In the 1860s, Fergusson reported performing a resectionarthroplasty of the knee for arthritisVerneuil --- performed the first interposition arthroplasty using jointcapsule.Other tissues were subsequently tried, including skin, muscle, fascia,fat, and even pig bladder.The first artificial implants were tried in the 1940s as molds fitted to thefemoral condyles
Combined femoral and tibial articular surface replacementsappeared in the 1950s as simple hinges.In 1971, Gunston recognized that the knee does not rotate on a singleaxis like a hinge, but the femoral condyles roll and glide on the tibiawith multiple instant centres of rotation .The total condylar prosthesis was designed by Insall at theHospital for Special Surgery in 1973.
Patients with painful, deformed, and unstable kneessecondary to degenerative or inflammatory conditions needa prosthesis that provides reproducible pain relief andimprovement in function.The morbidity and complications from the procedure shouldbe minimal.The complexities of a normal knee joint, however, are notreproducible with modern techniques, and patients shouldunderstand that they will not have a normal knee.The prosthesis should be durable, requiring patients toundergo only one definitive procedure in their lifetime,although this may simply be unrealistic in younger patients
Knee AnatomyLigaments, Cartilage, Tendons,BoneLargest joint in the bodyFemur-Tibia-Fibula-PatellaMovement of the knee jointhaving 6 degrees of freedom:3 translations (anterior /posterior ,medial/ lateral , inferior /superior)3 rotations (flexion/extension , internal/ external , abduction/ adduction)
Knee Anatomy (cont,)Movements of the knee joint are determined by the shapeof the articulating surfaces of the tibia and femur and theorientation of the 4 major ligaments ACL , PCL and themedial and lateral collateral ligaments as a 4-bar linkagesystem.
Knee flexion/extension involves a combination of rolling andsliding called femoral rollback, which is an ingenious way ofallowing increased ranges of flexionFemoral rollback To properly understand different knee prostheticdesigns one must understand the concept of femoral rollback. Is the posterior transition of the femoral-tibial contact with progressive flexion it reduces bony impingement and allows increase physiologic flexion. it is controlled by ACL and PCL. rollback with a PCL alone exists but it is not as smooth as a rollback with both an ACL and PCL in the native knee can occur due to a relatively flat tibia with minimal congruence with the femoral condyles .
Knee Anatomy (cont,). Because of asymmetry between the lateral and medial femoralcondyles , the lateral condyle rolls a greater distance than themedial condyle during 20 degrees of knee flexion. This causescoupled external rotation of the tibia, which has been described asthe screw-home mechanism of the knee that locks the knee intoextension.Movement of the patellofemoral joint can be characterized asgliding and sliding.
The primary function of the MCL is to restrain valgus rotation of the knee joint, withits secondary function being control of external rotation. LCL restrains varus rotation and resists internal rotation.The primary function of the (ACL) is to resist anterior displacement of the tibia on thefemur when the knee is flexed and control the screw-home mechanism of the tibia in terminal extension of theknee. A secondary function of the ACL is to resist varus orvalgus rotation of the tibia, especially in the absence ofthe collateral ligaments. The ACL also resists internalrotation of the tibia.
The main function of the(PCL) is to allow femoral rollback in flexion and resistposterior translation of the tibia relative to the femur. ThePCL also controls external rotation of the tibia withincreasing knee flexion. Retention of the PCL in total knee replacement has been shown biomechanically to provide normal kinematic rollback of thefemur on the tibia. This also is important for improvingthe lever arm of the quadricepsmechanism with flexion of the knee
Designs include Unconstrained o1. posterior- cruciate retaining o2. posterior- cruciate substituting (posterior stabilized) Constrained 3. non hinged 4. constrained-hinged
1. Unconstrained Posterior Cruciate Retaining (PCR) •. Most common prosthesis used today •Relies on native PCL to provide stability in flexion by keeping PCL some degree of femoral rollback is allowed that allows improved flexion however because ACL is sacrificed, rollback is not anatomic, and has a component of both roll and slide which can accelerate wear
1. Unconstrained Posterior Cruciate Retaining (PCR) - (cont.)In addition, to allow rollback, you need a flat and less congruent tibial component.This leads to increased contact stress andaccelerated wear modern PCL retaining implants favor a more congruent prosthesis that obtainsextra flexion by moving the center ofrotation further posterior than it is inan anatomic knee.Disadvantagesloss of native PCL will lead to flexion instability and failure
2. Unconstrained Posterior Cruciate Substituting (PCS)A posterior cruciate substituting implantuses a tibial post and a femoral cam to substitute for thefunction of the PCL and create a mechanical rollbackphenomenon. at a designated flexion point, the tibial post engages on the femoral cam and forces mechanical rollback, thus improving flexion.
