Knee dislocation

Background

Popliteal artery injury occurs in ~25% of cases
- Neurologic injury/deficit may indicate vascular injury
Spontaneous reduction occurs in up to 50% of dislocations; often occurs prior to ED arrival

Anterior (40%)
- hyperextension mechanism
- often involves PCL, ACL and either medial or lateral ligaments are injured
Posterior (33%)
- popliteal artery often injured
- dash board injury
Lateral (18%)
Medial (4%)

Suggested by severely injured knee that is unstable in multiple directions
Lateral collateral ligament injured with peroneal nerve palsy = knee dislocation
Usually associated with high energy mechanism of injury or low energy mechanism in patients with BMI>40
Observe for hyperextension in injured knee when leg is lifted by the heels compared to contralateral extremity.

Popliteal injury
- The presence of normal distal pulses and a normal Ankle Brachial Index >0.9 (ABI) does not completely rule out occult popliteal artery injury. Serial exams are necessary.
Nerve injury
- Common peroneal nerve injury (25%)
  - Test for sensation in 1st dorsal web space, dorsiflexion of foot, extension of toes
- Tibial nerve injured less often
Fractures
- Femur and tibia most common
- Check hip and ankle joints for associated fracture
- Avulsion fractures common
Compartment syndrome risk high with vascular compromise

Plain lateral X-ray of the left knee showing a posterior knee dislocation

A lateral dislocation of the knee

Knee x-ray (to rule-out fracture)
Vascular assessment
- Assess popliteal and distal pulses
- Measure ABIs
  - ABI >0.9 - serial exams
  - ABI <0.9 - arterial duplexes or CT angio
Consider CT Angiography:
- Asymmetric pulses
- ABI <0.9
- Clinical concern of vascular injury (ischemia, hemorrhage, or expanding hematoma)

Reduce immediately
- Posterior dislocation
  - Assistant holds distal femur and gently pulls counter-traction
  - Provider pulls proximal tibia longitudinally then anteriorly
  - Prevent additional arterial injury by limiting excessive force
- Anterior dislocation
  - As above, but reversed. Provider pulls gently counter traction on proximal tibia while assistant pulls distal femure proximally then anteriorly
- Splint in 10-15 degrees of flexion ^[1]
Monitor for compartment syndrome
- no pulses: reduce immediately
- no pulses post reduction: surgical exploration
  - ischemic time >8 hours has amputation rates as high as 86%
Neurological assessment
- Peroneal nerve most commonly injured
  - Test for sensation in 1st dorsal web space, dorsiflexion of foot, extension of toes

Institution will dictate admission process
- Suggested algorithm
  - If: Strong pulses + ABI >0.9 + normal doppler, admit for obs and serial vascular exams
  - If: Good perfusion + asymmetric pulses or ABI <0.9 or abnormal doppler, consult vascular surgery + obtain CTA
  - If: Weak pulses or signs of ischemia = emergent vascular surgery consult and OR
Consider trauma consult depending on mechanism and additional injuries

↑ Davenport M. Procedures for orthopedic emergencies. In: Bond M, ed. Orthopedic Emergencies: Expert Management for the Emergency Physician. Cambridge: Cambridge University Press; October 31, 2013.

Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
Levy BA, Fanelli GC, Whelan DB, Stannard JP, MacDonald PA, Boyd JL, Marx RG, Stuart MJ. Knee Dislocation Study Group. Controversies in the treatment of knee dislocations and multiligament reconstruction. J Am Acad Orthop Surg. 2009 Apr;17(4):197-206. http://www.ncbi.nlm.nih.gov/pubmed/19307669
Tintinalli, J. E., Stapczynski, J. S., Ma, O. J., Yealy, D. M., Meckler, G. D., & Cline, D. (2016). Injuries to Bones and Joints In Tintinalli's emergency medicine: A comprehensive study guide (Eighth edition.) (pp1863-1864). New York: McGraw-Hill Education.