Surgeons are constantly looking for ways to improve a surgery. Total knee replacements have morphed over the years to become less invasive and improve recovery times. A new style of total knee replacement surgery is emerging that doesn't replace any ligaments. Traditional surgeries replace one or two out of the four knee ligaments.
Depending on the type of surgery you have, two or fewer of the four ligaments in your knee may be removed.
Knee Joint Ligaments
The knee works like the hinge of a door. Your big thigh bone, called the femur, meet the smaller shin bone, called the tibia, at the knee joint. The femur sits in the tibia and glides smoothly if the knee is working normally. While there is some twisting of the knee as you move, it's mostly a unidirectional joint.
Other than bones and cartilage, your knee has ligaments to hold it in place. Ligaments are tough, thick bands of connective tissue that connect bone to bone. They're different from tendons, which connect muscle to bone. Ligaments have to be incredibly stiff to keep your knee intact.
Medial Collateral Ligament
Each of the four ligaments in your knee does an important job. On the left and right side of the knee are the collateral ligaments. The medial collateral ligament (MCL) runs along the inside of your knee. It prevents your knee from buckling in towards the center of the body.
Lateral Collateral Ligament
The lateral collateral ligament runs along the outside of your knee and prevents it from moving too far out. Without the MCL or LCL your knee will feel wobbly, especially if you do a side-to-side cutting motion. Thankfully, neither the MCL nor the LCL are removed during a total knee replacement surgery.
However, on rare occasions, the MCL can be damaged during surgery. A 2017 study published in Medicine says that this is a rare occurrence, so there's no need to be worried. If it happens, the surgeon can repair your MCL and your knee may only be slightly affected.
Anterior Cruciate Ligament
The cruciate ligaments are the ligaments you need to be aware of if you're getting a total knee arthroplasty. Your anterior cruciate ligament, also called the ACL, is the most well-known. Many athletes injure this ligament when they stop suddenly or cut to one side or the other.
Running from the top, inside part of your shin bone to the bottom, outside part of your femur, the ACL connects the two bones at an angle. It's mostly used to stop your shin bone from sliding out from under your femur. That's why many athletes injure the ligament when they stop violently.
It also prevents the knee from bending too far forward or backwards, according to an article from the University of Missouri-Columbia. Along with the posterior cruciate ligament, the ACL keeps your knee centered as it bends and straightens. You could say that they both act as guides for your knee joint.
Posterior Cruciate Ligament
The posterior cruciate ligament runs up the back of your knee from the top of your shin bone to the bottom of your femur. It's short but very strong and isn't injured as frequently as the ACL. Since it's at the back of your knee, the PCL prevents the knee from hyperextending too far. It also prevents your shin bone from sliding backwards when your knee is bent.
Total Knee Replacement Procedure
Cartilage may wear down, which results in bone-on-bone contact in your knee. When your bones rub together, they're slowly damaged and cause more pain. Putting a smooth metal surface over the bones or replacing a part with smooth plastic can get rid of your knee pain.
Depending on the type of surgery you have, both the ACL and PCL may be removed. This is known as a posterior-stabilized design, according to an article from OrthoInfo. Since the PCL is removed, the new device has to have its own way of preventing hyperextension of the knee.
To prevent this, the new knee has to have a locking mechanism that prevents it from moving too far. The posterior-stabilized design has its own locking mechanism, which prevents it from extending too far. It also prevents the femur sliding forward on the shin bone.
Another design, the cruciate-retaining design, lets you keep your PCL but removes your ACL. This device has a built-in groove where the PCL can sit comfortably. This design will work if your PCL is healthy enough to keep stabilizing your knee joint.
Only one type of total knee replacement lets you keep both the ACL and PCL. It's called the bicruciate-retaining design because you get to keep both ligaments. The point of this style of knee replacement is to keep the movement of your knee feeling as natural as possible. However, the procedure is still relatively new and is still being perfected.
A 2016 study in the American Journal of Orthopedics shows that the bicruciate design is better for patient satisfaction. However, doctors admit that the surgery is more difficult than a more traditional approach. A study published in 2018 in the Journal of Arthroplasty confirms that patients are happier with the bicruciate-retaining design than designs that remove one or more ligaments.
A 2018 paper published in Orthopaedic Proceedings explains that the bicruciate-retaining design initially didn't work because the prosthetics used fell apart. However, the article says that there are new and improved designs that are more promising.
There is an option for knee replacements that doesn't require replacing the entire knee. It's called a unicompartmental implant, and it only replaces the parts of your knee that are damaged or worn away. For that reason, the surgery is much less invasive and ligaments don't need to be removed. However, if you need a total knee replacement, this isn't an option.
- Medicine: Clinical Outcomes of Medial Collateral Ligament Injury in Total Knee Arthroplasty
- University of Missouri-Columbia: Anterior Cruciate Ligament
- Hopkins Medicine: Knee Replacement Surgery Procedure
- OrthoInfo: Knee Replacement Implants
- American Journal of Orthopedics: The Cruciate Ligaments in Total Knee Arthroplasty
- Journal of Arthroplasty: Modern Day Bicruciate-Retaining Total Knee Arthroplasty: A Short-Term Review of 146 Knees
- Orthopaedic Proceedings: The Bi-Cruciate Retaining Knee: A Bridge Too Far - Opposes
- Harvard Health Publishing: Posterior Cruciate Ligament (PCL) Injuries