Total Knee Arthroplasty 

Introduction

Total knee replacement in some form has been practiced for over 50 years, but the complexities of the knee joint only began to be understood 30 years ago. Because of this, total knee replacement initially was not as successful as Sir John Charnley's artificial hip. However, dramatic advancements in the knowledge of knee mechanics have led to design modifications that appear to be durable.

Significant advances have occurred in the type and quality of the metals, polyethylene, and, more recently, ceramics used in the prosthesis manufacturing process, leading to improved longevity. As with most techniques in modern medicine, more and more patients are receiving the benefits of total knee arthroplasty (TKA).^{[1, 2]} Approximately 130,000 knee replacements are performed every year in the United States.

History of the procedure

In the 1860s, Fergusson reported performing a resection arthroplasty of the knee for arthritis. Verneuil is thought to have performed the first interposition arthroplasty using joint capsule. 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 the femoral condyles following similar designs in the hip. In the next decade, tibial replacement was also attempted, but both designs had problems with loosening and persistent pain.

Combined femoral and tibial articular surface replacements appeared in the 1950s as simple hinges. These implants failed to account for the complexities of knee motion and consequently had high failure rates from aseptic loosening. They were also associated with unacceptably high rates of postoperative infection.

In 1971, Gunston importantly recognized that the knee does not rotate on a single axis like a hinge, but rather the femoral condyles roll and glide on the tibia with multiple instant centers of rotation. His polycentric knee replacement had early success with its improved kinematics over hinged implants but was ultimately unsuccessful because of inadequate fixation of the prosthesis to bone.

The highly conforming and constrained Geomedic knee arthroplasty introduced in 1973 at the Mayo Clinic ignored Gunston's work, and a kinematic conflict arose. Other designs followed, either following Gunston's principle in attempting to reproduce normal knee kinematics or allowing a conforming articulation to govern knee motion.

The total condylar prosthesis was designed by Insall at the Hospital for Special Surgery in 1973. This prosthesis concentrated on mechanics and did not try to reproduce normal knee motion. In 1993, Ranawat et al reported a rate of survivorship of 94% at 15 years of follow-up, which is the most impressive reported to date.^[3]

The component was subsequently altered to artificially introduce normal kinematics to improve range of motion of the component. At the same time, a prosthesis with more natural kinematics was developed at the Hospital for Special Surgery, relying on the retained cruciate ligaments to provide knee motion.

The argument as to whether knee ligaments should be preserved or sacrificed continues to this day. Long-term follow-up studies do not show any significant differences, although gait appears to be less abnormal if ligaments are preserved, especially when walking up and down stairs. One theoretical way of incorporating normal kinematics and maximal conformity is with mobile tibial bearings. Current midterm follow-up studies of these prostheses have so far shown encouraging results.

Cemented total knee replacements will remain the criterion standard for total knee arthroplasty, but use of uncemented designs with bioactive surfaces (eg, hydroxyapatite) are showing promising midterm results (see the image below).^[4]

Indications

The primary indication for total knee arthroplasty is to relieve pain caused by severe arthritis. The pain should be significant and disabling. Night pain is particularly distressing. If dysfunction of the knee is causing significant reduction in the patient's quality of life, this should be taken into account.

Correction of significant deformity is an important indication but is rarely used as the primary indication for surgery. Roentgenographic findings must correlate with a clear clinical impression of knee arthritis. Patients who do not have significant loss of joint space tend to be less satisfied with their clinical result following TKA. Exhaust all conservative treatment measures before considering surgery.

Knee replacement has a finite expected survival that is adversely affected by activity level.^{[3, 5, 6]} Generally, it is indicated in older patients with more modest activities. It is also clearly indicated in younger patients who have limited function because of systemic arthritis with multiple joint involvement. Young patients requesting knee replacement, especially those with posttraumatic arthritis, are not excluded by age but must be significantly disabled and must understand the inherent longevity of joint replacement.

