• Instruct complete cessation of sports and pivoting activities until orthopedic evaluation 4
• Explain that ACL reconstruction is typically recommended for active patients who want to return to jumping, cutting, or pivoting sports, or those with physically demanding occupations 6
• Younger, more active patients particularly benefit from reconstruction to reduce future meniscal pathology 1, 2

Surgical Timing Counseling

• Warn against delaying surgery beyond 3 months unless medically necessary—this significantly increases the risk of secondary meniscal tears and progressive cartilage damage 2
• Explain that up to 90% of patients with ACL tears develop knee osteoarthritis long-term, but early appropriate treatment may reduce this risk 3

Critical Pitfalls to Avoid

• Do not discharge without orthopedic follow-up arranged—delayed diagnosis increases disability and worsens outcomes 1
• Do not recommend "wait and see" approach for active patients—the 3-month window for optimal surgical timing is critical 1, 2
• Do not miss concomitant MCL injuries—combined ACL/MCL tears require ACL reconstruction but the MCL can be treated non-surgically in most cases 1
• Do not order functional knee braces from the ED—these provide no clinical benefit after ACL reconstruction and are not recommended for routine use 1
• Do not immobilize for longer than 10 days—this delays necessary rehabilitation and muscle reactivation 5