Knee Dislocations: High risk, can’t miss!

By: Dr. Maddie Boyle


A 19-year-old male presents with left knee pain. He injured his knee yesterday while wrestling with friends and was seen in a local ED where his knee was reduced. He was discharged in a knee immobilizer and now returns with complaints of increasing pain and recurrent deformity after removing the immobilizer to shower.


Imaging demonstrates lateral tibiofemoral subluxation. He has a normal neurovascular exam, including strong distal pulses. Orthopedics is consulted and performs closed reduction of his knee. His ABI is subsequently measured at 0.92, and the knee is immobilized in 20° of flexion.


Image 1

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What would you do next?

(a) Call an emergency Vascular Surgery consult
(b) Admit for serial physical exams and ABI measurements
(c) Obtain a CTA of the lower extremity
(d) Discharge home in a knee immobilizer with outpatient Orthopedic follow-up

Answer: B


-Knee dislocation (KD) is an uncommon injury with the potential for grave consequences if not recognized and appropriately managed.

-KD is classically associated with high-energy mechanisms: Motor vehicle accidents, and falls from a significant height.
-However, KD can also result from low energy mechanisms, such as athletic injuries or walking and/or falls from standing in the morbidly obese patient population.

Why is knee dislocation so concerning?

-KD is a potentially limb-threatening injury.
-Vascular risk: The popliteal artery is tethered above-and-below the knee at the adductor magnus muscle and soleus arch, respectively. This positioning renders the vessel vulnerable to disruption (vasospasm, intimal tear with resulting thrombosis, transection).
-Vascular injury is most commonly seen in posterior dislocations, but can occur in all types of dislocations.

Initial ED Management:

-Up to 50% of KD spontaneously reduce prior to ED arrival.
-KD requires a high level of clinical suspicion (consider mechanism, patient body habitus, history of deformity provided by patient).
-Examine for signs of gross deformity:

  • Swelling
  • Effusion
  • Ecchymosis
  • If the patient can tolerate, assess for joint laxity

-Perform a timely reduction of obvious knee dislocations.

  • Stabilize femoral condyles
  • Pull tibial longitudinal traction
  • Additional directive movements should be guided by the direction of the dislocation (ie: pull anteriorly if the knee appears posteriorly dislocated)

Post Reduction Management:

-Obtain post reduction films, reassess neurovascular status.
-Promptly recognize “hard signs” of vascular injury:

  • Limb ischemia
  • Expanding or pulsatile hematoma
  • Bruit/thrill
  • Active hemorrhage

-If you observe hard vascular signs; immediate consult to vascular surgery.
-Evaluate for “soft signs” of vascular injury:

  • Peripheral nerve deficits
  • Reduced but palpable pulses
  • History of moderate hemorrhage

-Recognize that normal peripheral pulses do not rule out vascular injury.
-Measure the ABI. This is essential.

3 minute review of ABI

The ABI:

-Injured SBP/uninjured brachial SBP.
-Normal >0.9.
-Historically, every KD underwent routine angiography (or CTA).
-The rationale: Normal pulses do not rule out vascular injury and a missed vascular injury can have serious consequences.
– Although many large trauma centers still perform angiography/CTA on every KD, the trend is toward a more selective approach to imaging in KD.
– The ankle-brachial index is a critical component of the physical exam for KD that many experts suggest can be used to guide the work-up.

-Mills (2004): Prospective study with 38 knee dislocations over four years. Patients with ABI >0.9 were immobilized, admitted for serial examinations and delayed arterial duplex examination. No patients with ABI >0.9 (n=27) were found to have vascular injury by serial clinical examination or duplex ultrasonography. None required revascularization. All patients with ABI <0.9 (n=11) required revascularization.

-Kleinburg (2004): Retrospective analysis of 57 knee dislocations over seven years. 32/57 patients had ABI >0.9, 0/32 had vascular injury as determined by angiography in 13/32 of cases and by serial examinations in 19/32 cases. 25/57 patients had abnormal ABI (<0.9), all 25 underwent angiography, 12/25 found to have substantial vascular injury.

-These and many other studies support the use of ABI as an initial screening tool for recognizing patients who require more advanced imaging.
-The ABI is a quick, easy and cost-effective screening tool that should be utilized by ER physicians to guide management decisions in KD patients.

Back to our case:

The patient had an initial ABI 0.92. He underwent a CTA, which was normal. He was discharged home within 24 hours. Based on review of the literature, the argument could be made that the CTA was unnecessary in the setting of a normal ABI. Would you have handled the case differently?

Summarizing the Management:

Flow ChartAdapted from

Hard and softThis post has been internally reviewed by Dr Jeffrey Feden, Attending and Assistant Professor and Dr Neha Raukar, Attending, Assistant Professor and Director, Division of Sports Medicine, Department of Emergency Medicine, Alpert Medical School of Brown University


  1. Peskun CJ, Levy BA, Fanelli GC , et al. Diagnosis and management of knee dislocations. Phys Sportsmed. 2010;38(4):101–11.
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  2. Georgiadis AG, Mohammad FH, Mizerik KT, et al. Changing presentation of knee dislocation and vascular injury from high energy trauma to low-energy falls in the morbidly obese. J Vascular Surgery 2012; 57(5):1196-1203.
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  2. Kleinberg EO, Crites, BM, Flinn WR. The role of arteriography in assessing popliteal artery injury in knee dislocations.J Trauma 2004; 56(4): 786-90.


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