knee dislocation

Question 1

what are the common mechanisms of injury for knee dislocation?

Answer 1

high or low energy
- high energy - RTC - dashboard injury - posterior
- lower energy - obese patient walking

50% self reduce!

Question 2

what are the commonly associated injuries?

Answer 2

• vascular injury
• CPN - 25%
• fracture - 60%
• soft tissue - patella tendon avulsion
• multi-ligament

Question 3

how do you classify knee dislocations?

Answer 3

direction of injury
direction is based on the position of the tibia

• anterior - hyperextension - 30-50% - PCL avulsion +/- intimal arterial traction injury
• posterior - dashboard - axial load to a flexed knee - highest rate of vascular injury - popliteal artery complete tears
• Lateral - varus/ valgus - ACL/PCL injury - highest rate of CPN injury
• Medial - varus/ valgus - injury to PLC
• Rotational - buttonholing of femoral condyle through capsule preventing reduction

Question 4

what is your initial management of a dislocated knee?

Answer 4

1. ATLS
2. Focused HX
3. Examination
   - pulses
   - colour/ temp
   - skin
   - CPN
4. Reduce - unless buttonholing - suggests MFC through capsule and risk of skin necrosis
5. Re-examine
6. Backslab in 15 deg flexion - takes pressure off NV structures and less risk of FFD

Question 5

how do you assess vascularity in dislocated knee patients?

Answer 5

Assess pulses and cap refill pre and post reduction - these don’t differentiate between intimal and complete arterial tear -

DO ABPIs

• APBI <0.9 has 100% sens, spec and PPV for identifying vascular injuries
• CT angiogram

Question 6

Management algorithm following vascular assessment in dislocated knee?

Answer 6

Pulse present
- ABPI >0.9 = serial ops and examination for 24hrs
- ABPI <0.9 = CT angio and d/w vascular

Pulse absent/ weak
- CT angio and d/w vascular team

Ischaemic Limb
- straight to theatre
- ischaemic time of 8hrs then 80% risk of amputation

Question 7

Ischaemic limb and knee dislocation - what is the sequence of treatment in theatre?

Answer 7

• Vascular shunt to reperfuse leg
• Spanning Ex-fix
• prone
• Vascular repair/ reconstruction
• prophylactic fasciotomies

Question 8

how do you apply a spanning external fixator?

Answer 8

Mid femur pins
- safe zone = lateral femur - blunt dissection through vastus lateralis
- pin trajectory = direct lateral
- risks - femoral nerve and artery
- size = 5mm

Mid tibial pins
- safe zone =anteromedial border of tibia, 1cm medial to tibial crest
- pin trajectory = 20 deg to the sagittal line
- risks - tibial artery/ vein and DPN run close to the posterolateral border of the tibia
- size = 5mm

Question 9

How do you manage multi-ligament injuries associated with knee dislocation?

Answer 9

• MRI scan - new Hoffman 3 frames are MRI compatible
• ACL and MCL - can treat MCL in brace but not if multilig then need to fix all ligaments to make knee stable

algorithim for multi-ligament
Repaired vascular injury
- Exfix for 4-5 weeks - EUA in theatre to assess for laxity of MCL and put in hinged knee brace
- plan delayed reconstruction

No vascular injury
- if multi-lig fix the MCL
- options, either:
- staged reconstruction (1) collaterals at 6 weeks and (2) cruciates at 12 weeks - easier to perform and less stiffness
- Reconstruction of all

Question 10

what are the common complications following knee dislocation?

Answer 10

• arthrogryposis - most common
• vascular injury
• laxity/ instability
• common peroneal nerve injury