Navigation

Aim

 

Attempt to reduce outliers in all 3 planes of the knee

- improve alignment

- theoretically improve survival and outcomes

 

TKR Valgus Femoral Implant Non Navigated

 

Types

 

Image based

 

Pre-op CT

- uncommon

- resource heavy

 

Image less

 

Anatomic mapping and kinematic analysis of the limb

- intra-operatively 

- builds up a working model of the patient's knee

 

Indications

 

Unable to use femoral / tibial IM or EM Jigs

- fracture / metal work / deformity

 

TKR Femoral FractureTKR Previous Femoral FractureTKR Tibial Deformity

 

Bilateral TKR

- reduce post op confusion in patient

- from bilateraly IM rod

 

TKR Bilateral Varus

 

Young patient < 65

- attempt to achieve perfect alignment / balancing

- want TKR to survive long term

 

Equipment

 

2 infra-red trackers

- tibia and femur

- bi-cortical fixation

- must not move intra-operatively

- angled / positioned to be in view of camera

- must be out of way of surgery

 

Camera / optical localiser

- connected to computer and monitor

 

Pointer with infrared

 

Standard cutting blocks

- modified to allow trackers to be attached

 

Registration

 

1.  Femoral head

- rotate hip whilst minimising pelvic rotation

- kinematic registration

 

2.  Knee

- distal femoral surfaces, epicondylar axis, Whiteside's line

- medial and lateral tibial plateaus, centre of knee, posterior tibial slope

 

3.  Ankle

- medial and lateral malleolus

- ankle centre

 

Technique

 

1. Distal Femoral Cut

- leave femoral tracker in place

- cutting blocks attached

- tibial tracker on cutting block

- place at 90o to MA

- set desired resection (depth of femoral implant +/- more if FFD)

- pin block in place and cut

 

2.  Femoral AP cut

- new programs will suggest size

- determines risk of notching

- set rotation from epicondylar axis

- creat drill holes

- place cutting block and cut distal femur AP / chamfers

 

3.  Proximal tibial cut

- reattach tibial tracker

- femoral tracker on cutting block

- cut at 90o to MA

- set posterior slope

- set rotation in line with centre ankle rotation

 

4.  Newer soft ware will assess flexion extension gap

 

Problems

 

1.  Dependent on registration

- rubbish in = rubbish out

- keep pointer on bone when registering

- accurate landmarks

- movement of pelvis with femoral head rotation

- inherent soft ware inaccuracies

 

2.  May not be as accurate in rotation and sagittal planes as coronal planes

 

3.  Reasons for inaccuracy

- registration

- inaccurate saw cuts (lack of rigid fixation of blocks, width of saw blade)

- uneven cement mantles

 

Results

 

1.  Reduces outliers

 

Will place 90% of TKR's within mechanical axis +/- 3o in coronal plane

- reduces outliers

- will take a long time to see if this improves implant survival

- require large numbers of patients in randomised trials followed over 15-20 years to see a significant result

 

Lutzner et al JBJS Br 2008

- RCT image less computer navigation

- reduced number of outliers in convential group

- CT analysis showed tibial rotation inaccurate

 

Spencer et al JBJS Br 2007

- RCT of navigated v conventional

- no difference in functional outcome at 2 years

 

2.  Reduces postoperative confusion

 

Likely due to lack of IM rod instrumentation

 

Kalairajah et al JBJS Br 2006

- doppler examination of patients RCT computer v conventional alignment

- significant reduction in emboli in computer navigation

 

3.  Takes longer 

 

Up to 10-15 minutes even with extensive experience

- takes time to insert trackers and perform registration

 

Bauwens et al JBJS Am 2007

- meta-analysis

- navigation takes 23% longer

 

4.  Reduces blood loss

 

Kalairajah et al JBJS Br 2005

- RCT

- significant reduction in blood loss in computer navigation group