ligament Archives - 360 Orthopaedics

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.

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.

Tag: ligament

7 Characteristics of Knee Replacement Products