ortho Archives - 360 Orthopaedics

Could Your Knee Replacement Fail?

Failure is a strong word, especially when it comes to your health. However, a total knee replacement (TKR), just like a healthy knee joint, can “fail” over time. It is important to know about primary and revision total knee replacement as well as reasons why your implant could fail and the possibility of a revision surgery in the future.

Primary: A TKR surgery for the first time on your knee joint.

Revision: A TKR surgery after a primary TKR has already been performed on the same knee joint.

Knowing the difference between a primary and revision TKR is important for patients to know. A healthy lifestyle will help patients avoid revision surgery and the consequences that may arise if revision is needed. Primary surgery is more straightforward and you can learn additional information about primary total knee replacement. Complications may lead to serious questions if revision TKR is needed to correct the primary surgery. Following are two reasons a revision TKR may be needed.

Implant wear is a normal process that can gradually take place over many years after a primary TKR is performed. Just like in a healthy knee joint, knee implants are liable to normal wear, which may require a revision TKR. This wear and tear may include the implant loosening away from the bone. The cause of loosening is not always clear, but high-impact activities, excessive body weight, and wear of the plastic spacer between the two metal components of the implant are all factors that may contribute.
Infection is a risk factor for both primary and revision TKR, although the risk of infection is slightly higher after a revision than after the primary surgery. According to the American Academy of Orthopaedic Surgeons, a revision TKR due to infection can be handled via different methods including:

Debridement: In some cases, the bacteria can be washed out, the plastic spacer can be exchanged, and the metal implants can be left in place.

Staged Surgery: In other cases, the implant must be completely removed to treat the infection. Your doctor will perform the revision in two separate surgeries. In the first surgery, the surgeon will remove the implant and place a temporary cement spacer in your knee for several weeks, which is treated with antibiotics to fight the infection. When the infection has been cleared, the surgeon will perform a second surgery to remove the cement spacer and insert a new implant. In general, removing the implant leads to a higher chance of curing the infection, but is associated with a longer recovery.

There are different types of revision surgery. In some cases, only one component of the implant must be revised. Other times, all three components—femoral, tibial, and patellar—need to be removed or replaced. When a primary implant is exchanged for a new implant during a revision TKR, there are differences in the implant shape, most notably the length of the stem on the metal components. The extra length of the stem provides increased stability for the patient after the revision TKR is performed.

According to a 2011 study titled “International survey of primary and revision total knee replacement” the average rate of combined primary and revision TKR surgery worldwide was 175 procedures/100,000 population while the average rate of revision TKR was 15 procedures/100,000 population.

Although it is unlikely to undergo a revision TKR, it is important to strive to live a healthy lifestyle every day, which will make preparing for either a primary or revision TKR much easier. Taking pride in a healthy lifestyle is especially important after you undergo a primary TKR in order to avoid a revision surgery as much as possible. Be sure to always consult a doctor when considering medical treatment, such as primary or revision total knee replacement, to discuss specific knee implants, treatment, and rehab.

7 Characteristics of Knee Replacement Products

Note: This article contains many anatomical terms that were identified in a previous article, “What is Total Knee Replacement.”

Many orthopedic device manufacturing companies exist, and many of them design and produce unique total knee replacement (TKR) products. The unique characteristics of each implant set it apart from other models within the company and within the industry. This article will identify 7 characteristics of knee replacement products and define terminology to explain the different products.

Fixed Bearing and Mobile Bearing

1. The fixed bearing implant is a more traditional type of knee implant that is designed with less active patients in mind. This implant is termed “fixed bearing” because the plastic surface is “fixed” into the tibial component, only allowing for front-and-back knee movement, meaning the implant is not designed to allow for pivoting or twisting movement about the knee joint.

2. The mobile bearing implant is a more complex design that is made for more active patients. It is termed “mobile bearing” because the plastic surface is attached to the tibial component in a way that allows for pivoting and twisting of the knee joint, in addition to the standard front-and-back movement. This additional mobility results from the ability of the plastic to move on the tibial surface.

