Total knee arthroplasty
Mark A. Brimer
Introduction
Total knee replacement (TKR), also referred to as total knee arthroplasty (TKA), is one of the most common surgical procedures performed for patients with severe arthritis of the knee (Mahomed et al., 2005). Between 1991 and 2010, annual primary TKA increased 161% from 93 230 to 243 802 and revision TKA volume increased 109% from 9650 to 19 871 (Cram et al., 2012). Although there are over 150 brand name implants currently on the market, along with custom prostheses (Bush et al., 2006), they may be divided into three categories: the linked prosthesis, the resurfacing implant and the conforming implant.
The three categories of implants
In the linked prosthesis, the femoral and tibial components are physically fastened together at the time of manufacture or at some point during the surgical procedure. The linked prosthesis may be fully constrained, thereby permitting only flexion and extension, or it may permit flexion, extension and limited axial rotation. Used primarily in the 1970s, the linked prosthesis is no longer commonly used because of the loosening of components that occurs when stresses are applied to the tibial side of the joint. These prostheses may, however, be appropriate for patients who have markedly unstable knees or after failure of one or more previous arthroplasties.
A resurfacing implant has a flat polyethylene tibial surface that articulates with the metallic femoral condylar component. A resurfacing implant requires proper balancing of the collateral and cruciate ligaments and, therefore, is not indicated in a case in which either the cruciate or the collateral ligament is absent or deficient. Because a large number of patients with advanced arthritis have a missing or attenuated cruciate ligament and compromised soft-tissue balancing, which is necessary for the procedure to succeed, resurfacing implants are not the primary choice of many surgeons.
A conforming implant consists of a metallic femoral condylar component and a polyethylene tibial component. Designed to resist some of the translatory and shear stresses, they have a long record of use: 95% of all TKR procedures (Heck et al., 1998). The design of the conforming implant requires surgical sacrifice of the anterior cruciate ligament and, in some cases, depending upon the design of the particular implant, of the posterior cruciate ligament as well. The posterior cruciate is almost always removed in cases in which the patient presents a fixed varus or valgus contracture of 15–20° and the associated fixed flexion deformity.
Fixation of the implant
The typical surgical approach has for many years been a conventional one. Recently, computer-navigated TKA has been investigated. Kim et al. (2012) reported no difference in clinical function, alignment or survivorship of the components that underwent computer-navigated versus conventional TKA. Regardless of approach, surgical fixation of all of the knee components is accomplished through one of two methods. The first involves the use of polymethylmethacrylate bone cement; one or both of the components is cemented to the bone surface. In the second method, the implants are inserted and one or both of the components are attached in a cementless manner. Although cemented knee components are still utilized, the preferred mechanism for attachment is cementless. Some of the problems that have been identified with the use of cemented components include the following:
The cementless technique relies upon bone growth into porous or roughened surfaces for firm fixation. Proper and precise surgical placement of cementless components is essential if firm component attachment is to be obtained. Studies indicate that bone will not grow across gaps greater than 1–2 mm.
The choice of component may be based upon the patient’s level of strenuous physical activity, age, health and wellbeing, and bone density. The primary contraindication to the use of a cementless component is severe osteoporosis. Loosening of the tibial tray is cited as the most common cause of failure in TKA but the mechanism remains unclear (Gebert de Uhlenbrock et al., 2012). Unicompartmental knee arthroplasty has been associated with consistently worse survival rates then TKA in worldwide arthroplasty registers (Baker et al., 2012).
Monitoring for potential infection is particularly important in TKA because a large amount of foreign material has been implanted in a superficial joint. Although a TKA is a relatively safe orthopedic procedure, wound-healing difficulties can occasionally be seen, including problems such as marginal wound necrosis, skin sloughing, sinus tract formation and hematoma formation (Norton et al., 1998). The presence of any of these complications may adversely affect the outcome. This is especially true with regard to range of motion (ROM) in cases in which therapy must be stopped until the problem can be resolved. The use of the minimally invasive TKR may reduce the potential for postoperative complications (Bonutti et al., 2004). However, more recent studies do not consistently report advantages of the minimally invasive approach for elderly patients (Liebensteiner et al., 2012; Reininga et al., 2012).
Rehabilitation
Preoperative care is beneficial for some individual patients but research has yet to support this in controlled studies and thus is best determined by the surgeon and the patient.
Inpatient postoperative rehabilitation considerations
The primary concern after a TKA is to see that the patient begins to walk (Katz et al., 2004). A patient with an uncomplicated TKA is generally encouraged to walk on postoperative day 1, even if ambulation time is brief. The role of the therapist is to encourage mobility, self-care, proper weight-bearing and gait, and getting into and out of bed in the proper manner (Kane et al., 2005). Quadriceps femoris muscle strength is an important determinant of physical function, therefore improving quadriceps weakness is an important goal for orthopedic surgeons and rehabilitation specialists (Saleh et al., 2010).
During the first few days after surgery, many surgeons ask their patients to use a continuous passive motion (CPM) device to maximize ROM results. These devices are used in conjunction with physical therapy exercises and ROM and gait training sessions two or three times a day. Patients are often encouraged to remain in the CPM device unless attending a physical therapy session or resting.
When a hospital rehabilitation department is preparing a patient to go home or to a skilled-nursing facility, staff members should consider the environment into which the patient is being discharged. For example, a patient returning home should be thoroughly trained in how to negotiate steps and flights of stairs, carpeted surfaces and surfaces that might be encountered outside the home. It is particularly important that the patient understand the proper positioning of the knee during sleep in order to prevent unwanted contractures.
Performance of the activities of daily living should be discussed with the patient and the immediate caregivers. Because a large majority of TKA procedures are performed in members of the geriatric population, special attention should be paid to any impairment in vision, balance, or endurance that may have occurred. A falls risk assessment should be performed and documented. Patients should be encouraged to monitor the integrity of the wound site on a daily basis and to use safe ambulation procedures until outpatient gait training needs can be addressed.
Outpatient and home healthcare rehabilitation considerations
In the outpatient or home healthcare rehabilitation environment the focus is on restoring the ability to perform normal activities of daily living, ROM of the knee and teaching safe ambulation. In the initial stages (0–4 weeks) it is vital to maximize ROM. Functional ROM is considered to be between 110° and 120° of flexion and full extension. Patients should be actively involved in home programs that focus upon the prevention of flexion or extension contractures of the knee. Neuromuscular electrical stimulation (NMES) can facilitate the recovery of quadriceps muscle strength after TKA, but the optimal intensity (dosage) of NMES on strength after TKA has yet to be determined (Stevens-Lapsley et al., 2012).
In the period between 0 and 4 weeks after surgery, rehabilitation should focus upon strength gains in the quadriceps, hamstring, hip flexor and hip extensor muscles. The patient may be allowed to progress to walking with full weight-bearing, as indicated by the physician. A patient who has undergone the cementless technique may be weight-bearing as tolerated immediately after surgery, or may be required to maintain limited weight-bearing for a period of 4–6 weeks or until sufficient new bone growth can be seen on an X-ray.
Desired rehabilitation outcomes for the TKA patient
Patients who undergo TKA commonly require extensive outpatient physical therapy for a period of approximately 6 weeks in order to maximize ROM. Swelling may persist for several months until sufficient collateral circulation can develop. The use of home ROM programs as well as general conditioning exercises allows the patient to resume normal activities quickly. Strenuous exercise is to be avoided until approved of by the physician. A knee evaluation scale is shown in Table 22.1; it may be helpful in documenting postsurgical outcomes.
Table 22.1
Knee Society clinical rating system
