Knee dislocations

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Mechanism:

High-energy:

- Usually from MVC (dashboard injury resulting in axial load to flexed knee) or fall from height

Low- energy:

- Often from athletic injury (with a rotational component)

Associated injuries:

- Vascular injury 

- Nerve injury: usually common peroneal nerve injury

Types:

Anterior: Most common (30-50%)

-        due to hyperextension injury

-        usually involves tear of PCL

Posterior: 2nd most common  (25%)

-        due to axial load to flexed knee (dashboard injury)

-       Highest rate of vascular injury (25%) – with complete tear of the popliteal artery

Lateral (13%)

-        due to varus or valgus force

-        usually involves tears of both ACL and PCL

-        highest rate of peroneal nerve injury

 

- An anteromedial skin furrow, or “dimple sign” at the medial joint line, is suggestive of a posterolateral dislocation, which are irreducible!

Physical exam:

-        no obvious deformity- 50% spontaneously reduce prior to ED arrival!

-        obvious deformity:

o   reduce immediately, especially if absent pulses

Management:

- considered an orthopedic emergency

  1. palpate the dorsalis pedis and posterior tibial pulses. Palpable pulses DON’T rule out a vascular injury
  2. reduce the knee

- apply longitudinal traction to the extremity (This is usually all that is required to reduce a knee)

- Anterior knee dislocations may require additional lifting of the distal femur

- Posterior dislocations may require lifting of proximal tibia to complete reduction.

- After reduction, the knee should be immobilized in a long leg posterior splint with the knee in 15-        20 degrees of flexion.

https://www.youtube.com/watch?v=aN7zDxtyHy8

  1. measure Ankle-Brachial Index (ABI):

            - ABI > 0.9

                        - monitor with serial vascular exams

            - ABI < 0.9

- perform a CT angio

- if arterial injury confirmed then consult vascular surgery

  1. Immediate surgical exploration is indicated if pulses are still absent following reduction. Ischemia time >8 hourshas amputation rates as high as 86%!
  2. The patient should be taken to the OR for external fixation if:

  - vascular repair (takes precedence)

- open fx and open dislocation

- irreducible dislocation

- Compartment syndrome

- obese

- multi trauma patient

Sources: Ortho bullets, emdocs

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