Introduction |
- Overview
- Knee dislocations are traumatic injuries characterized by a high rate of vascular injury and seen in high and low energy injuries
- treatment is generally emergent reduction and assessment of limb perfusion
- Epidemiology
- incidence
- 0.02% of orthopedic injuries
- likely underreported as approximately 50% self-reduce and misdiagnosed
- demographics
- location
- tibiofemoral articulation
- risk factors
- morbid obesity is a risk factor for "ultra-low energy" knee dislocations with activities of daily living
- Pathophysiology
- mechanism of injury
- high-energy vs low energy
- high energy is usually from MVC, crush injury, fall from a height, or dashboard injury resulting in axial load to a flexed knee
- low energy may be from an athletic injury, routine walking, or morbidly obese ultra-low injury
- hyperextension injury leads to anterior dislocations
- posteriorly directed force across the proximal tibia (dashboard injuries) leads to posterior dislocations
- Associated injuries
- vascular injury
- nerve injury
- usually common peroneal nerve injury (25%)
- tibial nerve injury is less common
- fractures
- present in 60% of dislocations
- soft tissue injuries
- patellar tendon rupture
- periarticular avulsion
- displaced menisci
- Prognosis
- complications frequent and rarely does knee return to a pre-injury state
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Anatomy |
- Osteology
- the knee is a ginglymoid joint and consists of tibiofemoral, patellofemoral and tibiofibular articulations
- Ligaments
- PCL, ACL, LCL, MCL, and PLC are all at risk for injury
- main stabilizers of the knee given the limited stability afforded by the bony articulations
- Blood supply
- popliteal artery injuries occur often due to tethering at the popliteal fossa
- proximal - fibrous tunnel at the adductor hiatus
- distal - fibrous tunnel at soleus muscle
- geniculate arteries may provide collateral flow and palpable pulses masking a limb-threatening vascular injury
- Biomechanics
- the normal range of motion of 0-140 degrees with 8-12 degrees of rotation during flexion/extension
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Classification |
- Descriptive
- Kennedy classification based on the direction of displacement of the tibia
- anterior (30-50%)
- most common
- due to hyperextension injury
- usually involves tear of PCL
- an arterial injury is generally an intimal tear due to traction
- posterior (30-40%)
- 2nd most common
- due to axial load to the flexed knee (dashboard injury)
- the highest rate of vascular injury (25%) based on Kennedy classification
- the highest rate of a complete tear of the popliteal artery
- lateral (13%)
- due to a varus or valgus force
- usually involves tears of both ACL and PCL
- the highest rate of peroneal nerve injury
- medial (3%)
- varus or valgus force
- usually disrupted PLC and PCL
- rotational (4%)
- posterolateral is most common rotational dislocation
- usually irreducible
- buttonholing of femoral condyle through the capsule
- Schenck Classification
- based on a pattern of multiligamentous injury of knee dislocation (KD)
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Schenck Classification (based on the number of ruptured ligaments) |
KD I |
Multiligamentous injury with the involvement of the ACL or PCL |
KD II |
Injury to ACL and PCL only (2 ligaments) |
KD III |
Injury to ACL, PCL, and PMC or PLC (3 ligaments). KDIIIM (ACL, PCL, MCL) and KDIIIL (ACL, PCL, PLC, LCL). |
KD IV |
Injury to ACL, PCL, PMC, and PLC (4 ligaments) KDIV has the highest rate of vascular injury (5-15%%) based on Schenck classification
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KD V |
Multiligamentous injury with periarticular fracture |
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Presentation |
- Symptoms
- history of trauma and deformity of the knee
- knee pain & instability
- Physical exam
- appearance
- no obvious deformity
- 50% spontaneously reduce before arrival to ED
- may present with subtle signs of trauma (swelling, effusion, abrasions, ecchymosis)
- obvious deformity
- reduce immediately, especially if absent pulses
- "dimple sign" - buttonholing of medial femoral condyle through the medial capsule
- indicative of an irreducible posterolateral dislocation
- a contraindication to closed reduction due to risks of skin necrosis
- vascular exam
- priority is to rule out vascular injury on exam both before and after reduction
- serial examinations are mandatory
- palpate the dorsalis pedis and posterior tibial pulses on injured and contralateral side
- if pulses are present and normal
- does not indicate the absence of arterial injury
- collateral circulation can mask a complete popliteal artery occlusion
- measure Ankle-Brachial Index (ABI) on all patients with suspected KD
- if ABI >0.9
- then monitor with serial examination (100% Negative Predictive Value)
- if ABI <0.9
- perform an arterial duplex ultrasound or CT angiography
- if arterial injury confirmed then consult vascular surgery
- If pulses are absent or diminished
- confirm that the knee joint is reduced or perform immediate reduction and reassessment
- immediate surgical exploration if pulses are still absent following reduction
- ischemia time >8 hours has amputation rates as high as 86%
- imaging contraindicated if it will delay surgical revascularization
