S. Mehdi Jafari and Javad Parvizi
DEFINITION
Total knee arthroplasty (TKA) is a successful surgical procedure that provides excellent and durable relief of pain and improvement in functional status for patients with osteoarthritic knees.
Cement fixation currently is the preferred method of fixation for TKA.
ANATOMY
The knee is a synovial hinge joint with little rotational motion.
The stability of the joint is provided by congruity of the joint as well as by the collateral and cruciate ligaments.
The mechanical axis is a line drawn from the center of the femoral head, to the center of the tibiotalar joint, forming a straight line, and the anatomic axis is the femorotibial axis, created by the intersection of the long axes of the femur and tibia (FIG 1A). The intersection of these two axes creates about a 6-degree angle of valgus. The 6-degree valgus angle of the knee is determined by the bony anatomy of the distal femur and the proximal tibia.
The proximal articular surface of the tibia usually is oriented in slight varus—3 degrees, on average. This varus position, combined with the offset of the hip center of rotation, results in the weight-bearing surface of the tibia being parallel to the ground during a single-leg stance. As a result of the slight varus in the tibia, the distal femur actually is in 9 degrees of valgus, resulting in a combined femorotibial alignment of 6 degrees when the knee is in extension.
The asymmetry of the distal femoral condyles is also carried over to their posterior surfaces. When the normal knee is flexed, the joint remains parallel to the floor. For this relationship to be maintained on the varus tibial surface, there must be an asymmetry of the posterior dimensions of the femoral condyles. When observed in flexion, the medial femoral condyle extends more posterior than the lateral femoral condyle.
The sagittal alignment of the tibial articular surface also is important. In the sagittal plane, the tibia is sloped posteriorly about 5 to 7 degrees (FIG 1B). In the normal knee, the asymmetry of the bony anatomy maintains the alignment of the joint and ligamentous tension.1
PATHOGENESIS
Knee osteoarthritis (OA), also known as degenerative joint disease (DJD), is usually the result of wear and tear of the articular cartilage and is seen mostly in elderly women and men.
Knee OA can be divided into two types:
Primary OA: articular degeneration without any apparent underlying reason
Secondary OA: a consequence of either an abnormal concentration of force across the joint, eg, post-traumatic arthritis (FIG 2), or abnormal articular cartilage, eg, rheumatoid arthritis.
NATURAL HISTORY
The natural history of OA usually is progression of disease leading to eventual disability. Although the intensity of the clinical symptoms may vary, they usually become more severe, more frequent, and more debilitating over time. The rate of progression varies from patient to patient.
Whereas medications can help control the progression of rheumatoid arthritis and other inflammatory conditions, no proven disease-modifying agents for treatment of knee OA currently exist.
It is believed that OA cases in which is a consequence of anatomic deformities, correction of these abnormalities (eg, high tibial osteotomy for correction of genu varum) may unload the joint, halt progression of disease, and even allow for biologic repair.
PATIENT HISTORY AND PHYSICAL FINDINGS
The initial evaluation should focus on identifying the extent to which knee pain is attributable to knee OA. Occasionally pain is referred from the hip joint or lumbar spine to the knee.
Although the distinction usually can be made on the basis of physical examination, selective anesthetic injection occasionally is necessary to elucidate the relative contributions of overlapping pathologies to a patient's symptoms.
With the patient standing, look for periarticular erythema and swelling, quadriceps muscle atrophy, and varus or valgus deformities. Observe the patient's gait for signs of pain or abnormal hip motion.
If surgery is being considered, systematically assess the surrounding skin for mobility and for the presence and location of scars from any previous surgical procedures (previous scars may influence surgical approach).
Palpate along the joint line, medial and lateral collateral ligaments, iliotibial band, and pes anserine to identify any tenderness suggestive of focal injury.
Active and passive range of motion (ROM) should be assessed. Normal ROM should be from full extension (0 degrees) to full flexion (135 degrees). Any deviation from this normal range should be documented.
The strength of the quadriceps and hamstring muscles should be assessed and documented using a five-point scale.
Palpate and document popliteal, dorsalis pedis, and posterior tibial pulses. Evaluate the patient's legs for shiny, hairless skin or venous stasis ulcers, which raise concern for vascular problems.
Other methods for examining the osteoarthritic knee before arthroplasty include the following:
A Q angle of more than 15 degrees often is the cause of patellar subluxation/dislocation or patellofemoral pain and arthritis.
Anterior drawer test: Increased anterior translation of the tibia compared to the other side plus a mushy endpoint indicates anterior cruciate ligament (ACL) deficiency.
FIG 1 • A. Mechanical and anatomic axes of the lower extremity. B. The posterior slope of the tibial plateau in the sagittal plane is approximately 5 to 7 degrees.
FIG 2 • AP and lateral radiographs showing posttraumatic arthritis following medial tibial plateau injury.
Posterior drawer test: Translation of the tibia more than 10 mm posterior to the femoral condyle is highly suggestive of multiligamentous knee injury and deficiency of the posterior cruciate ligament (PCL).
Varus and valgus stress test: Instability at 30 degrees of flexion suggests isolated collateral ligament injury. Instability at both 0 and 30 degrees is suggestive of a multiligamentous injury.
Patellar apprehension test: A patient with a history of patellar instability may report a sensation that his or her patella feels as if it is about to dislocate.
Patellar tilt test: More than 15 degrees of lateral tilt is suggestive of laxity. Lack of patellar tilt is suggestive of a tight lateral constraint.
