Background

DefinitionKnee dislocation

 

Multi-ligament knee injury (MLKI)

- 2 or more ligaments disrupted

 

Knee dislocation

- ACL + PCL + one of collaterals 

 

Epidemiology

 

Male/Female: 4:1

 

Mechanism of injury

 

High energy (MVA)

 

Low energy (sport)

- low energy has 5% arterial injury

 

Ultra-low energy

- morbid obesity

- knee dislocation occurs with minimal trauma

 

Shenck Anatomic Classification 1992

 

KD-I: One cruciate + one collateral

 

KD-II: ACL and PCL torn

 

KD-IIIM: ACL / PCL + MCL 

 

KD-IIIL: ACL / PCL + LCL / PLC

 

KD-IV: Both cruciates and both collaterals

 

KD-V: fracture dislocation

 

N nerve C arterial

 

Kennedy Classification

 

Based upon direction of the tibia

 

Anterior dislocation of tibia

- most common 

- hyperextension + varus/valgus

 

Knee Dislocation Posterior SubluxationAnt knee dislocationAnterior knee dislocation 2

Anterior knee dislocations

 

Posterior dislocation of tibia

- second most common

- flexed knee, posterior force

- high risk of popliteal artery transection

 

Posterior tibia knee dislocationKnee dislocation posterior

Posterior knee dislocations

 

Lateral dislocation of tibia

- KD-III L

- ACL / PCL / MCL

 

Knee dislocation medial

Lateral knee dislocation

 

Medial dislocation of tibia

- ACL / PCL / Posterolateral corner

 

Knee dislocation lateral

Medial knee dislocation

 

Incidence

 

Rare

 

However incidence likely underreported

- many spontaneously reduce

 

Knee dislocation

Obvious knee dislocation

 

Vascular Injury

 

Incidence

 

Medina et al. CORR 2014

- systematic review of knee dislocation

- 171/862 (18%) had vascular injury

- 80% underwent repair

- 12% resulted in amputation

- most common in posterior dislocations (tibia) and with ACL / PCL / MCL

 

Anatomy

 

Popliteal artery tethered

- proximally in Hunters Canal under fibrous arch of adductor magnus

- distally under fibrous arch of soleus

- in middle by 5 geniculate arteries

 

Genicular vessels provide poor collateral flow 

- amputation with vascular injury > 8 hours = 85%

 

More common in

- high energy injuries

- obese patients

 

Indications for vascular investigation

 

Weinberg et al. CORR 2016

- angiography indicated if any of the three findings NOT PRESENT

- palpable dorsalis pedis, palpable posterior tibial artery, ABI > 0.9

 

Ankle brachial index (ABI)

 

Divide systolic pressure of the ankle by the systolic blood pressure of the arm

 

Options

 

CT angiogram

On table / vascular lab angiogram

 

CT angiogram

 

Knee Dislocation Normal CTaPopliteal artery stenosisPopliteal artery stenosis

Normal CT angiogram                                 Popliteal artery stenosis following knee dislocation

 

Popliteal artery transection 1Popliteal artery transection 2

Popliteal artery transection following left knee dislocation

 

Advantages

- readily available, non invasive

- extremely accurate

- also used confirm the site and mechanism of injury

 

Inaba et al. J Trauma 2006

- multi-detector CT

- 100% sensitive and specific in detecting clinically significant arterial injury

 

Gakhal et al. Vascular and Interventional Radiology 2009

- CTA signs of lower extremity vascular trauma

 

Angiogram

 

Angiogram Normal 1Angiogram Normal 2

Normal angiogram

 

Angiogram Popliteal Artery InjuryPop artery angio

Popliteal artery injury on angiogram

 

Disadvantages

- technically demanding

- potentially less accurate than CTA

- operator dependant

 

Technique

- open approach to proximal femoral artery

- place catheter in artery with 3 way tap

- 20mls Omnipaque / water soluble dye 

- fluoroscopy over distal femur

- repeat for proximal tibia

- must show films to radiologist for interpretation of subtle signs

 

Rose et al. American J Roengenology 1987

- angiography 98% sensitive and specific for major arterial injury

- 16% technically compromised

 

Management of vascular injury

 

1. Bridging external fixation

 

Knee dislocation external fixation

Knee dislocation external fixationKnee dislocation external fixator

Bridging external fixator for knee dislocation

 

2. Vascular repair

 

Patient supine

- abduct hip, flex knee

- incision over sartorius proximally, running posterior border of knee

- detach medial head of gastrocnemius

- identify popliteal artery (medial) / popliteal vein / tibal nerve (lateral)