Rarely, severe patellofemoral arthritis (see the image below) may justify arthroplasty because the expected outcome of arthroplasty is superior to patellectomy. Isolated patellofemoral replacement still is undergoing clinical investigation.

Deformity can sometimes become the principal indication for knee replacement in patients with moderate arthritis when flexion contracture or varus or valgus laxity is significant. In such cases, often a more constrained prosthesis is required, leading to greater technical difficulty in surgery and more uncertain long-term survival.

Contraindications

Absolute contraindications to total knee replacement include the following:

• Knee sepsis
• A remote source of ongoing infection
• Extensor mechanism dysfunction
• Severe vascular disease
• Recurvatum deformity secondary to muscular weakness
• Presence of a well-functioning knee arthrodesis

Relative contraindications include medical conditions that preclude safe anesthesia and the demands of surgery and rehabilitation. Other relative contraindications include the following:

• Skin conditions within the field of surgery (eg, psoriasis)
• Past history of osteomyelitis around the knee
• Neuropathic joint
• Obesity

Surgical Alternatives to Arthroplasty

A number of operative procedures should be considered in patients with degenerative disease of the knee. Arthroscopic debridement is sometimes indicated in mild degenerative joint disease with mechanical symptoms and recurrent persistent effusions. Proximal tibial valgus osteotomy should be reserved for patients with medial tibiofemoral compartment disease, stable collateral ligaments, and a correctable varus deformity of the knee joint (see the image below).

Similarly, a distal femoral varus osteotomy can be considered for patients with lateral tibiofemoral compartment disease, stable collateral ligaments, and a valgus deformity of the knee joint (see the image below).

These procedures restore the mechanical axis of the lower limb and off-load the diseased compartment. Proximal tibial valgus osteotomy and distal femoral varus osteotomy are generally reserved for young high-demand patients because of concerns about the durability of TKA in this patient group.

A prospective, randomized, controlled trial in England compared unicompartmental knee replacement with TKA over 8, 10, 12, and 15 years follow-up. At 5 years, the number of failures were equal in the 2 groups. At 15 years follow-up, the survivorship rate was 89.8% for unicompartmental knee replacement and 78.7% for TKA. Four of the unicompartmental knees failed, and 6 of the TKA knees failed. Newman et al determined from their findings that the results of their study justify increased use of unicompartmental replacement.^[7]

Arthrodesis or fusion of the knee is rarely performed but should be considered in patients with chronic sepsis, younger patients with tricompartmental disease (eg, following trauma) who require stability and durability, and patients with deficient extensor mechanisms. TKA is performed in patients with symptomatic advanced degenerative changes in one or more compartments of the knee joint.

Relevant Anatomy

Movement of the knee joint can be classified as having 6 degrees of freedom: 3 translations and 3 rotations. Translations include anterior/posterior, medial/lateral, and inferior/superior; rotations include flexion/extension, internal/external, and abduction/adduction.

Movements of the knee joint are determined by the shape of the articulating surfaces of the tibia and femur and the orientation of the 4 major ligaments of the knee joint. The anterior and posterior cruciate ligaments (see the image below) and the medial and lateral collateral ligaments serve as a 4-bar linkage system.

Knee flexion/extension involves a combination of rolling and sliding called femoral rollback, which is an ingenious way of allowing increased ranges of flexion. Because of asymmetry between the lateral and medial femoral condyles, the lateral condyle rolls a greater distance than the medial condyle during 20 degrees of knee flexion. This causes coupled external rotation of the tibia, which has been described as the screw-home mechanism of the knee that locks the knee into extension.

Medial collateral ligament

The primary function of the medial collateral ligament is to restrain valgus rotation of the knee joint, with its secondary function being control of external rotation. The lateral collateral ligament restrains varus rotation and resists internal rotation.

Anterior cruciate ligament

The primary function of the anterior cruciate ligament (ACL) is to resist anterior displacement of the tibia on the femur when the knee is flexed and control the screw-home mechanism of the tibia in terminal extension of the knee. A secondary function of the ACL is to resist varus or valgus rotation of the tibia, especially in the absence of the collateral ligaments. The ACL also resists internal rotation of the tibia.

