What is the recommended evaluation and management of a knee dislocation?

Evaluation and Management of Knee Dislocation

Begin with immediate plain radiographs (anteroposterior and lateral views) and simultaneous vascular assessment, followed by CTA of the lower extremity if any vascular concern exists, as popliteal artery injury occurs in approximately 30% of posterior knee dislocations and represents a limb-threatening emergency requiring urgent intervention. 1, 2

Immediate Assessment in the Emergency Department

Vascular Evaluation (Priority #1)

• Perform serial ankle-brachial index (ABI) measurements on all patients with suspected knee dislocation, even if pulses are palpable, as equal pulses do not exclude vascular injury 3, 4
• If ABI is <0.9 or any clinical signs of vascular compromise are present (absent pulses, pallor, cool extremity, delayed capillary refill), obtain CTA of the lower extremity immediately 2, 5, 4
• CTA is less invasive than conventional angiography with similarly high accuracy for detecting popliteal artery injuries 1, 5
• High-risk features requiring heightened vascular surveillance include fracture dislocations, high-energy trauma, morbidly obese patients, lateral-sided injuries, concomitant peroneal nerve injuries, and ipsilateral limb fractures 4

Neurological Examination (Priority #2)

• Test systematically for peroneal nerve injury (foot drop, dorsal foot numbness) and tibial nerve injury (inability to plantar-flex, sole numbness) 2
• Document neurological status both before and after any reduction attempt, as nerve injuries cause significant long-term morbidity 1, 2

Recognition of Spontaneously Reduced Dislocations

• Maintain high suspicion in patients with globally unstable knees, as 50% of knee dislocations spontaneously reduce before emergency department arrival 3, 6
• These cases still require the same rigorous vascular and neurological assessment 5, 3

Initial Imaging Protocol

Plain Radiographs (First-Line Study)

• Obtain anteroposterior and lateral views (lateral with knee at 25-30 degrees flexion) as the initial imaging study 1, 5
• Radiographs identify fractures, joint space abnormalities, and confirm dislocation or reduction 5
• Obtain radiographs regardless of patient age or ability to bear weight when gross deformity, palpable mass, penetrating injury, or suspected dislocation is present 1

Computed Tomography Angiography (When Indicated)

• Order CTA and plain radiographs as complementary studies (both performed simultaneously) for significant knee trauma including motor vehicle accidents and confirmed dislocations 1
• CTA is the preferred vascular imaging modality over conventional angiography due to lower invasiveness and comparable accuracy 1, 5

Immediate Management

Reduction

• Perform closed reduction quickly in the emergency department if the knee remains dislocated 3, 6
• After reduction, immobilize the knee in 15-20 degrees of flexion using a removable splint rather than a rigid cast 2
• Avoid immobilization in full extension, as this increases tension on neurovascular structures 2

Post-Reduction Care

• Obtain repeat radiographs after reduction to confirm adequate alignment and identify associated fractures 2
• The removable splint permits ongoing neurovascular monitoring, which is critical in the first 24-48 hours 2

Advanced Imaging

MRI Without IV Contrast (Next Study After Radiographs)

• Order MRI without IV contrast after initial radiographs to evaluate multiligamentous injury, meniscal tears, osseous injuries, and neural injuries 1, 5
• MRI is accurate for evaluating soft-tissue, osseous, and neural injuries after knee dislocation 1, 5
• Do not order MRI with IV contrast or MR arthrography for acute knee dislocation, as non-contrast MRI is sufficient and appropriate 1, 5
• MRI may be deferred until after admission and does not need to be performed emergently 3

CT Without IV Contrast (Alternative for Fracture Characterization)

• Consider CT for better characterization of complex fractures, particularly tibial plateau fractures identified on radiographs 1, 5
• CT achieves 100% sensitivity for tibial plateau fractures versus 83% for plain radiographs 1

MRA (Limited Role)

• MRA may be performed simultaneously with MRI for combined evaluation of internal derangement and vascular injuries when CTA is not available 1
• MRA shows complete agreement with conventional angiography for popliteal artery injuries 1

Disposition and Follow-Up

Admission Criteria

• Admit all patients with confirmed vascular injury for urgent surgical intervention, as arterial injuries must be repaired first to preserve limb viability 5
• Most pediatric knee dislocations can be managed as day-surgery cases when reduction is performed in the emergency department 2

Outpatient Management

• Patients may be discharged with knee immobilized in a removable splint only if vascular status is definitively normal and serial examinations are reassuring 2
• Arrange urgent orthopedic follow-up within 24-48 hours for definitive assessment of ligamentous injury 2

Critical Pitfalls to Avoid

• Do not rely on palpable pulses alone to exclude vascular injury; perform ABI measurements and serial examinations 3, 4, 7
• Do not delay vascular imaging if any concern for arterial injury exists, as time to revascularization is critical for limb salvage 5
• Do not apply rigid casts immediately after reduction, as they impede ongoing neurovascular monitoring 2
• Do not dismiss the diagnosis in patients presenting with spontaneously reduced knees and globally unstable joints 3, 6
• Do not order MRI as the initial imaging study; plain radiographs must precede MRI to exclude fracture 1, 5