2. Unconstrained Posterior Cruciate Substituting (PCS) by using mechanical rollback, you can use a more congruent articular surface, and thus decrease contact stress of note, the tibial post is not wide enough to provide any varus and valgus stability•Disadvantages cam jump - if flexion gap is loose or knee hyperextends the knee can jump over post and dislocate oreduction requires sedation oavoid in knee with anticipated flexion > 130°
•Indications of (PCS) previous patellectomy oweak extensor mechanism leads to anterior dislocation even with a cruciate retaining prosthesis with an intact PCL inflammatory arthritis oinflammatory process leads to late PCL rupture. Therefore, you can not rely on the PCL and it should be sacrificed prophylacticly deficient PCL rupture or attenuation of the PCL either during surgery or from a previous injury is an indication for a posterior cruciate substituting prosthesis
3. Constrained NonhingedDesign prosthesis has a large central post that substitutes for MCL and LCL the tibial post is wider and taller than it is for a posterior cruciate substituting design so it actually provides varus / valgus stability•Indications LCL attenuation or deficiency MCL attenuation or deficiency (deficiency of MCL is controversial because load may lead to breaking of central post) flexion gap laxity
4.Constrained Hinged with rotating platform Hinged implants. One degree of freedom Design femur and tibia connected by bar and bearing tibial component rotates within yoke allow internal and external rotation during gait early designs did not have a rotating platform and had a very high loosening rate due to the rotational forces that were placed on the implant intramedullary stem needed to address high rotational loads
•Indications global ligament deficiency hyperextension instability (seen with polio or tumor resection) knee resection for tumor charcot arthropathy (relative) complete MCL deficiency (relative and controversial)
5. Mobile Bearing•Design mobile-bearing poly i.e. : non fixed to tibia creates a dual surface interface of metal and poly increases conformity of metal and poly•Indications theoretically reduces wear oincreased contact area reduces pressures placed on poly (pressure=force/area)
Surgical ApproachesSubvastus approach: Midvastus approach: Intact extensor Preserve genicular a. mechanism. to the patella.Decreasing pain. Contraindication in More limited. limited preoperative flexion.Postoperative hematoma. Postoperative hematoma.
TKA techniquesApproaches•Antibiotic loaded bone cement routine use in all TKA increases the risk of aseptic loosening reduces deep infection in revision TKA indications for use in primary TKA are controversial
•Technical goals Restore mechanical alignment (mechanical alignment of 0°) Restore joint line ( allows proper function of preserved ligaments. e. g: PCL ) Balanced ligaments (correct flexion and extension gaps) Maintain normal Q angle (ensures proper patellar femoral tacking)
Indications for TKA•Relieve pain caused by osteoarthritis of the knee (the mostcommon).Deformity in patients with variable levels of pain: Flexion contracture > 20 degrees. Severe varus or valgus laxity.Osteoarthritis American College of Rheumatology classification criteria:• Knee pain and radiographic osteophytes and at least 1 of thefollowing 3 items:Age >50 years.Morning stiffness <=30 minutes in duration.Crepitus on motion.
Relative contraindications1-medical conditions that compromise the patientsability to withstand anesthesia and wound healing2- significant atherosclerotic disease of the operativeleg3- skin condition such as psoriasis within the operativefield , venous stasis disease with recurrent cellulitis .4-neuropathic arthropathy5-morbid obesity6-recurrent urinary tract infection 7-history of osteomyelitis in the proximity of the knee
Contraindications for TKA•Recent or current knee sepsis.•Remote source of ongoing infection.•Extensor mechanism discontinuity or severedysfunction.•Painless, well functioning knee arthrodesis.