The patellar grind test reveals pain or crepitus.
Quadriceps active test: Forward translation of the tibia after attempted knee extension is positive for PCL insufficiency (reduction of posterior tibial sag).
IMAGING AND OTHER DIAGNOSTIC STUDIES
The standing anteroposterior (AP) radiograph best reveals joint space narrowing and any potential dynamic instability. It also shows any marginal osteophytes, tibial and patellar spurs, subchondral sclerosis, joint space narrowing, flattening, squaring of the condyles, and joint line angulation.
Standing lateral in extension
Skyline view of the patella
Occasionally, specialized views of the knee such as the 45-degree posteroanterior (PA) view of the knee (Rosenberg view) or a long-leg view may be required to determine the degree of deformity, and also to obtain information about the status of the femur and tibia in patients with a history of previous trauma or fracture.
DIFFERENTIAL DIAGNOSIS
Any potential cause of local or diffuse knee pain should be considered in the differential diagnosis of knee osteoarthritis, including:
Hip arthritis
Low back pain / spinal stenosis
Patellofemoral syndrome
Meniscal tear
Bursitis
Infectious arthritis
Gout, pseudogout
Iliotibial band syndrome
Collateral or cruciate ligament injury
NONOPERATIVE MANAGEMENT
A wide range of nonoperative modalities are available for treatment of knee OA. These interventions do not alter the underlying disease process, but they may substantially diminish pain and disability.
Health and behavior modifications, including patient education, physical therapy, weight loss, and knee braces, can result in improvement of knee pain and function. In all stages of knee OA, weight loss (if the patient is overweight) is valuable. An unloader-type knee brace shifts load away from the involved knee compartment, whereas a support-type brace supports the entire knee load.
Drug therapy includes acetaminophen, nonsteroidal antiinflammatory drugs (NSAIDs), COX-2 inhibitors, and glucosamine and/or chondroitin sulfate.
Intra-articular injections
Corticosteroid injections in knees with considerable inflammatory component (eg, swelling) are useful.
Hyaluronic acid (viscosupplementation)
SURGICAL MANAGEMENT
Osteotomy may be indicated for unicompartmental knee OA associated with malalignment, or for correction of symptomatic posttraumatic malunions about the knee.
Arthroscopic débridement and lavage has a minimal role in the treatment of knee OA.
Arthroplasty: total or partial knee replacement
Indications
TKA is regarded as a valuable intervention for patients who have severe daily pain along with radiographic evidence of arthritis. The discrepancy between the severity of radiographic changes and symptoms poses a problem. A painful knee without associated radiographic findings dictates a systematic search to exclude other possible sources of knee and leg pain (ie, referral pains from hip or nerve root compression in the spine). The need for correction of significant or progressive deformities sometimes may be considered an indication for knee replacement in patients with moderate arthritis.
Contraindications
Absolute
Active or latent (<1 year) knee sepsis
Presence of active infection elsewhere in the body
Incompetent quadriceps muscle or extensor mechanism
Relative
Neuropathic arthropathy (eg, Charcot arthropathy)
Poor soft tissue coverage or skin conditions such as uncontrolled psoriatic lesions in the vicinity of the incision
Well-functioning and painless knee ankylosed in a good position
Morbid obesity
Noncompliance due to major psychiatric disorders, including dementia, hostile personality, or alcohol or drug abuse
Insufficient bone stock for reconstruction
Poor health or presence of comorbidities that make the patient an unsuitable candidate for major surgery and anesthesia
Patient's poor motivation or unrealistic expectations
Severe peripheral vascular disease
Preoperative Planning
A comprehensive medical and drug history is mandatory to confirm that the patient is an appropriate candidate for a major surgery and anesthesia, because an overlooked detail may lead to a serious or life-threatening complication.
Good-quality radiographs must be obtained, as described earlier. Radiographs are position-sensitive, and care must be taken to obtain the films in neutral rotation. A full-length radiograph from the hip to the ankle is helpful in determining the mechanical axis of the limb and noting unusual shaft bowing or deformities in some cases.
Template overlay is used to estimate component size and bone defects.
The patient is required to complete an informed consent regarding the possible risks.
Positioning
The skin around the knee is shaved using clippers shortly before the procedure in a holding area outside the room where the procedure will be performed. Shaving should be performed in such a manner that skin integrity is preserved.
The patient is positioned supine on the operating table in an operating room equipped with laminar airflow. The upper torso is secured with a protective belt to allow tilting of the table as needed. A bump is taped to the table in such a position that it supports the heel when the patient's knee is flexed and frees the assistant's hands (FIG 3A).
A tourniquet is applied snugly and as far proximally as feasible to the upper thigh on soft Webril (Medco, Tonawanda, NY) padding. In obese or short-limbed patients, it may be necessary to use a sterile tourniquet to ensure adequate access to the surgical field.
The heel is suspended in a leg holder (FIG 3B).
An adhesive drape is put in place distal to the tourniquet to prevent antimicrobial solutions from dripping under the tourniquet.
Surgical skin preparation is begun using a broad-spectrum germicidal agent, eg, combined povidone-iodine and isopropyl alcohol solution. Chlorhexidine may be used if the patient is hypersensitive to iodine.
Meticulous and secure draping technique is important to reduce the risk of infection. Bulky drapes obscure the palpable bony landmarks, such as malleoli or metatarsal bones, that are routinely used for accurate bone cuts, rotation, and alignment in knee arthroplasty.