Fixation

Perhaps the most important characteristic of a knee implant is how the metal components adhere to the bones for fixation. There have been many product recalls in the orthopedic device world regarding this issue. The metal components can be attached to the bones in one of two ways: with cement or without.

3. The most common method of attachment is to use bone cement as a glue to properly adhere the metal to the bone. If the cement does not adhere properly, the metal components may become loose, which could cause severe pain along with a dysfunctional knee.

4. Advancements in material properties have led to the development of a cementless system of fixation. The special material used on these implants is a type of porous metal. Porous metal has holes (pores) in it that allow the bone to grow into the metal for proper attachment. Again, if the bone does not properly grow into the metal component, it may become loose; leading to pain and dysfunction.

Fate of the Ligaments

Additional characteristics regard the outcome of the ligaments of the knee. The medial collateral ligament (MCL) and lateral collateral ligament (LCL) are generally kept during the operation, so the discussion of whether to keep or remove the knee ligaments centers around the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL).

5. The traditional way of dealing with the ACL and PCL is to remove them, which would be called cruciate sacrificing. As discussed previously, the ligaments help to stabilize the knee joint, allowing for pivoting and twisting movements; once these ligaments are removed, pivoting and twisting becomes more difficult.

6. Through scientific advancements, a method for keeping the PCL has been developed in some models of knee implants; these models are called cruciate retaining. In some knee implants, a method has been developed to keep both the ACL and PCL during the operation; this model implant is termed a bicruciate retaining model.

7. Lastly, another type of knee implant is called posterior stabilized. This implant procedure removes both the ACL and PCL, but the implant is designed to mimic the actions of the PCL, which will stabilize the movements that would normally be stabilized by the PCL.

Conclusion

In this article, the main characteristics of total knee replacement products were identified. This includes fixed bearing, mobile bearing, cemented, non-cemented, cruciate sacrificing, cruciate retaining, bicruciate retaining, and posterior stabilizing.

Without being informed and asking your orthopedic physician the right questions, you could end up with a fixed bearing, cemented knee implant and your ligaments (ACL and PCL) removed without even knowing. Not that this type of implant would be harmful to you, but when considering a TKR, you should be aware of the options available to you and which models would best suit your lifestyle. Read here about shopping for knee replacement.

Always consult a doctor to discuss specific knee implants along with their characteristics and functionalities. The appropriate knee implant system for you should be chosen in accordance with your doctor.

3 Considerations when Preparing for Total Knee Replacement

Total knee replacement (TKR) is an orthopedic surgical operation that can enhance people who may suffer from knee pain. Read here for more information about the total knee replacement surgical operation. Although TKR helps thousands of people every year, candidates for TKR should be prepared for the surgery in order to improve outcomes.

Most TKR candidates suffer from knee pain and a decrease in the range of motion of their knee joint. If someone suffers from these obstacles, they may be interested in a TKR operation; but not all patients that are interested may be good candidates. Although an interested patient may face difficulties in everyday life, they must be as healthy as possible to undergo a TKR operation. There are a few health considerations an orthopedic surgeon will investigate to determine if a patient is a good candidate for a total knee replacement. These considerations are included in the current health of the patient as well as past medical experiences.

A patient may be interested in surgery to increase the flexion of their knee joint.
Degrees of knee flexion (image from Military Disability Made Easy)

