Knee Replacement Surgery
Knee replacement surgery, also known as Knee Arthroplasty, is regarded as a modern surgical procedure that can accurately be described as "knee resurfacing". This procedure entails restoring the weight bearing facade of the knee joint that is damaged, worn out, or diseased to relieve pain and movement disability. It is performed through the implant of an orthopaedic metal and plastic component shaped as a joint so that the knee can move properly.
Arthroplasty is a field of medicine which deals with the surgical reconstruction and total replacement of degenerated joints. Arthroplasty uses artificial body parts (prosthetics). Arthroplasty literally means "the surgical repair of a joint".
When the articular cartilage of the knee becomes damaged or worn out, it becomes painful - the patient finds it extremely hard to move the knee. The bones, rather than sliding over each other with the minimum of friction, rub and crush together.
If an artificial prosthesis is surgically implanted, the patient will feel much less pain, possibly none, and his knee will move properly. Replacement surgery in a damaged knee joint by placing an artificial prosthesis will alleviate pain and help better movement of the knee. Today, every year, over 600,000 knee replacement surgeries are carried out in the United States and more than 70,000 in England and Wales. Most patients are seniors - aged over 65 years.
For most patients, a replacement knee surgical procedure will last for at least 15 to 20 years, especially if cared for properly and not put under too much strain. More than 90% of people who have total knee replacement surgery experience a dramatic decrease in knee pain and a significant improvement in their ability to perform common activities of daily living.
When Total Knee Replacement Surgery is recommended?
1. Osteoarthritis
2. Rheumatoid arthritis
3. Post-traumatic arthritis, etc.
Two major types of knee replacement surgeries:
1. TKR (Total Knee Replacement) the surgery involves the replacement of both sides of the knee joint. It is the most common procedure.
2. PKR (Partial Knee Replacement)
Here, being a crucial part of our project, we shall discuss in detail only about the TKR (Total knee replacement).
Understanding Knee Morphology
The knee is one of the largest and most complex joints in the body. The knee joins the thigh bone (femur) to the shin bone (tibia). The smaller bone that runs alongside the tibia (fibula) and the kneecap (patella) are the other bones that make the knee joint.
Tendons connect the knee bones to the leg muscles that move the knee joint. Ligaments join the knee bones and provide stability to the knee:
1. The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur).
2. The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur).
3. The medial and lateral collateral ligaments prevent the femur from sliding side to side.
Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia.
Normal Knee and Arthritic knee
The above x-ray shows the two conditions of the knee. The healthy knee and the arthritic knee. As we can see in the second case the soft tissues and the cartilage that separate the two knee has worn out and the two knee surfaces are exposed to each other. They now rub against each other and this is where the acute pain arises and Total Knee Arthroplasty is recommended.
Total Knee Arthroplasty: The Surgery
TKA is performed as follows:
- The knee joint is usually approached anteriorly through a medial par patellar approach, although some surgeons use a lateral or subvastus approach.
- Bone cuts in the distal femur are made perpendicular to the mechanical axis, typically using an intramedullary alignment system (which is then checked against the centre of the hip).
- The proximal tibia is cut perpendicular to the mechanical axis of the tibia using either intramedullary or extra medullary alignment rods.
- Restoration of mechanical alignment is important to allow optimum load sharing and prevent eccentric loading through the prosthesis
- Sufficient bone is removed so that the prosthesis recreates the level of the joint line.
- Ligaments around the knee that are contracted because of preoperative deformity are carefully released in a stepwise fashion.
- Once the definitive prosthetic components have been selected, they are cemented into place with polymethyl methacrylate cement.
Alignment in total knee Arthroplasty remains a crucial factor in the function and longevity of the replacement joint. Studies demonstrate that misalignment causes increased wear of the implant and premature failure of the construct.
After the surgery alignment of the mechanical axis of the Tibia and Femur individually should align in one straight line and can have a maximum deviation of 3°-5° with the anatomical axis of the limb.
In a normal limb the mechanical load bearing axis of the Femur and that of the Tibia aligns in one straight line and that line happens to pass through the centre of the Knee.
But this is not the case in general. In most people this alignment is not found basically due to by birth deformity or deformity acquired due to an accident.
To avoid pain and increase the longevity of the prosthesis the surgeon has to achieve this alignment after the surgery.
This alignment is achieved by making the Distal Femur Cut perpendicular to the mechanical load bearing axis of the Femur and making the Tibial cut perpendicular to the mechanical load bearing axis of the Tibia.
Patient Specific Instrumentation
Patient specific instrumentation takes 15-20 min of extra surgery time as compared to TKA of a normal Knee. The extra time is consumed by the surgeon performing the surgery to figure out the mechanical load bearing axis of the Femur and the Tibia. This extra time puts the patient under lot of risk while undergoing Total Knee Replacement.
Risk of undergoing Total Knee Replacement
Risks of total knee replacement include blood clots in the legs that can travel to the lungs (pulmonary embolism). Pulmonary embolism can cause shortness of breath, chest pain, and even shock. Other risks include urinary tract infection, nausea and vomiting (usually related to pain medication), chronic knee pain and stiffness, bleeding into the knee joint, nerve damage, blood vessel injury, and infection of the knee which can require reoperation. Furthermore, the risks of anaesthesia include potential heart, lung, kidney, and liver damage.
Our Project: Helping Hand
In most of Patient Specific surgery the surgeon predicts the mechanical load bearing axis by using mechanical tools and his experience on the surgery table while operating. Besides they see very less of the knee (through the open wound) and have to predict the deformation of the entire leg. And this estimation is not very accurate. So the extra time taken to make the discussed estimation increases the chance of mishaps mentioned above.
So with this project we intend to create a 3D model of the knee joint with the help of MRI images. Helping the doctors with the 3D model of the Knee will give them a fair idea of the deformation and help them making the judgement of the mechanical load bearing axis with fairly good accuracy. And this will help them reduce 15-20 min of the operation time.