Knee replacement


Knee replacement, also known as knee arthroplasty, is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve pain and disability, most commonly offered when joint pain is not diminished by conservative sources. It may also be performed for other knee diseases, such as rheumatoid arthritis. In patients with severe deformity from advanced rheumatoid arthritis, trauma, or long-standing osteoarthritis, the surgery may be more complicated and carry higher risk. Osteoporosis does not typically cause knee pain, deformity, or inflammation, and is not a reason to perform knee replacement.
Knee replacement surgery can be performed as a partial or a total knee replacement. In general, the surgery consists of replacing the diseased or damaged joint surfaces of the knee with metal and plastic components shaped to allow continued motion of the knee.
The operation typically involves substantial postoperative pain and includes vigorous physical rehabilitation. The recovery period may be 12 weeks or longer and may involve the use of mobility aids to enable the patient's return to preoperative mobility. It is estimated that approximately 82% of total knee replacements will last 25 years.

Medical uses

Knee replacement surgery is most commonly performed in people with advanced osteoarthritis and should be considered when conservative treatments have been exhausted. Total knee replacement is also an option to correct significant knee joint or bone trauma in young patients, treat complex fractures in elderly, either due to previous symptomatic osteoarthritis or situations where internal fixation with plates and screws is deemed too hazardous. Similarly, total knee replacement can be performed to correct mild valgus or varus deformity. Serious valgus or varus deformity should be corrected by osteotomy. Physical therapy has been shown to improve function, and may delay or prevent the need for knee replacement. Pain often is noted when performing physical activities requiring a wide range of motion in the knee joint.

Outcomes

Knee replacement provides significantly better results than exercise training in terms of reducing pain 6 months to 2 years afterwards. People who have had knee replacements have lower death rates than the matched population for 10 years after surgery, but increased rates from 11 years onwards. For this reason it is sometimes argued that the age group 65-75 is the best time to consider having a knee replacement if activity is being severely curtailed by knee pain. Although knee replacement has superior 24 month results in terms of pain relief than exercise treatment, it may not be cost effective compared to the option of initial exercise treatment followed by crossover to knee replacement if results are unsatisfactory.

Pre-operative preparation

To indicate knee replacement in case of osteoarthritis, its radiographic classification and severity of symptoms both should be substantial. Such radiography should consist of weightbearing X-rays of both knees: AP, lateral, and 30 degrees of flexion. AP and lateral views may not show joint space narrowing, but the 30-degree flexion view is most sensitive for narrowing. Full-length projections also are used in order to adjust the prosthesis to provide a neutral angle for the distal lower extremity. Two angles used for this purpose are:
  • Hip-knee-shaft angle, an angle formed between a line through the longitudinal axis of the femoral shaft and its mechanical axis, which is a line from the center of the femoral head to the intercondylar notch of the distal femur.
  • Hip-knee-ankle angle, which is an angle between the femoral mechanical axis and the center of the ankle joint. It is normally between 1.0° and 1.5° of varus in adults.
The patient is to perform range-of-motion exercises, and hip, knee and ankle strengthening as directed daily. Exercises that include strengthening of hip flexors, hip abductors and knee flexors helps to recover faster post operatively. Before the surgery is performed, pre-operative tests are done: usually a complete blood count, electrolytes, APTT and PT to measure blood clotting, chest X-rays, ECG, and blood cross-matching for possible transfusion. About a month before the surgery, the patient may be prescribed supplemental iron to boost the hemoglobin in their blood system. Accurate X-rays of the affected knee are needed to measure the size of components which will be needed. Medications such as warfarin and aspirin will be stopped some days before surgery to reduce the amount of bleeding. Patients may be admitted on the day of surgery if the pre-op work-up is done in the pre-anesthetic clinic or may come into hospital one or more days before surgery. As of 2017, there was insufficient quality evidence to support the use of pre-operative physiotherapy in older adults undergoing total knee arthroplasty. However, as of 2022, there has been renewed interest in improving patient outcomes and "prehab" has become standard practice.
Preoperative education is currently an important part of patient care. There is some evidence that it may slightly reduce anxiety before knee-replacement surgery, with low risk of detrimental effects.
Knee replacement referrals are often blocked if a person is overweight because it is believed they may benefit less from surgery. However, knee replacements have been found to reduce pain and improve function, regardless of people's weight. After 10 years, most people did not need repeat surgery. In addition, weight loss surgery before a knee replacement does not appear to change outcomes.

