Knee replacement, or
knee arthroplastyArthroplasty is an operative procedure of orthopedic surgery performed, in which the arthritic or dysfunctional joint surface is replaced with something better or by remodeling or realigning the joint by osteotomy or some other procedure.-Background:Previously, a popular form of arthroplasty was...
, is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve the pain and disability of
osteoarthritisOsteoarthritis , is a group of diseases and mechanical abnormalities involving degradation of joints, including articular cartilage and the subchondral bone next to it...
. It may be performed for other knee diseases such as rheumatoid arthritis and psoriatic 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.
OsteoporosisOsteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered...
does not typically cause knee pain, deformity, or inflammation and is not a reason to perform knee replacement.
Other major causes of debilitating pain include meniscus tears, cartilage defects, and ligament tears. Debilitating pain from osteoarthritis is much more common in the elderly.
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 involves substantial postoperative pain, and includes vigorous physical rehabilitation. The recovery period is 6 weeks or longer and involves use of a walker and then a cane.
History
Following
John CharnleySir John Charnley was a British orthopaedic surgeon. He pioneered the hip replacement operation, which is now one of the most common operations both in the UK and elsewhere in the world...
's success with
hip replacementHip replacement, also hip arthroplasty, is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Such joint replacement orthopaedic surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage as part of hip fracture treatment.-History:The...
in the 1960s numerous attempts were made to design knee replacements. Gunston and Marmor were pioneers in North America. Marmor's design allowed for unicompartmental operations but these designs did not always last well. In the 1970s the "Geometric" design found favor as well as John Insall's Condylar Knee design. Hinged knee replacements for salvage date back to Guepar but did not stand up to wear. The history of knee replacement is the story of continued innovation to try to limit the problems of wear, loosening and loss of range of motion.
Indications
Knee replacement surgery is most commonly performed in people with advanced osteoarthritis. It should be considered when conservative treatments have been exhausted.
Physical therapyPhysical therapy is a health care profession which provides services to individuals in order to develop, maintain and restore maximum movement and functional ability throughout life...
has been shown to improve function and may delay or prevent the need for knee replacement.
Pre-operative preparation
Knee Arthroplasty is major surgery. Before the surgery is performed, pre-operative tests are done: usually a
complete blood countA complete blood count , also known as full blood count or full blood exam or blood panel, is a test requested by a doctor or other medical professional that gives information about the cells in a patient's blood...
, electrolytes, APTT and
PTThe prothrombin time and its derived measures of prothrombin ratio and international normalized ratio are measures of the extrinsic pathway of coagulation. They are used to determine the clotting tendency of blood, in the measure of warfarin dosage, liver damage, and vitamin K status...
to measure
blood clottingCoagulation is a complex process by which blood forms clots. It is an important part of hemostasis , wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
,
chest X-rayIn medicine, a chest radiograph, commonly called a chest x-ray , is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures...
s, ECG, and blood
cross-matchingCross-matching blood, in transfusion medicine, refers to the complex testing that is performed prior to a blood transfusion, to determine if the donor's blood is compatible with the blood of an intended recipient, or to identify matches for organ transplants. Cross-matching is usually performed...
for possible
transfusionBlood transfusion is the process of transferring blood or blood-based products from one person into the circulatory system of another. Blood transfusions can be life-saving in some situations, such as massive blood loss due to trauma, or can be used to replace blood lost during surgery...
. Accurate X-rays of the affected knee are needed to measure the size of components which will be needed. Medications such as
warfarinWarfarin is an anticoagulant. It was initially marketed as a pesticide against rats and mice and is still popular for this purpose, although more potent poisons such as brodifacoum have since been developed...
and
aspirinAspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
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
hospitalA hospital is an institution for health care providing patient treatment by specialized staff and equipment, and often but not always providing for longer-term patient stays....
one or more days before surgery.
Technique
The
surgerySurgery is a medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, to help improve bodily function or appearance, or sometimes for some other reason...
involves exposure of the front of the knee, with detachment of part of the
quadriceps muscleThe quadriceps femoris , also called simply the quadriceps, quadriceps extensor, quads, is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the great extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur...
(
vastus medialisThe vastus medialis, often called the 'teardrop' muscle, is a medially located muscle of the quadriceps.-Function:The vasti instead appear to act largely in a co-ordinated manner throughout the control of knee extension...
) from the
patellaThe patella, also known as the knee cap or kneepan, is a thick, circular-triangular bone which articulates with the femur and covers and protects the knee joint. It is the largest sesamoid bone in the human body. It is attached to the tendon of the quadriceps femoris muscle, which contracts to...
. The patella is displaced to one side of the joint allowing exposure of the distal end of the
femurThe femur, or thigh bone, is the most proximal bone of the leg in vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs...
and the proximal end of the
tibiaThe tibia, shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates and connects the knee with the ankle bones.The tibia is named for the greek aulos flute, also known as a tibia.-In humans:...
