Knee
Knee Dislocation
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Knee Dislocation
, Tibial Femoral Dislocation, Knee Subluxation, Multiligament Knee Injury
See Also
Acute
Knee Injury
Knee Pain
Patella
Dislocation
Background
Uncommon, but potentially limb threatening injury
Pathophysiology
High energy knee injuries result in shearing forces that tear multiple ligaments
Knee Dislocation requires the disruption of 2-3 of the four major knee ligaments
Anterior Cruciate Ligament Tear
Posterior Cruciate Ligament Tear
Knee Medial Collateral Ligament Tear
Knee Lateral Collateral Ligament Tear
Instability results from multiple ligamentous injuries
Allows for translation of tibia and fibula in relation to the femur
Associated Popliteal Artery Injury
Popliteal artery is tethered above (tendinous hiatus) and below (soleus tendinous arch) the popliteal fossa
Dislocation stretches the popliteal artery which has decreased flexibility due to its tethering
Causes
Motor Vehicle Accident
(two thirds of cases)
Collision Sport
s (e.g. football, rugby, soccer)
Fall from height
Downhill Skiing
Cutting sports
Knee Dislocation may occur with lower energy if there is rotation prior to shearing forces
Athlete attempts to change direction with a planted lower extremity
Results in knee hyperextension
Severe
Obesity
Single condition in which Knee Dislocation may occur even without high velocity
Trauma
Obesity
also complicates the dislocation diagnosis (obscured landmarks) and vascular monitoring
Typically requires slight rotation of the knee prior to experiencing shearing forces
Change in direction during ambulation
Multiple case studies demonstrating low mechanism dislocations, typically in BMI >40
Popliteal artery injury in 40%
Peroneal nerve injury in 40%
High risk of amputation (as high as 20% of Knee Dislocations)
Ankle
brachial index (and CTA if <0.9)
References
Azar (2011) Am J Sports Med 39(10): 2170-4 [PubMed]
Folt (2012) Am J Emerg Med 30(9): 2090.e5-2090.e6 [PubMed]
Georgiadis (2013) J Vasc Surg 57(5): 1196-203 [PubMed]
Total
Knee
Arthroplasty (TKA)
Anterior dislocation is more common than posterior dislocation
Prevalence
of Knee Dislocation after TKA: 0.15 to 0.5%
Causes
Implant malposition
Flexion-Extension gap mismatch
Excessive soft tissue release or laxity
Incorrect primary implant selection
Emergent Management is the same for native Knee Dislocation (see below)
Emergent knee relocation to reduce the risk of neurovascular compromise
Neurovascular exam and evaluation including ABI or CTA as indicated (see below)
Revision of TKA
References
Rashidzada (2020) Crit Dec Emerg Med 34(12): 12-3
Types
Most common types
Anterior Dislocation (40% of cases, most common)
Severe
Knee
hyperextension injury (>30 degrees with torn posterior stabilizing elements)
Posterior Dislocation
Direct blow to the proximal tibia (e.g. knee strikes car dashboard in MVA)
Less common types
Medial dislocation
Results from valgus force
Lateral Dislocation
Results from varus force
Rotary Dislocation
Planted foot with counter rotation of the body
May result in a posterolateral dislocation (non-reducible without surgery)
Exam
See
Knee Exam
Perform before and after reduction
Observation
Knee Effusion
or swelling,
Ecchymosis
or deformity
Palpation
Focal tenderness over joint line and bony prominences
Range of motion
Passive and active range of motion if patient is able
Multidirectional instability
Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
At least 2-3 of four ligaments are likely injured (
ACL Tear
,
PCL Tear
, LCL tear, MCL tear)
Evaluate each knee ligament
Vascular exam (especially popliteal artery distribution)
Perfusion Assessment
Dorsalis pedis pulse
Posterior tibial pulse
Capillary Refill
Ankle-Brachial Index
(ABI)
Normal ABI (as well as pulses,
Capillary Refill
) may not exclude popliteal artery disruption
Ankle-Brachial Index
(ABI) < 0.9 requires advanced imaging
Hard signs of vascular injury
Distal pulse loss or ischemia (e.g. pallor, coolness)
Active bleeding
Expanding
Hematoma
Palpable thrill or bruit over popliteal artery
Paresthesia
s or paralysis
Neurologic Exam
(especially peroneal nerve)
First web space and dorsal foot
Sensation
Ankle
dorsiflexion
Skin changes
Dimple Sign
Anteromedial skinfold at medial joint line
Seen in posterolateral dislocation (not reducible without surgery)
Skin necrosis
Entrapped skin at femoral condyle
Overlying
Laceration
Suggests open Knee Dislocation (accompanies 20-30% of Knee Dislocations)
Imaging
Ankle-Brachial Index
(ABI) under exam as above
Normal ABI (as well as pulses,
Capillary Refill
) may not exclude popliteal artery disruption
Ankle-Brachial Index
(ABI) < 0.9 requires advanced imaging
Knee XRay
Pre-reduction
Do not delay reduction for imaging if any signs of vascular compromise
XRay evaluates for
Fracture
Post-reduction XRay
Associated lower extremity