The limb is exsanguinated by applying an elastic wrap. The incision is marked on the front of the knee along with several horizontal lines that will be used to align the skin properly during closure (FIG 3C). An adhesive plastic surgical drape is placed around the leg without covering the incisional site.
A single dose of cefazolin or cefuroxime is administered 30 to 60 minutes before the skin incision is made and 10 minutes before the tourniquet is inflated. If the patient has a β-lactam allergy, alternatives such as vancomycin or clindamycin can be used.
Approach
Classically, an anterior longitudinal midline incision is used for TKA. This incision may sacrifice the infrapatellar branch of the saphenous nerve, causing an area of lateral numbness; the patient should be warned about this possibility before the surgery.
Blood is primarily supplied to the skin of the anterior aspect of the knee from the medial side, so before the skin incision is made, the exact site and size of any previous scars should be taken into consideration; otherwise the viability of the lateral flap is endangered. In most cases, the preexisting anterior longitudinal scar on the knee is incorporated into the incision, provided that it gives adequate exposure without placing any undue tension on the skin during the operation.
FIG 3 • A. A bump is taped to the table in such a position that it supports the heel when the knee is flexed. B. The heel is suspended in a leg holder for surgical skin preparation. C. The incision is marked on the front of the knee along with several horizontal lines.
When parallel anterior longitudinal scars are present, the most lateral one should be used if possible. If this is not possible, a wide bridge of intact skin (8 cm) should be allowed between the new incision and the previous scar. The horizontal scars can be crossed at right angles, and the short oblique ones may be ignored. Acute angles of intersection must be avoided.
Arthrotomy can be performed by the medial parapatellar approach, the subvastus (Southern) approach, or the midvastus approach.
The medial patellar approach provides excellent exposure and is associated with a very low incidence of tibial or femoral complications.
TECHNIQUES
EXPOSURE
With the knee in 90 degrees of flexion, the incision (TECH FIG 1) is made from the superior edge of the quadriceps tendon proximally (one hand-breadth above the superior pole of the patella) to the inferomedial aspect of the tibial tuberosity. Flexion tenses the skin and retracts the skin margins as the incision is made.
The skin, fat, and fascia are incised directly down to the extensor mechanism, and the medial and lateral flaps are reflected only as far as necessary to have adequate exposure while preserving their blood supply.
Once the deep fascia is opened, the prepatellar bursa is incised and retracted medially and laterally. The paratenon of the patellar tendon should be exposed and protected.
TECH FIG 1 • The incision is made with the knee in 90 degrees of flexion.
ARTHROTOMY
Bring the knee into extension and perform the arthrotomy.
Several approaches are described in the following sections, these differ mainly in the proximal part of the incision (TECH FIG 2).
Medial Parapatellar Approach
The quadriceps tendon is cut longitudinally from proximal to distal along its medial border, leaving a cuff of tendon approximately 5 to 10 mm wide. Then the incision is carried further, skirting along the medial border of the patella and patellar tendon.
The arthrotomy incision is made through the medial retinaculum, capsule, and synovium, leaving a 5-mm cuff of retinaculum attached to the patella to facilitate repair at the end of the procedure. Distally, the incision should stop at the inferior aspect of the patellar tendon insertion, proximal to the insertion of the pes anserine tendons on the superomedial tibia.
TECH FIG 2 • Planes of dissection for the medial parapatellar approach, the midvastus approach, and the subvastus approach.
Subvastus (Southern) Approach
Blunt dissection is carried from the medial intermuscular septum. Care should be taken to avoid damaging the intermuscular septal branch or the articular branch of the descending genicular artery. This should be avoided by limiting proximal dissection to 10 cm or less.
A transverse incision is made at the mid-patella through the medial retinaculum and inferior to the vastus medialis.
This incision is stopped once the patellar tendon is reached, and a second incision is made along the medial border of the patellar tendon approximately 1 cm along the medial border to the tibial tubercle.
Midvastus Approach
Blunt finger dissection is begun at the superomedial pole of the patella in the midsubstance and through the full thickness of the vastus medialis muscle, and is extended parallel to its fiber, to a maximum of 4 cm proximomedial to this starting point. By doing this, the incision does not extend far enough medially to violate the saphenous nerve to the vastus medialis obliquus. The medial superior geniculate artery and the muscular branches of the descending geniculate artery are similarly preserved.
KNEE JOINT EXPOSURE
The soft tissue sleeve is dissected from the proximal medial tibial metaphysis (TECH FIG 3) by taking the amount of varus or valgus deformity into account.
More extensive dissection is performed for knees with varus deformity, and limited or no dissection for knees with valgus deformity.
With sharp dissection or cautery, a subperiosteal layer that includes the deep medial collateral ligament (MCL) is raised carefully from the medial tibial flare to the sagittal midline of the tibia. The dissection must not be extended more than 2 to 3 cm distal to the medial joint line.
TECH FIG 3 • The soft tissue sleeve is dissected from the proximal medial tibial metaphysis as much as necessary for the correction of a varus deformity of the knee.
Patellar Eversion
The patella is everted, and the knee is flexed (TECH FIG 4A). The medial flap of the quadriceps must be reflected medially off the face of the femur. There should be no undue tension at the patellar tendon insertion. Placing one smooth pin in the tibial tuberosity may provide some protection against tendon avulsion.
A 90-degree angled Hohmann retractor is inserted laterally to the lateral meniscus (TECH FIG 4B).
The synovial layer surrounding the patella is excised to expose the insertion of the quadriceps and patella tendons. Osteophytes are trimmed with a rongeur to establish the true size and thickness of the patella.