. The ends of these bones are then accurately cut to shape using cutting guides oriented to the long axis of the bones. The
cartilageCartilage is a stiff yet flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
s and the
anterior cruciate ligamentThe anterior cruciate ligament is one of the four major ligaments of the human knee. In the quadruped stifle , based on its anatomical position, it is referred to as the cranial cruciate ligament....
are removed; the
posterior cruciate ligamentThe posterior cruciate ligament is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur...
may also be removed but the
tibialThe medial collateral ligament of the knee is one of the four major ligaments of the knee. It is on the medial side of the knee joint in humans and other primates. It is also known as the tibial collateral ligament, or abbreviated as the MCL.- Structure :It is a broad, flat, membranous band,...
and
fibularThe fibular collateral ligament is a ligament located on the lateral side of the knee, and thus belongs to the extrinsic knee ligaments.- Structure :...
collateral ligaments are preserved. Metal components are then impacted onto the bone or fixed using polymethylmethacrylate (PMMA) cement. A round ended implant is used for the femur, mimicking the natural shape of the bone. On the tibia the component is flat, although it often has a stem which goes down inside the bone for further stability. A flattened or slightly dished high density
polyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging .- Description :Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene...
surface is then inserted onto the tibial component so that the weight is transferred metal to plastic not metal to metal. During the operation any deformities must be corrected, and the ligaments balanced so that the knee has a good range of movement and is stable. In some cases the articular surface of the patella is also removed and replaced by a polyethylene button cemented to the posterior surface of the patella. In other cases, the patella is replaced unaltered.
Variations
Different implant manufacturers require slightly different instrumentation and technique. No consensus has emerged over which one is the best. Clinical studies are very difficult to perform requiring large numbers of cases followed over many years. The most significant variations are between cemented and uncemented components, between operations which spare or sacrifice the
posterior cruciate ligamentThe posterior cruciate ligament is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur...
and between resurfacing the patella or not. Some also study patient satisfaction data associated with pain.
Minimally invasive procedureThere are three main categories which describe the invasiveness of surgical procedures. These are: non-invasive procedures, minimially invasive procedures, and invasive procedures ....
s have been developed in total knee replacement (TKR) to that do not cut the quadriceps femoris muscle. There are different definitions of minimally invasive knee surgery, which may include a shorter incision length, retraction of the patella (kneecap) without eversion (rotating out), and specialized instruments. There are few randomized trials, but studies have found less postoperative pain, shorter hospital stays, and shorter recovery. However, no studies have shown long-term benefits.
Partial knee replacement
Unicompartmental arthroplasty (UKA), also called partial knee replacement, is an option for some patients. The knee is generally divided into three "compartments": medial (the inside part of the knee), lateral (the outside), and patellofemoral (the joint between the kneecap and the thighbone). Most patients with arthritis severe enough to consider knee replacement have significant wear in two or more of the above compartments and are best treated with total knee replacement. A minority of patients (the exact percentage is hotly debated but is probably between 10 and 30 percent) have wear confined primarily to one compartment, usually the medial, and may be candidates for unicompartmental knee replacement. Advantages of UKA compared to TKA include smaller incision, easier post-op rehabilitation, shorter hospital stay, less blood loss, lower risk of infection, stiffness, and blood clots, and easier revision if necessary. While most recent data suggests that UKA in properly selected patients has survival rates comparable to TKA, most surgeons believe that TKA is the more reliable long term procedure. Persons with infectious or inflammatory arthritis (Rheumatoid,
LupusLupus erythematosus is a connective tissue disease. Lupus is a chronic inflammatory disease that occurs when the body's immune system attacks its own tissues and organs. Inflammation caused by lupus can affect many different body systems, including joints, skin, kidneys, blood cells, heart, and lungs...
, Psoriatic ), or marked deformity are not candidates for this procedure.
Post-operative rehabilitation
Post-operative hospitalization varies from one day to seven days on average depending on the health status of the patient and the amount of support available outside the hospital setting. Protected
weight bearingIn orthopedics, weight bearing is the amount of weight a patient puts on the leg on which surgery has been performed. It is generally described as a percentage of the body weight, because each leg of a healthy person carries the full body weight when walking, in an alternating fashion.After...
on crutches or a
walkerA walker or walking frame is a tool for disabled or elderly people who need additional support to maintain balance or stability while walking...
is required until the quadriceps muscle has healed and recovered its strength.
