Overview of Knee Arthroplasty
Knee arthroplasty, more commonly known as total knee replacement, is a surgical procedure done to rebuild the knee joint. It’s a widely trusted procedure known for successful outcomes. Doctors consider it an excellent treatment for those suffering from painful osteoarthritis in at least 2 out of the 3 parts of the knee, especially when other non-surgical treatments haven’t worked. There’s also partial knee arthroplasty, a great treatment choice for people with painful osteoarthritis in just one part of their knee, again when non-surgical treatments have been unsuccessful. The main goal of both surgeries is to relieve persistent pain and improve the patient’s mobility and quality of life.
The practice of total knee replacement dates back to the late 1800s when the earliest designs used ivory for implants, securing them to the bone with a mixture of resin and plaster. Unfortunately, these early designs didn’t prove successful. By the 1930s, metal implants replaced ivory. In the ’50s, a new design emerged that replaced the femur and tibia – the two primary bones in the knee – as well as the stabilizing ligaments around the knee. While the results were satisfactory, there was a high rate of failure in the long run because this kind of replacement couldn’t accurately mimic the knee’s natural movement.
Later developments saw knee prosthetics that replicated the shape of the distal femur while preserving important ligaments, and included the use of a plastic bearing on the tibia. Since these advancements in the 1970s, the focus has been on designing implants that closely mimic the natural structure and function of the knee joint. On top of this, methods of securing the implant and improving the wear characteristics of the contact surface have also advanced, all of which have led to longer-lasting knee replacements.
Anatomy and Physiology of Knee Arthroplasty
The knee is a type of joint in your body known as a synovial hinge joint. This type of joint has a limited twisting motion and involves three key parts: the lower part of the thigh bone (distal femur), the upper part of the shin bone (proximal tibia), and the kneecap (patella). It’s made up of three separate sections: the inner section where the thigh and shin bones connect (medial femorotibial), the outer section where these bones connect (lateral femorotibial), and where the kneecap connects with the thigh bone (patellofemoral).
What makes the knee joint stable is how nicely the joint parts fit together (congruity of the joint) and some strong bands of tissue on each side of the knee (collateral ligaments). A tissue layer called the capsule completely surrounds the knee joint and extends upwards into a space above the kneecap known as the suprapatellar pouch.
The ends of the thigh bone and shin bone, the groove in the thigh bone that the kneecap slides through, and the kneecap itself, all have a special layer of tissue (articular cartilage) covering them. This cartilage helps to protect the knee joint. There are also additional protective layers of tissue called menisci, which are located in between the thigh and shin bone on the inner and outer sections of the knee.
The alignment of the knee is quite unique. The thigh bone is slightly leaned inwards (3 degrees valgus) compared to the straight up and down line of the body. The alignment of the shin bone is slightly leaned outwards (3 degrees of varus) though. This causes the top surface of the shin bone, where our body weight is carried, to be parallel to the ground. Finally, there is a backward tilt to the top of the shin bone (5 to 7 degrees posteriorly). This unique alignment helps the knee joint to stay properly positioned and the ligaments to maintain tension.
Why do People Need Knee Arthroplasty
Total Knee Arthroplasty (TKA), also known commonly as a knee replacement surgery, is an effective treatment for people suffering from persistent knee pain due to a condition called osteoarthritis, especially when other non-surgical treatments haven’t helped. It is a surgery recommended for easing pain and improving your mobility.
If your knee is significantly deformed or misshaped due to osteoarthritis, your doctor may recommend knee replacement surgery.
If you have nagging knee pain but no visible signs of osteoarthritis in your knee x-rays, your doctor will likely dig deeper to find out what’s causing your discomfort.
Common symptoms of osteoarthritis include:
– Knee pain
– Pain that increases with activity and decreases with rest
– Pain that gets progressively worse over time
– Difficulty in walking or reduced walking ability
During your doctor’s visit, expect:
– A comprehensive knee examination assessing movement and stability
– X-rays of your knee from different angles (front, side, back, and view of your kneecap)
X-ray evidence of osteoarthritis often shows:
– Space reduction between the joints
– Hardening of the bone beneath the cartilage (“subchondral sclerosis”)
– Bone cysts beneath the cartilage (“subchondral cysts”)
– Abnormal bone growths (“osteophytes”)
Before considering surgery, the following non-surgical treatments might be recommended:
– Anti-inflammatory medication
– Weight loss
– Modifying certain activities to avoid pain
– Using knee braces
– Physical therapy
– Viscosupplementation (a treatment where lubricating fluid is injected into a joint)
– Steroid injections into your knee joint.