•Unicondylar Knee Arthroplasty•Indications: ►Younger patients with unicompartmental disease ►Elderly thin patient with unicompartmental disease (shorter rehabilitation, greater ROM)•Contraindications: ►Flexion contracture >= 5 degrees. ►ROM < 90 degrees. ►Angular deformity >= 15 degrees. ►Cartilaginous erosion in the weight-bearing area of the opposite compartment.
Important consideration pre-op planning component insertion ligament balancing prosthetic design selectionThe femoral component usually is implanted in 5 to 6degrees of valgus, the amount necessary to reestablisha neutral mechanical axis of the limb
Mechanical axis of lower limbExtends from center of femoralhead to center of ankle joint andpasses near or through center ofknee.The line drawn on a standing longleg anteroposterior radiograph fromthe center of the femoral head tothe center of the talar dome.
Mechanical axis of LimbAxis from center of femoral head to center of ankle.Femoral Alignment•Anatomic axis femur (AAF) a line that bisects the medullary canal of the femur determines entry point of femoral medullary guide rod femoral guide goes down mechanical axisAnatomical axis of femur is in 6 degrees of valgusfrom mechanical axis of lower limb and 9 degrees ofvalgus from true vertical axis of body.
•Mechanical axis femur(MAF) Defined by line connecting center of femoral head to pointwhere anatomic axis meets intercondylar notch. Obtaining a neutral mechanical axis allows even loadsharing between the medial and lateral condyles of a kneeprosthesis.It is in 3 degrees of valgus from vertical axis of body.
•Valgus cut angle (~5-7° from AAF ) difference betweeen AAF and MAF perpendicular to mechanical axis jig measures 6 degrees from femoral guide (anatomic axis) will vary if people are very tall (VCA < 5°) or very short (VCA > 7°) can measure on a standing full length AP x- ray
Tibial alignmentAnatomic axis of tibia (AAT) •a line that bisects medullary canal •Tibia medullary guide (internal or external) runs parallel to it •determines entry point for tibial medullary guide rod
Mechanical axis of tibia •Line from center of proximal tibia to center of ankle •Proximal tibia is cut perpendicular to mechanical axis of tibia •Usually mechanical axis and anatomic axis of tibia are coincident and therefore you can usually can cut the proximal tibia perpendicular to anatomic axis (an axis determined by an intramedullary jig) •If there is a tibia deformity and the mechanical and anatomic axis are not the same, then the proximal tibia must be cut perpedicular to the mechanical axis (therefore an extramedullary tibial guide must be used)
Longitudinal Alignment Of Knee:Posterior tibial tilt is about 5 – 7degrees.•Usually depend on the articulardesign.
RotationalAlignment Of Knee:•Create a rectangularflexion space.•External rotation ofthe femoral component3 degrees .
Two primary techniques are used to align the tibial component rotationally.The first technique aligns the center of the tibialtray with the junction of the medial third ofthe tibial tubercle with the lateral two thirdsThe second technique places the knee through arange of motion with trial components inplace, allowing the tibia to align with theflexion axis of the femur.
Patellofemoral Alignment Q angle : angle between axis of extensor mechanism (ASIS to center of patella) and axis of patellar tendon(center of patella to tibial tuberosity) o Abnormal patellar tracking, although not the most serious is the most common complication of TKA. o The most important variable in proper patellar tracking is preservation of a normal Q angle (7°) .
Any increase in the Q angle will lead to increased lateral subluxation forces on the patella relative to the trochleargroove, which can lead to pain and mechanicalsymptoms, accelerated wear, and even dislocation. It is critical to avoid techniques that lead toan increased Q angle. Common errors include internal rotation of the femoral prosthesis medialization of the femoral component internal rotation of the tibial prosthesis placing the patellar prosthesis lateral on the patell
Patellar Resurfacing:•Indication for leaving the patellaunresurfaced: ►Congruent patellofemoral tracking. ►Normal anatomical patellar shape. ►No evidence of crystalline or inflammatory arthropathy. ►Lighter patient.
