TOTAL KNEE ARTHROPLASTY

PRESENTER:

MANOJ KUMAR R

INTRODUCTIONArthroplasty is the surgical reconstruction of a joint which aims to relieve pain , correct deformities and retain movements of a joint.Total Knee Arthroplasty(TKA) is the surgical procedure to replace the weight-bearing surfaces of the knee joint. The primary indications for TKA are : Relieve pain caused by severe arthritis, with or without

deformity. Young patients with limited function due to systemic arthritis

with multiple joint involvement. Osteonecrosis with sub-chondral collapse of a condyle. Severe Patello-femoral arthritis. Severe deformity associated with moderate arthritis and variable

pain.

The contra-indications to TKA are :

Recent Knee Sepsis Source of ongoing infection elsewhere in body Extensor mechanism discontinuity or dysfunction Recurvatum deformity secondary to muscle weakness Painless, Well functioning Knee Arthrodesis

Relative contraindications are numerous and debatable and can include:

Medical conditions compromising patient’s ability to withstand anaesthesia, metabolic demands of surgery and wound healing.

Severely osteoarthritc ipsilateral hip, which should be operated first, because it is easier to rehabilitate a THR with OA Knee than to rehabilitate a TKR with OA Hip.

Atherosclerotic disease of operative leg Skin conditions such as psoriasis within operative field Venous stasis disease with recurrent cellulitis Morbid obesity h/o Osteomyelitis in proximity of knee

RELEVANT ANATOMY

The Knee Joint is the largest & complex joint in the body

It consists of 3 Joints:

Medial Condylar Joint : Between the medial condyle “of the femur” & the medial condyle “of the tibia” .

Latral Condylar Joint : Between the lateral condyle “of the femur” & the lateral condyle “of the tibia” .

Patellofemoral Joint : Between the patella & the patellar surface of the femur.

PCL

Stronger of the two

Arises from post intercondylar area of tibia, passes sup and ant on medial side of ACL to attach to the anterior part of lateral surface of medial condyle of femur

Tightens during flexion of knee joint

Preventing anterior displacement of femur on tibia or posterior displacement of tibia on femur

Main stabilizer in the weight bearing flexed knee

Movements:

Extension 5 - 10°Flexion 120° with hip extended 140° with hip flexed

Muscles producing movements:

Flexion Brceps femoris, semi tendinosus,Semimembranosus assisted by gracilis, Sartorius, popliteus, gastrocnemius. ExtensionQuadriceps femories, tensor fascia latae.Medial rotation Popliteus, semitendinosus, semimebrnaosus. Lateral rotation Popliteus, biceps femoris

POPLITEUS:

 origin: popliteus muscle has 3 origins, strongest of which is from lateral femoral condyle, just anterior and inferior to the LCL origin’  Another origin is from fibula and from the posterior horn of the lateral meniscus;   Femoral and fibular origins form the arms of an oblique Y shaped ligament, the arcuate ligament                           insertion: posterior surface of tibia above soleal or popliteal line popliteus tendon runs deep to LCL and passes thru a hiatus in the coronary ligament to attach to the femur at a point anterior and distal to the femoral attachment of LCL

SCREW HOME MECHANISM — LOCKING AND UNLOCKING OF THE KNEE

BIOMECHANICS

Knee joint may appear to be a simple joint but its biomechanics is complex. The knee is a mobile trocho-ginglymus (a pivotal hinge type of synovial joint).Knee motion during gait occurs in flexion and extension, abduction and adduction, and rotation around the long axis of the limb.

Knee flexion which occurs around a varying transverse axis, is a function of the articular geometry of the knee and the ligamentous restraints.

Dennis et al. described the flexion axis as varying in a helical fashion in a normal knee, with an average of 2mm of posterior translation of the medial femoral condyle on the tibia during flexion compared with 21mm of translation of the lateral femoral condyle.

