Amputations about the Knee

BKA / Below Knee Amputation / Transtibial

 

Best results

- long posterior musculocutaneous flap 

- well cushioned mobile muscle mass

- full thickness skin

- very anterior scar

 

Contraindication

- non-ambulator

- get FFD

- better with through knee amputation

 

Advantages over AKA 

 

1.  Good Healing 

- > 90% in DM with BKA

 

2.  Higher prosthesis wearing rates 

- 74% vs 26% for AKA

 

3.  Reduced energy required for walking

- 74% BKA < 45 year old walk > 1 mile

 

4.  Reduced mortality 

- 10% vs 30%

 

Technique 

 

Tourniquet

- no tourniquet if PVD

- tourniquet in trauma (patients can bleed to death)

 

Posterior flap

- mark long posterior flap

- avoid suture line over anterior aspect of tibia / problems frequent here

 

Anterior flap

- short anterior flap at level of tibia cut

- want to extend posterior flap over distal tibia

 

Anterior Dissection

- find anterior NV bundle between T anterior and EHL

- deep peroneal nerve on interossesous bundle

- divide anterolateral muscles at tibial level to avoid bulbous stump

 

Tibial resection

- 15cm stump from joint

- no advantage in > 15cm as skinny poor stump

- < 3cm stump worse than through knee

- sharp dissect periosteum 2 cm above

- leave periosteal flap so can suture muscle flap to it

- bevel sharp edges

 

Fibula resection

- divide fibula 2cm above this

- need to ensure is stable (well connected to tibia via interosseous membrane)

- if not may need to create arthrodesis in young active patient

 

Fibular arthrodesis / unstabile fibula

- create wedge in tibia

- elevate periosteal sleeve to place over top of graft

- use 1 cm of fibula

- can get pain for 6-9 months as the graft unites

 

Posterior dissection

- find posterior tibial artery and tibial nerve

- on tibialis posterior between FDL and FHL

- divide deep muscles and allow to retract

- remove soleus leaving only gastrocnemius flap

- ensure vascularity flap

 

Myodesis gastrocnemius

- through drill holes in tibia and to periosteum of tibia

- fascial repair over muscle bellies

 

Closure

- over drain

- DPC if trauma or infection

- careful pressure dressings with tape to ensure good shaping

 

Through Knee

 

Indications

 

1.  Non ambulators

- aids sitting balance

- avoids FFD and subsequent problems

 

2.  < 3-5 cm tibia

 

3.  ST tissue loss means BKA not possible

 

Advantage over AKA

- improved socket suspension

- longer lever arm 

- muscle balanced amputation

- end-bearing potential

- less volume changes

 

Disadvantage

- asymmetrical knee joint

- bulky prosthesis

- overcome by newer prosthetic techniques

 

Technique

 

Tourniquet 

- patients can bleed to death

 

Flaps

- equal anterior / posterior flaps

- 5cm distal to knee joint

- fish mouth

- can make posterior flap slightly longer

 

Patella 

- depends on technique 

- original method is to retain patella

- Mazet & Hennessy excise patella from tendon

 

Knee dissection

- divide PT off tibial tuberosity

- cruciates and collaterals divided at level of below meniscus

- aim to keep them long

- this preserves the rich proprioceptive function of the capsule

 

Deep dissection

- divide posterior capsule

- find and ligate popliteal artery and vein

- finding tibial nerve, tension, sharp divide, diathermy

 

Myodesis

- PT sutured to cruciate stumps

- biceps tendon sutured to PT

- gastrocnemius to anterior capsule

 

AKA / Transfemoral

 

Issues

- energy expenditure increased by 65%

- residual abduction as A Magnus released from adductor tubercle

- myodesis in 10o adduction maintains abductor strength and prevents abductor lurch

- residual flexion due to quads / hamstring inbalance

 

Technique

 

Position

- sandbag under buttock

- avoid having leg in flexed position

 

Tourniquet 

- if able 

- can bleed to death

 

Flaps

- actually want scar slightly posterior, with larger anterior muscle flap

- fish mouth

- larger anterior flap skin and muscle 

 

Dissection

- cut quadriceps tendon above patella

- detach sartorius / gracilis / hamstrings 2 cm longer for myodesis

- detach A Magnus

 

Vessels

- SFA below vas medialis in Hunter's canal / subsartorial canal

- profunda femoris posterior to femur

- can cut femur first to give access to NV bundles

 

Femoral transection

- save all possible femoral length

- increasing length increases muscle strength

- minimum 12 cm above knee to fit in prosthetic knee joint

- has to be >18 cm from GT or fixation difficult

- if stump < 5 cm below lesser trochanter then fitted as hip disarticulation

 

Adductor myodesis

- maintain stump in 10° adduction

- anatomical position

- suture through drill holes in lateral femoral cortex

 

Anterior musculature

- myodesis of quadriceps to posterior femur avoids FFD

- through anterior drill holes

 

Posterior musculature

- myoplasty to A Magnus or quads

 

Soft spica

- suspend dressing from waist

- support medial thigh

 

Post-op

- positioning important to prevent contractures

- stump flat on bed

- intermittent prone positioning