STL 20070915

The role of computer assisted surgery

(CAS)

Søren Toksvig-LarsenDept Orthopedics Hässleholm Hospital

Lund University

Sweden

STL 20070915

WHAT’S WRONG WITH THIS SCENARIO 2007?

• Orthopaedic Surgeon:

• Mallet and a Goniometer

STL 20070915

WHAT’S WRONG WITH THIS SCENARIO 2007?

STL 20070915

introduction

The purpose of modern technique:The purpose of modern technique:

• improve the duration of implantsimprove the duration of implants

• reduce the human errorreduce the human error

• simplification of the surgical techniquesimplification of the surgical technique

STL 20070915

Not necessarily make every case better

• prevent the outliersprevent the outliers

• explore the possibilities of enhancedexplore the possibilities of enhanced

ROM, stability, and alignment– knowing the functional Kinematics

STL 20070915

My background

Istituti Ortopedici Rizzoli

EU projects

STL 20070915

CAOSCAOSComputer Assisted Orthopaedic Computer Assisted Orthopaedic

SurgerySurgery

STL 20070915

Robot surgery”active”

STL 20070915

Formula 1

Robot surgery

STL 20070915

3-D op technique

STL 20070915

ProblemToo troublesome

Feed back systemsSafety systems

STL 20070915

STL 20070915

Why continue Why continue using modern technique??using modern technique??

STL 20070915

Who is a non-responderMy problemMy problem

Non respondersNon responders

STL 20070915

Satisfaction - TKA

18 % were dissatisfied or uncertain

• O. Robertsson et al. 2000

Distribution of satisfaction, percent

0

20

40

60

80

100

Female Male Female Male

OA RA

Very sat isf ied

Satisf ied

Uncer tain

Unsat isf ied

STL 20070915

Possible Malalignment

Rotational malalignment

Translational malalignment

Varus Valgus Flexion Extension Internal rotation External rotation

Medial Lateral Proximal Distal Anterior Posterior

CAOSCAOS1212º freedom for each componentº freedom for each component

STL 20070915

Navigation

“passive”

Surgical set up

STL 20070915

Navigation gives information Navigation gives information during surgery to position the during surgery to position the

instruments and implants instruments and implants according the “anatomy”according the “anatomy”

STL 20070915

Knee Navigation workflow

HIP center

STL 20070915

Knee Navigation workflow

STL 20070915

STL 20070915

NAV as other computers”shit in, shit out”

STL 20070915

Record Alignment

STL 20070915

More sophisticated instruments

STL 20070915

Tibia cut

STL 20070915

Gap balancing/tension

??????????????????????????

STL 20070915

Navigation

Fewer outliersFewer outliers

• Positioning of TKA with and without navigationSparmann et al. JBJS-Br 2003

– improved mechanical, frontal and sagital femoral axis and frontal tibial axis

– 240 patients (120 CAOS, 120 conventional)

STL 20070915

Navigation

60 cases TKA superior results for the CAOS group compared to the

conventional grouphowever

no statistically difference for • the mechanical axis• the tibial axis, the femural axis• a tendency for valgus positioning the femural component in the

CAOS group– Miehlke et al. Z. Orthop 2001

STL 20070915

• A prospective randomised study– 50 TKA knees, Genesis knee

Conclusion

CAOS excellent, but not better than conventional» J. Victor D. Hoste (Efort 2003)

TKA navigation

STL 20070915

•A prospective randomised study

–50 knees, Genesis knee

–Accuracy CAOS – excellent

Outcome Conventional CAOS

•Torniquet time 56 min 72 min p 0.002

•Operative time 70 min 93 min p<0.001

•Blood loss 3.3 g/dl 4 g/dl ns

•Patellar alignment no tilt>5º no tilt>5º

•Patellar alignment no subluxation no subluxation

•Tibial slope 3.5º 3º

»J. Victor D. Hoste (Efort 2003)

TKA navigation

STL 20070915

Sample-sizes needed in prospective randomised trialsSample-sizes needed in prospective randomised trials

• Detect a difference in outcome of 2.5% (i.e., 92.5 vs. 95 %) Detect a difference in outcome of 2.5% (i.e., 92.5 vs. 95 %) after 10 years with 80 % power at a 5 % level of after 10 years with 80 % power at a 5 % level of significanse.significanse.

• 2000 patients are required!!!2000 patients are required!!!

???Does it matter??????Does it matter???

STL 20070915

OVERALL SYSTEM ERROR 2 mmthe average difference between point distance in the virtual scene and the

corresponding point distance in the real world, is given by:

ACQUISITION ERROR: 1 mm

errors in surface position produced by the segmentation algorithm

SIMPLIFICATION ERROR: 0.4 mm

ACCURACY OF THE TRACKING SYSTEM: 0.5 mm

REGISTRATION ERROR: 1 mm

ACCURACY OF THE POSITION SENSOR: 1.0 mmdefined as the standard deviation of a set of measures with respect to the “real” value, obtained by means of a calibration instrument.

STL 20070915

Intraoperative cutting errors

Some of my experience using navigation

Pinning the cutting block can change the position of the block 1 - 2 degree

The cutting process can change the surface additional 1 - 2 degree

Can partly be corrected using navigation

STL 20070915

Evaluation

Methods with a lower accuracy than the CAOS systems

STL 20070915

z

Alignment – outliers (2-D)

Femural component too extended

valgus positioning the femural component

Less bloodloss

Individuality

Tibial rotation

STL 20070915

So far

The purpose of modern technique:The purpose of modern technique:

• improve the duration of implantsimprove the duration of implants

• reduce the human errorreduce the human error

• simplification of the surgical techniquesimplification of the surgical technique

NOT ACHIEVEDNOT ACHIEVED

But it willBut it will

STL 20070915

The CAOSThe CAOS technique technique

The cost-effective problemsThe cost-effective problems

• Longer operation timeLonger operation time

• Additional surgical interventionAdditional surgical intervention

• Complications?Complications?

STL 20070915

The CAOSThe CAOS technique technique

The cost-effective problemsThe cost-effective problems

• Big investment/costs to run the Big investment/costs to run the equipmentequipment

•Troublesome techniqueTroublesome technique

saved co

sts fo

r revisio

ns

saved co

sts fo

r revisio

ns

STL 20070915

New technique

A new technique becames viable if it makes a process or service deliveries either

–easier –faster –cheaper–better

–2 of these benefits would make a technology more popular

–For arthroplasty all 4 are required??!!