Osteokinematics Gross movements of bones at joints

Flexion / extension Abduction / adduction Internal rotation / external rotation

Arthrokinematics Small amplitude motions of bones at joint surface

Roll Glide (or slide) Spin

FLEXION - EXTENSION

Instantaneous centre of motion

FLEXION - EXTENSION

Instantaneous center pathway

Sliding/Rocking of femur

FLEXION - EXTENSION

Gliding/Rolling of femur

Knee glides & SlidesRocks & Rolls!

FLEXION - EXTENSION

Abduction - Adduction

Normal angulation of 7 Degrees with knee extended

Motion permitted by cruciate and collaterals

No movement in flexion

AXIS OF LOWER LIMB

The anatomical axis of the femur and the tibia form a valgus angle of 6 degrees ± 2 degrees.

The anatomical axis of the tibia is almost vertical.

So the femur is angled off from the vertical, creating a physiological valgus angle at knee

The mechanical axis of the lower limb is defined as the line drawn on a standing long leg Anteroposterior roentgenogram from the center of the femoral head to the center of the talar dome. This is the Wt. bearing line.

Mechanical axis of the femur and tibia.

Aline from the center of the femoral head to the centerof the intercondylar notch, and extending this line distally.

The mechanical axis of the tibia runs from the center the tibial plateau to the center of the tibial plafond.

The angle formed between these separate mechanical axes of the femur and tibia determines the varus or valgus deviation from the neutral mechanical axis

Knee with the TKA prosthesis:

The aim of the knee replacement is to recreate the normal biomechanical axis and kinematics of the limb.

Thus the tibial components are generally implanted perpendicular to the mechanical axis of the tibia in the coronal plane, with posterior tilt dictated by flexion extension gaps.

The femoral component usually is implanted in 5 to 6 degrees of valgus, the amount necessary to re establish a neutral limb mechanical axis.

During normal gait, mechanical axis is inclined 3 degrees from the vertical axis of the body, with the feet closer to midline than the hips.

When the mechanical axis lies to the lateral side of the knee, knee is in mechanical valgus alignment and if the axis medial to the knee joint, it is in varus.

In normal knee, tibial articular surface is in approximately 3 degrees of varus with respect to the mechanical axis, and femoral articulating surface is in a corresponding 9 degrees of valgus.

Rotational alignment is difficult to discern radiographically, making intra-op assessment important. The effects of femoral component rotation are not only on flexion space but also on patella-femoral tracking

Patellofemoral Joint :

The primary function of the patella is to increase the lever arm of the extensor mechanism around the knee, improving the efficiency of quadriceps contraction. The quadriceps and patellar tendons insert anteriorly on the patella, with the thickness of the patella displacing their respective force vectors away from the center of rotation of knee. The extensor lever arm is greatest at 20 degrees of flexion and the quadriceps force required for knee extension increases significantly in the last 20 degrees of extension.

Patellofemoral contact zones :

The contact areas between the patella and femur changes with knee flexion.

At 200 : Inferior surface of patella is in contact with trochlea

At 600 : Mid portion of patella with trochlea

At 900 : Superior surface of patella with trochlea

At 1200 : patella articulates only medially and laterally with the femoral condyles and quadriceps articulates with trochlea.Changes in patellar area of contact have a significant effect on prosthetic patellofemoral joint & patellar tracking

Q angle :It was described as the angle between the extended anatomical axis of the femur and the line between the center of the patella and the tibial tubercle. The quadriceps acts primarily in line with the anatomical axis of the femur, with the exception of Vastus medialis obliquis, which acts to medialize the patella in terminal extension. Limbs with larger Q-angles have a greater tendency for lateral patellar subluxation. Because the patella does not contact the trochlea in early flexion, lateral subluxation is prevented by the vastus medialis obliquis fibres. As the angle of flexion increase, bony and subsequent prosthetic constaints play a dominant role in preventing subluxation.