Continuous Passive MotionContinuous passive motion is a treatment method designed to aid in the recovery of joints immediately after trauma or surgery. CPM is carried out by a CPM device, which constantly moves the joint through a controlled range of motion, the exact range is dependent upon the joint, but in most cases...
or
CPM is commonly used, but its effectiveness is questioned. Patients typically undergo several weeks of
physical therapyPhysical therapy is a health care profession which provides services to individuals in order to develop, maintain and restore maximum movement and functional ability throughout life...
to restore motion, strength and function. Often range of motion to the limits of the prosthesis is recovered over the first two weeks (the earlier the better). At 6 weeks patients have usually progressed to full weight bearing with a cane. Complete recovery from the operation involving return to full normal function may take three months and some patients notice a gradual improvement lasting many months longer than that.
Risks and complications
The most serious complication is infection of the joint, which occurs in <1% of patients.
Deep vein thrombosisIn medicine, deep vein thrombosis is the formation of a blood clot in a deep vein...
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.
Deep Vein thrombosis
According to the American Academy of Orthopedic Surgeons (AAOS), "blood clots in the leg veins are the most common complication of knee replacement surgery. Your orthopedic surgeon will outline a prevention program, which may include periodic elevation of your legs, lower leg exercises to increase circulation, support stockings and medication to thin your blood."
Fractures
Periprosthetic fractures are becoming more frequent with the aging patient population and can occur intraoperatively or postoperatively.
Loss of Motion
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 improve post operative stiffness. There are also many implants from manufacturers that are designed to be "high-flex" knees, offering a greater range of motion.
Instability
In some patients, the kneecap is unstable post-surgery and dislocates to the outer side of the knee. This is painful and usually needs to be treated by surgery to realign the kneecap. However this is quite rare.
In the past, there was a considerable risk of the implant components loosening over time as a result of wear. As medical technology has improved however, this risk has fallen considerably. One implant manufacturer claims to have reduced this risk of wear by 79% in fixed-bearing knees. Another implant manufacturer claims to have reduced the risk of wear by 94% in mobile-bearing, also known as rotating platform, knees. Knee replacement implants can last up to 20 years in many patients; whether or not they actually survive that long depends largely in part upon how active the patient is after surgery.
Infection
The current classification of AAOS divides prosthetic infections into four types.
- Type 1 (Positive intraoperative culture): 2 positive intraoperative cultures
- Type 2 (early postoperative infection): Infection occurring within first month after surgery
- Type 3 (acute hematogenous infection): Hematogenous seeding of site of previously well-functioning prosthesis
- Type 4 (late chronic infection): Chronic indolent clinical course; infection present for >1 month
While it is relatively rare, periprosthetic infection remains one of the most challenging complications of joint arthroplasty.
A detailed clinical history and physical remain the most reliable tool to recognize a potential periprosthetic infection. In some cases the classic signs of fever, chills, painful joint, and a draining sinus may be present, and diagnostic studies are simply done to confirm the diagnosis. In reality though, most patients do not present with those clinical signs, and in fact the clinical presentation may overlap with other complications such as aseptic loosening. In those cases diagnostic tests can be useful in confirming or excluding infection.
According to a recent review the following tests can be used in the diagnosis of a periprosthetic infection.
- Conventional radiograph: Rule out other conditions such as loosening and/or osteolysis.
- Radionucleotide Imaging: Technetium-99m Sulfur imaging combined with indium-111-labeled leukocytes probably offers improved specificity than either test alone. Gallium 67 scans alone have low sensitivity for infection. FDG-PET imaging has been shown to have variable specificity and sensitivity.
- Serology: Elevated serum C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR) more than three months following arthroplasty are good screening tests.
- Cultures: High sensitivity and specificity, but only if done two weeks following antibiotic discontinuation. Gram stains have low specificity and sensitivity. The predictive value of a positive culture increases if the culture is performed in patient with high clinical suspicion, rather than a screening test.
- Joint fluid leukocyte counts: A joint fluid white blood cell count of more than 500/μl is suggestive of an infection.
- Frozen sections of implant membranes: More than five white blood cells/High power field is indicative of infection.
- Newer tests: Polymerase chain reactions involving the bacterial 16S rRNA have high rates of false positives because they can detect necrotic bacterial debris even in the absence of active infection.
None of the above laboratory tests has 100% sensitivity or specificity for diagnosing infection. Specificity improves when the tests are performed in patients in whom clinical suspicion exists. ESR and CRP remain good 1st line tests for screening (high sensitivity, low specificity). Aspiration of the joint remains the test with the highest specificity for confirming infection.
The choice of treatment depends on the type of prosthetic infection.
- Positive intraoperative cultures: Antibiotic therapy alone
- Early post-operative infections: debridement, antibiotics, and retention of prosthesis.
- Late chronic: delayed exchange arthroplasty. Surgical débridement and parenteral antibiotics alone in this group has limited success, and standard of care involves exchange arthroplasty.
- Acute hematogenous infections: debridement, antibiotic therapy, retention of prosthesis.
Appropriate antibiotic doses can be found at the following instructional course lecture by AAOS