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Knee Dislocation
Aka: Knee Dislocation, Tibial Femoral Dislocation, Knee Subluxation
- See Also
- Acute Knee Injury
- Knee Pain
- Background
- Uncommon, but potentially limb threatening injury
- Pathophysiology
- Knee Dislocation requires the disruption of three of four major knee ligaments
- Anterior Cruciate Ligament Tear
- Posterior Cruciate Ligament Tear
- Knee Medial Collateral Ligament Tear
- Knee Lateral Collateral Ligament Tear
- Causes
- Motor Vehicle Accident (two thirds of cases)
- Collision Sports (e.g. football, rugby, soccer)
- Downhill Skiing
- 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
- 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
- Prevalance 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
- 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
- Perform before and after reduction
- Knee deformity
- 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
- 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
- Neurologic Exam (especially peroneal nerve)
- First web space and dorsal foot sensation
- Ankle dorsiflexion
- Multidirectional instability
- Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
- Three of four ligaments are likely injured (ACL Tear, PCL Tear, LCL tear, MCL tear)
- 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:
- Knee XRay
- Pre-reduction
- Do not delay reduction for imaging if any signs of vascular compromise
- Evaluates for Fracture
- Post-reduction
- Vascular Ultrasound
- Arterial Doppler Ultrasound
- CT 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 immediation 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
- 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) in up to 20-40% of patients
- 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 in 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 (e.g. posterolateral dislocation) or cannot be maintained
- 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, Paresthesias, 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
- 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
- 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