Knee replacement

Knee replacement, or knee arthroplasty, is a common surgical procedure most often performed to relieve the pain and disability from degenerative arthritis, most commonly osteoarthritis, but other arthritides as well. [ cite web|url=http://www.emedicine.com |title=Total Knee Arthroplasty |accessdate=2007-11-09 |archiveurl=www.emedicine.com |archivedate=2007-11-09 ] Major causes of debilitating pain include meniscus tears, osteoarthritis, cartilage defects, and ligament tears. [Luks, Howard J., MD, Associate Professor of Orthopedic Surgery, New York Medical College. "Frequently Asked Questions About The Knee," http://www.howardluksmd.com/about-me] Knee replacement surgery can be performed as a partial or a total knee replacement. [http://orthoinfo.aaos.org/topic.cfm?topic=A00389] 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.

Incapacitating pain from injury or arthritis of the knee that affects everyday activities -- particularly walking and standing -- is the main reason to consider knee replacement surgery. The procedures for knee replacement have changed significantly in the last few years. Surgeons now have access to improved prostheses, and it's rarely necessary any more to cut through muscle to access the knee joint for surgery. The "muscle-sparing approach" allows a surgeon to employ computer-navigated equipment to align the knee implant.

Over the last years, promising techniques have been elaborated to postpone or even prevent the need for (partial) knee replacement in the case of articular cartilage damage. These articular cartilage repair procedures help people suffering from cartilage damage to regain their mobility without having to undergo the heavy consequences of knee replacement.

Technique

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 are then accurately cut 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 may also be removed but the 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 polyethylene 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

There are many different implant manufacturers and all require slightly different instrumentation and technique. No consensus has emerged over which design of knee replacement 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 ligament and between resurfacing the patella or not. Some also study patient satisfaction data associated with pain.

Minimally Invasive Surgery is being developed in Total Knee Replacement to provide a less painful and invasive surgery for the patient. The goal is to spare the patient the large cut in the quadriceps muscle which could increase post-operative pain or lengthen disability. This type of less invasive procedure is done by using gender-specific or patient-specific knee implants that fit the knee better and more precise, and have better long-term affects on the patient.

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 total knee replacement (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, Lupus, Psoriatic ), or marked deformity are not candidates for this procedure.

Pre-operative preparation

Knee Arthroplasty is major surgery. 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. 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.

Post-operative rehabilitation

Protected weight bearing on crutches or a walker is required until the quadriceps muscle has healed and recovered its strength. Continuous Passive Motion or CPM is commonly used, but its effectiveness is questioned.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. Usually full range of motion 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

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."

Periprosthetic fractures are becoming more frequent with the aging patient population and can occur intraoperatively or postoperatively.

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.

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.Fact|date=August 2007

Infection

The current classification of AAOS divides prosthetic infections into four types. cite journal |author=Leone JM, Hanssen AD |title=Management of infection at the site of a total knee arthroplasty |journal=Instr Course Lect |volume=55 |issue= |pages=449–61 |year=2006 |pmid=16958480 |doi=]
* 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. cite journal |author=Bauer TW, Parvizi J, Kobayashi N, Krebs V |title=Diagnosis of periprosthetic infection |journal=J Bone Joint Surg Am |volume=88 |issue=4 |pages=869–82 |year=2006 |pmid=16595481 |doi=10.2106/JBJS.E.01149]

* 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.cite journal |author=Spangehl MJ, Masri BA, O'Connell JX, Duncan CP |title=Prospective analysis of preoperative and intraoperative investigations for the diagnosis of infection at the sites of two hundred and two revision total hip arthroplasties |journal=J Bone Joint Surg Am |volume=81 |issue=5 |pages=672–83 |year=1999 |pmid=10360695 |doi=]
* Cultures: High sensitivity and specificity, but only if done two weeks following antibiotic discontinuation. Gram stains have low specificity and sensitivity. The predicitive 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.cite journal |author=Corless CE, Guiver M, Borrow R, Edwards-Jones V, Kaczmarski EB, Fox AJ |title=Contamination and sensitivity issues with a real-time universal 16S rRNA PCR |journal=J. Clin. Microbiol. |volume=38 |issue=5 |pages=1747–52 |year=2000 |pmid=10790092 |doi=]

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. cite journal |author=Segawa H, Tsukayama DT, Kyle RF, Becker DA, Gustilo RB |title=Infection after total knee arthroplasty. A retrospective study of the treatment of eighty-one infections |journal=J Bone Joint Surg Am |volume=81 |issue=10 |pages=1434–45 |year=1999 |pmid=10535593 |doi=]

#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. cite journal |author=Chiu FY, Chen CM |title=Surgical débridement and parenteral antibiotics in infected revision total knee arthroplasty |journal=Clin. Orthop. Relat. Res. |volume=461 |issue= |pages=130–5 |year=2007 |pmid=17438469 |doi=10.1097/BLO.0b013e318063e7f3]
#Acute hematogenous infections: debridement, antibiotic therapy, retention of prosthesis.