To permit full eversion of the patella, the capsular folds of the suprapatellar pouch proximal to the patella are released.
If the patella will not evert, the dissection across the lateral tibial plateau is revisited, and the incision in the proximal quadriceps is examined to see whether it has been opened proximally enough. Division of the lateral patellofemoral ligament makes it easier to evert the patella.
Release of a portion of the medial portion of the patellar tendon and elevation of a small cuff of periosteum immediately adjacent to the patellar tendon insertion can be helpful.
TECH FIG 4 • A. The patella is everted, and the knee is flexed. B. A Hohmann retractor is inserted laterally for soft tissue retraction, and a retractor is positioned posteriorly to push the tibia forward.
PREPARATION OF THE TIBIA
The ACL is excised, allowing further anterior translation of the tibia.
When combined with external rotation as the knee is flexed, complete anterior subluxation of the tibia from beneath the femur can be accomplished, providing complete exposure of the tibial plateau, femoral condyles, and posterior horn attachments of the menisci.
Rarely, this maneuver may be blocked by osteophytes, which should be removed. If the posteromedial corner and posterior capsular structures are not released adequately, anterior translation and external rotation cannot be accomplished.
A retractor is applied to gently retract the tibia forward so that exposure of the posterior tibial plateau is achieved.
With the tibia completely subluxed anteriorly, the medial and lateral menisci are excised and the PCL exposed, released, or excised, as the surgeon prefers. The popliteus tendon is protected during all soft tissue and bone resection.
If adequate exposure cannot be obtained, the femoral cuts should be made first, allowing access to the back of the joint.
An anterior synovectomy is performed to expose the supracondylar region of the femur. This is essential to allow for proper and precise sizing of the femoral implant and to prevent notching.
BONE CUTS
The five standard bone cuts for any TKA are as follows:
Transverse upper tibial cut
Distal femoral condyles resection
Anterior and posterior condylar resections
Anterior and posterior chamfer cuts from the distal femur
Retropatellar cut
The sixth step of the intercondylar box cut is performed only for posterior stabilized designs.
The surgeon performs either the femoral or the tibial cut first. Generally, when the tibia can be easily shifted anteriorly, the tibia is cut first, but if the knee is tight or good exposure is difficult to obtain on the tibial plateau, the femoral condyles are the first to be cut.
Bone cuts can be made using open or slotted cutting guides (TECH FIG 5). The cutting slots are more accurate and reduce human error. In practice, however, they obscure the saw blade tip, potentially increasing the risk of injury to important structures such as the MCL. Most newer femoral cutting blocks provide slots for performing distal, anterior, posterior, and chamfer cuts by using a single block, thereby reducing the time.
Clinical success of TKA is correlated with correct orientation of the components and the resultant lower extremity alignment. Accuracy of component positioning relies on alignment guides for making precise and accurate bone cuts.
TECH FIG 5 • Open (A) and slotted (B) cutting guides.
Upper Tibial Cut
An intramedullary (IM) rod can be used provided that there is no deformity, bowing, offset to the tibial shaft, or blockage in the medulla. By and large, the extramedullary (EM) alignment guide is preferable, because it can bypass any potential deformity of the tibial shaft.
In obese patients those bony landmarks are masked, however, and an EM guide may cause more error.
Tibial cut using an extramedullary guide
Attach the strap of the distal end of the alignment guide above the ankle, and pin the proximal end to the upper tibial metaphysis (TECH FIG 6A). Necessary adjustments must be made to make the guide align with the center of the interspinous eminence of the plateau, the tibial shaft, and the middle of the ankle mortis, which is, in fact, 3 to 5 mm medial to the intermalleolar axis.
By sliding the distal end of the guide mediolaterally at the ankle, a final adjustment can be made to centralize it over the center of the talus and to minimize the risk of varus inclination of the cut.
Set the proximal part to obtain 3 to 5 degrees of posterior slope in the sagittal plane.
Bear in mind that jig systems fitted to the anterior surface of the proximal tibia will have a tendency to align in excessive internal rotation due to the everted patellar tendon. To avoid this error, center the jig on the medial third of the tibial tuberosity.
Fit the proximal cutting block snugly up against the tibial cortex to improve the accuracy of the resection.
This cut should be made at right angles to the anatomic axis of the tibia in the coronal plane.
Remove 10 mm of cartilage and bone from the least involved plateau. The bone resected should have approximately the same thickness as the final tibial component, including the metal base plate and polyethylene liner.
Make the tibial cut using an intramedullary guide.
If you opt to use an IM guide, accurately choose the pilot hole that is at the junction of the tibial insertion of the ACL and the anterior horn of the lateral meniscus (TECH FIG 6B). By irrigation and aspiration of the canal, insertion of a fluted, hollow rod, and drilling a hole slightly larger than the size of the IM rod, the risk of fat embolization can be reduced.
Insert the IM rod and fix the cutting block in the desired position, then remove the rod together with its outrigger.
Use an oscillating saw to cut the bone. To protect the posterior neurovascular bundle, stop cutting the last few millimeters of bone by saw and crack the rest afterward by levering or using an osteotome.
Carefully protect the MCL and LCL by proper insertion of retractors.
Remove the osteotomized bone along with the remnants of menisci. Establish the anatomic boundary of the tibial metaphysis by removing the osteophytes.
