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Total Knee Arthroplasty (TKA)

Practice Essentials

The primary indication for total knee arthroplasty (TKA; also referred to as total knee replacement [TKR]) is relief of significant, disabling pain caused by severe arthritis. (See the image below.)

Total knee arthroplasty. Radiograph demonstrating

Total knee arthroplasty. Radiograph demonstrating posttraumatic osteoarthritis.

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Preparation

Anesthesia

TKA may be performed with the patient under regional or general anesthesia. Which of these is used depends partly on the medical condition of the patient, though cardiovascular outcomes, cognitive function, and mortality rates associated with 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 (DVTs). Whether this has an overall positive benefit for the patient is not known.

Equipment

Types of TKA prostheses include the following:

Fixed bearing

Medial pivot

Rotating platform and mobile bearing

Posterior cruciate ligament (PCL)-retaining

PCL-substituting

Patient evaluation

Preoperative medical evaluation of the patient includes the following:

Medical evaluation – Patients must have good cardiopulmonary function to withstand anesthesia and to cope with a blood loss of 1000-1500 mL over the perioperative period; routine preoperative electrocardiography should be performed on elderly patients

Laboratory studies – These include (1) complete blood count (CBC), (2) erythrocyte sedimentation rate (ESR), (3) serum electrolytes, (4) renal function studies, (5) prothrombin time (PT) and activated partial thromboplastin time (aPTT), (6) urinalysis, and (7) urine culture

Imaging studies – These include (1) standing anteroposterior (AP) view, (2) lateral view, (3) patellofemoral (skyline) view, (4) long leg radiographs (to assess malalignment), and (5) standing radiographs with the knee in extension or in 45º of flexion (Rosenberg view)

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.

Technique

TKA is performed as follows:

The knee joint is usually approached anteriorly through a medial parapatellar approach, though some surgeons use a lateral or subvastus approach

Bone cuts in the distal femur are made perpendicular to the mechanical axis, typically 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

Ligaments around the knee that are contracted because of preoperative deformity are carefully released in a stepwise fashion

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

Once the definitive prosthetic components have been selected, they are cemented into place with polymethyl methacrylate cement

If an uncemented system is being used, press-fit and bony ingrowth provide fixation of the component

Foot pulses are checked at the end of the procedure

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.

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. Thromboembolism prophylaxis is often continued at home for a period of time.

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