When a Person Should Avoid Knee Arthroplasty
There are some conditions that might prevent a person from having surgery on the knee:
If someone has an active infection in the knee, or if there has been an infection in the past year, it’s not safe to have surgery. The same goes if there’s an active infection somewhere else in the body.
Another problem can be if the muscles or tendons that straighten the knee are not working properly, or if the patient is in overall poor health and not stable enough for surgery.
There are also some conditions that might make the surgery less likely to succeed or more risky, although this does not automatically mean that the surgery can’t be done:
For example, if a person has nerve damage in the joint (‘neuropathic joint’), has poor skin condition over the knee, or is very obese, they might not be a good candidate for surgery. The same is true if they struggle with obedience to their doctors because of things like mental health problems, alcohol, or drug abuse.
If there isn’t enough healthy bone to attach the new parts to (‘insufficient bone stock for reconstruction’), or if the patient is not motivated or has unrealistic expectations about what the surgery can do, it might be better to avoid surgery. If the blood vessels in the leg are severely diseased (‘severe peripheral vascular disease’), the risk of complications is higher.
Equipment used for Knee Arthroplasty
A Total Knee Arthroplasty (TKA) system, also known as a knee replacement, uses specific tools that help the doctor get your thigh bone (femur), shin bone (tibia), and kneecap (patella) ready for a new joint. The tools used are tailored to match the specific type and brand of joint replacement being used. Each type of replacement joint and each brand has its unique requirements.
Generally, the tools involved include:
- A guide for the inside of your thigh bone to properly align the lower part of the bone for the new joint
- A bone cutting guide for the lower part of your thigh bone
- A sizing guide for the new thigh bone part of the joint
- A complex, 4-in-1 cutting guide for the thigh bone part of the joint
- A guide for either the inside or outside of your shin bone
- A bone cutting guide for the upper part of your shin bone
- A sizing guide for your kneecap
- A trial or test piece for the new thigh bone part of the joint
- A trial or test piece for the baseplate of the new shin bone part of the joint
- A trial or test piece for the new button part of the kneecap
- A trial piece for the plastic spacer that goes between the new thigh and shin bone parts of the joint
The new joint pieces will all be individually packaged and kept sterile until they are needed. Here’s what you can expect:
- A thigh bone piece, usually made from a cobalt-chrome metal
- A shin bone piece, typically made of cobalt-chrome metal or titanium
- A plastic spacer for your shin bone, composed of a specialized type of plastic known as ultra high molecular weight (UHMW) polyethylene
- A kneecap button, made of UHMW polyethylene
Who is needed to perform Knee Arthroplasty?
The medical professionals involved in your surgery include a team of specialized doctors known as anesthetists, who will put you to sleep so you won’t feel any pain during the procedure. Also present in the operating room will be a nurse, who is trained to assist in surgeries and look after your wellbeing. A person called a surgical technician is also a part of the team; they handle the surgical equipment and make sure everything is prepared for your operation. Additionally, a surgical assistant will be there to directly aid the surgeon during the procedure.
Preparing for Knee Arthroplasty
Before a knee surgery, a series of steps are usually taken. First, your doctor needs to know your complete medical history including any medicines you take. This is so they can properly prepare for the surgery and avoid any potential complication. Next, your doctor will conduct a series of check-ups or “pre-surgical workup”, and will get a formal go-ahead or “clearance” for the surgery. This check-up process helps ensure your body is in good condition to recover from the procedure.
Then, your doctor will do a special type of imaging test called radiographs to get detailed pictures of your knee. These images help get a better understanding of what’s exactly going on inside your knee and can be used to plan the surgery. Doctors also determine the size of the equipment or “component” they’ll use during the surgery based on these images by a process called “templating”.
During the operation, the surgeon will have a variety of implants or artificial parts of various sizes available. This is just in case the size they estimated before the surgery isn’t exactly right and they need other sizes as options. They will also have different grades of connecting or “prosthesis constraint” options available depending on the strength that’s needed for your knee. In rare situations, where the primary artificial knee part isn’t adequate, they even have a “revision total knee replacement system” available.
In some cases, the surgeon may also use a special type of bone cement that contains antibiotics. This cement helps secure the artificial knee parts in place and the antibiotics help prevent infections after the surgery. But this is based on the surgeon’s preference, and not all patients may receive this type of cement.
