Knee dislocation

Background

  • Popliteal artery injury is common
    • About 25% of cases
    • Neurologic deficit may indicate vascular injury
  • Spontaneous reduction common
    • About 50% self-reduce, usually en route to ED

Types

  • Anterior (40%)
    • Hyperextension
    • Associated injuries to PCL, ACL, and medial or lateral ligaments common
  • Posterior (33%)
    • Usually due to impact with dashboard during motor vehicle collision
    • Popliteal artery often injured
  • Lateral (18%)
  • Medial (4%)

Clinical Features

  • Instability in multiple directions
  • Evidence of collateral ligamentous injury combined with peroneal nerve palsy
  • History of high-energy mechanism
    • Patients with BMI > 40 commonly report low-energy mechanism
  • Affected knee may hyperextend relative to unaffected knee when leg is lifted by the foot

Associated Injuries

  • Popliteal artery injury[1]
    • Cannot rule out based on normal distal pulses and Ankle Brachial Index (ABI) > 0.9
      • Requires definitive vascular imaging or serial exams
  • Neurologic injuries
    • Common peroneal nerve injury (25%)
      • Test for:
        • Sensation in 1st dorsal web space
        • Dorsiflexion of foot
        • Toe extension
    • Tibial nerve injured (less common)
  • Fractures
    • Femur and tibia most common
    • Check hip and ankle joints for associated fracture
    • Avulsion fractures common
  • Compartment syndrome risk high with vascular compromise

Differential Diagnosis

Knee diagnoses

Acute knee injury

Nontraumatic/Subacute

Evaluation

Plain lateral X-ray of the left knee showing a posterior knee dislocation
A lateral dislocation of the knee
CT angiogram 3D reconstruction, posterior view showing a normal artery on the left, and occlusion to right popliteal artery as a result of a knee dislocation
  • 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)

Management

  • Reduce immediately
    • Avoid additional arterial injury by limiting excessive force during reduction

Posterior dislocation[2]

  1. Grasp proximal tibia
  2. Have assistant grasp distal femur and provide gentle counter-traction
  3. Apply longitudinal traction to proximal tibia
  4. Move proximal tibia anteriorly
  5. Immobilize in 10-15 degrees of flexion
  6. Assess neurovascular status
  7. Obtain post-reduction imaging

Anterior dislocation[2]

  1. Grasp distal femur
  2. Have assistant grasp proximal tibia and provide gentle counter-traction
  3. Pull distal femur proximally
  4. Move distal femur anteriorly
  5. Immobilize in 10-15 degrees of flexion
  6. Assess neurovascular status
  7. Obtain post-reduction imaging


  • 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%

Disposition

  • 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

See Also

External Links

References

  1. 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.
  2. 2.0 2.1 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