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 !!!
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”.
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.
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
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.
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.
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
Use extramedullary tibial instrumentation here!
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
When working intramedullary, check extramedullary
In varus knees, you will cut off more laterally than medially. In valgus cases, you will cut about the same amounts medially and laterally.
Reference landmarks 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
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.
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.
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.