Preserving joint line and angle (includes rotation)Goal is to restore the joint line by inserting aprosthesis that is the same thickness as the boneand cartilage that was removed this preserves appropiate ligament tension if there are bone defects they must be addressed so the joint line is not jeopardized
elevating the joint line (> 8mm leads to motionproblems) and can lead to omid-flexion instability opatellofemoral tracking problems oan "equivalent" to patella baja onever elevate joint line in a valgus knee until after balancing to obtain full Extension lowering joint linecan lead to• lack of full extension• Flexion instability
coronal balancingIntroductionBoth medial and lateral ligaments may bestretched or contracted with time. It is essential tobalance these ligament in both the coronal andsagittal plane to obtain an optimum outcomePrinciples of ligament balancing for deformities isto release the tight ligaments tighten the stretched ligaments
Varus DeformityGoal is to release the tight medial ligaments andtighten the lax lateral ligamentsMedial releases (usually osteophytes and deepMCL is adequate) osteophytes deep MCL (meniscotibial ligament) and capsule (usually osteophytes and deep MCL is sufficient release)
semimembranosus superfical MCL •can find as it blends into pes anserine complex •can not completely release or will have valgus instability (requires constrained prosthesis). Therefore perform subperiosteal elevation only •Differential release: performed with two component of superficial MCL posterior oblique portion is tight in extension (release if tight in extension) anterior portion is tight in flexion (release if tight in flexion) PCLLateral tighteninguse a prosthesis that is sized to "fill up" the gap and makethe stretched lateral ligaments taut
Valgus Deformity (medial is convex side ofdeformity)Goal is to release the tight lateral ligaments and tighten thelax medial ligamentsLateral release order osteophytes lateral capsule iliotibial band if tight in extension (release if tight in extension) with Z-plasy or release off Gerdys tubercle popliteus if tight in flexion (release if tight in flexion for severe deformities release both the iliotibial band and the popliteus
LCLSome authors prefer to release this structure first if tightin both flexion and extensionOthers prefer this should be the last structure to release,if you need to release it consider of constrained prosthesisDifferential release: performed by differentiallyrelease the IT band and popliteus
•Medial tightening fill up medial side until medial ligament complex is taut•Peroneal nerve palsycorrection of valgus and flexion contracture deformity has highestrisk of peroneal nerve palsy if patient presents with a peroneal palsy in recovery room then: then take of dressing and flex the knee if it does not return test it to see if it is cut if not cut, watch for three months explore if no return after 3 or 4 months
Flexion / Contracture DeformityOrder of posterior release osteophytes posterior capsule gastronemius muscles (medial and lateral)You do not want to address by removing too much tibiawill change joint line and lead to patella alta
*sagittal(gap)balancing •Goal is to obtain a gap that is equal in flexion and extension. This will ensure that the tibial Go insert is stable throughout the arc of motion. balancing is complex due to two radii of curvatures (patellofemoral articulation and tibiofemoral articulation) often requires soft tissue release and bony resection to obtain balance
•General Rules adjust femur if asymmetric odistal femur cut affects extension gap oposterior femur cut affects flexion gap adjust tibia if problem is symmetric (same in both flexion and extension) otibia cut affects both flexion and extension gap remember increasing/decreasing the size of the femoral component only changes the AP diameter and does not affect the height of the prosthesis.
Evaluation & TreatmentThe following chart shows different conditions found with the trials in placeand the treatment strategy for each conditionScenario Proplem SolutionTight in Extension Symmetric gap: Solution:(cant fully extend) Problem: Cut more proximal tibiaTight in Flexion Did not cut(can not fully flex) enough tibiaExtension good Cut too much Solution: posterior femur. 1) Increase size of femoral component (APFlexion loose (large only next size )drawer test ) 2) Posteriorize femoral component (augment posterior femur by bone cement or metal augmentation ).
