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Knee Replacement Surgery and Beyond

knee replacement implant

Knee Replacement Surgery and Beyond

Osteoarthritis (OA) is the disease process by which the cartilage and the ends of the bones, the femur and tibia are worn down and diseased. This disease process can also occur between the femur or thigh bone and the knee cap, termed patellofemoral arthritis. Under normal circumstances the cartilage is smooth and white tissue. In diseases such as OA the cartilage has globally degenerated or developed specific defects in its surface. Healthy cartilage allows bones to glide smoothly over one another smoothly with little or no fiction. In Osteoarthritis (OA) the cartilage is degraded and, the bones are grinding together one atop the other. Osteoarthritis is a progressive joint disease characterized by joint inflammation, pain and decreased range of motion resulting in diminished quality of life. We can see success with improvements in pain and physical function from several advances in knee surgery for those with moderate to severe osteoarthritis.

Definitive treatment is available, with approximately 600,000 knee replacements performed annually with joint prostheses in the form of metal alloys, plastic and polymers. These joint prostheses behave much the same way as a healthy joint. Your orthopedist will take into account your age, activity level and general overall health in order to determine the proper prosthesis for you. Some techniques involve less invasive arthroscopic techniques using a scope passed through three small incisions and attempting to heal the diseased cartilage and are appropriate for select groups we will discuss the types of prosthetic implants used in total knee replacement as well as less aggressive surgical techniques in determining which is right for you.

First, let’s take a look at OA of the knee. Arthritis involves the femur or thigh bone, superiorly, the tibia, beneath it and the knee cap or patella. Within the knee joint it lie the medial or inside compartment and the lateral or outside compartment as well as the compartment between the femur and the knee cap or the patellofemoral compartment. OA may affect all aspects of the knee joint or may be limited to one segment. This is an important factor to consider when determining which surgical approach is best for you.

Total Knee Replacement or TKR is the gold standard of care for moderate to severe OA that has exhausted all conservative levels of treatment. Surgical treatment is indicated when more conservative treatment such as which pain medications or analgesics, physical therapy, injections and attempts at weight loss have failed. There are several varying types of surgical remedies. Let us begin discussing the varying types of total knee replacement. TKR involves a prosthetic implant which has a femoral component, a tibial component and, may or may not have a patellar component. These components are made of metal alloys, plastics and are fixed in place by specialized bone cements. The combination of these parts forms the prosthesis. The goal of all TKR is to provide optimal pain free range of motion and ultimately enhanced quality of life. There are three primary types of prostheses, all with an average “life-span” of ten years:

  • Fixed Bearing prostheses: These are most common and used more is older, less active adults. The term “fixed” refers to the plastic cushion atop the tibial component. It is firmly fixed to a metal platform base. The femoral component rolls over the cushion with movement. Overall, it offers a good range of motion and has similar durability in comparison to its counterparts.
  • Mobile bearing Implants: This device rotating platform/mobile bearing device if you are younger and more active. This device also may be right for you if you are overweight. It has the benefit of improved pivot function however, requires he support of the ligaments to avoid dislocation. These provide improved flexion after surgery though at long term follow up do not provide superior durability or improvement in function compared to fixed bearing prosthetics.
  • Medial Pivot Implants: These prosthetics are designed to mimic the biomechanical structure of the natural knee. Medial Pivot implants replicate rotting, twisting, bending and flexion of your natural knee joint. The downside, is that they are more prone to dislocation should you have any deficient strength or imbalance in your surrounding knee ligaments.

Of the three options, different prosthesis may be formed to salvage your Posterior Cruciate Ligament (PCL) or not. If the implant is to leave your PCL intact it will be structured as to contain special grooves in its architecture to allow a resting place for the PCL. The type of prosthetic implant your surgeon recommends for you will be based on his or her experience with the implant, your weight and activity level, as well as his/her expertise and comfort level. The implants may be fixed with special bone cement. Other implants are designed for the bone to grow in around them and may take a bit longer to heal completely, at least 6 weeks.

One of the primary aims of TKR is to achieve pain free activity. Some consider your ability to flex beyond 120-150 degrees a good indicator of success. Activities that require a partial squat position include toileting and exiting your car, which clearly play a part in overall satisfaction with your TKR. No one implant has been proven statistically significant over another in achieving this. The best predictor of range of motion is your preoperative range of motion. As stated most implant have a life span of ten years, after which point degradation is a risk. Like all lower extremity surgeries, there is a risk of infection, which thankfully is less than 1%. This could require removal of the implant and a protracted course of intravenous antibiotics, and subsequent replacement of a new implant. Other risks include a blood clot, or deep vein thrombosis carries about a 5% rate, and you will be placed on medication to decrease the chances of this occurring. However, development of a DVT is a possibility and this clot could travel to the lungs causing a life-threatening pulmonary embolism. Some patients will not receive a resolution in their pain, even after surgery. Late complications could include implant failure,

The expected recovery will begin with physical therapy on the day after surgery. You will likely require pain medication for some 3 months after surgery on average. You should be able to return to work once you have achieved mobility, in 3-4 weeks.