Increase in Q-angle can be caused by : Increased external rotation of tibia Excessive tibio-femoral angle

CONCEPT OF IDEAL KNEE Extends fully & achieves excellent stability.Flexes beyond 110 &

still retains stability Gliding and sliding occurs simultaneously.Allows more rotation

as knee flexes Articular contact maximum throughout range Reduplicate the function of menisci and cruciates Achieve excellent ligament balance and have anatomic femur &

tibial surface

FEMORAL ROLL BACK the posterior translation of  the femur with progressive flexion  Importance : improves quadriceps function and range of knee

flexion by preventing posterior impingement during deep flexion 

biomechanics :rollback in the native knee is controlled by the ACL and PCL

design implications :both PCL retaining and PCL substituting designs allow for femoral rollback

PCL retaining :native PCL promotes posterior displacement of femoral condyles similar to a native knee

PCL substituting :tibial post contacts the femoral cam causing posterior displacement of the femur 

CONSTRAINT the ability of a prosthesis to provide varus-valgus and flexion-

extension stability in the face of ligamentous laxity or bone loss importance :in the setting of ligamentous laxity or severe bone

loss, standard cruciate-retaining or posterior-stabilized implants may not provide stability

design implications :in order of least constrained to most constrained

cruciate-retaining posterior-stabilized (cruciate-substituting) varus-valgus constrained (non-hinged) rotating-hinge

MODULARITYthe ability to augment a standard prosthesis to balance soft tissues and/or restore bone loss

options include metal tibial baseplate with modular polyethylene insert  metal augmentation for bone loss  modular femoral and tibial stems 

advantage :ability to customize implant intraoperatively

disadvantage :increased rates of osteolysis in modular components and backside polyethylene wear  

Hemiarthroplasty (1940)

Hinged Implants(1950)

Biocompartmental Prosthesis(1970)- Duocondylar Knee

Tricompartmental Prosthesis Tibial articular surface

Femoral component

Meniscal Bearing Prosthesis Low Contact Stress Prosthesis High Flexion Prosthesis

Types of implants:Unicompartmental

Indication:Medial or lateral tibiofemoraldegenerative disease

Contraindications:a) Inflammatory conditionsb) Damage to articular cartilagec) Flexion contracture of 5° or mored) Preoperative arc of motion less than 90°e) Angular deformity of more than 15°f) ACL deficiency

Bicompartmental:Here replacement of the apposing articular surfaces of both the medialand lateral compartments is done.

Tricompartmental:Here there is replacement of both medial and lateral articular surfaces of tibia and femur along with re-surfacing of patellofemoral articulation.

Most of the current complaints are of this design.

Types

Constrained : Are the ones that restrict movement in all planes

a) Hingedb) Non hinged

Semi-constrained: Here the joint surface alone are replaced. Femoralcomponents articulate with grooved tibial components.

Currently, almost all TKA's are accomplished with this.

These are sub classified into:1) PCl retaining design2) PCl substitution3) PCl sacrificing design

Components of TKR:

1) Femoral component (metal alloy, right and left, PCl - substituting orretaining, sizes 1.5, 2, 2.5, 3,4 and 5)

2) Tibial tray (universal for right and left, sizes matching the femoralcomponents)

3) Patellar button (eccentric, dome shaped with three buttons)

Preoperative evaluation:

Most important part of pre operative evaluation is determining that TKR Is clearly indicated.

Radiological assessment Templating of pre operative X-rays

Rule out and evaluate for potential serious vasculardisease in the lower extremity

Assessment of the skin is also important in arthroplasty

Administer a dose of prophylactic antibiotics beforeinflation of the tourniquet.

