Ortho Case of the Week – Knee Dislocation Answers
Case 1: A 45-year-old male presents with right knee pain after a fall, with his leg getting twisted.
1. Describe the pathology shown on this x-ray.
Anterior dislocation of the right knee (tibiofemoral articulation).
2. Describe your reduction technique.
For an anterior dislocation:
- Grasp distal femur
- Have assistant grasp proximal tibia and provide gentle counter-traction
- Pull distal femur proximally
- Move distal femur anteriorly
- Immobilize in 10-15 degrees of flexion
- Assess neurovascular status
- Obtain post-reduction imaging
Posterior dislocation reduction video
3. What splint would you use after reduction?
Posterior long leg splint in 15-30 degrees of flexion, or a knee immobilizer.
4. What is the most common vascular structure injured in this pathology?
The popliteal artery, most commonly with posterior dislocations.
50% of dislocations spontaneously reduce, so it is important to have a high suspicion for this injury.
5. Describe your decision-making algorithm for assessment of vascular injury.
Immediate reduction, then:
- Strong, symmetric pulses + ABI >0.9 + symmetric doppler -> admit for serial vascular exams
- Good perfusion + asymmetric pulses or ABI <0.9 or abnormal doppler -> consult vascular surgery + obtain CTA
- Weak/absent pulses or signs of ischemia -> emergent vascular surgery
Limb ischemia time >8 hours has amputation rates up to 86%.
6. What is the most common nerve injured in this pathology?
The common peroneal nerve, injured in 25% of dislocations.
Test for ankle dorsiflexion, toe extension, and sensation to the first dorsal webspace.
Less commonly, the tibial nerve is injured.
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