Extension good Problem: Solution: Did not cut enough posterior 1) Decrease size of femoral componentFlexion Tight femur, PCL scarred and too tight. 2) Recess & release PCL 3) Resect posterior slope in tibia 4) Resect more posterior femoral condyle 5) Release posterior capsuleTight in Extension, Tight in Extension, Balanced in Solution: Flexion 1) Release posterior capsuleFlexion good Problem: 2) Cut more distal femur Did not cut enough distal femur (1-2mm) or did not release enough posterior capsuleExtension Loose , Problem: Solution: Cut too much distal femur or 1) Augment distal femurFlexion good anteroposterior diameter too big 2) small size femur 3)use thicker polyethyleneLoose in Problem: Solution:Extension, Loose Cut too much tibia. 1) Use thicker tibia PEin Flexion 2) Use thicker tibial metal insert
A: The flexion gap in A is largerthan the extension gap seen in B.As seen in A, this results in aknee that is too tight in flexion,producing a flexion contracture.As seen inB, if this problem is approachedby using a thinner tibialcomponent, the prosthesis willbe too loose in flexion. As seen inC, the solution is to excise morebone from the distal femur. B: InAâ€³ and Bâ€³, the extension gapis excessive. As seen in Câ€³, thisis solved by a â€œbuild-upâ€ onthe femoral side
Precision is paramount because an asymmetry of only 5%can lead to liftoff of the femoral component on the tibia,with compressive forces all on one side and tensile forceson the other. Subtle malalignment can magnify with timeas soft tissues attenuate under excessive forces.Specifically, varus alignment of the tibial component hasbeen associated with a higher rate of radiolucency aboutthe prosthesis and a higher rate of looseningMalalignment in aTKA significantlyreducessurvivorship of theimplant
Preoperative EvaluationSoft tissue defects around the knee.Vascular status to the limb.Extensor mechanism.Preoperative range of motion.Preoperative Radiographs
Preoperative RadiographsArthritis seriesStanding full-length radiographs (AP and Lateral) areindicated to determine an accurate valgus cut anglewhen the patient has femoral or tibial deformity very tall or short statureStanding AP and lateral of knee to evaluate for joint space narrowing collateral ligament insufficiency (look for lateral gapping) subluxation of femur on tibia bone defectsExtension and flexion laterals Sunrise viewA skyline view of the patella.
YOUR INVESTIGATIONS MAY INCLUDE-Blood tests Urinalysis X-rays (chest, knees, other involved areas)ECG
TO GET MOST BENEFIT FROM YOUR TKR YOU NEED TO PREVENT POSSIBLE COMPLICATIONS-
TO PREVENT TEETH & MOUTHINFECTIONS: Get a dental check up Brush regularly Eat a balanced diet Visit dentist in case of any problem without overlooking it
TO PREVENT SKIN INFECTIONS:Have a Betadine bath & scrub 3 times Pre- operative.Have no injections on the side of your operation.Avoid cuts & scratches. Cut toe nails straight across to prevent in growing of nails.
TO PREVENT URINARY INFECTIONS:Drink adequate amount of fluids. Keep your genitals clean. Visit the Dr. immediately in case of any discomfort.
TO PREVENT RESPIRATORYINFECTIONS:Such as – Pneumonia, Atelectasis You should :- Turn & move around in bed frequently.Practice Deep Breathing & Coughing.Exercise your lungs with the help of your Physiotherapist.
He will:-Evaluate the amount of movement in your jointscalled “Range of Motion”Test your Muscle strengthTeach Gait training, with appropriate equipment(walker, crutches, sticks, etc)Teach transfers with appropriate equipment(Bed, Toilet, Bathtub, Chair, Car, etc.)