APPROACHES TO THE KNEE Surgical approach may be dictated by surgeon preference,prior

incisions,degree of deformity,patella baja,patient obesityAPPROACHES "simple" primary knee arthroplasty approaches medial parapatellar(A) midvastus(B) subvastus(C) minimally invasive "complex" primary or revision total knee arthroplasty lateral parapatellar(D) quadriceps snip V-Y turndown tibial tubercle osteotomy

COMPLEX PRIMARY APPROACHES

TECHNIQUE

It consists of:

Exposure and dislocation Bone preparation Ligamentous balancing Component fixation Wound closure

PROBLEMS

KINEMATICS STABILITY DURABILITY

FEMORAL ROLL BACK

RANGE OF FLEXION

LIGAMENTS

BONY GEOMETRY

ALLIGNMENT

FIXATION

PCL RETAINING

FLEXION

EXTENSION

PCL SUBSTITUTING

VIDEO

BONE PREPARATION

appropriate sizing of the individual components, alignment of the components to restore the mechanical axis, re-creation of equally balanced soft tissues and gaps in flexion

and extension, and optimal patellar tracking.

The anterior and posterior femoral cuts determine the rotation of the femoral component and the shape of the flexion gap. Excessive external rotation widens the flexion gap medially and may result in flexion instability. Internal rotation of the femoral component can cause lateral patellar tilt or patellofemoral instability.

Femoral component rotation can be determined by one of several methods.

The transepicondylar axis, anteropos terior axis, posterior femoral condyles, and cut surface of the proximal tibia all can serve as reference

points

Regardless of the method used of rotational alignment, the thickness of bone removed from the posterior aspect of the femoral condyles should equal the thickness of the posterior condyles of the femoral component. This is determined directly by measuring the thickness of the posterior condylar resection with “posterior referencing” instrumentation.

“Anterior referencing” instruments measure the anteroposterior dimension of the femoral condyles from an anterior cut based off the anterior femoral cortex to the articular surface of the posterior femoral condyles. The femoral component chosen must be equal to or slightly less than the measured anteropos terior dimension to avoid tightness in flexion.

Posterior referencing instruments are theoretically more accurate in re-creating the original dimensions of the distal femur; however, anterior referencing instruments have less risk of notching the anterior femoral cortex and place the anterior flange of the femoral component more reliably against the anterior surface of the distal femur

Cut the tibia perpendicular to its mechanical axis with the cutting block oriented by an intramedullary or extramedullary cutting guide. The amount of posterior slope depends on the individual implant system being used. Many systems incorporate 3 degrees of posterior slope into the polyethylene insert, which allows more accurate slope to be aligned by the

GAP TECHNIQUE

Before any soft tissue release, remove any medial or lateral osteophytes about the tibia and femur. Remove posterior condylar osteophytes because they can block flexion and tent posterior soft tissue structures in exten sion, causing a flexion contracture.

The flexion and extension gaps must be roughly equal. If the extension gap is too small or tight, extension is limited. Similarly, if the flexion gap is too tight, flexion is limited. Laxity of either gap can lead to instability

INTRAMEDULLARY AND EXTRAMEDULLARY ALIGNMENT INSTRUMENTATION

Intramedullary alignment instrumentation is crucial on the femoral side of a TKA because femoral landmarks are not easily palpable. The entry portal for the femoral alignment rod typically is placed a few millimeters medial to the midline, at a point anterior to the origin of the PCL

Extramedullary femoral alignment is useful only in limbs with severe lateral femoral bowing, femoral malunion, or ste nosis from a previous fracture, or when an ipsilateral total hip replacement or other hardware fills the intramedullarycanal. A palpable marker can be placed over the center of the femoral head based on preoperative hip radiographs or by fluoroscopic imaging with the patient on the operating table. The anterior superior iliac spine has been shown to be unreli able for determining the hip center and should not be used as the primary landmark when extramedullary femoral align ment is chosen

The relative accuracy of intramedullary and extramedul lary tibial alignment also has been debated.Currently most surgeons prefer intramedullary femoral alignment with extramedullary tibial alignment

LIGAMENTOUS BALANCING

Soft tissue balancing is essential to providing a stable joint after TKA. After bone preparation is completed, the flexion and extension gaps should be evaluated for symmetry for equal height in flexion and extension. This can be done with laminar spreaders, spacer blocks, or computer navigation techniques

Before release of any anatomical soft tissue sup porting structure about the knee, all peripheral osteophytes should be removed from the femur and tibia. The removal of osteophytes alone may be enough to balance existing coronal plane deformities.

