Definition

Arthroplasty involves the reconstruction by natural modification or artificial replacement of a diseased, damaged, or ankylosed joint. The knee joint functions as a complex hinge, allowing flexion, extension, rotation, and gliding. The knee joint itself is made up of three compartments, lateral, medial, and patellofemoral. Disease processes that cause damage to the cartilage of any or all of the three compartments may lead to the need for total knee arthroplasty (TKA). Examples of these diseases include osteoarthritis (idiopathic or traumatic), inflammatory arthritis (e.g., rheumatoid, psoriatic), avascular necrosis, tumors, and congenital abnormalities. The principal diagnoses most commonly associated with total knee replacement procedures are osteoarthrosis and allied disorders (90.9%), followed by rheumatoid arthritis and other inflammatory polyarthropathies (3.4%) [1].

TKA is a procedure that is widely performed for advanced arthropathies of the knee; it consistently alleviates pain, improves function, and enhances quality of life [2]. As the elderly population in the United States grows and indications for the procedure broaden, it is projected that an increasing number of patients will undergo TKA. The most common age group for total knee replacements is 65 to 84 years. Women in this age range are more likely to undergo TKA than are their male counterparts.

Approximately 700,000 TKAs are performed annually in the United States. With the aging of the U.S. population, this number is projected to increase to more than 3 million yearly by 2030 [3]. Younger and more active patients are electing to proceed with TKA.

TKA consists of resection of abnormal articular surfaces of the knee with resurfacing predominantly using metal and polyethylene components. The surgical use of a total condylar prosthesis (replaces all three compartments of the knee) dates to the early 1970s. There are three basic types of TKA: totally constrained, semiconstrained, and totally unconstrained. The amount of constraint built into an artificial joint reflects the amount of stability the hardware provides. As such, a totally constrained joint has the femoral portion physically attached to the tibial component and requires no ligamentous or soft tissue support. The semiconstrained TKA has two separate components that glide on each other, but the physical characteristics of the tibial component prevent excessive femoral glide. The totally unconstrained device relies completely on the body’s ligaments and soft tissues to maintain the stability of the joint. The semiconstrained and totally unconstrained knee implants are most often used. In general, the totally unconstrained implants afford the most normal range of motion and gait.

In unicompartmental knee arthroplasty, only the joint surfaces on one side of the knee (usually the medial compartment) are replaced. Unicompartmental knee arthroplasty provides better relief than does a tibial osteotomy and greater range of motion than does a TKA as well as improved ambulation velocity. More recently, the concept of minimally invasive TKA has evolved from the procedures and investigations of unicompartmental knee arthroplasty. The distinctive features include decreased skin incision length, inferior and superior patellar capsular releases (necessary to gain exposure of the entire joint and to mobilize the patella), lack of patellar eversion (reducing risk of permanent dysfunction of the quadriceps muscle), and no tibiofemoral joint dislocation (minimizing capsular damage and postoperative pain).

The need for longer lasting TKAs continues, given the more active and anticipated longer living patient population. Efforts to design a better, longer lasting knee are focusing on alternative bearings and surfaces to reduce osteolysis. Areas being studied include the use of cross-linked ultrahigh-molecular-weight polyethylene inserts, alternative metal and ceramic bearing surfaces, and different mobile bearing designs. The goals of new designs are to minimize wear debris and to decrease risk of loosening and implant failure. The most important determinant of TKA long-lasting success remains a well-balanced, well-aligned, and well-fixed implantation procedure [4].

The increasing use of TKA has raised several public and clinical policy issues, including apparent racial and ethnic disparities in TKA use [5], broadening indications for TKA to include younger and older patients, and evidence that outcomes are better when TKA is performed in higher volume centers [6]. These issues were partially addressed in the Agency for Healthcare Research and Quality report [7]. That report concluded that there is no evidence that age, gender, or obesity is a strong predictor of functional outcomes. Patients with rheumatoid arthritis show more improvement than those with osteoarthritis, but this may be related to their poorer functional scores at the time of treatment and hence the potential for more improvement. The underlying indication, though, is consistent across all these groups, namely, that advanced osteoarthrosis of the knee compromises functional activities as the patient’s knee pain becomes recalcitrant and unresponsive to conservative therapeutic interventions. Absolute contraindications to TKA include knee sepsis or other source of ongoing infection, extensor mechanism dysfunction, severe vascular disease, recurvatum deformity due to muscle weakness, and presence of a well-functioning knee arthrodesis. Relative contraindications may include neuropathic joint, morbid obesity, past history of osteomyelitis around the knee, and skin conditions such as psoriasis within the field of surgery [8].

