Knee replacement

Surgical procedure

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 (e. g. walking frames, canes, crutches) to enable the patient's return to preoperative mobility. It is estimated that approximately 82% of total knee replacements will last 25 years.

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.

The surgery involves exposure of the front of the knee, with detachment of part of the quadriceps muscle (vastus medialis) 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.

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.

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.

The regional analgesia techniques (neuraxial anesthesia or continuous femoral nerve block or adductor canal block) 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.

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. The evidence did not show any clear benefit on patient function, treatment success or quality of life.

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.

There is debate regarding denervating the patella. Anterior knee pain is thought to be related to the association of the patella and femoral component. Some surgeons believe that by using electrocautery to denervate the patella, it reduces the chance of anterior knee pain postoperatively.

Many surgeons in the USA perform patella resurfacing routinely, while many surgeons in Asia and Europe do not. Patella resurfacing is performed by removing the cartilage from the surface of the knee and replacing it with polyethylene. Surgeons who do not routinely resurface the patella do not believe that it is a significant contribution to pain, when there is no evidence of arthritis to the patellofemoral joint. Some surgeons believe it is not cost effective routinely to resurface the kneecap and that routine patella resurfacing may lead to increased complications such as patella fracture. Other surgeons are concerned that patients with an unresurfaced patella may have increased pain postoperatively. A meta analysis evaluating outcomes following patella resurfacing found that routine resurfacing more reliably relieves patient's pain.

Polyethylene is the plastic component that is inserted between the femoral and tibial components. There are several different polyethylene component designs that have been published,
including posterior stabilized (PS), cruciate retaining (CR), bicruciate retaining (BCR), medial congruent (MC) and mobile bearing.

The posterior cruciate ligament (PCL) is important to the stability of the knee by preventing posterior subluxation of the tibia, reducing shear stress, increasing flexion and lever arm of the extensor mechanism by inducing femoral rollback upon flexion, and thus minimizing polyethylene abrasion through reducing stress applied to the articular surface. The PS implant uses a post that is built into the implant to accommodate for the loss of PCL. Proponents of retaining the PCL advise that it is difficult to balance a CR knee and unnatural physiologic loads may increase wear of the polyethylene.

MC knee replacements attempt to mimic a more natural knee motion by decreasing motion on the medial aspect of the knee and allowing for increased motion on the lateral aspect of the joint. This mimics the external rotation and abduction of the tibia that is seen during normal ambulation. While several studies have shown improved gait profiles, long term studies are needed to demonstrate improved results. Conversely, the BCR knee retains the Anterior and posterior cruciate ligaments to try to mimic the normal tension of the knee's ligaments. Concerns over increased revision frequency have led to some designs being pulled from the market.

A mobile bearing design allows for free motion of the polyethylene within the tibial component. Other component designs have the polyethylene member fixed to the tibial component, and only articulate at the femur/polyethylene junction. There is no strong evidence that this approach improves knee function, mortality, adverse events, or amount of pain, compared with a fixed bearing approach for total knee replacement.

Minimally invasive procedures have been developed in total knee replacement that do not cut the quadriceps tendon. There are different definitions of minimally invasive knee surgery, which may include a shorter incision length, retraction of the patella without eversion (rotating out), and specialized instruments. There are few randomized trials, with studies finding less postoperative pain, shorter hospital stays, and shorter recovery times. These studies have not shown long term benefits. Many studies demonstrate higher revision rates associated with partial knee replacements. There is significant variation in revision rates, depending on implant design and implantation technique.

Standardized zones around the components are used for specifying, for example, signs of loosening on radiographic follow up. There are various classification systems for specifying such zones, including by KS (Knee Society) zones published in 2015. are similar to those associated with all joint replacements. The most serious complication is infection of the joint, which occurs in <1% of patients. Risk factors for infection are related to both patient and surgical factors. Deep vein thrombosis occurs in up to 15% of patients, and is symptomatic in 2–3%. Nerve injuries occur in 1–2% of patients. Persistent pain or stiffness occurs in 8–23% of patients. Prosthesis failure occurs in approximately 2% of patients at 5 years. The morbidly obese should be advised to lose weight before surgery and, if medically eligible, would probably benefit from bariatric surgery. Smokers have a higher risk of surgical complications (deep wound infection, superficial wound infection, and wound dehiscence) compared with nonsmokers. They also have a higher risk of pneumonia after surgery. Fracturing or chipping of the polyethylene platform between the femoral and tibial components may be of concern. These fragments may become lodged in the knee and create pain or may move to other parts of the body. Advancements in implant design have greatly reduced these issues but the potential for such an event is still present over the life span of the knee replacement.

According to the American Academy of Orthopedic Surgeons (AAOS), deep vein thrombosis in the leg is "the most common complication of knee replacement surgery prevention may include periodic elevation of patient's legs, lower leg exercises to increase circulation, support stockings and medication to thin your blood." This is specifically the case for those people who have additional risk factors for venous thromboembolisms, and those people who are at risk of aspirin resistance.

Periprosthetic fractures are becoming more frequent with the aging patient population and can occur intraoperatively or postoperatively. Depending on the location of the fracture and the stability of the prosthesis, these can be treated surgically with open reduction and internal fixation or revision of the prosthesis.

The knee at times may not recover its normal range of motion (0–135 degrees usually) after total knee replacement. Much of this is dependent on pre operative function. Most patients can achieve 0–110 degrees, but stiffness of the joint can occur. In some situations, manipulation of the knee under anesthetic is used to reduce post operative stiffness. There are also many implants from manufacturers that are designed to be "high flex" knees, offering a greater range of motion.

In some patients, the kneecap dislocates to the outer side of the knee after surgery. This is painful and usually needs to be treated by surgery to realign the kneecap. However, this is quite rare.

Loosening of the prosthesis can be indicated on X ray by thin radiolucent spaces around the implant, or more obviously by implant displacement.

With 718,000 hospitalizations, knee arthroplasty accounted for 4.6% of all United States operating room procedures in 2011—making it one of the most common procedures performed during hospital stays. The number of knee arthroplasty procedures performed in U. S. hospitals increased 93% between 2001 and 2011. A study of United States community hospitals showed that in 2012, among hospitalizations that involved an OR procedure, knee arthroplasty was the OR procedure performed most frequently during hospital stays paid by Medicare (10.8 percent of stays) and by private insurance (9.1 percent). Knee arthroplasty was not among the top five most frequently performed OR procedures for stays paid by Medicaid or for uninsured stays. By 2030, the demand for primary total knee arthroplasty is projected to increase to 3.48 million surgeries performed annually in the U. S.

With osteoarthritis (OA) being the most common reason for total knee arthoplasty (TKA) surgery, it is important to understand that balance deficits significantly impact the quality of daily living in patients with knee OA and are also linked to greater risk of falling and poor mobility. Annually in the US, 40% of all patients with OA report a history of falls. TKA surgery has shown to decrease fall risk and fear of falling in pre operative fallers with OA versus non operative fallers by 54% following TKA.