Distal Femur Cuts
Because of a lack of reliable palpable external landmarks, the IM alignment guide is superior to the EM guide for preparation of the femur, except in cases of excessive femoral bowing, previous fracture, Paget disease, or an ipsilateral long-stemmed total hip replacement.
Drill an entry hole 1 cm anterior to the origin of the PCL, slightly medial to the midportion of the intercondylar notch (TECH FIG 7A). Touching the anterior surface of the femoral shaft with the other hand can be a good guide to the direction of drilling.
TECH FIG 6 • A. The strap of the distal end of the extramedullary alignment guide is attached above the ankle, tunings are done, and the proximal end is pinned to the upper tibial metaphysis. B. Entry hole for the intramedullary guide at the junction of the tibial insertion of the anterior cruciate ligament (ACL) and the anterior horn of the lateral meniscus.
TECH FIG 7 • A. Entry hole of the femoral intramedullary guide 1 cm anterior to the origin of the PCL, slightly medial to the midportion of the intercondylar notch. B,C. Osteotomy of the distal femur.
Simple measures such as slight overdrilling, using a fluted IM guide, and aspiration of the marrow contents before insertion of the guide are recommended to decompress the femoral canal and to subsequently reduce the risk of fat emboli.
Insert the IM guide and pass it directly in the center of the canal without making any contact with the femoral cortices—otherwise, the angle of resection will be changed. Attach the cutting block to the IM rod, adjust it at 5 to 6 degrees of valgus, and then fix it in place.
Cut valgus knees in no more than 5 degrees of femoral valgus. Check to be sure that there is no soft tissue in the area below the guide.
Remove the IM rod and cut the bone. It is crucial to prevent the saw blade from bending or going forward in an undesired direction while proceeding through the osteotomy line, particularly during resection of hard and sclerotic bone.
The amount of bone to be resected should be precisely equivalent to the thickness of the final femoral component. In the sagittal plane, the distal femur should be cut at 90 degrees to the femoral mechanical axis and, after soft tissue balancing, should be parallel to the resected surface of the proximal tibia (TECH FIG 7B,C).
Anterior and Posterior Femoral Condyle Cuts
Making accurate cuts is essential to obtain proper size and rotation of the final femoral component.
Use the AP sizing guide to aid in setting 3 degrees of external rotation of the femoral component in relation to the posterior condylar axis. External rotation means counterclockwise rotation for the right knee and clockwise rotation for the left knee. In knees without deformity, external rotation usually results in removal of more bone from the medial posterior condyle. Erosion of the posterior femoral condyles can distort this posterior condylar axis.
Appreciating that the posterior cut should be parallel to the transepicondylar line, perpendicular to the Whiteside line (AP axis of the femoral sulcus), and parallel to the upper tibial cut can help the surgeon reduce any error in the rotation of the femoral component (TECH FIG 8A).
Maximally flex the knee to reduce the chance of injury to the posterior neurovascular bundle during posterior sawing. Adjust the stylus that indicates where the anterior cut exits the femur. Pass the anterior cut tangential to the anterior femoral cortex to avoid notching and subsequent stress rising for a fracture (TECH FIG 8B–D).
Conversely, a cut that is too high causes an oversized femoral component and overstuffing of the patellofemoral articulation, which can subsequently cause patellar maltracking or limit range of flexion.
Anterior and Posterior Chamfer Cuts
Anterior and posterior chamfer cuts are essential for the prosthesis to fit over the distal femur.
A chamfer guide is placed on the distal femur. In some systems this step is integrated into the same block as that used for the anterior and posterior femoral cuts (TECH FIG 9A,B).
When the sawing is complete, use a lamina spreader to open the space between the femur and the tibia, and then use an osteotome to free small remnant portions of uncut bone (TECH FIG 9C).
Patellar Preparation
Remove the osteophytes, synovial insertions, and fat to demarcate the anatomic margins of the patella.
Use a caliper (TECH FIG 10A) to assess the patellar thickness before the cut and after the patella is resurfaced to ensure that the patellar thickness is equal to the original thickness and that at least 12 mm of bone stock remains.
To obtain an exact measurement of the patellar thickness, the prepatellar bursa should be dissected to completely expose the anterior surface of the patella.
Use a patellar cutting jig or a freehand technique. Pass the patellar cut parallel to the anterior surface of the patella through the chondro-osseous junction, completely resecting both facets (TECH FIG 10B). Proximally, the cut passes just superficial to the quadriceps insertion; distally, it passes through the nose of the patella.
TECH FIG 8 • A. Femoral component rotation is determined by reference lines used for performing the distal femoral cut. B–D. Anterior and posterior femoral condylar osteotomies.
Make a flat cut removing any remnants of cartilage.
Center and firmly hold the appropriate drill guide and drill three lug holes in a triangular arrangement (TECH FIG 10C,D).
To accommodate the post–cam mechanism in the posterior stabilized prosthesis, place the finishing guide onto the distal femur to make the intercondylar box cut (TECH FIG 10E). Center the guide mediolaterally and secure it firmly by pin or screw.
Use a reciprocating saw to resect the bone from the notch. Complete the resection with a chisel or osteotome.
TECH FIG 9 • A,B. Anterior and posterior chamfer cuts. C. An osteotome is used to free small remnant portions of uncut bone and removing posterior osteophytes.
TECH FIG 10 • A. Calipers are used to assess the patellar thickness before the retropatellar osteotomy. B. Retropatellar osteotomy parallel to the anterior surface of the patella. C,D. Three lug holes are drilled in a triangular pattern. E. Intercondylar box cut.
