Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Knee Dislocation

Basics
Description
  • Dislocation of the knee is an orthopaedic emergency.
  • The most common causes are motor vehicle accidents, followed by sports and falls from heights.
  • Classification:
    • Anterior
    • Posterior
    • Medial
    • Lateral
    • Rotary: Subclassified as anteromedial, anterolateral, posteromedial, posterolateral
General Prevention
Seat belts and airbags are the best methods of prevention.
 
Epidemiology
Incidence
Rare
 
Associated Conditions
  • Neurovascular injury, particularly to the popliteal artery or peroneal nerve
  • Fractures of the tibia or femur
  • Rupture of the collateral and/or cruciate ligaments
Diagnosis
Signs and Symptoms
History
  • Classically, patients with knee dislocations present with obvious deformity, swelling, pain, and inability to move the knee.
  • Many knee dislocations are reduced before examination by a physician; thus, deformity may not be present.
  • It is critical to assess the neurovascular status of all patients with possible knee dislocations because:
    • Injury to the popliteal artery occurs in 32-45% of cases.
    • Nerve injury (most commonly the peroneal nerve) occurs in 16-40% of all knee dislocations.
  • Urgent vascular evaluation is required for absent pulses; ecchymosis in the popliteal fossa; a cold, cyanotic extremity; or loss of sensorimotor function.
Physical Exam
  • Inspect the extremity for obvious deformity, swelling, and ecchymosis.
  • Perform a thorough neurovascular examination.
    • Palpate pulses or assess them by Doppler, note warmth of skin, and examine sensory and motor function.
  • The presence of pulses does not rule out vascular injury because an intimal flap tear of the vessel may be present.
  • Any sign of vascular injury necessitates an emergent vascular surgery consultation.
  • Examination for laxity of the knee should be performed systematically for injury to any of the 4 knee ligaments (ACL, OSD, MCL, or LCL).
  • Laxity of 2 or more knee ligaments leads to a presumptive diagnosis of knee dislocation.
  • Patients should be examined carefully at regular intervals to exclude the possibility of compartment syndrome.
    • The most reliable signs for compartment syndrome are intractable, unrelenting pain out of proportion to the injury and pain with passive stretch of the ankle and toes.
Tests
Imaging
  • Radiography:
    • AP and lateral views of the knee should be obtained, but doing so should not delay reduction of an obvious dislocation.
  • MRI:
    • May be useful in assessing soft-tissue and ligamentous injury, but it should not be performed acutely.
    • Also allows visualization of the vascular system
Diagnostic Procedures/Surgery
Any patient with a vascular injury should undergo angiography or MRI.
 
Differential Diagnosis
  • Dislocation of the patella
  • Neurovascular injury unrelated to dislocation
  • Fracture of the tibia or femur
Treatment
General Measures
  • Many knee dislocations are the result of motor vehicle crashes; therefore, all such patients should be assessed by a trauma protocol.
    • Initial assessment should include evaluation of airway, breathing, circulation, and vital signs.
  • Immediate reduction is recommended.
    • Anterior dislocations are reduced with longitudinal traction and the lifting of the femur anteriorly.
    • Posterior dislocations are reduced with longitudinal traction and the lifting upward of the proximal tibia while extending the knee.
    • Medial and lateral dislocations are reduced with longitudinal traction and the appropriate medial or lateral pressure on the tibia and femur.
  • The neurovascular status should be assessed before and after reduction.
  • Orthopaedic and vascular surgeons should be notified.
  • The knee should be immobilized in a splint or spanning external fixator, with careful attention to the neurovascular status and the development of compartment syndrome.
  • Nonoperative treatment:
    • Indicated for patients who are sedentary or elderly or who have substantial comorbidities preventing surgical repair.
    • A splint should be followed by 6-8 weeks of protected immobilization.
Activity
  • Nonoperatively treated patients:
    • 6-8 weeks of protected immobilization
    • May begin quadriceps setting exercises in the splint, followed by active leg-lifting exercises after the immobilizer is removed
  • Operatively treated patients:
    • Activity is determined by which structures were injured, repaired, and reconstructed.
    • After 6 weeks, patients may begin active ROM exercises.
  • Average return to previous activity for both treatments:
    • Sports, 9-12 months
    • Sedentary jobs, 2 months
    • Heavy labor, 6-9 months
Special Therapy
Physical Therapy
  • ROM and strengthening exercises should be started after immobilization.
  • Quadriceps setting exercises can begin in the splint/fixator.
Medication
First Line
Narcotics
 
Surgery
  • Emergent surgery is required for patients with vascular injury; saphenous vein grafting often is required.
  • Fasciotomies may be required for patients with prolonged ischemic time or with compartment syndrome.
  • Open dislocation requires immediate surgical intervention.
  • Definitive surgical repair usually is performed 10-14 days after the injury, to allow swelling to diminish and to facilitate arthroscopic procedures.
  • Methods of repair and reconstruction depend on the extent and nature of the injuries.
Follow-up
Disposition
Patients should be followed at 4-6-week intervals until they achieve maximum recovery.
 
Issues for Referral
  • An orthopaedic surgeon should be consulted emergently.
  • Any vascular injuries require immediate consultation with a vascular surgeon.
Prognosis
  • Prognosis depends on the associated limb injuries and the interventions for those injuries.
  • Viability of the limb in the presence of vascular compromise is directly related to the time between injury and revascularization.
  • The most common residual effects are arthrofibrosis (knee stiffness) and postoperative arthritis.
Complications
  • Loss of limb:
    • Usually secondary to prolonged ischemia
    • The amputation rate is 86% when ischemia lasts >8 hours.
  • Arthrofibrosis (stiff knee):
    • In nonoperative treatment, residual stiffness provides stability for injured ligaments.
    • Operative treatment may increase the incidence of arthrofibrosis unless reconstruction is strong enough to allow early ROM.
  • Neurologic deficit:
    • Nerve injury, most often the peroneal nerve, is a common sequela of knee dislocation.
    • Recovery may take months to years, and prognosis varies.
  • Knee instability:
    • Secondary to injury to the ligamentous structures
    • Redislocation is rare.
  • Posttraumatic arthritis:
    • Secondary to cartilage injury during the trauma
    • Can lead to long-term disability
Miscellaneous
Codes
ICD9-CM
  • 836.5 Closed knee dislocation
  • 836.6 Open knee dislocation
Patient Teaching
Activity
Emphasize ROM and, later, strengthening exercises.
 
FAQ
Q: Do all patients with a knee dislocation require an arterial study to document the status of the popliteal artery?
A: No. Although as many as 50% of knee dislocations from high-energy motor vehicle accidents have a popliteal artery injury, <10% of athletic knee dislocations have an arterial injury. Patients with diminished distal pulses before surgical evaluation require urgent vascular consultation.

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