Useful Facts on Knee Replacement Surgery |
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DESCRIPTION Total knee replacement (TKR) is a procedure in which the articular surfaces of the femur (thigh bone), tibia (leg bone) and sometimes the patella (knee cap), are replaced with an artificial joint. The aim is to alleviate pain, restore function and reproduce normal anatomy.
HISTORY Knee arthroplasty is not a new technology, for example in 1861; W. Fergusson was first to perform excision arthroplasty of the knee for arthritis. Verneuil a French orthopaedic surgeon in 1860s is thought to have performed first interposition arthroplasty using joint capsule. Following that various substances including skin, muscle, fascia, fat and even pig bladder used over the bone ends to form a new articular surface. In 1890, T Gluck in Berlin described a system of total knee arthroplasty using ivory. In 1940, W Campbell, successfully implanted a Vitallium interposition mold into three patients. This involved moulds to the femoral condyles. Over the next decade, tibial replacement was attempted. Both techniques were unsuccessful due to implant loosening and persistent pain. During the 1950s knee arthroplasty diverged into two theories. One theory was that of interposition surface arthroplasty, and the other was the mechanical hinge. Both theories have applications to date. In 1971, Frank Gunston recognized that the knee does not rotate around a single axis, like a hinge but instead the femur rolls and glides on the tibia, with multiple different centres of rotation through its range of motion (polycentric). The total condylar prosthesis was developed by John Insall (1953-2001) in New York. This design relied on mechanics and not trying to reproduce knee motion. This design has formed the basis of today’s knee prostheses.
ANATOMY OF THE KNEE JOINT The knee joint is the articulation between the femur (thigh bone) and the tibia (lower leg bone). It also involves two other bones, the fibula, which is to the outside of the tibia in the lower leg, and the patella (knee cap). Adding stability to the joint are the ligaments of the knee. These are the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) in the middle of the knee joint, and the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) on the inside and outside of the knee respectively. The knee also has 2 C-shaped discs of cartilage, each called a meniscus that sits in the joint between the femur and the tibia. They both add stability to the joint, and acts as a ‘cushion’ to absorb impact. There are 2 groups of muscles, which cross the knee. They are the quadriceps group to the front and the hamstrings at the back. The muscles are the prime movers for flexing (bending) and straightening out (extending) your knee. There is cartilage on the femur and the tibia where they articulate. Its function is to allow the two bones to glide smoothly on each other. In osteoarthritis, this cartilage is progressively eroded, with the end result being bone on bone contact, causing pain, stiffness and deformity later on. Osteoarthritis usually appears as a phenomenon of aging, without an initiating cause. The knees and hands are most commonly affected in females and the hips in males.
Figure 1. Anatomy of the knee
IMPLANT DESCRIPTION Knee prostheses are composed of up to 3 different components. They are typically manufactured from chromium-cobalt based alloys. A metal femoral component replaces the articular surfaces of the femur. A metal tibial component replaces the articular surface of the tibia. In between the two, a polyethylene bearing facilitates articulation between the two.
The implants may be fixed to the bones using special bone cement, or are fixed without cement, in which case they have specialized coating which promotes bone ingrowth.
Figure 2. Schematic showing a TKR in place
Figure 3. Photograph of an actual TKR showing the femoral and tibial components and polyethylene liner between the two
INDICATIONS The primary indication for TKR is severe degenerative arthritis of the knee joint. Knee replacement aims to alleviate the pain associated with arthritis including night pain, limitation in movement and later deformity. The main indication is in Osteoarthritis. Other indications include rheumatoid arthritis, osteonecrosis (death of the bone of the femoral condyle) and those with moderate osteoarthritis with a flexion contracture or significantly lax knee ligaments causing misalignment in the knee.
CONTRAINDICATIONS Absolute contraindications to TKR include knee sepsis (infection), ongoing systemic infection, extensor mechanism dysfunction and severe vascular disease. Relative contraindications include, medical conditions that preclude safe anaesthesia, skin conditions around the knee and peripheral neuropathy.