SOFT TISSUE AND LIGAMENT BALANCING
Soft tissue and ligament balancing is a vital portion of the surgical procedure.6,11
In knees with minimal deformity, balancing is not challenging, and it often can be achieved by performing a minimal soft tissue release, making the bone cuts, and then checking the knee by insertion of trial components.
In knees with complex or severe deformity, however, cautious stepwise release is necessary. Insert the trial components and check the balance of the knee after each step of the procedure. If no release is necessary, proceed to the next step. When the deformity is severe and leads to loss of the integrity of the ligaments, be ready for application of a constrained prosthesis.
To achieve a proper soft tissue balance, initially remove the offending osteophytes until the anatomic margins of the bone are determined.
Correction of Flexion Contracture
Use a curved osteotome to release osteophytes in the back of the femur and then extract them with a rongeur.
Strip the adherent capsule from the posterior aspect of the femur to reestablish the original recess.
In knees with preoperative moderate to severe flexion contracture, it also is necessary to cut the posterior capsule transversely and to release the tendinous origins of the gastrocnemius.
Perform recession or resection of the PCL if it is still preserved.
Resect additional bone from the distal femur.
Correction of Varus Deformity
The medial capsulotomy, along with subperiosteal medial release, which is included in the initial approach and exposure, can correct minimal varus deformities.
Extend the medial subperiosteal release for an additional 2 to 3 cm.
If the medial knee is tight in flexion only, release the anterior portion of the superficial MCL.
If the medial knee is tight in extension only, release the posterior oblique fibers of the superficial MCL
If the medial knee is tight in both flexion and extension, release elements of the superficial MCL.
Correction of Valgus Deformity
If the lateral knee is tight in extension, release the iliotibial band. Some surgeons prefer the “pie-crusting” technique.
If the lateral knee is tight in flexion, release first the popliteal tendon and then the LCL subperiosteally from the femoral condyle.
If the lateral knee is tight in both flexion and extension, sequentially release the iliotibial band, the popliteal tendon, the LCL, and finally the posterior capsule.
Release the biceps femoris tendon only when absolutely necessary.
Correction of Valgus Knee With Incompetent Medial Collateral Ligament
A valgus knee with an incompetent medial collateral ligament occurs in knees with severe, longstanding valgus deformity.
Treatment strategies include the use of a varus–valgus constrained articulation, MCL advancement, or MCL reconstruction.
COMPONENT INSERTION AND TRIAL REDUCTION
Insert provisional femoral and patellar components of the correct size (TECH FIG 11A).
Next, insert a tibial sizing tray that matches the surface area of the tibial cut. This sizing tray is a jig for drilling final fixation holes for the tibial component and determines its ultimate mediolateral, anteroposterior, and rotational position.
Some rotational change is still possible at this point. Internal rotation of the component must be avoided.
Check all around the tray to ensure that there is no overhang, especially on the medial side, where overhang may be easily overlooked.
Insert a spacer of the proper height and reduce the joint. Check the ROM and ligament stability. Apply varus and valgus stresses in both flexion and extension to determine the stability of the knee and the appropriate thickness of the tibial insert.
At this stage it is particularly important to do meticulous ligament balancing for PCL-retaining designs by using different thicknesses of tibial trial components.
Align the center of the tibial tray over the medial third of the tibial tubercle and pin it in place (TECH FIG 11B). Place the appropriately-sized a stem drill guide on the sizing tray and drill for the stem (TECH FIG 11C).
Assemble the proper size of tibial broach on the broach impactor. Seat the impactor on the tray and impact the broach to the proper depth (TECH FIG 11D). Impact the stemmed tibial trial to ensure proper fit before implanting the final prosthesis.
Check the patellar tracking during ROM.
Once trial reduction is complete, extract all components.
TECH FIG 11 • A. Trial reduction. B. Aligning the tibial tray. C. Drilling for the stem. D. Impacting the broach to the proper depth.
COMPONENT FIXATION
Polymethylmethacrylate is used for fixation of the components in knee arthroplasty. The setup of all components and basic instruments for component insertion should be done before the cement is prepared (TECH FIG 12A,B).
Drill the tibial plateau in the sclerotic parts (1 to 2 mm deep) to achieve adequate anchorage of the tibial component.
Plug the IM hole of the distal femur with small pieces of cancellous bone (TECH FIG 12C).
Use pulsatile lavage to thoroughly irrigate the cut surfaces with normal saline in order to remove all debris and increase the depth of cement penetration into the trabecular bone. When done, be sure to dry the bone completely.
Put some gauze sponges on the cut surfaces and use a hand to press down on the sponges to keep the bones dry until the cement has been prepared by vacuum mixing.
When the cement is in a doughy state, apply it to the tibial plateau (TECH FIG 12D). Add a thin layer of cement, then impact the tibial component and polyethylene liner into place (TECH FIG 12E).
TECH FIG 12 • All components (A) and basic instruments for component insertion (B) are set up in advance of cement preparation. C. The intramedullary hole of the distal femur is plugged with small fragments of cancellous bone. D. Cement is applied to the tibial plateau. E. A thin layer of cement is added to the tibial tray, and the tibial component and polyethylene liner are impacted into place. F. Cement is applied to the femoral cut surfaces and the femoral component. G. The femoral component is impacted into position. H. Cement is applied to the patella. I. The patellar component is inserted and clamped firmly.
Trim and remove the excess cement as it extrudes from under the plateau.
Apply cement to the femoral cut surfaces (TECH FIG 12F), especially the posterior condyles, which tend to be undercemented.