If a tibial resection first technique is being done, the osteophytes should be removed before determining any bony cuts on the femur. Eventual knee range of motion can be restricted by excessive collateral or PCL tension, and excessive laxity may lead to clinically unacceptable instability.

As a general guideline, 1 to 2 mm of balanced varus-valgus play in the prosthetic knee is a reasonable goal.

Regardless of the type of deformity being corrected, stability should be checked after each stage of soft tissue release because over release can lead to excessive coronal plane instability and require conversion to a constrained prosthesis

CORRECTION OF VARUS DEFORMITY: IF DOING A PCL STABILIZED TKA,make sure the PCL is

resected before balancing. Because the PCL is a secondary medial stabilizer, take care not to release the entire soft tissue sleeve off the tibia because it may overshoot the gap. In general, less soft tissue release is needed to balance a varus knee once the PCL is resected.

Assess the flexion and extension gaps. If the gaps are tight, release the superficial medial collateral ligament subperiosteally off the proximal tibia but do not com pletely release it off the tibia. Recheck the gaps in flexion and extension.

With a cruciate-retaining TKA with the PCL intact, the release may need to be carried out up to 6 cm distal to the joint line to effectively balance the gap.

If the extension gap is tight only medially, the posterior oblique ligament portion can be subperiosteally released now or later in the soft tissue balancing procedure. If the extension gaps remains tight medially, the semimembra nosus and posteromedial capsule can be released.

If the flexion gap is tight, the anterior aspect of the superficial medial collateral ligament and the pes anseri nus insertion can be released.

If the entire soft tissue sleeve is released and the medial gap is still tight, consider balancing the lateral collateral ligament.If a posterior drawer maneuver indicates that the PCL is not functioning, consider conversion to an anterior-lipped, deep-dish insert

CORRECTION OF VALGUS DEFORMITY

Valgus deformity is common in patients with rheumatoid and inflammatory arthropathies and also can occur in those with hypoplastic lateral femoral condyle or previous trauma or reconstructive procedures that change the weight-bearing axis of the lower extremity or tighten the lateral side of the joint.

The three-layer anatomy of the lateral side of the knee joint makes its soft tissue balancing more complex than with varus deformity. The surgeon should have detailed knowledge of the three soft tissue layers to understand the release and balancing techniques used to correct tight lateral gaps in valgus deformity

During exposure, release the lateral capsule from the tibia.

The structure released first depends on whether both the extension and flexion gaps are tight on the lateral side. If both are tight, release the lateral collateral ligament off the lateral epicondyle, taking care to leave the insertion of the popliteus tendon intact

If at any point during the balancing of the valgus knee only the extension gap is tight, release the iliotibial band by a Z-lengthening or pie-crusting of the band 2 cm above the joint line. Make certain all fibers are released, and evaluate the biceps aponeurosis to make sure it is not involved in the contracture.

Release of the posterolateral corner has been shown to effectively increase the extension space more than the flexion space and should be considered before release of the lateral collateral ligament if only a small amount of correction is needed.

Release of the popliteus tendon will increase the flexion gap laterally more than the extension gap.

If the knee is still not balanced in full extension after release of all of these structures, release the posterior capsule off the lateral femoral condyle; then release the lateral head of gastrocnemius if further correction is needed.

CORRECTION OF FLEXION CONTRACTURE

Most preoperative flexion deformities improve with appro priate soft tissue balancing for coronal plane deformity. If a flexion contracture persists despite balanced medial and lateral soft tissues, the shortened posterior structures must be effectively lengthened. If the contracture persists, the joint line may need to be elevated by increasing the amount of distal femoral bone resection. With severe flexion contrac ture, elevation of the joint line more than 4 mm should be avoided because it can create mid-flexion instability, and an increase in implant constraint may be necessary.

