II. Epidemiology
- Knee Dislocation is uncommon, but potentially limb threatening injury
III. 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
- 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
IV. Causes
- Motor Vehicle Accident (two thirds of cases)
- Collision Sports (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
- 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
V. 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)
- Anterior Dislocation (40% of cases, most common)
- 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)
- Medial dislocation
VI. Exam
- See Knee Exam
- Perform before and after reduction
- Observation
- Knee Effusion or swelling, Ecchymosis
- Deformity may be present if persistent dislocation at presentation
- 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
- Knee Anterior Drawer Test or Lachman Test (ACL Tear)
- Knee Posterior Drawer Test or PCL Sag Test (PCL Tear)
- Knee Valgus Stress Test (Knee MCL Tear)
- Knee Varus Stress Test (Knee LCL Tear)
- 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
- Paresthesias or paralysis
- Perfusion Assessment
- Neurologic Exam (especially peroneal nerve)
- 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)
- Dimple Sign
VII. Imaging
-
Ankle-Brachial Index (ABI, see exam as above)
- Ankle-Brachial Index (ABI) < 0.9 requires advanced imaging
- Normal ABI (as well as pulses, Capillary Refill) may not exclude popliteal artery disruption
- However, ABI Test Sensitivity approaches 100% for significant arterial injury
- Medina (2014) Clin Orthop Relat Res 472(9): 2621-9 [PubMed]
-
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
- Most common associated Fractures
- Tibial Plateau Fracture
- Tendon avulsion Fracture at lateral tibial condyle
- Pre-reduction
- 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)
- MR is ideal when rapidly available without delay, as it characterizes the associated soft tissue injuries
VIII. Differential Diagnosis
-
Patellar Dislocation
- Patellar Dislocation and Subluxation are diagnoses of exclusion
- In obese patients, even low mechanism injuries may result in occult Knee Dislocation/relocation
- Patellar Dislocation is NOT associated with ligamentous instability (ACL, PCL, MCL, LCL)
- Spontaneous relocation occurs frequently with both Knee Dislocation and Patellar Dislocation
- However, misdiagnosing a Knee Dislocation as a Patella dislocation risks delays and Limb Amputation
IX. 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 >6 to 8 hours is associated with Limb Amputation in 85% of patients
- With early diagnosis and management, amputation risk is <18%
- (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
- Popliteal artery repair delayed >6 to 8 hours is associated with Limb Amputation in 85% of patients
X. 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
XI. 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
- Findings
- 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)
- Findings
- 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
- Findings
XII. Management: Multiligament Instability
- Knee Dislocation requires severe knee ligamentous disruption (ACL, PCL, MCL, LCL)
- Refer all patients to orthopedics following Knee Dislocation (after emergently excluding neurovascular injury)
- Operative repair within 3 weeks of multi-Ligamentous Injury results in best longterm outcomes
- Scarring interferes with repair if delayed >3 weeks
- Consider non-operative management in sedentary or elderly patients
- References
XIII. 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)
- Loss of first web space and dorsal foot Sensation
- Loss of ankle dorsiflexion and toe extension
- Lower leg Compartment Syndrome
- Late finding if due to popliteal artery injury
- Multiligament instability (see management above)
- Deep Vein Thrombosis
- Tibial Plateau Fracture
- Tibial shaft Fracture
- Fibular Head Fracture
XIV. 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
- Long and Lynch (2023) Crit Dec Emerg Med 37(12): 18-9
- 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
- Kelleher in Brenner (2013) Knee Dislocation, Medscape Emedicine, accessed 6/5/2014