| Introduction |
.jpg) Devastating injury resulting from high or low energy
- high-energy
- usually from MVC or fall from height
- commonly a dashboard injury resulting in axial load to flexed knee
- low-energy
- often from athletic injury
- generally has a rotational component
- morbid obesity is a risk-factor
- Pathoanatomy
- associated with significant soft tissue disruption
- 3/4 of ligaments generally disrupted
- Associated injuries
- vascular injury
- 5-15% in all dislocations
- 50-60% in anterior/posterior dislocations
- due to tethering at the politeal fossa
- proximal - fibrous tunnel at the adductor hiatus
- distal - fibrous tunnel at soleus muscle
- nerve injury
- usually common peroneal nerve injury (25%)
- tibial nerve injury is less common
- fractures
- present in 60%
- tibia and femur most common
- Prognosis
- complications frequent and rarely does knee return to pre-injury state
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| Classification |
- Descriptive
- based on direction of displacement of the tibia
- anterior
- most common type of dislocation (30-50%)
- due to hyperextension injury
- usually involves tear of PCL
- arterial injury is generally an intimal tear due to traction
- posterior
- 2nd most common type (25%)
- due to axial load to flexed knee (dashboard injury)
- highest rate of complete tear of popliteal artery
- lateral
- 13% of knee dislocations
- due to valgus force
- usually involves tears of both ACL and PCL
- highest rate of peroneal nerve injury
- medial
- varus force
- usually disrupted PLC and PCL
- rotational
- posterolateral is most common rotational dislocation
- usually irreducible
- Schenck Classification
- based on pattern of multiligamentous injury of knee dislocation (KD)
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| Schenck Classification |
| KD I |
Multiligamentous injury with involvement of 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) |
| KD IV |
Injury to ACL, PCL, PMC, and PLC (4 ligaments) |
| 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 (therefore underdiagnosed)
- may present with subtle signs of trauma (swelling, effusion, abrasions)
- obvious deformity
- do not wait for radiographs, reduce immediately, especially if absent pulses
- "dimple sign" - buttonholing of medial femoral condyle through medial capsule
- indicative of an irreducible posterolateral dislocation
- a contraindication to closed reduction due to risks of skin necrosis
- stability
- diagnosis based on instability on exam (radiographs and gross appearance may be normal)
- may see recurvatum when held in extension
- assess ACL, PCL, MCL, LCL, and PLC
- 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
- if pulses are present and normal
- does not indicate absence of arterial injury
- collateral circulation can mask a complete politeal artery occlusion
- measure Ankle-Brachial Index (ABI)
- if ABI >0.9
- then monitor with serial examination (100% Negative Predictive Value)
- if ABI <0.9
- perform 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%
- if pulses present after reduction then measure ABI then consider observation vs. angiography
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| Imaging |
- Radiographs
- 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
- MRI
- required to evaluate soft tissue injury (ligaments, mensicus) and for surgical planning
- obtain MRI after acute treatment
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| Treatment |
- Initial Treatment
- reduce knee and re-examine vascular status
- considered an orthopedic emergency
- splint knee in 20-30 degrees of flexion
- confirm reduction is held with repeat radiographs in brace/splint
- vascular consult indicated if
- if arterial injury confirmed by arterial duplex ultrasound or CT angiography
- pulses are absent or diminished following reduction
- Nonoperative
- indications
- limited and most cases require surgical stabilization
- Operative
- emergent surgical intervention
- indications
- vascular injury repair (takes precedence)
- open fx and open dislocation
- irreducible dislocation
- compartment syndrome
- technique
- vascular intervention
- perform external fixation first
- excision of damged segment and repair with reverse saphenous vein graft
- always perform fasciotomies after vascular repair
- delayed ligamentous reconstruction/repair
- indications
- generally instability will require some kind of ligamentous repair or fixation
- patients can be placed in a knee immobilizer for 6 weeks for initial stabilization
- improved outcomes with early treatment (within 3 weeks)
- technique
- PLC
- recommend early reconstitution
- PCL
- reconstruct prior to ACL reconstruction
- postoperative
- recommend early mobilization and functional bracing
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| Complications |
- Stiffness (arthrofibrosis)
- is most common complication (38%)
- more common with delayed mobilization
- Laxity and instability (37%)
- Peroneal nerve injury (25%)
- most common in posterolateral dislocations
- poor results with acute, subacute, and delayed (>3 months) nerve exploration
- neurolysis and tendon transfers are the mainstay of treatment
- Vascular compromise
- in addition to vessel damage, claudication, skin changes, and muscle atrophy can occur
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