Knee Dislocation

See Also

Acute Knee Injury
Knee Pain
Patella Dislocation

Epidemiology

Knee Dislocation is 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
Instability results from multiple ligamentous injuries
1. Allows for translation of tibia and fibula in relation to the femur
Associated Popliteal Artery Injury (esp. posterior dislocation)
1. Popliteal artery is tethered above (tendinous hiatus) and below (soleus tendinous arch) the popliteal fossa
2. Dislocation stretches the popliteal artery which has decreased flexibility due to its tethering

Causes

Motor Vehicle Accident (two thirds of cases)
Collision Sports (e.g. football, rugby, soccer)
Fall from height
Downhill Skiing
Cutting sports
1. Knee Dislocation may occur with lower energy if there is rotation prior to shearing forces
2. Athlete attempts to change direction with a planted lower extremity
  1. Results in knee hyperextension
Severe Obesity
1. Single condition in which Knee Dislocation may occur even without high velocity Trauma
2. Obesity also complicates the dislocation diagnosis (obscured landmarks) and vascular monitoring
3. Typically requires slight rotation of the knee prior to experiencing shearing forces
  1. Change in direction during ambulation
4. Multiple case studies demonstrating low mechanism dislocations, typically in BMI >40
  1. Popliteal artery injury in 40%
  2. Peroneal nerve injury in 40%
5. High risk of amputation (as high as 20% of Knee Dislocations)
  1. Ankle brachial index (and CTA if <0.9)
6. References
Total Knee Arthroplasty (TKA)
1. Anterior dislocation is more common than posterior dislocation
2. Prevalence of Knee Dislocation after TKA: 0.15 to 0.5%
3. Causes
  1. Implant malposition
  2. Flexion-Extension gap mismatch
  3. Excessive soft tissue release or laxity
  4. Incorrect primary implant selection
4. Emergent Management is the same for native Knee Dislocation (see below)
  1. Emergent knee relocation to reduce the risk of neurovascular compromise
  2. Neurovascular exam and evaluation including ABI or CTA as indicated (see below)
  3. Revision of TKA
5. References
  1. Rashidzada (2020) Crit Dec Emerg Med 34(12): 12-3

Types

Most common types
1. Anterior Dislocation (40% of cases, most common)
  1. Severe Knee hyperextension injury (>30 degrees with torn posterior stabilizing elements)
2. Posterior Dislocation
  1. Direct blow to the proximal tibia (e.g. knee strikes car dashboard in MVA)
Less common types
1. Medial dislocation
  1. Results from valgus force
2. Lateral Dislocation
  1. Results from varus force
3. Rotary Dislocation
  1. Planted foot with counter rotation of the body
  2. May result in a posterolateral dislocation (non-reducible without surgery)

Exam

See Knee Exam
Perform before and after reduction
Observation
1. Knee Effusion or swelling, Ecchymosis
2. Deformity may be present if persistent dislocation at presentation
Palpation
1. Focal tenderness over joint line and bony prominences
Range of motion
1. Passive and active range of motion if patient is able
Multidirectional instability
1. Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
2. At least 2-3 of four ligaments are likely injured (ACL Tear, PCL Tear, LCL tear, MCL tear)
  1. Evaluate each knee ligament
  2. Knee Anterior Drawer Test or Lachman Test (ACL Tear)
  3. Knee Posterior Drawer Test or PCL Sag Test (PCL Tear)
  4. Knee Valgus Stress Test (Knee MCL Tear)
  5. Knee Varus Stress Test (Knee LCL Tear)
Vascular exam (especially popliteal artery distribution)
1. Perfusion Assessment
  1. Dorsalis pedis pulse
  2. Posterior tibial pulse
  3. Capillary Refill
  4. Ankle-Brachial Index (ABI)
    1. Normal ABI (as well as pulses, Capillary Refill) may not exclude popliteal artery disruption
    2. Ankle-Brachial Index (ABI) < 0.9 requires advanced imaging
2. Hard signs of vascular injury
  1. Distal pulse loss or ischemia (e.g. pallor, coolness)
  2. Active bleeding
  3. Expanding Hematoma
  4. Palpable thrill or bruit over popliteal artery
  5. Paresthesias or paralysis
Neurologic Exam (especially peroneal nerve)
1. First web space and dorsal foot Sensation
2. Ankle dorsiflexion
Skin changes
1. Dimple Sign
  1. Anteromedial skinfold at medial joint line
  2. Seen in posterolateral dislocation (not reducible without surgery)
2. Skin necrosis
  1. Entrapped skin at femoral condyle
3. Overlying Laceration
  1. Suggests open Knee Dislocation (accompanies 20-30% of Knee Dislocations)

Imaging

Ankle-Brachial Index (ABI, see exam as above)
1. Ankle-Brachial Index (ABI) < 0.9 requires advanced imaging
2. Normal ABI (as well as pulses, Capillary Refill) may not exclude popliteal artery disruption
  1. Normal ABI should be accompanied by palpable dorsalis pedis and posterior tibial pulses
  2. ABI Test Sensitivity approaches 100% for significant arterial injury
  3. Medina (2014) Clin Orthop Relat Res 472(9): 2621-9 [PubMed]
Knee XRay
1. Pre-reduction
  1. Do not delay reduction for imaging if any signs of vascular compromise
  2. XRay evaluates for Fracture
2. Post-reduction XRay
  1. Associated lower extremity Fracture in almost 60% of Knee Dislocations
  2. Most common associated Fractures
    1. Tibial Plateau Fracture
    2. Tendon avulsion Fracture at lateral tibial condyle
Vascular Ultrasound
1. Arterial Doppler Ultrasound
CT Angiogram (or MR Angiogram)
1. Indicated post-reduction if signs of vascular compromise (popliteal artery disruption)
2. Critical Limb Ischemia requires emergent vascular surgery without delay of angiogram (see below)
3. MR is ideal when rapidly available without delay, as it characterizes the associated soft tissue injuries

