after 8 hours of ischaemia, most will require an above knee amputation!!!
urgent reduction is critical!
assume all patients have a vascular injury until proven otherwise
introduction
an important time critical red flag of the acutely injured knee in ED is the possibility of a knee dislocation having occurred (not a patellar dislocation), as this requires urgent investigation to exclude a possible vascular injury to the popliteal vessels and potential
knee dislocation is uncommon and mainly occurs with high energy injuries such as motor vehicle accidents, falls from a height, high impact sports, downhill snow skiiing, etc.
knee dislocations are an increasingly common complication of gym exercises such as:
falling awkwardly when doing hamstring stretches with foot caught on bar
leg presses with heavy loads eg. 200kg single leg press
most dislocations are clinically evident and require urgent reduction as they may be limb threatening due to vascular injury
some spontaneously reduce but there is still potential vascular injury which needs emergent assessment.
potential complications
popliteal artery injury
after 8 hours of ischaemia, most will require an above knee amputation!!!
lesions or thrombosis may not become clinically apparent for several weeks after injury
an anteromedial skin furrow suggests posterolateral dislocation and these are irreducible by closed reduction methods due to buttonholing of the femoral condyle - these patients need urgent open reduction
other dislocations:
if good peripheral pulses, consider pre-reduction imaging
if peripheral pulses impaired, immediate reduction in ED is indicated to save the limb.
closed reduction in ED
care and precautions as per usual ED Mx of conscious sedation
two clinicians required to reduce the knee while a third manages airway, sedation, etc
one clinician grasps femur, the other the tibia - avoid applying pressure in popliteal fossa as this may exacerbate vascular injury
apply longitudinal traction, and most will reduce
if unsuccessful, reverse the direction of the dislocation
if still unsuccessful, urgent ortho team consult
post-reduction Mx
check for signs of vascular injury
document popliteal and pedal pulses - but note that presnce of pulses does not exclude injury!
consider measuring the ankle-brachial index (ABI)
consider urgent doppler USS
if any vascular injury present, urgent consult with vascular surgeon
post-reduction plain Xrays
many advocate routine CT angiography after any knee dislocation given the poor sensitivity of physical examination
admit all patients
3-4hrly neurovascular obs for at least 24 hours
post-discharge instructions:
repeat Xrays within 1 week to confirm still reduced
patient to return ASAP if any vascular symptoms
close orthopaedic follow up to determine need for and timing of surgical reconstruction of knee joint
features suggestive of a spontaneously reduced knee dislocation
presence of a significant posterolateral corner injury which is suggested by either:
fibular styloid fracture on lateral Xray (“arcuate sign”) is pathognomic of posterolateral corner injury and note that this is a different fracture to a fibular head fracture
Segond avulsion fracture from the tibial condyle on AP Xray is associated with ACL injury and posterolateral corner injury
Medial Segond avulsion fracture from the medial tibial condyle on AP Xray is associated with PCL injury and posterolateral corner injury
External Rotation Recurvatum Test:
The great toes are held by the examiner as both legs are raised simultaneously. A positive test results in hyperextension, external rotation of the tibia, and apparent tibia vara of the affected limb.
the Dial Test:
This test is performed with the knee flexed at 30deg and 90deg. The patient may be supine or prone.
The thighs are stabilized by an assistant or a strap, while the lower legs are synchronously externally rotated.
The amount of external rotation at the tibial tuberosity is compared with the other side. If prone, the external rotation may be measured by the thigh-foot angle. An increase of 10 to 15 degrees is considered a positive test and suggests a significant posterolateral corner injury.