Appropriate antibiotic doses can be found at the following instructional course lecture by AAOS cite journal |author=Leone JM, Hanssen AD |title=Management of infection at the site of a total knee arthroplasty |journal=Instr Course Lect |volume=55 |issue= |pages=449–61 |year=2006 |pmid=16958480 |doi=]

Controversies

The minimally invasive approach to surgery is controversial. Opponents say that surgery is made more difficult without altering the long-term prognosis. They suggest that more technical errors will be made particularly during the "learning curve" when the surgical team is less familiar with the procedure. They also say that the procedure is not backed by clinical results.

Proponents, however, say there are significant benefits for patients. The smaller incision in the knee causes less trauma to the underlying muscles and soft tissue in the joint. Post-surgery pain is thus reduced, with patients able to return sooner to physical activity. [http://howardluksmd.com/lessinvasive/]

We still do not know whether cemented or uncemented components last longer in the knee. Many surgeons cement the tibial component, but opinion is divided about the femoral component. Sacrifice of the posterior cruciate is also controversial, with some surgeons performing this routinely and others trying to preserve as much normalcy as possible.

Resurfacing the patella is also subject to scrutiny. Some studies have suggested that there is no advantage to resurfacing the patella. However, many surgeons continue to do this because resurfacing the patella during a later procedure is often necessary.

There are many different components designed for total knee replacement. Studying the results of one design versus another is expensive, time-consuming and relatively unrewarding -- because designs change frequently and may be withdrawn by the time a reliable long-term study has been completed. Many nations, led by Sweden, have set up registries of joint replacements with voluntary or mandatory reporting of the components and techniques used. These registries may yield information about the outcomes of different designs.

New research by Dr. Robert Litchfield, September 2008, of the University of Western Ontario concluded that routinely practiced knee surgery is ineffective at reducing joint pain or improving joint function in people with osteoarthritis. The researchers did however find that arthroscopic surgery did help a minority of patients with milder symptoms, large tears or other damage to the meniscus — cartilage pads that act like shock absorbers between upper and lower leg bones. [ [http://www.cbc.ca/health/story/2008/09/10/knee-surgery.html Therapy for arthritic knees often as effective as surgery: study] ]

Implant loading

For understanding normal and pathologic knee function knowledge of forces in the knee joint is essential. It forms the basis for joint replacement surgery, for optimizing implant design and fixation and for improving and verifying analytical biomechanical models of the knee joint. With instrumented knee implants [In vivo measurements with an instrumented knee joint at the [http://jwi.charite.de/en/research/instrumented_implants/knee_joint/ Julius Wolff Institut, Charité - Berlin] ] developed at the "Julius Wolff Institut" (Charité Berlin) the knee joint forces and moments can be measured in vivo during different activities. Six strain sensors and an inductively powered telemetry transmitter inside the tibia component of the knee joint measure the load components an transmit the data to an external computer system. First results show that the knee joint is heavily loaded. During walking the resultant force is typically about 250 % of the body weight (BW). Going downstairs the knee joint is even loaded with up to 350 %BW.

History

Following John Charnley's success with hip replacement 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.

ee also

* Autologous chondrocyte implantation
* Microfracture surgery
* Autologous Mesenchymal Stem Cell Transplant for Cartilage Growth

References

13.Design of an artificial high flexion knee Sudesh, S; Mathew, Lazar; Life Science Systems and Applications Workshop, 2007. LISA 2007. IEEE/NIH 8-9 Nov. 2007 Page(s):112 - 115

14.Modelling an artificial knee for customized needs of Indian population Sudesh Sivarasu & Lazar Mathew, INCOB-08, VITU, Feb 6-8, Pages 138-139

External links

* [http://www.oxfordclinic.org.uk/education-research/knee/OxfordPartialKnee.php Information for patients - Partial Knee Replacement]
* [http://www.oxfordclinic.org.uk/education-research/knee/PatellofemoralResurfacing.php Information for patients - Patellofemoral Knee Resurfacing]
* [http://www.oxfordclinic.org.uk/education-research/knee/OxfordClinic-TotalKneeReplacement.php Information for patients - Total Knee Replacement]