- reversed saphenous vein graft / synthetic graft

- fasciotomy if vascular injury - reperfusion raises risk of compartment syndrome

- apply external fixator - can flex but need to ensure that knee remains reduced

 

Popliteal Artery RepairPopliteal Artery transection 1Popliteal artery transection 2

 

Popliteal artery graft 1Popliteal Artery Graft 2

Medial approach and saphenous nerve graft for popliteal artery transection following knee dislocation

 

Nerve Injury

 

Incidence

 

Medina et al. CORR 2014

- systematic review of knee dislocation

- incidence of nerve injury 25%

 

Patterns

 

1. Tibial nerve

- not tethered proximally 

- not commonly injury

 

2. Common Peroneal Nerve

- tethered behind biceps and around neck of fibula

- most commonly injury

 

Prognosis

 

Woodmass et al Knee Surg Sports Traumatol Arthrosc 2015

- systematic review of 214 CPN palsies

- 40% of patients with complete nerve injury recovered foot dorsiflexion

- 87% of patients with partial nerve injury recovered foot dorsiflexion

 

Management options for CPN injury

 

1.  Nerve obviously disrupted at surgery

- tag and return for sural nerve graft

 

2.  Nerve intact

- EMG at 3 months

- if no evidence of re-inervation

- sural nerve gaft

 

3.  Failure of sural nerve graft

- consider tendon transfers for foot drop

 

Samson et al EFORT Open Reviews

- management of CPN injury after knee dislocation

 

Examination

 

Extensive soft tissue injury with significant swelling

 

Open / compound wounds

 

Open Knee Dislocation

Knee dislocation with obvious recurvatum and postero-lateral knee wound

 

Cmpd KD 1Cmpd KD 2

Complete knee dislocation, compound, KDIV

 

Obvious ligamentous laxity

 

Knee dislocation examinationKnee dislocation lateral instability

Excessive recurvatum                                                           Grade 3 Lateral laxity

 

Neurovascular status

- pulses, capillary refill, skin colour

- must have palpable dorsalis pedis, posterior tibial, as well as ABI > 0.9

- any concern, vascular investigation

 

Reduction of knee dislocation

 

Reduce in ER

- if stable can leave in brace

- if unstable, need external fixator

 

Dimple sign  

 

Due to trapping of medial capsule & MCL

- after closed reduction of posterolateral dislocation

- get dimpling along the medial joint line

- MFC buttonholes through medial soft tisse

- non anatomic reduction achieved

- requires open reduction

 

Knee Dislocation Medial DimplingIrreducible knee MRIIrreducible knee MRI 2

Medial dimpling                             Entrapped vastus medialis post knee dislocation on Coronal and Sagittal MRI

 

Knee dislocation button holed MFC

Open reduction of knee dislocation with medial approach and removal vastus medialis

 

External fixation

 

Indications

- open wounds

- unstable once relocated

- vascular injury

 

Associated Injuries

 

Fibula head avulsion / dislocation

 

Will typically have LCL and biceps femoris ligament attached

 

Fibula Head AvulsionFibular head avulsion

Fibular head avulsion

 

CT fibular head

Fibula head avulsion and medial tibial plateau fracture

 

Patella fractures / extensor mechanism injuries

 

Knee dislocation patella tendon rupture

Sagittal MRI demonstrating patella tendon avulsion and ACL / PCL tear

 

PCL bony avulsions

 

PCL bony avulsion

 

Tibial plateau fractures

 

Knee dislocation tibial plateau fractureKnee dislocation tibial plateau fracture

CT demonstrating medial tibial plateau in setting of knee dislocation and posterolateral corner injury

 

MRI

 

ACL / PCL rupture

 

Knee Torn ACL and PCL0001Knee Torn ACL and PCL0001

Sagittal MRI demonstrating complete tear of ACL and PCL

 

ACL PCL MRIACL PCL MRI 2

Sagittal MRI demonstrating complete tear of ACL and mid substance tear of PCL

 

ACL / PLC / MCL

 

Knee Dislocation ACL PCL MCL MRI 1Knee Dislocation ACL PCL MCL MRI 2

Coronal MRI of left knee demonstrating proximal MCL tear, with sagittal demonstrating complete disruption of ACL / PCL

Popliteus

 

 LCL avulsion femur PLC

Coronal MRI of left knee demonstrating femoral avulsion of popliteus

 

LCL

 

Harder to see on a single image.  Need to scroll through coronal images

 

LCLLCL 2

Coronal MRI with normal femoral insertion of LCL and popliteus

 

LCLLCL 2

Coronal MRI of same patient demonstrating distal LCL avulsion from fibula