What is the next step after reduction of a posterior knee dislocation?

Management of Posterior Knee Dislocation

After reduction of posterior knee dislocation, the patient should undergo angiogram to evaluate for potential vascular injury.

Rationale for Angiography

Posterior knee dislocations carry a significant risk of vascular injury, particularly to the popliteal artery, which can lead to limb-threatening ischemia if not promptly identified and treated. The decision to perform angiography is based on the following considerations:

• Vascular injury has been reported in up to one-third of patients with posterior knee dislocations 1
• Popliteal artery disruption can occur due to stretching of the artery between points of relative anchorage in the adductor ring and soleus arcade 2
• Early identification and treatment of vascular injuries significantly improves outcomes and reduces the risk of limb loss

Clinical Assessment and Management Algorithm

1. Initial Assessment After Reduction:

   • Evaluate distal pulses (dorsalis pedis and posterior tibial)
   • Assess for signs of vascular compromise (pallor, coolness, delayed capillary refill)
   • Calculate Ankle-Brachial Index (ABI)

2. Decision Pathway:

   • If hard signs of vascular injury present (absent pulses, distal ischemia, active bleeding, bruit/thrill):
     • Immediate angiography and vascular surgery consultation
   • If normal pulses and ABI > 0.90:
     • Angiography still recommended due to risk of intimal tears or delayed occlusion
     • Consider MR angiography as an alternative if available 3

3. Post-Angiography Management:

   • Normal angiogram: Splinting and orthopedic follow-up
   • Abnormal angiogram: Vascular surgery consultation for potential revascularization

Evidence Considerations

While some studies suggest that physical examination may be reliable in detecting significant vascular injuries requiring surgery 1, the consequences of missing a vascular injury are severe, including limb loss. Complete occlusions of the popliteal artery have been successfully treated with reversed saphenous vein bypass grafts when identified early 1.

The literature shows that even patients with normal pulses may have intimal injuries that could lead to delayed thrombosis and ischemia. In one study, MR angiography identified normal popliteal arteries in patients with normal exams, suggesting it may be a less invasive alternative to conventional angiography 3.

Splinting After Vascular Assessment

After vascular assessment and any necessary intervention:

• Apply posterior splint with knee in slight flexion (15-20 degrees)
• Avoid complete extension which may increase tension on neurovascular structures
• Maintain immobilization until definitive ligamentous treatment is planned

Common Pitfalls to Avoid

1. Relying solely on physical examination: Even patients with normal pulses can have occult vascular injuries that may progress to occlusion
2. Delaying vascular assessment: Limb ischemia beyond 6-8 hours significantly increases risk of amputation
3. Inadequate immobilization: Improper splinting can lead to redislocation or further vascular compromise
4. Overlooking associated injuries: Posterior knee dislocations often have multiple ligamentous injuries and possible peroneal nerve damage

In conclusion, while some controversy exists regarding the universal use of angiography following knee dislocation, the potential consequences of missing a vascular injury are severe. Therefore, angiography remains the recommended approach following reduction of posterior knee dislocation to ensure optimal outcomes regarding morbidity, mortality, and quality of life.