- if pulses present after reduction then measure ABI then consider observation vs. angiography
- neurologic exam
- assess sensory and motor function of peroneal and tibial nerve as nerve deficits often occur concomitantly with vascular injuries
- stability
- diagnosis based on instability on physical exam (radiographs and gross appearance may be normal)
- may see recurvatum when held in extension
- assess ACL, PCL, MCL, LCL, and PLC
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Imaging |
- Radiographs
- recommended views
- pre-reduction AP and lateral of the knee
- may be normal if spontaneous reduction
- look for asymmetric or irregular joint space
- look for avulsion fxs (Segond sign - lateral tibial condyle avulsion fx)
- osteochondral defects
- post reduction AP and lateral of the knee
- optional views
- 45-degree oblique if fracture suspected
- CT
- indications
- fracture identified on post reduction plain films
- obtain post reduction CT for characterization of fracture
- findings
- tibial eminence, tibial tubercle, and tibial plateau fractures may be seen
- MRI
- indications
- obtain MRI after acute reduction but prior to hardware placement
- required to evaluate soft tissue injury (ligaments, meniscus) and for surgical planning
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Treatment |
- Nonoperative
- emergent closed reduction followed by vascular assessment/consult
- indications
- considered an orthopedic emergency
- vascular consult indicated if
- pulses are absent or diminished following reduction
- if arterial injury confirmed by arterial duplex ultrasound or CT angiography
- immobilization as definitive management
- indications (rare)
- successful closed reduction without vacular compromise
- most cases require some form of surgical stabilization following reduction
- outcomes
- worse outcomes are seen with nonoperative management
- Operative
- open reduction
- indications
- irreducible knee
- posterolateral dislocation
- open fracture-dislocation
- obesity (may be difficult to obtain closed)
- vascular injury
- external fixation
- indications
- vascular repair (takes precedence)
- open fracture-dislocation
- compartment syndrome
- obese (if difficult to maintain reduction)
- polytrauma patient
- delayed ligamentous reconstruction/repair
- indications
- instability will require some kind of ligamentous repair or fixation
- patients can be placed in a knee immobilizer until treated operatively
- improved outcomes with early treatment (within 3 weeks)
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Technique |
- Closed reduction
- approach
- anterior dislocation - traction and anterior translation of the femur
- posterior dislocation - traction, extension, and posterior translation of the tibia
- medial/lateral - traction and medial or lateral translation
- rotatory - axial limb traction and rotation in the opposite direction of deformity
- splinting
- 20 to 30 degrees of flexion
- Open reduction
- approach
- midline incision with a medial parapatellar arthrotomy
- soft tissue
- the medial capsule may need to be pulled over medial condyle if buttonholed
- acute associated soft tissue injuries (patellar tendon rupture, periarticular avulsion, or displaced menisci) may benefit from acute repair
- bone work
- periarticular fractures may be fixed acutely or spanned with external fixator depending on surgeon preference
- instrumentation
- place knee-spanning external fixator in 20-30 degrees of flexion with knee reduced in AP and sagittal planes
- Early ligamentous reconstruction (<3 weeks)
- approach
- arthroscopic versus open
- arthroscopic may not be possible if large capsular injury and creates a risk of fluid extravasation and compartment syndrome
- PLC and PMC require open reconstruction given subcutaneous nature and proximity to neurovascular structures
- soft tissue work
- arthroscopic reconstruction of ACL and/or PCL
- address intraarticular pathology (menisci, cartilage defects, capsular injury)
- open repair versus reconstruction of collateral ligaments
- outcomes
- acute reconstruction (<3 weeks) has been shown to lead to improved clinical and functional outcomes
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Complications |
- Vascular compromise
- incidence
- 5-15% in all dislocations
- 40-50% in anterior and posterior dislocations
- risk factors
- KD IV injuries have the highest rate of vascular injuries
- treatment
- emergent vascular repair and fasciotomies
- Stiffness (arthrofibrosis)
- incidence
- is the most common complication (38%)
- risk factors
- more common with delayed mobilization
- treatment
- avoid stiffness with early reconstruction and motion
- arthroscopic lysis of adhesion
- manipulation under anesthesia
- Laxity and instability
- incidence
- 37% of some instability, however, redislocation is uncommon
- treatment
- arthroscopic lysis of adhesion
- manipulation under anesthesia
- Peroneal nerve injury
- incidence
- 25% occurrence of a peroneal nerve injury
- 50% recover partially
- risk factors
- posterolateral dislocations
- treatment
- AFO to prevent equinus contracture
- neurolysis or exploration at the time of reconstruction
- nerve repair or reconstruction or tendon transfers if chronic nerve palsy persists
- dynamic tendon transfer involves transferring the posterior tibial tendon (PTT) to the lateral cuneiform.
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