A Knee Out of Place

A 30yM presents to the Canadian Janus General ED at 11:30 pm with acute onset knee pain immediately after stopping awkwardly on his motorcycle. He had placed his left foot down while the vehicle was in motion, causing his leg to lock and hyperextend during a pivot-type movement. He denies any other injuries.

On exam he is in a lot of discomfort. Vital signs are all normal. His left knee is swollen and obviously deformed. Pedal pulses (DP and PT) are intact and equal quality bilaterally. You cannot appreciate a popliteal hematoma or a bruit/thrill. The colour of his lower limb is normal There is normal sensation in the lower leg and foot. Moving his knee/ankle/foot however, is very uncomfortable. There are no other injuries.

You suspect a knee dislocation. You give him a dose of fentanyl 1 mcg/kg while awaiting some portable X-rays. Fifteen minutes later you have your films. X-rays are shown below:


As suspected there is an anterior left knee dislocation. You plan to reduce the knee. As you think about your drug of choice, the nurse tells you that the patient consumed a sandwich and soft drink approximately 90 minutes ago. “Should we wait a few hours? I’ll make him NPO?”

You recall reading the recent clinical policy on ED procedural sedation from Ann Emerg Med “Clinical policy: procedural sedation and analgesia in the emergency department.”

To answer the question “In patients undergoing procedural sedation and analgesia in the emergency department, does preprocedural fasting demonstrate a reduction in the risk of emesis or aspiration?

Level B recommendations. Do not delay procedural sedation in adults or pediatrics in the ED based on fasting time. Preprocedural fasting for any duration has not demonstrated areduction in the risk of emesis or aspiration when administering procedural sedation and analgesia.”

You decide to proceed with the sedation and reduction.

Then the nurse says to you, “I will page RT, but which other ED doc will assist you with the sedation? Don’t you need two docs?”

You look at the ED tracker and see that all sections of the department are busy, with 2-3 hour wait times and a waiting room full of patients. You then recall that the “Clinical policy: procedural sedation and analgesia in the emergency department” paper also addressed this issue.

To answer the question “In patients undergoing procedural sedation and analgesia in the emergency department, what is the minimum number of personnel necessary to manage complications?

“Level C recommendations. During procedural sedation and analgesia, a nurse or other qualified individual should be present for continuous monitoring of the patient, in addition to the provider performing the procedure. Physicians who are working or consulting in the ED should coordinate procedures requiring procedural sedation and analgesia with the ED staff.”

You take this to mean that having an ED nurse and respiratory therapist in the room to monitor the patient is safe and efficient while you perform the reduction and keep an eye on the patient during sedation as well. Your nursing and RT colleagues agree with this plan. You proceed.

The nurse then asks, “So fentanyl and propofol? That’s what Dr Smith usually uses.”

You kindly reply and suggest that ketamine and propofol is a better option. It is associated with fewer adverse events (Messenger et al) and is very effective (Andolfatto et al). You have the nurse draw up 100 mg of propofol and 100 mg of ketamine for this 85 kg patient.

ketamine Propofol

After 50 mg of ketamine followed by 40 mg of propofol, you successfully reduce the knee by longitudinal traction and splint the joint in a Zimmer knee immobilizer. The sedation goes uncomplicated. His neurovascular exam is still normal.

Repeat X-ray is below:


The reduction is satisfactory, and you can now appreciate an associated fracture of the medial femoral condyle. You page your on-call orthopedic surgeon and while you order a post-reduction film. Pulses are still normal and the patient, now awake, has intact motor and sensory function in the lower extremity. You know that knee dislocations are associated with popliteal artery injury, with reported rates of 7-64% (E-medicine). Your orthopod calls back and you ask whether your patient needs angiography to rule out vascular injury. He says that serial (normal) exams overnight followed by admission and observation for 1-2 days would be sufficient enough to rule out a significant vascular injury. Just to be sure you call your vascular surgeon and they agree.

Is this a safe practice?

According to a prospective cohort study by Stannard et al, of 138 patients with knee dislocation, 116 had normal physical exams. Of these, 17 had angiography, in whom 1 had an intimal tear that was observed without consequence. Thus all 138 patients with normal vascular exams had good outcomes. Of note, all were admitted for a minimum of 48 hours for observation.