Fracture
in almost 60% of Knee Dislocations
More common
Fracture
s include
Tibial Plateau Fracture
, tendon avulsion
Fracture
at lateral tibial condyle
Vascular
Ultrasound
Arterial
Doppler Ultrasound
CT Angiogram (or MR Angiogram)
Indicated post-reduction if signs of vascular compromise (popliteal artery disruption)
Critical Limb Ischemia
requires emergent vascular surgery without delay of angiogram (see below)
Precautions
Knee Dislocation is a surgical emergency requiring immediate reduction
Delay in reduction risks limb-threatening vascular compromise
Pre-reduction imaging is only indicated if no signs of vascular compromise
Knee
spontaneous reduction prior to presentation occurs in >50% of patients
Do not dismiss patient report of "popping out-and-in
Sensation
" simply as
Patella
subluxation
Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
Knee Dislocation may occur with low energy mechanism and confers much higher risk than
Patella
subluxation
Follow the same vascular evaluation and monitoring if Knee Dislocation is suspected
Have a high index of suspicion for vascular injury (popliteal artery injury in up to 20-40% of patients)
Popliteal artery repair delayed >8 hours is associated with
Limb Amputation
in 85% of patients
(2007) J Trauma 63(4): 855-8 [PubMed]
Vascular injury may be present in up to 9% of cases despite normal distal pulses (high risk of amputation)
Confirm with ABI and
Doppler Ultrasound
Obtain CT Angiogram if
Ankle-Brachial Index
<0.9
More than 50% of Knee Dislocations spontaneously relocate prior to emergency department presentation
Follow post-reduction plan below
Management
Knee Joint
Reduction
Perform knee reduction without delay
Procedural Sedation
Technique (requires 2 providers)
One provider grasps the distal femur to stabilize
Other provider grasps the proximal tibia
Avoid compression at the popliteal fossa (popliteal artery)
Apply longitudinal traction to tibia
Reverse the dislocation if traction alone does not reduce the dislocation
Continue longitudinal traction
Push the tibia posteriorly in anterior dislocation
Pull the tibia anteriorly in posterior dislocation
Splint knee after reduction
Apply
Knee Immobilizer
or long leg splint
Prevents repeat dislocation in the acute period
Splint or
Knee Immobilizer
in 15 to 20 degrees flexion
Failed reduction
Emergent orthopedic
Consultation
Posterolateral dislocations are not reducible without surgery
Emergent Surgical Intervention Indications
Prolonged ischemia or other hard signs of vascular injury (see exam above)
Knee
reduction fails or cannot be maintained
Posterolateral dislocation (requires both emergent orthopedic consult and vascular consult)
Open Knee Dislocation
Management
Evaluate for vascular compromise (popliteal artery injury)
No vascular injury
Findings
Strong dorsalis pedis pulse and posterior tibial pulse
Ankle-Brachial Index
>0.9
Bedside arterial duplex
Ultrasound
normal
Management
Observation hospital stay
Serial distal vascular examinations
Observe for distal extremity paleness,
Paresthesia
s, paralysis
Orthopedic
Consultation
for reconstructive surgery
Possible vascular injury
Findings
Adequate limb perfusion despite abnormal vascular findings
Asymmetric dorsalis pedis pulse or posterior tibial pulse
Ankle-Brachial Index
<0.9
Bedside duplex
Ultrasound
abnormal
Management
Urgent vascular surgery
Consultation
Urgent CT angiogram (or other angiographic assessment of popliteal artery)
Vascular compromise (limb-threatening)
Findings
Weak or absent dorsalis pedis pulse and posterior tibial pulse
Signs of limb ischemia or vascular injury
Management
Emergent vascular surgery
Consultation
for immediate repair
Complications
Popliteal artery injury (32-40% of Knee Dislocations)
Results in limb threatening vascular injury
Popliteal vein injury may also occur
Devascularization results in nearly 100% amputation rate at 8 hours
Peroneal nerve injury (14-35% of Knee Dislocations)
Results in loss of first web space and dorsal foot
Sensation
Results in loss of ankle dorsiflexion and toe extension
Lower leg
Compartment Syndrome
Late finding if due to popliteal artery injury
Cruciate Ligament Teat (ACL, PCL)
Deep Vein Thrombosis
Tibial Plateau Fracture
Tibial shaft
Fracture
Fibular Head Fracture
Severe knee ligamentous disruption
References
Grozenski and Kiel (2019) Crit Dec Emerg Med 33(10):10-1
Kirwin, Conroy, McGrath (2021) Crit Dec Emerg Med 35(7): 15-24
Mason and Campagne in Herbert (2018) EM:Rap 18(3):12-3
Bachman in Wolfson and Stack (2014) Knee Dislocation and Reduction, UpToDate, accessed 6/5/2014
http://www.uptodate.com/contents/knee-tibiofemoral-dislocation-and-reduction
Kelleher in Brenner (2013) Knee Dislocation, Medscape Emedicine, accessed 6/5/2014
http://emedicine.medscape.com/article/823589-clinical#showall
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