Total knee replacement or arthroplasty (TKR or TKA) is an effective treatment of knee osteoarthritis after other treatment attempts have failed to provide the patient with lasting pain relief. According to the Centers for Disease Control (2008), the year 2002 saw over 380,000 TKA procedures in the United States. These common but complex procedures are being performed more frequently as we find older athletic knees suffering the results of injuries that occurred at earlier ages.
Total knee arthroplasties are not usually performed on young patients. For this reason, most physicians will cement the prosthesis in place. Some surgeons prefer to use a hybrid TKA. These TKAs have a porous-coated femoral component, encouraging bone ingrowth, rather than being cemented into the medullary canal. Patients undergoing cemented TKAs are permitted full weight bearing immediately following surgery. Some surgeons are also now permitting immediate full weight bearing in patients with cementless TKAs. If full weight bearing is not permitted, toe-touch weight bearing is the limitation for about six weeks postoperatively.
There are three basic components to a total knee prosthesis: the femoral, tibial, and patellar components. The femoral and tibial components are often metal. The tibial platform, which interfaces with the femoral component, has a polyethylene plate to ensure reduced wearing between the two metal surfaces. Some of the new metallic products may eventually lead to metal-on-metal joint surfaces, a design that would last longer than the metal-on-polyethylene design; but for now, the metal-on-polyethylene joint is considered the state-of-the-art model. The patella component is a button-like device. It is a polyethylene structure that is placed on the posterior side of the resurfaced patella bone.
As with THAs, there are different types of TKAs. The primary difference between the various TKAs has to do with posterior cruciate stability. One type retains the person’s posterior cruciate ligament (PCL), and the other provides a posterior-stabilized substitution in its design. Both provide for anterior-posterior stability, but the former allows the body’s existing PCL to provide stability while the latter creates anterior-posterior stability through the conformity of the two implant segments.
The surgeon may opt to perform a patellar resurfacing or leave the patella alone and not install a patellar button. People who do not undergo a resurfacing are likely to suffer anterior knee pain and joint swelling for several weeks following surgery (Brander and Stulberg, 2006). Patellar resurfacing includes shaving of the posterior patella surface and attachment of a patellar button on the posterior aspect of the patella (figure 16.3).
As with THA, computer-assisted techniques are available for TKA procedures and provide the most accurate bone cuts, sizing, and orientation of the prosthetic segments. Computer-assisted procedures are not yet universally performed with all TKA surgeries. However, since joint replacements that are properly implanted have the greatest survival and longevity rate, it is anticipated that all surgeons will eventually convert to this system of arthroplasty implants. Because of the materials now used and the installation techniques employed, surgeons are currently optimistic that computer-assisted total knee joint implants will last more than 20 years (Brander and Stulberg, 2006).
Surgical approaches for TKAs are anterior. The surgeon’s selection of a medial parapatellar approach through the quadriceps tendon, a vastus-splitting approach through the vastus medialis muscle, or a subvastus approach medial to the vastus medialis is based primarily on personal preference. The incision is more than 8 in. (20 cm) long. As with the hip, a minimally invasive technique is also possible for the knee. This technique usually requires an incision from the superior aspect of the patella to the tibial tubercle. Either the traditional incision or the minimally invasive incision is closed with metal staples.
Once the various skin, fascia, and muscle layers are opened in the surgical procedure and the patella is laterally dislocated, the knee joint is exposed. The collateral ligaments, if intact, are maintained. The anterior cruciate ligament is excised, but as mentioned previously, the posterior cruciate may be left intact or removed, depending on the surgeon’s preference and condition of the PCL. Precise osteotomies remove the arthritic joint surfaces, and the tibia and femur are prepared to accept the component parts. Once the sizing and alignment are complete, the joint segments are inserted and cemented in place, and the patella is resurfaced and then restored to its proper position.
As with the hip, risk of DVT necessitates the use of TED hose. These stockings are usually used for six weeks. Although the tibiofemoral joint is not usually at risk of dislocation following this surgery, the patella is at risk for subluxation (Brady et al., 2000). There are no restrictions on sitting as there are with THA. Walking and exercises begin the day following surgery. Depending on the age, agility, and strength of the patient, a walker or crutches are used to initiate gait training.