Differential Diagnosis

Patellar Dislocation
1. Patellar Dislocation and Subluxation are diagnoses of exclusion
2. In obese patients, even low mechanism injuries may result in occult Knee Dislocation/relocation
3. Patellar Dislocation is NOT associated with ligamentous instability (ACL, PCL, MCL, LCL)
4. Spontaneous relocation occurs frequently with both Knee Dislocation and Patellar Dislocation
  1. However, misdiagnosing a Knee Dislocation as a Patella dislocation risks delays and Limb Amputation

Precautions

Knee Dislocation is a surgical emergency requiring immediate reduction
1. Delay in reduction risks limb-threatening vascular compromise
2. Pre-reduction imaging is only indicated if no signs of vascular compromise
Knee spontaneous reduction prior to presentation occurs in >50% of patients
1. Do not dismiss patient report of "popping out-and-in Sensation" simply as Patella subluxation
2. Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
3. Knee Dislocation may occur with low energy mechanism and confers much higher risk than Patella subluxation
4. 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)
1. Popliteal artery repair delayed >6 to 8 hours is associated with Limb Amputation in 85% of patients
  1. With early diagnosis and management, amputation risk is <18%
  2. (2007) J Trauma 63(4): 855-8 [PubMed]
2. Vascular injury may be present in up to 9% of cases despite normal distal pulses (high risk of amputation)
  1. Confirm with ABI and Doppler Ultrasound
  2. Obtain CT Angiogram if Ankle-Brachial Index <0.9
3. More than 50% of Knee Dislocations spontaneously relocate prior to emergency department presentation
  1. Follow post-reduction plan below

Management
Knee Joint Reduction

Perform knee reduction without delay
Procedural Sedation
Technique (requires 2 providers)
1. One provider grasps the distal femur to stabilize
2. Other provider grasps the proximal tibia
  1. Avoid compression at the popliteal fossa (popliteal artery)
  2. Apply longitudinal traction to tibia
  3. Reverse the dislocation if traction alone does not reduce the dislocation
    1. Continue longitudinal traction
    2. Push the tibia posteriorly in anterior dislocation
    3. Pull the tibia anteriorly in posterior dislocation
Splint knee after reduction
1. Apply Knee Immobilizer or long leg splint
2. Prevents repeat dislocation in the acute period
3. Splint or Knee Immobilizer in 15 to 20 degrees (up to 30 degrees) flexion
Failed reduction
1. Emergent orthopedic Consultation
2. Posterolateral dislocations are not reducible without surgery
Emergent Surgical Intervention Indications
1. Prolonged ischemia or other hard signs of vascular injury (see exam above)
2. Knee reduction fails or cannot be maintained
3. Posterolateral dislocation (requires both emergent orthopedic consult and vascular consult)
4. Open Knee Dislocation

Management
Evaluate for vascular compromise (popliteal artery injury)

No vascular injury
1. Findings
  1. Strong dorsalis pedis pulse and posterior tibial pulse
  2. Ankle-Brachial Index >0.9
  3. Bedside arterial duplex Ultrasound normal
2. Management
  1. Observation hospital stay
  2. Serial distal vascular examinations
  3. Observe for distal extremity paleness, Paresthesias, paralysis
  4. Orthopedic Consultation for reconstructive surgery
Possible vascular injury
1. Findings
  1. Adequate limb perfusion despite abnormal vascular findings
  2. Asymmetric dorsalis pedis pulse or posterior tibial pulse
  3. Ankle-Brachial Index <0.9
  4. Bedside duplex Ultrasound abnormal
2. Management
  1. Urgent vascular surgery Consultation
  2. Urgent CT angiogram (or other angiographic assessment of popliteal artery)
Vascular compromise (limb-threatening)
1. Findings
  1. Weak or absent dorsalis pedis pulse and posterior tibial pulse
  2. Signs of limb ischemia or vascular injury
2. Management
  1. Emergent vascular surgery Consultation for immediate repair

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
1. Scarring interferes with repair if delayed >3 weeks
2. Consider non-operative management in sedentary or elderly patients
References
1. Richter (2002) Am J Sports Med 30(5): 718-27 [PubMed]
2. Levy (2009) Arthroscopy 25(4): 430-8 [PubMed]

Complications

Popliteal artery injury (32-40% of Knee Dislocations)
1. Results in limb threatening vascular injury
2. Popliteal vein injury may also occur
3. Devascularization results in nearly 100% amputation rate at 8 hours
Peroneal nerve injury (14-35% of Knee Dislocations)
1. Loss of first web space and dorsal foot Sensation
2. Loss of ankle dorsiflexion and toe extension
Lower leg Compartment Syndrome
1. 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

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
1. http://www.uptodate.com/contents/knee-tibiofemoral-dislocation-and-reduction
Kelleher in Brenner (2013) Knee Dislocation, Medscape Emedicine, accessed 6/5/2014
1. http://emedicine.medscape.com/article/823589-clinical#showall