If necessary, release the posterior capsule further by strip ping more proximally up the posterior aspect of the femur and releasing the tendinous origins of the gastrocnemius muscles if necessary.

If the flexion contracture persists, increase the distal femoral bone cut by 2mm and re-check to see if the knee will move into full extension with the trial components in place. This can be increased by another 2 mm (total of 4 mm over a matched resection), but make certain that mid-flexion instability does not exist

MANAGEMENT OF BONE DEFECTS

Bone deficiencies encountered during total knee replacement can have multiple causes, including arthritic angular defor mity, condylar hypoplasia, osteonecrosis, trauma, and previ ous surgery such as HTO and previous total knee replacement. The method used to compensate for a given bone defect depends on the size and the location of the defect. Contained or cavitary defects have an intact rim of cortical bone sur rounding the deficient area, whereas noncontained or seg mental defects are more peripheral and lack a bony cortical rim

Small defects (<5 mm) typically are filled with cement Contained defects can be filled with impacted cancellous bone graft.

Larger noncontained defects can be treated by a variety of methods, including the use of structural bone grafts, metal wedges attached to the prosthesis, or screws within cement that fills the defect

Convert the concave, irregular defect to a flat one by minimal bone removal with a saw

Attach bone removed from the distal femur or proximal tibia to the flattened defect, and secure it with threaded Steinmann pins or screws

Carefully recut the upper tibial surface to create a flat upper tibial surface.

During cementing, premix a small batch of cement and use it to seal the junction of the bone graft with the tibia to prevent extrusion of cement into this interface during final component cement fixation.

PATELLOFEMORAL TRACKNG

Patellofemoral tracking is affected by multiple factors, each of which must be inspected during trial reduction and before final component implantation. Any factor that increases the Q angle of the extensor mechanism can cause lateral maltrack ing of the patella.

Internal rotation of the tibial component lateralizes the tibial tubercle, increasing the Q angle and the tendency to lateral patellar subluxation. Simi larly, internal rotation or medial translation of the femoral component can increase lateral patellar subluxation by moving the trochlea medially

If the patella is to be resurfaced, the prosthetic patella should be medialized to approximate the median eminence of the normal patella, rather than simply centering the prosthetic button on the available bone .

Centralization of the patellar component requires the bony patella to track medially, which forces it to function with a higher Q angle. Increasing the anterior displacement of the patella during knee motion also can lead to patellar instability or limited flexion. Anterior displacement can be caused by placing the trochlea too far anterior with an oversized femoral component or by underresection of the patella, which results in an overall increase in patellar thickness

POSTOPERATIVE MANAGEMENT

Postoperative physical therapy and rehabilitation greatly influence the outcome of TKA. Initially, a compressive dress ing is worn to decrease postoperative bleeding and a knee immobilizer may be used until quadriceps strength is ade quate to ensure stability during ambulation.

Range-of-motion exercises are performed postopera tively, with or without the assistance of a continuous passive motion machine.

In addition to range-of-motion exercises, the postoperative rehabilitation protocol includes lower extremity muscle strengthening, concentrating on the quadriceps; gait training, with weight bearing as allowed by the particular knee recon struction; and instruction in performing basic activities of

RESULTS OF PRIMARY TKA:

COMPLICATIONS

THROMBOEMBOLISM

One of the most significant complications after TKA is the development of deep venous thrombosis (DVT), possibly resulting in life-threatening pulmonary embolism (PE). Factors that have been correlated with an increased risk of DVT include age older than 40 years, estrogen use, stroke, nephrotic syndrome, cancer, prolonged immobility, previous thromboembolism, congestive heart failure, indwelling femoral vein catheter, inflammatory bowel disease, obesity, varicose veins, smoking, hypertension, diabetes mellitus, and myocardial infarction.

The overall prevalence of DVT after TKA without any form of mechanical or pharmaceutical pro phylaxis has been reported to range from 40% to 84%

Thrombi in the calf veins have a propensity to propagate proximally, as documented in 6% to 23% of patients.