Technique

The surgery involves exposure of the front of the knee, with detachment of part of the quadriceps muscle from the patella. The patella is displaced to one side of the joint, allowing exposure of the distal end of the femur and the proximal end of the tibia. The ends of these bones then are cut accurately to shape, using cutting guides oriented to the long axis of the bones. The cartilages and the anterior cruciate ligament are removed; the posterior cruciate ligament also may be removed but the tibial and fibular collateral ligaments are preserved. Whether the posterior cruciate ligament is removed or preserved depends on the type of implant used, although there appears to be no clear difference in knee function or range of motion favoring either approach. Metal components are then impacted onto the bone or fixed using polymethylmethacrylate cement. Alternative techniques exist that affix the implant without cement. These cement-less techniques may involve osseointegration, including porous metal prostheses. Finally, stability and range of motion are checked, followed by irrigation, hemostasis, placement of hemovacs, and closure.

Femoral replacement

A round-ended implant is used for the femur, mimicking the natural shape of the joint. On the tibia the component is flat, although it sometimes has a stem that goes down inside the bone for further stability. A flattened or slightly dished high-density polyethylene surface is then inserted onto the tibial component so the weight is transferred metal to plastic, not metal to metal. During the operation any deformities must be corrected, and the ligaments balanced so the knee has a good range of movement, and is stable and aligned. In some cases the articular surface of the patella also is removed and replaced by a polyethylene button cemented to the posterior surface of the patella. In other cases, the patella is replaced unaltered.
Image:Prothese-genou-IMG 0033.jpg|150px|thumb|left|Model of total knee replacement

Technology

In recent years, there has been an increase in technology assistance with implantation of total knee replacements. Traditionally, knee replacements were performed using mechanical jigs, not unlike those used in carpentry. These mechanical jigs rely on vision and human judgment. Using computer assistance to provide navigation, navigated knee replacements provide assistance in more accurate placement of implanted knee replacements based on mechanical axis. While these implants are placed more accurately, there has not been much improvement in long-term outcomes. Similarly, sensor-based guidance provides accurate feedback to demonstrate soft-tissue tension to assist in guidance of insertion of knee replacements. Robotic-assisted knee replacements take into account both mechanical axis and soft-tissue balancing in order to assist the surgeon in placement of a knee replacement. Short-term outcomes of robotic-assisted knee replacements are promising.

Post-operative pain control

The regional analgesia techniques are used most commonly. Local anesthesia infiltration in the pericapsular area using liposomal bupivacaine provides good analgesia in the post-operative period without increasing the risk for instability or nerve injury. Some benefits in femoral nerve blocks are a reduction in morphine consumption and a decrease in pain intensity. A combined approach of local infiltration analgesia and femoral nerve block to achieve multimodal analgesia is common.

Modified intervastus approach

Introduced in 2018, a modified intervastus approach to the anterior knee may be used for total knee arthroplasty. The procedure is intended to preserve the quadriceps tendon and vastus medialis.

Tourniquet use

To reduce blood loss, a pressurized pneumatic tourniquet may be used during this operation. The current body of evidence suggests if a tourniquet is used in knee replacement surgery, it probably increases the risk of severe side effects and postoperative pain. The evidence did not show any clear benefit on patient function, treatment success or quality of life.

Controversies

Cemented or cementless

The femoral, tibial and patellar components of a total knee replacement are fixed to the bone by using either cement or cementless total knee replacement implants. Cemented fixation is performed on the vast majority of total knee replacements. However, short-term trials suggest that there may be relief of pain. There are concerns regarding tibial loosening after implantation, prohibiting widespread adoption of cementless knee replacements at this time.