The standard normal flexion of a knee joint is 120 degrees, although many daily activities may require flexion beyond that. Surgeons may expect patients to flex their knee reasonably well pre-surgery (roughly 100-120 degrees). This will enhance the patient’s probability of achieving maximum flexion after the surgery.
A key characteristic when considering a total knee replacement is the pre-surgery stability of the patient’s knee. This primarily concerns the health of the ligaments and cartilage in the patient’s knee joint. If the patient has previously torn a ligament or has undergone a ligament reconstruction surgery, it may inhibit the patient’s ability to recover as quickly as possible after the surgery, meaning post-surgery rehab may take longer.
Another characteristic considered by orthopedic surgeons is the overall health of the patient. The Body Mass Index (BMI) of the patient is an important consideration for the surgeon. An orthopedic surgeon may consider overall health factors such as diabetes, obesity, and any previous illness or disease of the patient. These are important considerations because if the patient is obese or has an illness, complications such as infection may arise after the surgery. If a patient is faced with a complication after surgery, they may have to undergo a revision surgery to correct the knee replacement. Completing a revision surgery is not an easy task for the healthcare team or the patient, so an effort must be made to avoid a revision. With today’s technology and medical practices, infections are not likely during a TKR, but all precautions must be taken seriously.

These are some general considerations of orthopedic surgeons when considering candidates for total knee replacement. If you feel you do not meet some of the considerations, do not consider yourself a “bad candidate.” If you are as healthy as possible before your total knee replacement surgery, your life should be much easier as you rehab after the surgery. Be sure to always consult a doctor when considering medical treatment, such as total knee replacement, to discuss specific knee implants, treatment, and rehab.

What is Total Knee Replacement?

Total knee replacement (TKR), also known as total knee arthroplasty (TKA), is an orthopedic surgical operation in which artificial implants are placed in a patient’s dysfunctional knee. The artificial parts in this type of joint reconstruction include metal and plastic that are meant to mimic the function of a healthy knee joint.

Knee Anatomy

A healthy knee joint is comprised of bones, cartilage, and ligaments. The bones of the knee joint include the femur (thigh bone) and tibia (shin bone). The ends of these two bones meet in the knee joint. The end of the tibia (shin) is flat and the end of the femur (thigh) is round. A cartilage structure, called the meniscus, sits on tibia to provide a cushion between the bones. Likewise, a cartilage structure, called articular cartilage, can be seen on the end of the femur, also providing a cushion between the bones.

Front view of a healthy knee joint (image from American Academy of Orthopaedic Surgeons)

The four ligaments in a healthy knee joint include the Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL), and Lateral Collateral Ligament (LCL). The LCL is on the outer side of the knee and the MCL is on the opposite side. The ACL and PCL are in the middle, between the tibia and femur. These ligaments provide stability so the knee can function properly while a person does things like walk, run, squat, and pivot. Without ligaments, the round femur sits on top of the flat tibia, which, as you can imagine, would be unstable.

What’s in a Total Knee Replacement

A total knee replacement procedure typically takes place when someone experiences chronic knee pain. Knee pain can arise after many years of active living, causing the cartilage in the knee to wear down. Damaged cartilage leads to no cushioning, which causes bone-on-bone interaction in the joint. Bone-on-bone interaction causes severe pain in the knee, especially when trying to participate in activities; even activities as simple as walking.

The important thing to remember about the components of a healthy knee (bones, cartilage, and ligaments) is that they provide structure and stability in order for a person to live a pain-free lifestyle. Any damage or hindrance to any of these knee structures can prevent a person from the life they want.

As mentioned previously, a reconstructed knee joint includes artificial parts made of metal and plastic. The artificial tibial (shin bone) component is a metal tray that sits on the end of the tibia. The artificial femoral (thigh bone) component is a metal “cap” that is placed on the end of the femur. The ends of the bones will be cut specifically so the metal parts can properly fit in place. The cartilage components of the knee will be replaced with a plastic piece between the two metal components. The new plastic piece will provide a cushioning. The ligaments of the knee joint may be removed, depending on the type of implant the patient receives. For more information about special characteristics of total knee replacement, read 7 Characteristics of Knee Replacement Products.

Someone may be a candidate for TKR if they struggle to live pain-free because of a dysfunctional knee. The candidate may find that pain is an obstacle when trying to complete activities such as walking, squatting, kneeling, and pivoting. If someone is hindered by their current knee function, they may be able to improve their quality of life after total knee replacement. Be sure to always consult a doctor when considering medical treatment, such as total knee replacement, to discuss specific knee implants, treatment, and rehab.