MANAGEMENT: Many methods of DVT prophylaxis are available, includ ing

mechanical devices such as compression stockings or foot pumps and pharmaceutical agents such as low-dose warfarin, low-molecular-weight heparin, fondaparinux (a pentasaccha ride factor Xa inhibitor), and aspirin.

Mechanical compres sion boots and foot pumps are advantageous because they are without significant risk to the patient, but they are limited by patient compliance and short duration of hospitalization.

INFECTION Infection is one of the most dreaded complications affecting

TKA patients, with reported frequencies of 2% to 3% in several large series.Preoperative factors associated with a higher rate of infection after TKA include rheumatoid arthritis (especially in seropositive men), skin ulceration, previous knee surgery, use of a hinged-knee prosthesis, obesity, con comitant urinary tract infection, steroid use, renal failure, diabetes mellitus, poor nutrition, malignancy, and psoriasis.

The diagnosis of infection after TKA should begin with a careful history and physical examination. The timing of an infection can have a profound effect on the outcome of its treatment and should be used in guiding treatment decisions. Infection should be considered in any patient with a consis tently painful TKA or an acute onset of pain in the setting of a previously pain-free, well-functioning arthroplasty. A history of subjective swelling, erythema, or prolonged wound drainage suggests TKA sepsis, but these signs are not uni formly present. Swelling, tenderness, painful range of motion, erythema, and increased warmth of the affected limb may accompany a TKA infection

MANAGEMENT Efforts to reduce bacterial contamination, optimize the status of

the wound, and maximize the available host response should be employed to minimize postoperative sepsis.

Pre vention of infection in TKA begins in the operating room, with strict adherence to aseptic technique. The number and ingress and egress of operating room personnel should be minimized as much as possible. Operating room surveillance with adherence to such policies has been shown to decrease the incidence of postoperative infection in total joint replacement.

The use of filtered vertical laminar flow operating rooms, body exhaust suits, and prophylactic antibiotics has greatly reduced postoperative infection rates in total joint arthro plasty

When the diagnosis of infection is established, treatment options include antibiotic suppression, débridement with prosthesis retention, resection arthroplasty, knee arthrodesis one-stage or two-stage reimplantation, and amputation

. The choice between the various options depends on the general medical condition of the patient, the infecting organism, timing and extent of infection, the residual usable bone stock, status of the soft tissue envelope, and extensor mechanism continuity.

PATELLOFEMORAL COMPLICATIONS

patellofemoral instabil ity, patellar fracture, patellar component failure patellar component loosening patellar clunk syndrome, and extensor mechanism rupture

NEUROVASCULAR COMPLICATIONS

Arterial compromise after TKA is a rare but devastating com plication that occurs in 0.03% to 0.2% of patients, with 25% resulting in amputation.

Peroneal nerve palsy is the only commonly reported nerve palsy after TKA, with a reported prevalence of less than 1% to nearly 2%.

Mild palsies may recover spontaneously and not be reported. Peroneal nerve palsy occurs primarily with correction of combined fixed valgus and flexion deformities, as are common in patients with rheumatoid arthritis. Suggested risk factors for peroneal palsy after TKA include postoperative epidural anesthesia, previous laminectomy, tourniquet time of more than 90 minutes, and valgus deformity

PERIPROSTHETIC FRACTURES

Supracondylar fractures of the femur occur infrequently after TKA (0.3% to 2%). Reported risk factors include anterior femoral notching, osteoporosis, rheumatoid arthritis, steroid use, female gender, revision arthroplasty, and neurological disorders. The anterior femoral flange of condylar-type prostheses creates a stress riser at its proximal junction with the relatively weak supracondylar bone.