Posterior cruciate ligament

The main function of the posterior cruciate ligament (PCL) is to allow femoral rollback in flexion and resist posterior translation of the tibia relative to the femur. The PCL also controls external rotation of the tibia with increasing knee flexion. Retention of the PCL in total knee replacement has been shown biomechanically to provide normal kinematic rollback of the femur on the tibia. This also is important for improving the lever arm of the quadriceps mechanism with flexion of the knee.

Patellofemoral joint

Movement of the patellofemoral joint can be characterized as gliding and sliding. During flexion of the knee, the patella moves distally on the femur. This movement is governed by the attachments of the patellofemoral joint to the quadriceps tendon, ligamentum patellae, and the anterior aspects of the femoral condyles. The muscles and ligaments of the patellofemoral joint are responsible for producing extension of the knee.

The patella acts as a pulley in transmitting the force developed by the quadriceps muscles to the femur and the patellar ligament. It also increases the mechanical advantage of the quadriceps muscle relative to the instant center of rotation of the knee.

Mechanical axis

The mechanical axis of the lower limb is an imaginary line through which the weight of the body passes. It runs from the center of the hip to the center of the ankle through the middle of the knee. This axis is altered in the presence of deformity and must be reconstituted at surgery, which allows normalization of gait and protects the prosthesis from eccentric loading and early failure.

Anesthesia

Total knee arthroplasty (TKA) may be performed with the patient under regional or general anesthesia. Selection of regional or general anesthesia is made following preoperative discussion between the anesthetist and the patient, with some input from the surgical team. This decision is affected partly by the medical condition of the patient, although cardiovascular outcomes, cognitive function, and mortality rates of regional and general anesthesia have not been proved to be significantly different.

Patients who have epidural anesthesia have been shown to develop fewer perioperative deep vein thromboses. Whether this has any overall positive benefit to the patient is not known. Another benefit of epidural anesthesia is the presence of an indwelling catheter for 48-72 hours postoperatively for pain control, thus avoiding the need for excessive amounts of centrally acting analgesics.

Adverse effects of continuous postoperative epidural analgesia include the following^{[8, 9]} :

• Pruritus
• Urinary retention
• Nausea
• Vomiting
• Epidural hematoma (rare)

In a study by Shum et al, continuous femoral nerve block for analgesia, versus no femoral nerve block, resulted in less pain, higher satisfaction, and lower morphine use in patients immediately after TKA. At 2-year follow-up, no significant differences in functional outcome were identified.^[9] IIfeld et al found that a 4-day ambulatory continuous femoral nerve block, using a portable infusion pump, helped decrease time to discharge following total knee arthroplasty. In a multicenter, triple-masked, placebo-controlled study, patients received a continuous femoral nerve block with perineural ropivacaine 0.2% from surgery until the following morning, at which time they were randomized to either continue perineural ropivacaine (n=39) or switch to normal saline (n=38). Time to reaching 3 predefined discharge criteria (adequate analgesia, independence from intravenous opioids, and ambulation 30 m) was reduced by an estimated 20% in the patients receiving ambulatory analgesia.^[10]

Equipment

Different types of TKA prostheses are available. These include the following:

• Fixed bearing
• Medial pivot
• Rotating platform and mobile-bearing
• PCL-retaining
• PCL-substituting

A TKA prosthesis is shown in the image below.

Positioning

The patient is set up on the operating table in a supine position following preoperative cleaning of the leg (see the image below).

Preoperative Evaluation

A thorough preoperative medical evaluation of patients undergoing TKA is important to prevent potential complications in the perioperative period. Complete the evaluation in an elective preadmission clinic well before the date for surgery. This allows for a careful and unhurried assessment with adequate time for investigations, specialist anesthetic and medical opinion, and consent. It also allows operating schedules to be reorganized if patients are deferred from surgery.

