Introduction
Total knee replacement in some form has been practiced for over 50 years. 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.
Total knee arthroplasty. A total knee replacement prosthesis before implantation.
Total knee arthroplasty. Radiograph of an uncemented hydroxyapatite-coated total knee replacement. No gaps present in the bone-prosthesis junction, indicating incorporation of the bone onto the prosthesis.
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) (see Image 1).1,2
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 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.
Problem
Patients with painful, deformed, and unstable knees secondary to degenerative or inflammatory conditions need a prosthesis that provides reproducible pain relief and improvement in function. The morbidity and complications from the procedure should be minimal. The complexities of a normal knee joint, however, are not reproducible with modern techniques, and patients should understand that they will not have a normal knee. The prosthesis should be durable, requiring patients to undergo only one definitive procedure in their lifetime, although this may simply be unrealistic in younger patients.
Frequency
Approximately 130,000 knee replacements are performed every year in the United States.
Etiology
Osteoarthritic destruction of the knee is the most common reason for total knee replacement. This is a disease of synovial joints, characterized by degenerative and reparative processes, and is observed in 40% of 40-year-old patients on radiographic examination. However, only 50% of these patients are symptomatic. Osteoarthritis may be primary or secondary. Mechanical derangements (eg, previous meniscal or cruciate ligament damage), pyogenic infection, ligamentous instability, and fracture into a joint [see Image 2]) are among the common causes of the secondary type. Other causes of cartilage destruction include rheumatoid arthritis, hemophilia, seronegative arthritides, crystal deposition diseases, pigmented villonodular synovitis, idiopathic or steroid-induced avascular necrosis, and rare bone dysplasias.
Total knee arthroplasty. Radiograph demonstrating posttraumatic osteoarthritis.
Studies of risk factors for severe osteoarthritis of the hip and knee have revealed that siblings of individuals undergoing joint replacement are 3-5 times more likely to require similar surgery than age-matched controls. This means that genes contribute around 30% of the overall risk for severe osteoarthritis. Laboratory-based studies have shown that chromosome 11 is linked to severe osteoarthritis of the hip and chromosome 2 to severe osteoarthritis of the knee. The precise genes involved are as yet unknown.4
Pathophysiology
The exact cause of the degenerative process in primary osteoarthritis is unknown. It may represent a defect in cellular (chondrocyte) repair processes. Osteoarthritic cartilage contains increased amounts of water; alterations in the type of proteoglycan; type II collagen abnormalities; and increased levels of cathepsins, metalloproteinase, interleukin-1, and others as a complex cascade of enzymatic process. Changes in the synovium include synoviocyte hyperplasia, an increased leukocyte population in the membrane and fluid, occasional giant cells, neovascularization with increased vessel permeability, and altered matrix and cellular cytokine formation.
Presentation
Clinical history in a patient with arthritis of the knee is dominated by pain. This predominantly occurs on weight bearing but in the end stages may be constant and unrelieved by rest. Night pain is a particularly disabling symptom that demands urgent attention. The pain may be localized to one compartment or may be diffuse. Other symptoms include stiffness, swelling, locking, and giving way. Try to quantify the level of pain on a simple scale (eg, mild, moderate, severe; numerical scale of 1-10) and assess how the patient's activities of daily living (ADL) are affected.
Ask the patient about maximum walking distance, recreational sporting ability and aspirations, stair climbing (which often gives clues about patellofemoral disease), the need for walking aids, the ability to dress and perform self-care, and the ability to perform activities that require knee flexion. Some patients may have considerable interference with social interaction, sexual function, and sleep, and may experience exhaustion and even depression from their disease.
Various structured outcome evaluations can be used to try to quantify disability from dysfunction of the knee and are useful as research tools in follow-up studies of total knee replacement. These include general health status measures (eg, Medical Outcomes Short Form 36 [SF 36]) or specific knee scoring systems (eg, those used by the Knee Society).5,6
Establish the integrity of the ligaments because deficiency may require use of a special prosthesis with intrinsic stability.
Seek and systematically exclude other sources of knee and leg pain. These include root pain from spinal disease, referred pain from the ipsilateral hip, peripheral vascular disease, meniscal pathology, and bursitis of the knee.
Roentgenographic findings must correlate with a clear clinical impression of knee arthritis. Knee roentgenography should include a standing anteroposterior (AP) view, a lateral view, a 45-degree posteroanterior (PA) view of the knee (Rosenberg view), and a skyline view of the patella. Loss of joint space, cysts, subchondral sclerosis, and osteophytes confirm the diagnosis of osteoarthritis (see Image 3).
