Considerations In Knee Artroplasty

CONSIDERATIONS IN TKA

JAVIER MATA

HISTORY OF TKA

• Total knee arthroplasty is one of the most important advances in orthopaedics during the last 30 years.

• Patients with severe arthritis have reduced pain, correction of deformity and improved function as well as life quality after TKA implantation.

• Today, increasing interest is showed in the mobile bearing type of knees. Long term results will have to prove that they are better!

• Several surgical points need to be considered !!!

The Surgeon Is One Of TheMost Important Factors

ANATOMY AND SOFT TISSUES

• A thorough knowledge of the knee anatomy, bones,mechanical, anatomical axis,ligaments and soft tissues must clearly be understood ( John Insall ).

• Total knee arthroplasty is the correct alignment of the components and soft tissue balancing. The last is the formula 1 “Fine Tuning”.

THE PEFECT KNEE IS BALANCED

The vertical axis.

The mechanical axis.

The anatomical axis

WHICH KNEE SHOULD WE USE ? ?

TODAY,THINGS ARE CHANGING

WHAT ABOUT CLINICAL RESULTS?

WHAT DOES THE CURRENT KNEE MARKET HAVE ?

Clinical Results

Some Notable Long Term (>10 Year) Clinical Results

TC 90.77%1

IB (Post Stabilised) Mark II 93.6%1

PFC 96.2%LCS (Meniscal) 94.7%2

Kinematic 95.0%TCCK * 97.5%3

IB (Post Stabilised) Mark I * 98.0%1

* Uniform Compressed Polyethylene

1 Survivorship of cemented TKA. Insall, AOAS San Francisco 19972 Orthopaedics. Sept 96. R.B. Sorrells3 Swedish Knee Register. AAOS, San Francisco 1997

Year % Survival References 15 98 Ritter - Current Concepts 1999

11.4 95 Emerson – Journal of Arthroplasty 2000

>10 98 Clinical Orthopaedics Dec. 95- 2001 AGC Knees Ritter et.al.

10 97.5 Swedish Knee Register - AAOS 1997

>7 97 Finish Knee Register - 988 AGC Knee 1995

>8 98.2 Oxford Group U. Kingdom – 1996 Published this Year

>10 96 Emmerson M.D. USA 1996

AGC Clinical Results

ARE WE GOING FOR A C.R. OR P.S. TOTAL KNEE?

• Retaining the posterior cruciate ligament is more natural, but in practice more difficult to achieve good tension.Or it is too tight or too loose. Rarely the correct tension( Stiehl)

• Implanting a PS knee gives the surgeon reproducible mechanical rollback.It is an easier operation!

• The available literature suggests that PS TKA is superior in results than CR TKA.

WHAT TYPE OF INCISION?

• Medial approach(varus or valgus knees)• Lateral approach(lateral knees)• Subvastus approach(varus knees)• Midvastus approach(varus knees)• Tibial tubercle osteotomy(L. Whitside)• Rectus snip(vastus turndown)

MEDIAL APPROACH

• Varus Deformities.• We start with a straight line incision if possible.• Medial parapatellar.• About 1 cm medial to the tibial tubercle.• Deep M.C.L.• Superficial M.C.L.• Semimembranosus.• Subluxation of the tibia(rotation).• patello-femoral ligament.

MEDIAL APPROACH

• Valgus Deformaties.• Straight line skin incision.• Medial parapatellar.• Anterior deep M.C.L.• Illiotibial band.• Straight anterior subluxation.• Lateral capsular ligament.• Arcurate ligament.• Popliteus&L.C.L.

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LATERAL APPROACH

• Valgus Deformities (Keblish)• Straight line skin incision.• Lateral parapatellar.• Lateral capsular ligament.• Partial tubercle release.

SUBVASTUS APPROACH

• Varus knees.• Straight line skin incision.• Medial parapatellar( not going into the quads).• Elevate proximally.• Avoid saphenous nerve.• Sometimes difficult patella exposure with

obese patients

MID VASTUS APPRAOCH

• Varus knees( Engh)• Same as subvastus but here we go slightly

into the vastus medialis.

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TIBIAL TUBERCLE OSTEOTOMY

• Straight line skin incision.• Medial parapatellar.• Tibial tubercle osteotomy of about 10cm.• Leave soft tissues intact laterally.• Fixation with wires,screws,staples etc..

RECTUS SNIP OR VASTUS TURNDOWN

• Straight line skin incision.• Medial parapatellar.• Transverse cut into the quads.• Medial closure.• No lateral release.