Symptoms

Refractory knee pain is the most common symptom among patients who undergo TKA. Stiffness, deformity, and instability are symptoms also commonly seen in advanced osteoarthrosis or inflammatory polyarthropathy. In the postoperative period, acute surgical pain is most intense during the first 2 weeks. Disruption and inflammation of the periarticular soft tissues are manifested as a soft tissue stiffness pattern that differs in the severity of limitation of range of motion from the preoperative rigid stiffness of advanced arthrosis. Joint proprioception impairment may give rise to a sense of mild knee instability in the postoperative period. Uncommonly, debris may generate a sense of cracking, popping, or locking.

Physical Examination

Physical examination should include palpation of the knee to evaluate for effusion and joint line tenderness, which may indicate meniscal disease. Gait pattern should be documented with attention to the possible presence of knee thrust (abnormal medial or lateral movement of the knee), which may indicate ligamentous instability. Preoperative knee range of motion should be recorded to assess the extensor mechanism. Because of the importance of preserving the medial and lateral collateral ligaments during a total knee replacement, preoperative assessment of the stability of these ligaments is indicated. The skin over both legs should be assessed for signs of vascular disease or infection. The lower back and hip should be examined to rule out referred pain to the knee [9].

Functional Limitations

Osteoarthritis of the knee can result in pain or stiffness that can affect a person’s functional ability to rise from a chair, to walk, or to use stairs. Table 80.1 depicts the required knee range of motion for specific functional mobility tasks. In an otherwise healthy patient population, osteoarthritis may impede participation in recreational or sporting activities, such as golf or tennis. The preoperative profile of a patient at risk for poor postoperative locomotor recovery is a woman with a high body mass index, many comorbidities, high intensity of knee pain, restriction in flexion amplitude, deficits in knee strength, and poor preoperative locomotor ability as measured by the 6-minute gait test. In addition, the preoperative gait power profiles, on the nonsurgical side, are characterized by low concentric push-off work by the plantar flexors and low concentric action of the hip flexors during early swing [10]. Postoperative pain scores and their associated psychological profiles ostensibly affect functional outcomes also [11].

Subsequent studies have further identified factors associated with a suboptimal postoperative functional outcome. Patients who have marked functional limitation, severe pain, low mental health score, and other comorbid conditions before TKA are more likely to have a worse outcome at 1 year and 2 years postoperatively [12]. One consistent finding is that preoperative joint function is a predictor of function at 6 months after TKA. Those patients who had lower preoperative functional status related to knee arthritis functioned at a lower level at 6 months than did patients with a higher preoperative functional status [13]. Studies have focused on quadriceps strength as a significant contributing factor. Functional measures underwent an expected decline early after TKA, but recovery was more rapid than anticipated and long-term outcomes were better than previously reported in the literature in patients with higher baseline quadriceps strength. The high correlation between quadriceps strength and functional performance suggests that emphasis on postoperative quadriceps strengthening is important to enhance the potential benefits of TKA [14]. However, preoperative quadriceps strength training has not been proved to enhance long-term functional outcome after TKA [15,16].

Diagnostic Studies

Plain radiographs of the knee remain the mainstay of diagnosis and preoperative planning. Three basic views include standing anteroposterior view (assesses medial and lateral joint space narrowing during normal leading of the joint), lateral view (assesses the patellofemoral joint and the position of the patella), and tangential patella or sunrise view (assesses the patellofemoral joint space) [9]. Magnetic resonance imaging is more sensitive than plain radiography in assessing cartilage but still may underestimate the amount of damage. Magnetic resonance imaging may also be used to evaluate meniscal or ligament disease [17].

In addition to the standard preoperative screening for surgical clearance, consideration should be given to radiographic evaluation of the cervical spine in rheumatoid arthritis patients. Rheumatoid arthritis patients are at increased risk for atlantodental instability and therefore may be at increased risk for spinal cord impingement as a result of perioperative manipulations with surgery and general anesthesia [18].

Rheumatoid arthritis patients are thought to be at 2.6-fold greater risk of infections than osteoarthritis patients are. Therefore, rheumatoid arthritis patients should be screened for potential sources of infections, including urinary tract infections, skin infections, and dental infections, before TKA. [19]

Medical therapeutic interventions address the following.