Most patients who undergo TKA are elderly with comorbid diseases. Patients must have good cardiopulmonary function to withstand anesthesia and to withstand a blood loss of 1000-1500 mL over the perioperative period. Routine preoperative electrocardiography should be performed on elderly patients. Patients with ischemic heart disease, congestive heart failure, and chronic obstructive airway disease should be seen by a medical specialist or anesthetist. Patients with significant peripheral vascular disease should be seen by a vascular surgeon.

Patients should have completed an informed consent for surgery and fully understand the risks and possible complications of the procedure. They should have had all medical conditions optimized before surgery and be free of intercurrent infections. Two units of blood should be available for perioperative transfusion, either from the blood bank or preferably as predonated blood. Full medical and surgical backup must be available in case unforeseen complications occur.

Laboratory studies

Preoperative laboratory evaluation should include the following:

• Complete blood count
• Erythrocyte sedimentation rate
• Serum electrolytes
• Renal function studies
• Prothrombin time and activated partial thromboplastin time (PT/aPTT)
• Urinalysis and urine culture

Urinalysis is performed to exclude occult urinary tract infection. Routine preoperative coagulation studies are not necessary except in patients with a history of bleeding, alcoholism, or previous liver disease.

Imaging studies

Radiographic views for the assessment of the patient with knee arthritis include the following:

• Standing anterior-posterior (AP) view
• Lateral view
• Patellofemoral (skyline) view (see the image below)Total knee arthroplasty. Skyline view of the patellofemoral joint demonstrating lateral and medial osteophytes and lateral subluxation of the patella.
• Long leg radiographs to assess malalignment - Helpful for preoperative planning
• Standing radiographs with the knee in extension or in 45 degrees of flexion (Rosenberg view) - Can improve the sensitivity of detection of cartilage degeneration

Loss of joint space, cysts, subchondral sclerosis, and osteophytes confirm the diagnosis of osteoarthritis (see the image below).

Routine chest roentgenography is not usually recommended as a screening tool. However, it is indicated in patients with cardiopulmonary disease or in patients with clinical signs identified in the preadmission clinic.

Other preoperative tests

Electrocardiography is performed in elderly patients and in patients with a history of cardiac issues. More sophisticated imaging modalities in the investigation of knee arthritis are of occasional benefit for the assessment of significant bone loss or bone infection and include the following:

• Indium white blood cell scanning
• Computed tomography scanning
• Magnetic resonance imaging
• Bone densitometry

Antibiotics and Antithromboembolic Devices

Antibiotics and antithrombotic prophylaxis are administered approximately 30 minutes before the incision is made. Mechanical antithromboembolic devices (eg, stockings, foot pumps) are used intraoperatively.

Overview

Total knee arthroplasty (TKA) should be performed in a laminar flow operating theater with meticulous attention to detail to prevent contamination of the operation site.

A thigh tourniquet is generally used to aid surgical exposure, although it should be avoided in patients with a history of previous deep vein thrombosis or significant vascular disease.

The knee joint is usually approached anteriorly through a medial parapatellar approach, although some surgeons use a lateral or subvastus approach. Osteophytes and intra-articular soft tissues are then cleared.

Bone cuts in the distal femur are made perpendicular to the mechanical axis, usually using an intramedullary alignment system, which is then checked against the center of the hip. The proximal tibia is cut perpendicular to the mechanical axis of the tibia using either intramedullary or extramedullary alignment rods. Restoration of mechanical alignment is important to allow optimum load sharing and prevent eccentric loading through the prosthesis.

Sufficient bone is removed so that the prosthesis recreates the level of the joint line. This allows the ligaments around the knee to be balanced accurately and prevents alteration in patella height, which can have a deleterious effect on patellofemoral mechanics.

Because of preoperative deformity, some ligaments around the knee are contracted. These are carefully released in a stepwise fashion to balance the soft tissues around the knee and allow optimum knee kinematics (see the image below).

Patellofemoral tracking is assessed with trial components in situ and balanced if necessary with a lateral release or medial reefing procedure. If the patellofemoral joint is significantly diseased, it can be resurfaced with a polyethylene button. The original width of the patella must be recreated.