Similarly, a prospective study by Miranda et al of 35 patients with knee dislocations found that all 27 patients with a negative exam for hard findings* (see below) of vascular injury, none developed ischemia during their hospitalization. Of note, only 12 of these were available for long-term followup.

A bit more about knee dislocation:

  • Often due to a significant trauma mechanism such as MVC, auto-ped collision, fall from height or sporting injuries (Seroyer et al)
  • There is a high spontaneous reduction rate, which may account for missing this injury unless a thorough physical exam is performed. (EM Cases Ep 1)
  • At least 3 major ligaments usually rupture in order for the usually-stable knee joint to dislocate, thus any knee exam with multiplanar/multiligamentous instability should be a suspected dislocation that spontaneously reduced prior to ED arrival. (EM Cases Ep 1)
  • About 50-60% of dislocations are associated with fractures as well (Stannard et al).
  • *Hard signs of vascular injury include absence of distal pulses, active bleeding from an open injury, expanding haematoma, bruit or thrill in the popliteal fossa and distal ischemia (Seroyer et al)
  • Presence of hard signs of vascular injury requires prompt reduction even before pre-reduction images are obtained (Seroyer et al)
  • Many institutions and surgeons still recommend more advanced vascular imaging for all knee dislocations, including duplex ultrasonography, CT angiography or direct arteriography. (E-Medicine)
  • Ankle-brachial index (ABI) can be used with a sensitivity and specificity of 95% and 97% respectively to rule out clinically significant arterial injury. (E-Medicine)
  • How is ABI done? According to Khan et al, ABI is performed by measuring the two upper extremity blood pressures and recording the higher systolic BP number, followed by the two ankle pressures and recording the lower systolic BP. In the case of acute vascular injury, one would only record the systolic BP of the limb in question. Use the ankle pressure as your numerator and the arm pressure as your denominator. If your value is <0.9 should prompt vascular imaging.

Case Resolution:

The patient and ED staff were satisfied with the sedation and prompt reduction, even though he didn’t have an empty stomach. Your department flow wasn’t compromised. His pain resolved with reduction and immobilization and he had normal serial vascular exams. After a brief admission he was discharged with outpatient followup. MRI of the knee demonstrated the following injuries:

  • complete tears of ACL, PCL, MCL, LCL, biceps femoris and popliteus tendons
  • partial tears of the medial and lateral patellar retinacula
  • partial tearing of adductor magnus and the adductor tubercle insertion
  • partial tears of the medial and lateral gastrocnemius tendons and biceps femoris at myotendinous junction
  • displaced fracture fragments of the medial aspect of medial femoral condyle
  •  increased signal of the common peroneal nerve compatible with injury

How would you have managed a similar case?

  • Do you wait before performing procedural sedation for patients who aren’t fasted?
  • What is your preferred cocktail of sedation medications?
  • How does your institution manage knee dislocations with negative vascular exams? Vascular imaging for all, or serial exams?

Leave your comments below or tweet me at @ETtube

Thanks to Dr Paul Koblic for review and suggestions.


Andolfatto G, Willman E. A prospective case series of single-syringe ketamine-propofol (ketofol) for emergency department procedural sedation and analgesia in adults. Acad Emerg Med. 2011;18:237-245.

Godwin et al. Clinical Policy: Procedural Sedation and Analgesia in the Emergency Department. Ann Emerg Med. 2014;63:247-258.

Kelleher B and Brenner B. Emedicine: Knee Dislocation Clinical Presentation Accessed Aug 14, 2014.

Khan et al. Critical Review of the Ankle Brachial Index. Curr Cardiol Rev. 2008. 4(2) 101-106

Messenger DW, Murray HE, Dungey PE, et al. Subdissociative-dose ketamine versus fentanyl for analgesia during propofol procedural sedation: a randomized clinical trial. Acad Emerg Med. 2008;15:877-886.

Miranda FE et al. Confirmation of the safety and accuracy of physical examination in the evaluation of knee dislocation for injury of the popliteal artery: a prospective study. J Trauma. 2002 Feb;52(2):247-51; discussion 251-2.

Seroyer ST et al. Management of the acute knee dislocation: the Pittsburgh experience. Injury. 2008 Jul;39(7):710-8.

Stannard JP et al. Vascular injuries in knee dislocations: the role of physical examination in determining the need for arteriography. J Bone Joint Surg Am. 2004 May;86-A(5):910-5.

Emergency Medicine Cases, Episode 1: Occult Fractures & Dislocations


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