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Knee Dislocation, Emergency Medicine

Basics

Description

- History of mechanism of injury - Complete and careful physical exam: - Pulses " ”palpation, Doppler, ankle " “brachial index (ABI), and cap refill - Neurologic " ”sensation to 1st web space and great toe, movement of toes, dorsiflexion of foot

  • Defined by the position of the tibia in relation to the distal femur:Anterior dislocation:Most common dislocation, accounts for 60%Hyperextension of the kneeRupture of the posterior capsule at 30 ‚ °Rupture of the posterior cruciate ligament (PCL) and popliteal artery (PA) occurs at 50 ‚ °Posterior dislocation:Direct blow to the anterior tibia with the knee flexed at 90 ‚ °, "dashboard injury " ťAnterior cruciate ligament (ACL) is usually spared.Medial dislocation:Varus stress causing tear to the ACL, PCL, and lateral collateral ligament (LCL)Lateral dislocation:Valgus stress causing tear to the ACL, PCL, and medial collateral ligament (MCL)
  • Associated injuries:PA injury:Occurs in 35% of dislocations.Anterior dislocations place traction on PA and cause contusion or intimal injury, which may result in delayed thrombosis.Posterior dislocations cause direct intimal fracture and transection of the artery with immediate thrombosis.Peroneal nerve injury:Less common than PA injuryIf present, must rule out concomitant arterial insultMedial dislocation causes injury by traction of the nerve.Rotary injuries have a high incidence of traction and transection.

Etiology

High-energy injuries such as motor vehicle crashes, auto " “pedestrian accidents, and athletic injuries (football most common) ‚

Diagnosis

Signs and Symptoms

  • Grossly deformed knee
  • Grossly unstable knee in AP plane or on varus/valgus stress
  • Lack of distal pulse:PA injury is primary concern.
  • Signs of distal ischemia:Pallor, paresthesia, pain, paralysis

History

Mechanism of injury with high level of suspicion ‚

Physical Exam

  • Distal pulses
  • Distal nerve function:Hypesthesia of 1st web space, inability to dorsiflex foot
  • Ligamentous laxity

Essential Workup

  • History of mechanism of injury
  • Complete and careful physical exam:Pulses " ”palpation, Doppler, ankle " “brachial index (ABI), and cap refillNeurologic " ”sensation to 1st web space and great toe, movement of toes, dorsiflexion of foot
  • AP and lateral knee radiographs
  • Documented repeat exam if any closed reduction is attempted

Diagnosis Tests & Interpretation

Imaging

  • AP/lateral radiograph of knee:Essential to rule out concomitant fractures
  • MRI within 1 wk of injury to define ligamentous injury

Diagnostic Procedures/Surgery

  • ABI " ”likelihood of significant arterial injury requiring surgery low if ≥0.9
  • Peripheral vascular ultrasonography
  • Arteriogram should be considered:High suspicion of PA injuryPoor pulses or distal perfusion after reductionPeroneal nerve injuryIschemic symptoms despite normal pulses

Differential Diagnosis

  • Tibial plateau fracture
  • Supracondylar femoral fracture
  • Ligamentous/tendonous avulsion fracture

Treatment

Pre-Hospital

  • Management of ABCs
  • Documentation of pulses and motor response essential
  • Splint knee in slight flexion to prevent PA traction or compression.

Initial Stabilization/Therapy

  • ABCs especially when motor vehicle crash or auto " “pedestrian accident
  • Fluid resuscitation; hypotension may alter distal pulses and perfusion.
  • Closed reduction immediately for any limb ischemia
  • Early surgical consult in an open injury or high suspicion of arterial injury

Ed Treatment/Procedures

  • Closed reduction by longitudinal traction and lifting femur into normal alignment without placing pressure on popliteal fossa
  • Posterior leg splint/knee immobilizer with knee in 15 " “20 ‚ ° of flexion
  • Repeat neurovascular exam after manipulation and at frequent intervals.
  • IV analgesia for patient comfort
  • Surgical consult (orthopedic and vascular): Open injury, PA injury, or unable to reduce

Medication

First Line

  • Narcotic analgesia IV
  • Avoid PO meds, as surgery may be necessary.

Follow-Up

Disposition

Admission Criteria

All patients require admission for observation of limb perfusion and PA repair if necessary. ‚

Discharge Criteria

All patients should be admitted. ‚

Issues for Referral

Eventual repair of ligamentous injuries: ‚

  • Usually at 3 wk
  • Arthroscopic surgery is contraindicated for 2 wk after injury to prevent compartment syndrome.

Follow-Up Recommendations

  • Orthopedics for ligamentous repair
  • Vascular for PA injury

Pearls and Pitfalls

  • Failure to revascularize PA within 6 " “8 hr: Amputation rate approaches 90%.
  • Peroneal nerve injury:Poor prognosis for recovery
  • Delayed compartment syndrome may occur.

Additional Reading

  • Kelleher ‚ HB, Mandavia ‚ D. Dislocation, knee. eMedicine [serial online]. 2011. Available at www.emedicine.medscape.com/article/823589-overview
  • Mills ‚ WJ, Barei ‚ DP, McNair ‚ P. The value of ankle-brachial index for diagnosing arterial injury after knee dislocation: A prospective study. J Trauma. 2004;56(6):1261 " “1265.
  • Nicandri ‚ GT, Chamberlain ‚ AM, Wahl ‚ CJ. Practical management of knee dislocations: A selective angiography protocol to detect limb-threatening vascular injuries. Clin J Sport Med. 2009;19(2):125 " “129.
  • Seroyer ‚ ST, Musahl ‚ V, Harner ‚ CD. Management of the acute knee dislocation: The Pittsburgh experience. Injury. 2008;97(7):710 " “718.

Codes

ICD9

  • 836.50 Dislocation of knee, unspecified, closed
  • 836.51 Anterior dislocation of tibia, proximal end, closed
  • 836.52 Posterior dislocation of tibia, proximal end, closed
  • 836.53 Medial dislocation of tibia, proximal end, closed
  • 836.54 Lateral dislocation of tibia, proximal end, closed
  • 836.59 Other dislocation of knee, closed

ICD10

  • S83.106A Unspecified dislocation of unspecified knee, init encntr
  • S83.116A Anterior disloc of proximal end of tibia, unsp knee, init
  • S83.126A Posterior disloc of proximal end of tibia, unsp knee, init
  • S83.136A Medial dislocation of proximal end of tibia, unsp knee, init
  • S83.104A Unspecified dislocation of right knee, initial encounter
  • S83.105A Unspecified dislocation of left knee, initial encounter
  • S83.146A Lateral disloc of proximal end of tibia, unsp knee, init

SNOMED

  • 58320001 Traumatic dislocation of knee joint (disorder)
  • 41359009 Closed anterior dislocation of proximal end of tibia (disorder)
  • 208938001 Closed traumatic dislocation knee joint, posterior (disorder)
  • 208939009 Closed traumatic dislocation knee joint, medial (disorder)
  • 208940006 Closed traumatic dislocation knee joint, lateral (disorder)
  • 64213003 Closed anterior dislocation of distal end of femur (disorder)