Prophylaxis for Deep Venous Thrombosis and Pulmonary Embolism

Warfarin, a vitamin K antagonist, can be started preoperatively or postoperatively to prevent deep venous thrombosis (DVT) and pulmonary embolism (PE). The anticoagulant effects of vitamin K antagonists are not achieved until the third or fourth day of treatment. Thus, postoperative initiation of warfarin may not prevent small thrombi from forming. Nevertheless, warfarin does appear to effectively inhibit the extension of small thrombi, thereby preventing clinically significant DVT or PE. Because of its delayed reaction and its similar bleeding rates to low-molecular-weight heparin, warfarin tends to be the preferred thromboprophylactic medication by United States orthopedic surgeons [20].

New oral antithrombotic agents that inhibit either activated factor X or activated factor XI (thrombin) are now approved for use in the United States. Rivaroxaban inhibits activated factor X. The RECORD3 study demonstrated the superiority of a 10-mg once-daily oral dose of rivaroxaban over 40-mg subcutaneous daily dosing of enoxaparin in reducing the incidence of symptomatic venous thromboembolism (VTE) after total knee replacement [21]. The RECORD4 study compared rivaroxaban 10 mg orally daily with enoxaparin 30 mg subcutaneously twice daily. No statistically significant difference was shown in the incidence of major or symptomatic VTE [22].

Dabigatran etexilate is a direct thrombin inhibitor. It is active against both free and clot-bound thrombi. The RE-MOBILIZE trial compared dabigatran with enoxaparin (30 mg subcutaneously twice daily). Data for major VTE or death and major bleeding events were comparable [23]. Low-molecular-weight heparins are used in VTE prophylaxis after TKA. They have an advantage in that they can be given subcutaneously once or twice daily with constant dosing without the need for daily laboratory monitoring. They also carry a significantly reduced risk for heparin-induced thrombocytopenia compared with unfractionated heparin.

Intermittent pneumatic compression prevents venous thrombosis by increasing venous blood flow in the deep veins of the legs and by reducing plasminogen activator inhibitor [24]. Intermittent pneumatic compression is contraindicated in patients with evidence of leg ischemia due to peripheral vascular disease. The optimal use of intermittent pneumatic compression, which includes initiation in the operating room or recovery room, is an alternative option for VTE prophylaxis for patients at a high risk for bleeding. Aspirin is thought to be highly effective in reducing major arterial thrombotic events, but the benefit in reducing VTE is less clear. The 2008 American College of Chest Physicians anticoagulation guidelines recommended against use of aspirin alone as prophylaxis for VTE for any medical or surgical patient group [25]. The 2012 American College of Chest Physicians guidelines, however, have included aspirin as a recommended agent for thrombosis prophylaxis in patients undergoing TKA. This recommendation was not unanimously supported by the entire panel [26].

For patients undergoing total knee replacement, UpToDate recommends extending thrombosis prophylaxis beyond 10 days and up to 35 days after surgery [20].

Postoperative Care

During the first 48 to 72 hours, patients often receive controlled analgesia therapy administered through the intravenous or epidural route. Some anesthesiologists use a perioperative femoral nerve block. Subsequently, patients are given oral opioids. Controlled-release and short-acting opioids may be used. Depending on the clinician’s and patient’s preferences, fixed or rescue dose opioid medications are selected. The opioids can be titrated to achieve balance of analgesia versus emerging side effects [27–30].

Dry, sterile gauze dressings are applied as long as drainage is present. Staples and sutures can safely be removed 10 to 14 days after surgery [31,32]. Knee immobilizers may be used postoperatively to maintain knee extension and to avoid flexion contracture. Range of motion exercises supervised by a physical therapist should be initiated as soon as possible. Properly fitting, thigh-high elastic compression stockings, a continuous passive motion (CPM) machine, and possibly local cryotherapy are used to manage swelling [33–36].

The overall blood lost after unilateral TKA has been estimated at 2.2 units. Blood loss is greater for uncemented than for cemented prostheses. Patients are often advised before surgery to donate 1 to 3 units of packed red blood cells for autotransfusion, although this practice has recently been questioned [37]. In addition, postoperative blood collection and reinfusion through the surgical drain have been shown to be effective in reducing the need for bank blood and have a low morbidity rate with current techniques. Some patients are advised to commence a course of recombinant erythropoietin in conjunction with iron supplementation before surgery [38