contd…He will instruct you in exercises that :-Help you gain & maintain Muscle strengthHelp you gain & maintain Range of MotionPromote blood circulationHelp you get the most benefit from yoursurgery
Exercises YOU NEED TO DOPRE-OPERATIVELY“Gluteal sets”To maintain & strengthen Hip Muscles (Buttocks) Lie flat on your back in bed Tighten the hip muscles together Hold tense for 10 sec. Relax for 5 sec. 10 repetitions (3-4 times a day)
“CALF PUMPING”Tones up & strengthens the lower leg & foot Lie flat in bed Point your toes towards the foot of bed Point your toes towards your knee 10 repetitions (3-4 times a day)
“QUADS SETS”Strengthen the muscle (Quadriceps) on the front of your thigh.Lie flat on bed Press the back of your knee against the bed Try to lift the heel off the bed 10 repetitions (3-4 times a day)
“STRAIGHT LEG RAISES (SLR)”Benefits the Quadriceps muscle Lie flat on your back Keep the knee as straight as possible Left your leg above the bed for 5 sec. Lower your leg slowly 10 repetitions (3-4 times a day)
Surgical PreparationSecure two separate bumps to the table on theoperated side as leg positionersfull extension30 of flexion100 of flexion whenthe second bump is used
Surgical Preparation(cont.)Administer a dose of a 1st generation cephalosporin (orvancomycin,clindamycin) Avoid pressure on peripheral nerves. (prolonged positioning in the recumbent position) Elevate the patients buttock on the operative side with a soft roll to produce a stable upright positioning of the knee
Surgical Preparation(cont.)The tourniquet should have been placed on the thigh ashigh as possible and the skin protected with soft padding.Shave the skin around the knee immediately before theprocedure to limit compromise of the skin surface. Extendedtime between shaving and surgery promotes colonization ofsmall nicks with bacteria.Surgically scrub the limb and do a final skin prep with anantibacterial solution. Take meticulous care during draping.Drape the skin sterilely as high as possible, and to at least 4inches below the tibial tubercle. Apply an adherent sterilevinyl dressing.Avoid excessively bulky drapes on the lower extremity.Precise alignment in total knee replacement depends on theability to palpate the tibial spine, the malleoli, or bones of thefoot. A bulky drape on the foot obscures landmarks andmakes surgery more difficult.
TECHNIQUEWith the patient prepped and draped, flex the knee to a 30position and mark the surgical incision. Flexion produces tension onthe anterior tissues, which allows a more precise surgical exposure.A midline longitudinal incision is preferred unless otherwise dictatedby prior skin incisions.The exposure extending approximately five fingerbreadths abovethe superior patella and five fingerbreadths below the inferiorpatellaarthrotomy longitudinally in a gentlecurve, which will start at the midpoint ofthe quadriceps tendon proximally, curvearound the patella so that it intersects apoint just medial to the patella, and thencurve back to a point on the tibial tuberclemedially
TECHNIQUE-cont.Transect the anterior horn of the medial meniscus.Elevate the patella, with the knee in extension and pulled towardthe surgeon. Release tight bands in the patellar retinaculum or plicawith electrocautery and avoid the patella.Place a retractor along the medial joint line and flex the knee to 90or 100 The potential for patella tendon avulsion exists in the tightknee, As the knee is flexed, carefully watch the insertion of thepatella tendon to avoid any excessive flexion that may avulse thepatella tendon. (extending the arthrotomy proximally, doing more distal soft-tissuereleases, or considering quadriceps release or tibial tubercleosteotomy )Once patella tendon avulsion occurs, it is very difficult to treat, sothis complication is best avoided
TECHNIQUE-cont.The anterior cruciate ligament is generally resected .remove medial and lateral osteophytes to expose the PCLattachment to the femur. Most knees will have an intactPCL.PCL is sacrificed .(The PCL lies immediately in front of theposterior capsule, which lies in front of the neurovascularstructures. The PCL should not be sacrificed in acavalier( fashion, but it should be doneprecisely. Place a curved clamp behind the PCL to define itssubstance and direction, then take electrocautery and removethe PCL subperiosteally off the femoral attachment)Release the anterior horn of the lateral meniscus andresected.
Bone PreparationBone surface preparation is based on the following principles:appropriate sizing of the individual components,alignment of the components to restore the mechanical axis,recreation of equally balanced soft tissues in flexion and extension,and optimal patellar tracking.odistal femur cutaffects extension gapoposterior femur cutaffects flexion gap
Bone Preparation – IM Femoral GuideThe goal of the femoral preparation is to resurface the abnormalfemur with a femoral implant articulating surface. The distal levelof the femoral implantation is critical to preserve the proper levelof the joint lineThe flexion and extension gapmust be correct. The varus andvalgus alignment and properexternal rotation are critical.