Impact the femoral component into position, and remove the excess cement from around the prosthesis (TECH FIG 12G).
In areas that are clearly visible, trim the cement by scalpel and then remove it by curette; in areas that are not easily seen, do not use a scalpel to trim the cement.
Reduce the knee and bring it to full extension.
With the knee extended, apply cement to the patella (TECH FIG 12H). Insert the patellar component and clamp it firmly in place (TECH FIG 12I). Trim and remove the excess cement.
Keep the knee in full extension until the cement is fully cured. Inspect all the corners of the joint, especially the posterior parts, to make certain that no extra cement remains, because extra pieces could block knee ROM or act as loose bodies in the knee, producing third-body wear.
Irrigate the knee thoroughly. For the last time before closing the joint, check the ROM, knee stability, and patella tracking.
PATELLA TRACKING
With the trial components in place and after the insertion of the final components, evaluate patella tracking throughout a full ROM. The patella should track centrally in the trochlear groove without lateral subluxation or lateral tilt in full flexion.
Perform the no-thumbs test by reducing the patella and taking the knee through the full flexion arc without closing the medial arthrotomy and without applying any medial force with the thumb to keep the patella in position.
Extensor mechanism balance has been achieved if the patella does not tilt, subluxate, or dislocate during flexion.4
If there is patellar tilting or slight subluxation with the nothumbs test, reapproximate the medial retinaculum at the superior pole of the patella with a single no. 0 suture. If the suture does not break through full flexion of the knee, a lateral release is not necessary. Doing this eliminates slight tilting or subluxation that occurs with the nothumbs test and avoids an unnecessary lateral release.
To improve the accuracy of these evaluations of extensor mechanism balance, these tests can be performed with the tourniquet deflated, because an inflated tourniquet can alter patellar tracking by binding the extensor mechanism, resulting in perceived patellofemoral maltracking.4
CLOSURE
Copiously irrigate the knee to ensure that no bone or cement particles remain.
Identify the formerly placed markings. Close the arthrotomy (quadriceps and medial retinaculum) in extension by interrupted suture, in order to produce a watertight seal.
Place the knee through a full ROM to make sure that the closure is strong enough not to disrupt during physical therapy, and to confirm that the patella is tracking normally.
Try to cover the prosthesis fully. Close subcutaneous tissue and superficial fascia with interrupted no. 2 Vicryl stitches or its equivalent in a single layer. (Use a double layer if the patient is obese.)
Close the skin with staples. Sutures that are either too taut or too loose can lead to wound healing problems or wound dehiscence.
POSTOPERATIVE CARE
At the conclusion of the operation, apply a compression bandage from toes to mid-thigh with 50% overlap of each turn to achieve a uniform double layer, then release the tourniquet. Compression dressings are removed after 24 hours.
Adequate analgesia via application of improved pain management modalities (eg, intravenous patient-controlled analgesia or patient-controlled epidural analgesia), should be a priority during rehabilitation to hasten early convalescence.
Administer antibiotics for 24 hours. Start the proper thromboprophylaxis.
The staples usually are removed after 2 weeks in the first postoperative follow-up visit.
The aim of rehabilitation is to restore the highest possible range of mobility in and full muscular control of the operated knee. Adequate rehabilitation is an important requirement for successful TKA; in fact, this starts preoperatively (1 to 2 weeks before surgery) by education on the surgical process and outcomes, instruction on a postoperative exercise program, and assessment of the patient's home and social circumstances. At the hospital and at home, physical therapists play an important role in the rehabilitation process.
The specific rehabilitation program after TKA is somewhat controversial. As a general rule, patients are encouraged to work on the ROM of the prosthetic knee and to progressively increase their activities as tolerated, but excess activity and stresses should be avoided. Overzealous physical therapy (PT) in the immediate postoperative period may lead to swollen stiff knees and damage.
Although the continuous passive motion (CPM) machine supposedly does not alter the ultimate amount of knee flexion and overall functional outcome, and CPM protocols vary considerably among institutions, a high degree of flexion in the immediate postoperative period produces quicker restoration of ROM, and CPM in conjunction with physical therapy may offer beneficial results compared to physical therapy alone in short-term rehabilitation. The patient should be informed that final ROM after surgery is directly related to preoperative ROM—in other words, if the preoperative ROM is limited the patient is less likely to achieve knee flexion more than 100 degrees postoperatively.
On the first postoperative day, bed mobility and transfer training (ie, from bed to chair and from chair to bed) and bedside exercises (eg, ankle pumps, quadriceps sets, and gluteal sets) begin.
With a cemented knee, full weight bearing under the supervision of a therapist is allowed on the first or second postoperative day.
Ambulation initially is done with a walker until the patient has achieved adequate balance to use canes.
A knee immobilizer sometimes may be worn by the patient until he or she can do straight leg raising without difficulty.
Ambulating with weak quadriceps muscles can lead to instability or giving way of the knee, which can be painful and may lead to unnecessary stress on the prosthesis.
On the second postoperative day, active ROM, activeassisted ROM, terminal knee extension, straight leg raises, and muscle strengthening exercises start. Gait training with an assistive device, moving from a sitting to standing position and vice versa, and toilet transfers continues.
On the third to fifth postoperative days, progression of ROM, strengthening exercises to the patient's tolerance, and ambulation on level surfaces and stairs (if applicable) with the least restrictive device possible are done.
During the hospital stay, the physical therapist teaches the patient stair climbing with a walker or crutch.