How is Knee Arthroplasty performed
The main goal of Total Knee Replacement (TKA) is the same for all doctors, regardless of the tools or method they use. The differences in the process come from how the surgery is done. Below are some of the ways that the surgery can differ:
– General anesthesia versus regional anesthesia: This refers to whether the patient is entirely unconscious for the surgery (general anesthesia) or just the lower part of their body is numbed while they remain awake (regional anesthesia).
– Using a tourniquet or not: A tourniquet is a device used to control blood flow to the area the doctor is operating on.
– Standard versus patient-specific tools: This is about whether the doctor uses standard surgical tools or ones that have been specially designed based on the patient’s individual anatomy.
– Standard versus patient-specific implants: Similarly, this refers to whether the doctor uses a standard knee implant or an implant that’s been uniquely made for the patient.
– Traditional versus robotic-assisted TKA: A surgeon can manually perform the surgery (traditional) or use a robot to assist them.
– Traditional versus navigation-assisted TKA: In navigation-assisted surgeries, the surgeon uses computer assistance to guide them during the procedure.
– Traditional versus sensor-assisted TKA: This is when a surgeon uses special sensors to help with the placement of the implant.
– Measured resection versus gap balancing: These are two techniques for ensuring the implant fits properly in the knee joint.
– Cruciate-retaining implant versus cruciate stabilized implant: These are two different types of knee implants that a surgeon can use depending on what’s best for the patient’s particular situation.
– Resurfaced versus non-resurfaced patella: This is about whether the surgeon reshapes (or resurfaces) the kneecap during the procedure or leaves it in its original state.
– Cement versus cement-less (press fit) TKA: Some surgeons use a special kind of cement to secure the implant, while others rely on the pressure and fit of the implant itself.
Possible Complications of Knee Arthroplasty
There are several possible complications that could arise during or after a certain medical procedure. Here’s a list:
Firstly, Infections could happen, and these could either be on the skin’s surface or deeper within the body. Deep infections involve organs or spaces within the body, while superficial infections occur on the body surface, like the skin.
Secondly, a blood clot might form. A blood clot is a clump of blood that changes from a liquid state to a semi-solid state. Clots are helpful when they respond to injury because they can stop bleeding. However, having a blood clot in the deep veins of your body (usually in your leg), can cause serious harm.
Another complication could be a Pulmonary embolism. This is a life-threatening condition that occurs when a blood vessel in your lungs gets blocked by a blood clot that’s travelled from elsewhere in your body, commonly your leg.
One might also experience a fracture, which means the breaking of a bone. Dislocation refers to the displacement of a bone from its joint, causing the joint to lose its function. Instability indicates that the joint is moving in an abnormal way or may even dislocate.
Osteolysis may occur, which refers to the loss of bone. In the case of a medical procedure, this might lead to the loosening of an implanted component.
Unavoidable issues like pain and stiffness could also be felt. There’re instances where injuries might happen to the blood vessels (vascular injury) or to the nerves (nerve injury), which could affect the normal functioning of the body.
In summary, while doctors and surgeons take every precaution to prevent these, there’s always a slight risk of complications. It’s important to have a discussion with your doctor about these potential risks before undergoing any procedure.
What Else Should I Know About Knee Arthroplasty?
The number of people dealing with knee pain due to a condition called osteoarthritis is expected to go up. This is especially true since people are living longer and obesity rates are climbing. Both age and weight can increase the wear and tear of the soft, cushioning tissue in our joints (known as articular cartilage), especially in joints that carry a lot of our body weight. This type of damage is common in osteoarthritis.
Osteoarthritis can also occur as a secondary condition because of abnormal pressure on a joint, such as with rheumatoid arthritis or following a joint injury. To properly diagnose osteoarthritis, doctors will look at your medical history, perform a physical exam, and take x-rays of your joints.
Initially, doctors often recommend non-surgical treatments such as rest, physical therapy, and medications to manage the symptoms of osteoarthritis. Once these conservative treatments are no longer helpful, surgery might become an option.
A common surgery for osteoarthritis of the knee is a knee replacement operation (known as a total knee arthroplasty or TKA). This procedure has proven to be reliable with predictable results. Studies show that more than 85% of these knee replacements are still working well even 10 to 25 years after surgery. Most people also experience significant improvements in their pain levels and ability to move and function normally after having a knee replacement surgery.