Bone Preparation – IM Femoral Guide(conti.)Make the center drill hole into the medullary canal, approximately3/ inch (9 mm), just medial to the center of the notch to provide 8the best line of axillary alignmentPlace the hole just above the insertion (point anterior to the origin ofthe posterior cruciate ligament) of the PCL, but not so anterior thatbec. risk of perforating the anterior cortex. Drill the hole straightand make it slightly larger than the intramedullary guide rod.Once the hole is drilled, aspiratemarrow products to preventembolization. Take care not to place the drill holein the midline of the femoralcondyles because an abnormalvalgus angulation will occurbecause this is not aligned with themedullary canal
Rotation of the Femoral ComponentRotation of the femoral component is key . The patellofemoral mechanics are altered dramatically by femoralcomponent rotation.An excessively internally rotated femoral component will have muchhigher rates of patellar subluxation and altered patellofemoralmechanics.In general, some external rotation ofthe femoral component is desirable.Also, because tibialresections are performedperpendicular to the long axis, notthe normal 3 medial inclination of the tibial plateauâ an externallyrotated femoral component isnecessary to make the flexion gapequal
Set the proper valgus angle and insert the IM Alignment Guide Proximal/Distal Positioning Varus/Valgus and Flexion/Extension Alignment for the Femur
TECHNIQUEMake the distal femoral cut at a valgus angle (usually 5 to 7 degrees)perpendicular to the predetermined mechanical axis of the femur. The amount of bone removed generally is the same as that to bereplaced by the femoral component. If a significant preoperativeflexion contracture is present, remove additional bone from thedistal femur at this time to widen the extension gap.The anterior and posterior femoral cuts determine the rotation ofthe femoral component and the shape ofthe flexion gap. Excessive external rotationwidens the flexion gap medially and mayresult in flexion instability..
Internal Rotation of Femoral Prosthesis will Increase Q angleby internally rotating the femoral prosthesis, you areeffectively bringing the groove and the patella medially. Thiswill increase the Q angle to the tibial tuberclewill also make the medial compartment tigh•Medialization of the Femoral Prosthesis will Increase Qangle a medialized femoral prosthesis will bring the trochlear groove to a more medial position, and thus bring the patella medial with it, thus increasing the Q angle therefore, you want the femoral component to be slighly lateral if anything
TECHNIQUE-cont.Femoral component rotation can be determined by one of severalmethods. The anteroposterior axis .transepicondylar axis,, posteriorfemoral condyles, and cut surface of the proximal tibia all can serveas reference points.anteroposterior axisdefined as a line running from the center of the trochlear groove tothe top of the intercondylar notcha line perpendicular to this definesthe neutral rotational axis
TECHNIQUE-cont.transepicondylar axisdefined as a line running from the medial and lateral epicondyles the epicondylaraxis is parallel to the tibial surface .A posterior femoral cut parallel to theepicondylar axis will create the appropriate rectangular flexion gapposterior condylar axisdefined as a line running across the tips of the two posterior condylesthis line is in ~ 3 degrees of internal rotation from the transepicondylar axis, thefemoral prosthesis should be externally rotated 3 degrees from this axis toproduce a rectangular flexion gapif the lateral femoral condyle ishypoplastic, use of the posterior condylaraxis may lead to internal rotation of thefemoral component
Regardless of the method used, the thickness of bone removed fromthe posterior aspect of the femoral condyles should equal the thicknessof the femoral component. This determined directly by measuring thethickness of the posterior condylar resection with posterior resurfacinginstruments.Posterior referencing instruments are theoretically more accurate inrecreating the original dimensions of the distal femur; however,anterior referencing instruments have less risk of notching theanterior femoral cortex and place the anterior flange of the femoralcomponent more reliably against the anterior surface of the distalfemur.
Fix the Distal Femoral Cutting GuideRemove the IM Alignment GuideResect the distal femur
Apply the A/P Sizing Guide to the distal femurAttach the Locking Boom and place it lateral on the anterior cortex Read the femoral size
Attach the External Rotation Plate to the Sizing GuidePlace Headless Pins throught the holes that correspond to desiredexternal rotationPin placement should be parallel to epicondylar line
Place the Femoral Finishing Guide over Headless PinsCheck mediolateral positionFix the Finishing Guide with screws or pinsCheck anterior cut with Resection Guide
Cut the femoral profile in the shown sequence
Drill distal holes with Patella/Femoral Drill BitCut trochlear recess with reciprocating saw
Complete the distal femoral preparation for a PCL-retainingprosthesis by making anterior and posterior chamfer cuts for theimplant. If a PCL-substituting design is chosen, remove theintercondylar box to accommodate the housing for the post andcam mechanism
If the distal femoral resection has not been completed, balance theflexion and extension gaps at this time by placing spacer blocks or atensioner within the gaps with the knee in flexion and extension.Varus-valgus balance can be fine-tuned with further medial orlateral releases .Remove any medial or lateral osteophytes that tent the collateralligaments.Remove posterior condylar osteophytes with a curved osteotomebecause they can tent the posterior capsule and narrow the extensiongap or impinge during knee flexion.The flexion and extension gaps must be roughly equal. If theextension gap is too small or tight, extension is limited. Similarly, ifthe flexion gap is too tight, flexion is limited. Laxity of either gap canlead to instability.