Patients usually are discharged 3 to 5 days after surgery, to home, inpatient rehabilitation, or a skilled nursing facility, based on individual need in consultation with social work and home health services. Discharge directly to home is preferred.
From day 5 to 6 weeks, the patient increases ambulation distance and independence in activities of daily living as tolerated.
Patients can start driving when they are able to operate the pedals safely and rapidly, which usually takes 4 to 6 weeks. Return to work usually takes 4 to 10 weeks, depending on work obligations. Laborers should bear in mind that they may not be able to return to their previous activity level.
Patients are followed up routinely at 6 weeks, 3 months, and 1 year after surgery. Once strength, mobility, and balance are regained, patients can resume low-impact sport activities (eg, cycling, swimming, gentle aerobic-style exercises, walking, hiking, golf, bowling). High-impact activities such as football, soccer, hockey, and baseball are discouraged.
OUTCOMES
TKA is a reliable and predictable surgery, with reported survival rates above 85% with 10 to 23 years of follow-up. Favorable gains for pain and functionality following TKA are well reported and recognized.
For most patients, overall satisfaction with the outcome of the surgery is good to excellent.
COMPLICATIONS
The overall mortality rate following TKA is very low, and this procedure does not considerably reduce the life expectancy in patients with OA.
Infection
Because pain is a strong associated symptom, infection should be considered in any persistently painful TKA or with the acute onset of pain in a previously well-functioning TKA.8
Radiographs must be carefully studied for signs of probable infection. Progressive prosthetic loosening is the most consistent radiographic sign. In the presence of infection, erythrocyte sedimentation rates and C-reactive protein levels are elevated. The white blood cell count is not a reliable indicator of infection. Aspirate from the knee joint should be evaluated by synovial fluid analysis, Gram stain, culture, and antibiotics sensitivity. Cultures of superficial wounds or sinus tracts are unreliable and misleading. The preferred specimens are joint aspirate, deep wound biopsy, or bone biopsy.8
Superficial incisional infection, characterized by erythema, dry wound, nonpurulence, and neither loculation nor induration, may be treated with systemic antibiotics with the understanding that once antibiotic therapy is initiated, the opportunity to diagnose a deep infection accurately may be lost. Despite understandable concern about inoculating an uninfected arthroplasty, arthrocentesis before antibiotic therapy usually is a sound practice, even if done adjacent to erythematous tissue. By contrast, a wound with either drainage or skin necrosis usually benefits from prompt surgical débridement, at which time reliable culture material may be obtained if antibiotic therapy has not been initiated.14
In the setting of early postoperative drainage without evidence of deep infection, and without erythema, purulence, or pain, where the surgeon does not otherwise suspect superficial or deep infection, immobilization and local wound care are warranted for a short period. If drainage does not stop or significantly decrease after a few days, operative débridement and closure should be considered. Observation times of 3 to 5 days and even up to 1 week have been advocated.
Surgeons generally agree that a draining hemarthrosis should be evacuated. A nondraining hematoma in and of itself does not necessarily warrant evacuation. However, if the hematoma delays physical therapy, increases tension on the skin edges or closure, and exacerbates pain, surgical evacuation is defensible.14
Anterior knee pain has been significantly reduced since the introduction of patellofemoral resurfacing.
Instability
Instability after TKA is a cause of failure and the reason for 10% to 22% of revisions. Successful outcomes are obtained in many of these cases, but without identifying the cause of instability, the surgeon risks repeating the mistakes that led to the instability after the initial TKA.9
Three types of instability may occur after a TKA: extension instability, flexion instability, and genu recurvatum. It is important to understand the causes and treatments of each type of instability. Surgical treatment is largely aimed at restoring balanced flexion and extension gaps at the time of revision TKA. Selective use of constrained and rotating-hinge TKA designs is appropriate for subgroups of patients with instability.9
Osteolysis
The most significant cause for late revision TKA is osteolysis, which occurs as the result of a foreign body response to particulate wear debris from the prosthetic joint. The ultimate result is loosening of the components. The incidence and extent of osteolysis after TKA are less than that after total hip arthroplasty.5 This complication has been noted with both cemented and cementless prostheses.
Clinical symptoms, plain radiographs, and CT scanning have been used to study the extent and the natural history of osteolysis. Early in the disease process, patients may be asymptomatic. Most patients, however, present with symptoms of pain, swelling, and acute synovitis, with or without osteolysis on radiographs. Serial radiographs are then necessary to evaluate its progression.11
Vascular Injury
Popliteal artery injury during TKA is rare but is potentially catastrophic. The injury may have acute or delayed presentation. Arterial thrombosis due to tourniquet application, arterial kinking during knee manipulation, and direct, sharp injury to the artery have been described. Direct, sharp arterial injury is believed to have a better prognosis than arterial thrombosis. Both hyperflexion and hyperextension of the knee during TKA can put the popliteal artery in danger. Prompt recognition of injury by the orthopedic surgeon and treatment by an experienced vascular surgeon are necessary to achieve a good outcome.3
Nerve Injury
Both tibial and peroneal nerves may be injured during TKA. Preoperative flexion contracture or valgus deformity, and postoperative hematoma increase the risk of peroneal nerve injury. Conservative treatment is the first line of therapy, aimed primarily at preventing further injury. The knee and hip are flexed to 20° to 45°, and constrictive dressings are removed or loosened. Surgical exploration of the non-neurolytic nerve can be employed if no functional recovery is noted after 3 months from the onset of the injury.12
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