Partial Knee Replacement is an option for those patients with OA, approximately 10-20 % with disease restricted to the medial, lateral or patellofemoral compartments of the knee joint. It may be a legitimate way to “buy some time” from a full TKR, while maintaining the option of easily converting to a total knee replacement should the time come. Of course, these patients also have failed conservative therapy Location of the pain is of critical importance, the patient should be able to point exactly where the pain is. This should correspond radiographically with the OA. The cornerstone to a successful outcome are meticulous surgical technique from an experienced surgeon and appropriate patient selection if your disease is not restricted to one compartment, you will not benefit and are therefore not a good candidate. Often times a traumatic event triggered the OA in these patients, such as an accident and fracture. However, a compromised Anterior Cruciate Ligament (ACL) is a contraindication to this surgery.

A partial TKR carries with it the same postoperative risk described above with respect to infection and DVT and late complications of loosening of the hardware.. It is contraindicated in patients less than 60 years old, weight of more than 82 kg, have pain at rest or pain over the patellofemoral compartment and with a decreased range of motion “arc” of at least 90 degrees. Research suggest a similar “life-span”, with a durability of 96% at ten years, and amenable to conversion to a TNR, should the need arise.

High Tibial Osteotomy or HTO is often recommended in OA isolated to one compartment of the knee and malalignment in young athletes. Young athletes with isolated compartment OA and/or angular deformity have proven a challenge to treat in the field, however, this operative technique shows promise and may indeed be the procedure of choice. The ideal candidates are those with malalignment, and or instability with or without injury to the meniscus. Surgeons have recommended HTO as a means of redistributing the forces over the medial and lateral compartments as a means of prevention further OA. Patients will often experience pain with even little activity and stiffness is also common, and often have often experienced high velocity trauma, with ACL tear. An incision is made in the bone high in the tibia, and plates are and screws are used to correct alignment. If there is ACL pathology it may be addressed at the same time with ACL grafting. Contraindications include smoking, obesity and patellofemoral osteoarthritis, as it will not be addressed with this modality. The risk of infection and blood clot are the same as with other lower extremity surgeries discussed, at <1% and 5% respectively. Physical therapy begins with toe touch weight bearing and quadriceps isometric exercises. After 6 weeks weight bearing is advanced. 90% of patients reported excellent satisfaction scores at 5 years.

Robotic Assisted TKR: The use of technology in obtaining enhanced precision in placement of implants is the goal of robotic assisted TKR. Hypothetically, a computer is able to calculate the precise location of implantation of prosthesis. Given that incorrect alignment can result in abnormal wear and early mechanical loosening of hardware as well as patellofemoral complaints. In studies with 3D CT scanning, precision was improved and hypothetically a case could be made for superior results in the hands of a skilled technician, however more research is required before in can be stated that this modality is absolutely superior to conventional TKR It carries with it the same risk profile as traditional TKR. The complications are also the same as is the patient satisfaction, to date. Further research will tell us if it is superior to traditional TKR as the modality of choice

Cartilage restoration techniques such as knee microfracture surgery offer an alternative in that they are performed through an arthroscope, a metal tube with a camera on one end and hooked up to a video monitor. Three holes or ports are used to gain access the joint and operate. A tool is passed through the port, called an awl, which is used to make very small holes ( microfractures) in the bones adjacent to the damaged cartilage. This promotes new cartilage formation in a way of “filling the potholes” in the road of the cartilage in order for it to regain its smooth texture once again. This is a good treatment technique for patellofemoral osteoarthritis. The downside is that the “new” cartilage that is created is not as strong as our native cartilage and is more prone to degradation. This is not advised for smokers. Physical therapy begins right away, in the recovery room. The therapy is time consuming, some 6-8 hours/day. Those who benefit most are those under 40 years old, with recent cartilage or meniscal injury, with specific location and size of less than 4cm squared and, at their optimal body weight. Recovery can be slow going however, progressing over 4-6 months.

Another cartilage restoration technique involves the use of stem cells in what is termed “synthetic scaffold resurfacing” small synthetic cartilage grafts are soaked in stem cells from the bone marrow of the patient. They are then transplanted via arthroscopic technique at the sites of the damaged cartilage, to fill in the defects. Since stem cells have the unlimited potential to grow into whatever type of tissue required, being placed in this environment triggers them to grow into chondrocytes, or cartilage cells and mature over time. Some researchers feel this may be the new frontier and provide the optimal venue for repairing OA related cartilage damage. The advantage is little if any hospital stay, and recovery similar to an arthroscopic procedure such as an ACL repair.

In healing the burden of osteoarthritis our technology is advancing, from newer prostheses, advancing in surgical techniques to the use of stem cells. Each option has advantages and disadvantages making it appropriate for a subset of osteoarthritis sufferers, your surgeon will help you to determine the best course of action for you.

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