TECHNIQUE The knee is approached anteriorly through a parapatellar incision (incision made along the inner side of the knee cap). Osteophytes (abnormal growth of bone due to osteoarthritis) and the soft tissues are removed. Bone cuts are made perpendicularly to the distal femur with the aid of alignment jigs, checked before to ensure good alignment. Cuts are then made perpendicularly to the tibia again with an alignment jig. The back of the patella is also cut, if a patella is being replaced. Ligaments around the knee may need to be released to balance the forces around the knee. Implant sizes are then selected and trialed. The tracking of the patella is checked. Once the definitive implants have been selected, they are either cemented into place with a bone cement or pressed into place with the ‘press fit’ uncemented components, that are coated with a material that promotes bone ingrowth. The knee is then closed. The optimal axial and rotational alignment of the implants has been shown to be a key factor in the success of TKR. There has been significant evolution in this over the decades. Initially, implants were inserted under visual guidance only, followed by the advent of anatomical jigs, then computer navigation. The latest advance in TKR allows the creation of patient specific cutting blocks based on MRI or CT scans of their knee. This technique, called patient specific instrumentation (PSI), ensures that the cuts made in the femur and the tibia are perfectly aligned for each patient to achieve the optimal positioning of the implant and accurately reproducing the original alignment and anatomy of the knee. Figure 4. PSI system, showing the computer planning of the cutting block based on the patient’s MRIs
Figure 6. The PSI femoral and tibial components
WHAT DOES THE TOTAL KNEE REPLACEMENT PROCESS INVOLVE?
The first step starts by visiting your general practitioner, who would organise simple X-Rays of your knee including weight bearing views, which should be sufficient to diagnose arthritis in the joint and if that was the case then the GP would refer you to an orthopaedic surgeon who specializes in knee arthroplasty. The orthopaedic surgeon would confirm the diagnosis and advise you on the best management plan and if surgery is required then he would go through the informed consent with you which include all processes and pros and cons of surgery, preoperative procedures, intraoperative and hospital stay, post discharge and rehabilitation.
The preoperative stage may include a preadmission clinic where you visit another doctor who may be part of the anesthetic team. Bloods and other investigations may be performed such as electrocardiogram; chest x-ray and urine samples may be taken. Once all the investigations are done and you are given the green light for surgery then you would be giving a date and time to present to the hospital on the day of surgery and fasting from midnight before surgery.
On the day of surgery you present to admissions where the team processes your admission papers and prepare your knee site with special antiseptics.
Surgery is performed under general anaesthesia, often with a spinal anaesthetic for additional pain relief after the operation. The surgery usually takes around an hour and a half hour. After surgery you spend around an hour in recovery and then you transfer to the orthopaedic ward. Usually you leave theatre with a drain in your wound and urinary catheter inserted in your bladder.
The hospital stay on average is between three to seven days. The first day after the surgery the physiotherapists sit you in a chair for a while and the nursing staff will remove the drain. The second day post surgery the physiotherapists would help with walking and the nurses will remove the urinary catheter. During the postoperative period you will be visited by your surgeons who monitor your progress and answer any questions you have. A postoperative radiograph is taken while you are in the hospital. Once your become safe enough with mobilisation you are discharged home or to a rehabilitation facility. The decision regarding where to go is made by you and your surgeon in consultation with the physiotherapists and the nursing staff. Two weeks after surgery the wound is checked and sutures removed if non-dissolvable material is used. At around six weeks post surgery you would visit your surgeon where new radiographs of your knee are organised. In this visit usually your surgeon would give you ‘all clear’ to start driving and perform most of your normal pre surgery activities. Full recovery may be achieved between six months to one-year post surgery. You should visit your surgeon one year following the procedure then every two to five years afterwards unless any new problems arise.
COMPLICATIONS Complications are uncommon, with some complications are more common than others:
CONCLUSION
Total knee replacement has improved dramatically both in its outcomes and technique over the past four decades. There is also a very high level of patient satisfaction upto 95% of recipients of knee replacement, with significant improvements in pain and function. 97% have their implants functioning still at 10 years post surgery. Complications have also significantly declined over the past 20 years with the use of anticoagulants to reduce the rate of deep vein thrombosis and improved antibioitics to reduce infections. Improvements in the design of the implants have also reduced the incidence of implant loosening and failure.
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