GOOD KNEE EXPOSURE

• It is very important to achieve good knee exposure. This will facilitate the whole procedure.

• First thing to do, is to take all protruding osteophytes away. This from the femur and the tibia.

• If partial ligament release is necessary, do it. Disadhere the ligaments.

• So, restore the anatomy.

ESTABLISH YOUR REFERENCES

• What is the valgus angle going to be?• Mark and draw the epicondylar axis line for

correct femoral exorotation. Check with the Whitsides line.

• Restore the joint line.Use available anatomical reference landmarks.

Epicondylar axis line and Whitsides’ line

Where is the “Joint Line” ?

• About 16 to 18mm from the fibula head.• 46mm off the medial distal femur at the

adductor tubercle ( A. Hofmann )• About 27mm distal off the medial femoral

epicondyle.• Look for the old meniscal scar in the joint

capsule= joint line

ANTERIOR REFERENCING

• Most of the knee instrumentations use anterior referencing of the femoral component.

• Here we respect the anterior part of the femur.• If , between 2 sizes, we can downsize.• The counterpart is that we cut more posterior

femoral condyle off. This elevates the joint line in flexion.

POSTERIOR REFERENCING

• We respect the posterior femoral condyles, thus re-establish the joint line in flexion.

• The counterpart is that we cannot downsize, if between sizes. Otherwise we will notch the anterior femoral cortex.

• There are instruments that compromise, like the Fudge A/P sizer.

The “ Fudger” A/P sizer permits downsizing if between 2 sizes

PERFORM ACCURATE BONE CUTS

• The key to success is the sawblade.• Go for the femur or the tibia. It’s surgeons

preference.• Restore the mechanical axis, joint line and

do a good soft tissue balance.• Achieve in flexion and extension exact

rectangles.

Be in the right place when drilling into the

femur or tibia!!

• Look at your X rays to establish your entry points into the bone.

TIBIAL PREPARATION

• You can prepare your tibial cut extramedullary or intramedullary.

• Be sure to check this cut because it is one of the most important cuts in TKA.

• A tibial cut should be perpendicular to it’s mechanical axis.

• A neutral cut is the best. Slight valgus cut is tolerated

• A VARUS CUT IS BAD

When using a posterior slope,

you must watch out!!!Internal rotation will result in a valgus cut of the tibia.

External rotation will result in a varus cut of the tibia

Be sure to be in exact A/P when using a tibial resection guide.

Extramedullary tibial resection guide over the top

Intramedullary resection guide

In varus knees, you will cut off more laterally than medially.

In valgus cases, you will cut about the same amounts medially and laterally.

The posterior cortical axis is 10° internally rotated.

The inermalleolar axis is 15° externally rotated.

The tibial crest is neutral.

The tuberosity is just lateral

Reference landmarks

INSTRUMENTATION

• Use the instrumentation correctly but don’t depend fully on it.

• Be like Einstein,use your brains and common sense.

• Establish correct flexion and extension gaps.How? Use spacer blocks or tensioners to achieve this.

This is the correct way

Not correct

CHECK YOUR FLEXION AND EXTENSION GAPS:

THEY MUST BE EXACT !!!!

Flexion and extension spacers

PATELLA TRACKING

• Patella tracking is extremely important in TKA.The following points are important to achieve good patella tracking.

• Surgical approach,correct femoral size,lateralisation,correct exorotation of the femoral component,slight exorotation and lateralisation of the tibial component,medialisation of the patella component.( AAOS comments )

PATELLA PREPARATION

• Surgeons have different approaches to implant a patella component.

• Some do it free hand.• Others resurface or inlay the patella button.• Some don’t and leave the natural patella in

situ.• Most do a “Denervation” around the natural

patella.

Check the natural, eroded patella size

Resurfacing the patella

Inlay patella technique

‘  Cut ‘  the cement away

TRIAL REDUCTION

• It is imperative to achieve full extension and good flexion with the trial components in place during the operation.

• Try the Bob Booths full extension test.• Try the gravity test for evaluation of the

flexion.• Try the P.O.L.O. test.• If using a PS knee, try and luxate the femur

from the tibia(hop over test).

CEMENTING

• Take good and meticulous care in cementing the components in place.

• Do not pressurize in full extension otherwise you will end up with an anterior tibial slope of your tibial component.Hold the leg at about 30 degrees of flexion.

METICULOUS IRRIGATION IS ESSENTIAL!!!!

GO FOR A CLEAN AND DRY BONE SITUATION

PRESSURIZE THE CEMENT INTO THE BONE

GRACIAS