Tibial Prosthesis•The preferred rotation of the tibial component is neutral,with no internal or external rotation.the best way to obtain this is to have the tibial componentcentered over the medial third of the tibial tuberclethis will leave a portion of the posteromedial tibia uncoveredand some overhang of the prosthesis over the tibia on theposterolateral tibia•Internal Rotation of Tibial Prosthesiswill increase Q angle .Medialization of tibia will increase Qangle
Bone Preparation – Tibial ResectionThe guide is aligned with the anterior tibial tendonand first web space of thetoes.
Intramedullary and Extramedullary Alignment InstrumentationIntramedullary alignment instrumentation is crucial on the femoralside of a TKA because femoral landmarks are not easily palpable.The entry portal for the femoral alignment rod typically is placed afew millimeters medial to the midline, at a point anterior to theorigin of the PCL. Preoperative radiographs should be scrutinized fora wide canal or excessive femoral bowing because these conditionsmay result in alignment errors.Extramedullary femoral alignment is useful only in limbs with severelateral femoral bowing, femoral malunion, or stenosis from aprevious fracture, or when an ipsilateral total hip replacement orother hardware fills the intramedullary canal. A palpable marker canbe placed over the center of the femoral head based on preoperativehip radiographs. The anterior superior iliac spine has been shown tobe unreliable for determining the hip center and should not be usedas the primary landmark when extramedullary femoral alignment ischosen
The use of tibial intramedullary alignment guides is morecontroversial.One concern about the use of these guides is the risk of fatembolism. Greater elevation of pulmonary arterial pressures andslightly diminished cardiac indices in patients undergoing bilateralTKAs using intramedullary tibial alignment guides compared withextramedullary tibial alignment guides and venting of the femoralintramedullary canals.They did not believe, however, that these slight changes constituted any contraindication to the use of intramedullaryalignment devices.a bout 12% prevalence of postoperative neurological changes believed to be consistent with fat embolism after bilateral TKA andrecommended the use of pulmonary arterial pressure monitoring.They showed that the negative cardiopulmonary effects ofintramedullary femoral alignment rods were eliminated by drillingan oversized 12.7-mm hole in the distal femur and using an 8-mmfluted rod.
TECHNIQUECut the tibia perpendicular to its mechanical axis with 0 to5 degrees of posterior slope, and remove approximately 6to 8 mm of the proximal tibia, as measured from the intactcompartment. Protect the patellar tendon and collateralligaments during this portion of the procedure.Alternatively, the proximal tibia can be cut beforecompletion of the distal femoral cutsPosition of tibial cutting jig: In A, theguide is aligned with the anterior tibialtendon and first web space of the toes,producing an appropriate cut. In B, thealignment jig is centralized on the anklejoint, which is too lateral, resulting inexcessive varus in the cut of the tibialplateaus
(GAP TECHNIQUE)If the extension gap is smaller than the flexion gap, remove morebone from the distal femoral cut surface, or release the posteriorcapsule from the distal femurIf the flexion gap is smaller than the extension gap, remove morebone from the posterior femoral condyles by making appropriatecuts for the next smaller available femoral component.If the flexion and extension gaps are equal, but there is not enoughspace for the desired prosthesis, remove more bone from theproximal tibia because bone removed from the tibia affects theflexion and extension gaps equally.When the flexion and extension gaps are equal but lax, a largerspacer block and a thicker tibial polyethylene insert are required toobtain stability.