TREATMENT Treatment of femoral fracture after TKA has varied, with early

studies generally recommending nonoperative manage ment. More recent studies have favored operative treatment by a variety of techniques: open reduction and internal fixation using blade plates, condylar screw plates, and buttress plates with bone grafting; Rush pins inserted under image intensification with minimal surgical dissection; or fixation with a locked supracondylar intramedullary nail

Tibial fractures below TKAs are uncommon. Felix, Stuart, and Hanssen classified these fractures on the basis of their location, implant stability, and timing (intraoperative vs. postoperative). Fractures associated with loose implants are treated with revision, bone grafting, and stemmed implants as needed. Nondisplaced, stable fractures with well-fixed implants are treated nonoperatively; displaced fractures with well-fixed implants are treated with internal fixation

Causes of failure of TKA:

1)Sepsis

2) Component loosening

3) Instability/ligamentous laxity

4) Polyethylene wear with osteolysis

5) Periprosthetic fractures

6) Patellofemoral complications

COMPUTER-ASSISTED ALIGNMENT TECHNIQUE The technique involves the attachment of active or passive

trackers on the femur and the tibia, which are then tracked by a computer-assisted camera, which must have a clear line of sight during the procedure The markers are removable from a reference base that is anchored to the bone to ensure that they are not damaged or loosened during the procedure.

Once the trackers are attached to the reference bases, the surgeon typically performs a registration of the anatomical landmarks so that the computer can deter mine and track the femoral and tibial anatomy during the procedure to guide the surgeon in alignment of the bony cuts and implants.

The anatomy within the surgical field typically is registered using a pointing device that has markers that the computer can track, and the center of the femoral head is determined by indirect means of a center-of-rotation mathematical algorithm. Palpated landmarks of a combination of center-of-rotation and external landmarks can be used to determine the center of the ankle.

Once the registration is complete, the computer can give real-time feedback about the alignment of the bony cuts of the femur and tibia in all three anatomic planes, which allows the surgeon to make changes and to measure the accuracy of the bony cuts rather than relying solely on the alignment of the cutting jig, which may not translate into an accurate bony cut because of sclerotic or osteopenic bone

Computer navigation systems also can aid in determin ing the proper implant size as well as alignment. Soft tissue balancing and measurement of flexion and extension gaps during the procedure are other significant advantages to computer-assisted TKA.

Objective measurement of the gaps ensures proper soft tissue balancing and gaps that will provide a stable joint throughout a range of motion.

Another advantage of computer navigation is avoidance of violation of the femoral intramedullary canal, which may reduce blood loss and cardiac-related complications because fewer emboli are placed into the venous system than with placement of an intramedullary alignment rod.

UNICONDYLAR KNEE ARTHROPLASTY

This simply means that only a part of the knee joint is replaced through a smaller incision than would normally be used for a total knee replacement. Unicondylar knee replacements have been performed since the early 1970's with mixed success.. Recent advances allow us to perform this through a smaller incision and hence is not as traumatic to the knee making recovery quicker.

Important selection criteria include an intact ante rior cruciate ligament, unicompartmental arthritis, passively correctable deformity, and reasonable body weight

Just as in primary TKA, the dif ferences between fixed and mobile-bearing techniques involve strict adherence to equalization of flexion and extension gaps to avoid bearing “spit-out.”

PATELLOFEMORAL ARTHROLASTY

Although historically controversial, new interest in patello femoral arthroplasty over the past few years has been fueled by contemporary implant designs that have produced improved clinical outcomes

The ideal candidate for patellofemoral arthroplasty is a patient who is younger than 65 years of age and has debilitating, isolated patellofemoral arthritis with no malalignment of the patellar mechanism

Good results have been reported after patellofemoral arthroplasty in patients with posttraumatic arthritis, primary patellofemoral osteoarthritis, and patellofemoral dysplasia without malalignment

Patellofemoral arthroplasty alone cannot correct patellar malalignment, and instability of the patellofemoral joint is not an indication for the procedure

TIME CONSTRAINTS

REVISION TKAUNICONDYLAR ARTHROPLASTYPATELLOFEMORAL ARTHROPLASTYUNCEMENTED TKA