Total knee arthroplasty. Radiograph demonstrating the features of osteoarthritis (same patient as in Image below).
Total knee arthroplasty. Photograph of a patient with a varus deformity of the right knee and a valgus deformity of the left knee.
The overall mortality rate from a total knee replacement 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.3,7,8
An assessment of the patient's social circumstances is important for organization of postoperative rehabilitation and placement.
Examination should include assessment of scars or soft-tissue defects around the knee. Consult a plastic surgeon if wound healing is predicted to be a problem. Similarly, perform an accurate assessment of the vascular status to the limb. Identify and treat chronic local or systemic infection.
Identify and treat deficiency of the quadriceps musculature and extensor mechanism through rehabilitation because this may improve mechanical pain and facilitate postoperative recovery.9 Measure range of motion, including fixed flexion deformity, with a goniometer and record findings. The best predictor of range of motion following total knee replacement is the preoperative range of motion. This is an important factor when obtaining consent from the patient for surgery (see Image 4).
Indications
The primary indication for total knee arthroplasty (TKA) 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.3,7,8 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 Image 5) may justify arthroplasty because the expected outcome of arthroplasty is superior to patellectomy. Isolated patellofemoral replacement still is undergoing clinical investigation.
Total knee arthroplasty. Lateral radiograph demonstrating severe patellofemoral osteoarthritis.
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.
Relevant Anatomy
Degrees of knee joint movement
Movement of the knee joint can be classified as having 6 degrees of freedom: 3 translations (including anterior/posterior, medial/lateral, and inferior/superior) and 3 rotations (including 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, including the anterior and posterior cruciate ligaments (see Image 6) and the medial and lateral collateral ligaments as a 4-bar linkage system.
Total knee arthroplasty. Sagittal MRI showing the anterior and posterior cruciate ligaments.
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 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.
Contraindications
Absolute contraindications to total knee replacement include knee sepsis, a remote source of ongoing infection, extensor mechanism dysfunction, severe vascular disease, recurvatum deformity secondary to muscular weakness, and the 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 skin conditions within the field of surgery (eg, psoriasis), a past history of osteomyelitis around the knee, a neuropathic joint, and obesity.
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References
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Lee K, Goodman SB. Current state and future of joint replacements in the hip and knee. Expert Rev Med Devices. May 2008;5(3):383-93. [Medline].
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Greene KA, Schurman JR 2nd. Quadriceps muscle function in primary total knee arthroplasty. J Arthroplasty. Oct 2008;23(7 Suppl):15-9. [Medline].
Newman J, Pydisetty RV, Ackroyd C. Unicompartmental or total knee replacement: the 15-year results of a prospective randomised controlled trial. J Bone Joint Surg Br. Jan 2009;91(1):52-7. [Medline].
Andersen LØ, Husted H, Otte KS, Kristensen BB, Kehlet H. A compression bandage improves local infiltration analgesia in total knee arthroplasty. Acta Orthop. Dec 2008;79(6):806-11. [Medline].
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Mockford BJ, Thompson NW, Humphreys P, Beverland DE. Does a standard outpatient physiotherapy regime improve the range of knee motion after primary total knee arthroplasty?. J Arthroplasty. Dec 2008;23(8):1110-4. [Medline].
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Buechel FF. Cementless meniscal bearing knee arthroplasty: 7- to 12-year outcome analysis. Orthopedics. Sep 1994;17(9):833-6. [Medline].
March LM, Cross M, Tribe KL, Lapsley HM, Courtenay BG, Cross MJ, et al. Two knees or not two knees? Patient costs and outcomes following bilateral and unilateral total knee joint replacement surgery for OA. Osteoarthritis Cartilage. May 2004;12(5):400-8. [Medline].
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Further Reading
Related eMedicine topics
Unicompartmental Knee Arthroplasty
Complications of Total Knee Arthroplasty
Ceramic Bearings in Total Joint Arthroplasty
Total Joint Replacement Rehabilitation
Clinical guidelines
Total knee replacement.
ACR Appropriateness Criteria® imaging after total knee arthroplasty.
American Academy of Orthopaedic Surgeons clinical guideline on prevention of symptomatic pulmonary embolism in patients undergoing total hip or knee arthroplasty
Clinical trials
Effectiveness of Minimally Invasive Total Knee Replacement in Improving Rehabilitation and Function
A Study to Evaluate the Safety and Effectiveness of the Exactech Optetrak Rotating Bearing Knee Total Knee System
Keywords
total knee arthroplasty, TKA, total knee replacement, knee replacement, knee replacement surgery, knee surgery, knee pain, osteoarthritis of the knee, total joint arthroplasty, artificial knee
