Arthrodesis

Issues

 

Like elbow arthrodesis, knee arthrodesis is an option of last resort

 

Example

- cannot sit on airplane toilet with door closed

 

Aims

 

Coapt 2 coplanar cancellous surfaces under compression with rigid fixation

 

Indications

 

Septic arthritis

Salvage failed TKR / infected TKR

Tumour

Charcot Join

PFFD

 

Contraindications

 

Bilateral knee fusion

Ipsilateral hip fusion

 

Problems

 

Fusion rates

- can be difficult to obtain fusion

 

Difficulties mobilising

- give patient trial in cylinder cast

 

Position

 

Short leg

- fuse straight 

 

Normal length

- in 10° for swing through

 

Valgus 5 - 7o

 

External rotation 5 - 10o

 

Options

 

1.  External fixator

2.  IMN

3.  Double plating

 

Results

 

Mabry et al Clin Orthop Related Research 2007

- arthrodesis for infected TKR

- union in 41 / 61 patients treated with external fixation, deep infection rate 4.9%

- union in 23/24 patients treated with IMN, deep infection rate 8.9%

 

1.  External Fixation

 

Knee Fusion External Fixation

 

Advantage

- simpler

- less blood loss

- better in infection

 

Disadvantage

- pin tract infection, loosening

 

Technique

 

Anterior longitudinal incision

- medial parapatellar arthrotomy

- patella excised

 

Bony cuts 

- use TKR jigs 

- aim to resect only 1-2 mm

- cut tibia at 90° 

- cut femur 10° flexion or 0° if short / 7° valgus / 5° ER

 

Bilateral & Biplanar external fixator

 

First construct bilateral frame in coronal plane

- 3 femoral & 3 tibial transfixion pins from medial to lateral

- bar on each side

 

Then add unilateral frame in sagittal plane

- 2 femoral & 2 tibial 1/2 pins anteriorly

- anterior bar

 

Circular frame

 

Advantage

- allows compression and weight bearing

- post operative alignment adjustment

 

Bone graft

 

If less than 50% apposition

- may use patella

 

Fixation remains for 12/52

 

2.  IMN

 

Options

 

A.  Long fusion nail S & N / Stryker

B.  Wichita nail / Stryker / Modular nail

 

Pre-operative assessment

 

Full-length AP & Lat XR with magnification marker

- determine length & diameter of nail

 

1.  Long fusion nail

 

Disadvantage

- different IM canal size between tibia and femur

 

Radio-lucent table

- drape to pelvis

- sand bag under hip

 

Medial parapatella approach to knee

- bone cut made

 

Guide wire passed down tibia

- reamed until cortical bone encountered

 

Trochanteric fossa exposed routinely

- guide wire passed & femur reamed

- ream to size determined in tibia

 

Insert nail antegrade from GT across knee to distal tibia

- nail should bend concave laterally to recreate anatomical alignment & slight flex

 

Should not end in diaphyseal portion of either bone 

- risk of stress fracture

 

Lock nail distally but not proximally

- proximally if rotationally unstable

 

2.  Wichita nail / Modular nails

 

Concept

- tibial and femoral components insert via knee & then join together

- different sizes for femur and tibia

- single knee incision

 

Problem

- very difficult to remove after fusion