Once the definitive components have been selected, they are cemented into place with polymethyl methacrylate cement. If an uncemented system is being used (see the first image below), press-fit and bony ingrowth provides the short-term and long-term fixation of the component (see the second image below). The tourniquet should be deflated prior to closure to allow accurate hemostasis, and the knee joint is usually drained and dressed in extension. Foot pulses are checked at the end of the procedure.

Essving et al reported that local infiltration analgesia, started during operation, provides excellent postoperative pain relief. In a double-blind study, 48 patients undergoing total knee arthroplasty were randomized into 2 groups. Patients in the treatment group received a periarticular injection of 400 mg ropivacaine, 30 mg ketorolac, and 0.5 mg epinephrine during surgery and an intra-articular injection of 200 mg ropivacaine, 30 mg ketorolac, and 0.1 mg epinephrine 21 hours postoperatively. Patients in the placebo group received a postoperative injection of saline. Overall, the treatment group had less postoperative pain, used less morphine, fulfilled discharge criteria more quickly, and had higher patient satisfaction.^[11]

Postoperative Care

The patient undergoes recovery and is usually observed for a 24-hour period in a high-dependency ward. Adequate hydration and analgesia are essential in this time of high physical stress. Analgesia is provided through continuation of the intraoperative epidural, patient-controlled intravenous analgesia or oral analgesia. Cryotherapy is used to reduce postoperative swelling and pain.

At this early stage, the patient begins knee movement, sometimes using a continuous passive motion (CPM) machine and exercises. These are continued under the supervision of a physiotherapist until discharge.^{[12, 13]} A randomized clinical trial by Labraca et al found that commencing early movement in the first 24 hours after surgery allows for early mobilization and discharge from the hospital.^[14]

Drains are usually removed within 24 hours, and the patient is encouraged to walk on the second postoperative day. Continual improvement is generally observed, and discharge occurs in 5-14 days.

Discharge is recommended only once wound healing is satisfactory, knee flexion of 90 degrees has been achieved, the patient is considered to be safe and supported in the home environment, and no complications are present. Thromboembolism prophylaxis is often continued at home for a period of time. The first outpatient review generally is in 6 weeks to 3 months (see the image below).

Complications

The overall mortality rate with TKA is less than 1%, but this figure increases with age, male sex, and the number of preexisting medical conditions. Identification and optimization of such conditions prior to surgery is important to reduce perioperative complications.^{[3, 5, 6]}

Complications of TKA include the following:

• Thromboembolism
• Infection
• Patellofemoral complications
• Neurovascular complications
• Periprosthetic fractures
• Aseptic loosening
• Arthrofibrosis

Thromboembolism

Thromboembolism includes deep vein thrombosis (DVT) with subsequent life-threatening pulmonary embolism (PE). Predisposing factors for increased risk of DVT include age older than 40 years, female sex, obesity, varicose veins, smoking, past history of DVT, diabetes mellitus, and coronary artery disease. Overall incidence of DVT following total knee replacement without any prophylaxis has been reported at 40-88%. Most of these are calf thromboses. The risk of fatal PE, however, is the important figure and varies from 0.1-1%.

Many current methods of DVT prophylaxis are available and are used, including mechanical compression stockings or foot pumps and pharmaceutical agents (eg, low-dose warfarin, low-molecular-weight heparin, aspirin). Many studies show evidence of reduction of rates of DVT, but how this affects overall death rates from PE is unclear at this time, with many of the current studies concluding after only 10 days.

Using a multifactorial approach to prevent DVT is probably prudent. Elements of such an approach may include the following:

• Intraoperative foot pumps
• Epidural anesthesia
• Pharmaceutical agents
• Antithromboembolic stockings
• Adequate hydration
• Early mobilization
• Regular postoperative surveillance

Infection

Prevention of infection in TKA begins in the preoperative examination to exclude intercurrent infection. In the operating room, personnel should be kept to the smallest number, and traffic in and out of the room should be kept to a minimum. Use of vertical laminar flow in operating theaters, prophylactic antibiotics, ultraviolet light, body exhaust systems to prevent bacterial shedding, and meticulous and expeditious surgery all help to reduce the occurrence of infections to less than 1% of operations performed.

