Posterior Knee Dislocation

00:01 Now, let's move on to posterior knee dislocation.

00:05 This is an incredibly high-yield and important clinical entity.

00:10 Classically, it’s associated with a direct force to anterior knee in an anterior-posterior trajectory.

00:15 What’s the most common scenario for this? Just like this dummy in a vehicle.

00:20 The dashboard hits the knee causing a posterior knee dislocation.

00:27 On physical examination, there may be laxity of the ligaments holding our knee joint together.

00:32 There can be significant pain and sometimes obvious deformities, including a posterior dislocation.

00:41 Imaging shows a clear demonstration of a posterior dislocation on the right side of the screen.

00:48 You can see on physical examination on the left side of the screen that knee is incredibly edematous and swollen.

00:54 Additionally, you see an obvious deformity, likely a posterior dislocation.

01:00 And surgery is usually necessary in these situations.

01:04 Again, we like to reduce and immobilize.

01:08 These patients often have a knee immobilizer, so there's no actual flexion or extension of the knee, allowing the bones to heal as well as the ligaments.

01:17 Remember what are they at high risk for for periods of – long periods of immobilization? That's right.

01:24 DVTs and pulmonary embolism.

01:27 Let's now discuss popliteal artery injuries.

01:30 Popliteal artery injury is incredibly important to recognize and you should have a high index of suspicion whenever a patient has a posterior knee dislocation.

01:40 It’s so commonly associated with posterior knee dislocation that whenever I have a patient that have the dislocation, I always seek to make sure that the patient does not also have I always seek to make sure that the patient does not also have a concomitant popliteal artery injury.

01:53 Warm ischemia time is critical to limb salvage.

01:55 What does that mean? Warm ischemia time is the time where the tissues distal to the artery injury is not getting oxygen.

02:04 This is different than cold ischemia time, which is talked about in transplantation.

02:10 Cold ischemia time is when organs are preserved in solutions and put on ice.

02:15 The theory behind cold ischemia time is there may be a better chance of salvage if something is put on ice and the metabolism has been lowered.

02:25 You must suspect a patient of popliteal artery injury if there's a posterior knee dislocation.

02:32 Remember that mechanism of injury.

02:34 That dashboard on a head-on collision has intruded on to the patient and pushed the knee back with enough force.

02:42 Therefore, it's not difficult to imagine that the popliteal artery, as you can see on this image, can become injured.

02:49 Reducing the knee joint is the first step if distal pulses are absent.

02:53 Pulses normally return immediately post-reduction, but if they remain absent, urgent operative treatment may be required.

03:01 Now, let's revisit some important clinical pearls and high-yield information.

03:06 Remember, any significant fracture, particularly long bone fracture, demands evaluation of the associated vessels.

03:15 You should always consider the potential for vascular injury in these situations.

03:20 Now, let me ask you.

03:21 How would you assess for vascular injury in these patients? I’ll give you a second think about this.

03:28 That's right.

03:29 You feel the patient's pulses.

03:31 There is a caveat, however.

03:33 There’s an additional test called the ankle brachial index, particularly for the lower extremities.

03:38 We generally have a differential pressure between our ankle systolic blood pressure and our arm systolic blood pressure.

03:45 Any index less than 0.9 warrants additional vascular injury workup.

03:53 High-yield information for your examination.

03:55 Remember, fat embolism after long bone fracture is a classic association.

04:01 However, it’s difficult to diagnose.

04:03 Therefore, you must have a high index of suspicion.

04:06 Treatment, though, is largely supportive.

04:08 And again, the diagnosis depends on your index of suspicion.

04:13 Unfortunately, there's no confirmatory study for this.

04:17 I would recommend, however, that on a clinical scenario, with a patient having a long bone fracture and mental status changes and hypoxia, your answer choice should be fat embolism.

04:30 Thank you for joining me on this discussion of classic fractures.