The following factors are associated with a higher rate of infection after TKA:

• Rheumatoid arthritis
• Skin breakdown
• Prolonged wound drainage (>6 d)
• Previous knee surgery
• Use of a hinged knee prosthesis
• Obesity
• Concomitant urinary tract infection
• Steroid use
• Renal failure
• Diabetes mellitus
• Malignant disease
• Psoriasis

Treatment of the infected total knee prosthesis often is laborious and time consuming and a disaster for the patient. The risk is minimized by a theater team obsessed with detail and supported by good nursing skills on the ward and vigilance by the surgeon in the postoperative period.

Patellofemoral complications

Patellofemoral complications include patellofemoral instability (see the image below), patellar fracture, patellar component failure, patellar clunk syndrome, and extensor mechanism tendon rupture. All of these complications have been cited as the common reasons for reoperation. These can be avoided by attention to detail, meticulous technique, and avoidance of component malposition.

Neurovascular complications

Arterial thrombosis following TKA is a rare (ie, 0.03-0.17%) but devastating complication, frequently resulting in amputation. Several authors have recommended performing TKA without the use of a tourniquet in patients with significant vascular disease. Such patients should undergo a vascular surgery consultation prior to knee replacement.

Peroneal nerve palsy is the most commonly reported nerve palsy following TKA. It usually occurs in the correction of combined fixed valgus and flexion deformities often observed in patients with rheumatoid arthritis. Approximately half of these patients undergo spontaneous recovery, and 50% undergo partial recovery with conservative treatment. Some good results have been obtained with surgical decompression.

Periprosthetic fractures

Supracondylar fractures of the femur are not common following TKA (ie, 0.2-1%). These fractures are observed if the anterior femoral cortex is notched and weakened during surgery and in patients with osteoporosis, rheumatoid arthritis, poor flexion, revision arthroplasty, and neurologic disorders. Treatment is with internal fixation or revision TKA. Tibial fractures are uncommonly observed.

Aseptic loosening

Loosening leads to the ultimate failure of the prosthesis and occurs in approximately 5-10% of patients at 10-15 years. It may be complicated by bone loss or osteolysis, which can lead to catastrophic deterioration and make revision surgery difficult. The etiology of this problem is not entirely understood but is related to polyethylene debris causing cellular alterations that result in bone resorption. Once a component is loose, it becomes mechanically unstable with worsening osteolysis. Treatment is revision with bone grafting.

Arthrofibrosis

This is a condition of excessive scar tissue causing restriction of knee movement. Etiology is unknown. It is more common in young patients and in patients taking warfarin. It occurs in less than 1% of patients. Conservative management includes anti-inflammatory medication, physiotherapy, and reassurance. More aggressive treatment includes manipulation under anesthetic with CPM therapy and excision of scar tissue.

Long-term Monitoring

Follow-up depends on the surgeon, the patient, and the health care system. A typical example would be a surgical follow-up appointment at 6 weeks, 3 months, 6 months, 1 year, 2 years, 5 years, 10 years, and thereafter as appropriate. This is modified for each patient according to age, degree of activity, and presence of complications.

Satisfactory knee function is usually restored following TKA, and the majority of patients are able to return to low-impact sporting activity.^{[15, 16]} Long-term studies confirm satisfactory functional scores and show a 91-96% prosthesis survival rate at 14-15 years of follow-up. No difference appears to exist between posterior cruciate ligament (PCL)-retaining and PCL-substituting designs. Cementless designs do not have the same length of follow-up, but studies at 10-12 years report a 95% prosthesis survival rate.^{[3, 5, 6, 17, 18]}

Patient Education

For patient education information, see the Foot, Ankle, Knee, and Hip Center, Bone Health Center, and Arthritis Center, as well as Knee Joint Replacement and Knee Pain.