How Are the Ligaments Affected in Total Knee Replacement?

A common question regarding (also known as total knee arthroplasty) is what happens to the ligaments in the knee as a result of knee replacement?

First, it is helpful to understand the location and function of these important soft-tissue structures.  There are four major ligaments in the knee joint.  Two of these ligaments act as “side-to-side” stabilizers in the knee:  the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).  These ligaments connect the femur (thigh-bone) to the tibia (shin-bone).  They are located on the inside (medial) and outside (lateral) parts of the knee.

The other two ligaments, the anterior cruciate ligament and the posterior cruciate ligament (ACL and PCL) limit “front-to-back” or anterior-to-posterior movement of the knee.  These ligaments are named based on their attachment site on the tibia and are found roughly in the middle of the joint.  The PCL runs from the back or posterior part of the tibia to the front of the femur.  The ACL runs in the opposite way.  These ligament cross, hence the name “cruciate”.

So what happens to these ligaments as a result of total knee replacement?   The collateral ligaments (ACL and MCL) are left intact as they are important for proper function and longevity of a total knee replacement since the function of these ligaments is, for the most part, not replaced by the prosthetic components.

The ACL is removed since the portions of the bone where it typically attaches are removed and replaced by the implant components.  Often this structure is severly compromised in patients requiring total knee replacement.

What is done with the PCL is not as straightforward.  Depending on the particular patient as well as surgeon preference, the PCL may either be retained or sacrificed. Implants specific to either scenario are available for the surgeon’s use.

For more on types of implants see our section on this topic.

So in summary, in a standard total knee replacement..

  • The collateral ligaments (LCL and MCL) are preserved
  • The ACL is removed
  • The PCL is either retained or sacrificed.

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Patellar Clunk Syndrome: Complication Following Knee Replacement Surgery

In general, (TKR) is a highly successful procedure. However, complications, although relatively rare, can sometimes occur. One such complication is known as .

To understand this condition, it helps to first understand a little bit about knee anatomy and function (Figure 1). During knee flexion and extension, the patella (knee-cap) rides within a groove in the femur (thigh bone).

Knee Anatomy

Figure 1: Basic Knee Anatomy

In knee replacement the worn ends of the bones are “resurfaced” with metal and plastic implants. The patellar groove is part of the metal femoral component that is implanted onto the prepared femur during the total knee replacement procedure. At the end of this groove there is a transition between the metallic implant and the native bony surface.

Following knee replacement, scar tissue can sometimes form at the top or “superior pole” of the patella. During particularly deep flexion, this scar tissue may move below the end of the groove in the femoral component and then “catch” on the end of the groove as the patella moves back with knee extension. It is this catching and then forceful release with extension that results in the “clunk” and pain characteristic of this condition.

This condition is more prevalent in a type of knee replacement known as Posterior Stabilized, or “PS” knee replacement, although it has also been reported in Cruciate Retaining (CR) knee designs as well. 1 In PS knee designs, where the posterior cruciate ligament is removed, the patellar groove tends to be shorter to avoid contact (in extension) between the end of the groove and a plastic post on the tibial component found in these types of designs. Consequently, the patella can come off the end of the groove during lesser degrees of flexion.

The publication cited at the end of this article provides more detailed information and a review of some of the literature on patellar clunk.

1 Niikura T, Tsumura N, Tsujimoto K, Yoshiya S, Jurosaka M, Shiba R. Patellar Clunk Syndrome After TKA with Cruciate Retaining Design: A Report of Two Cases. Orthopedics. 2008: 31:90

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“Total Knee Replacement: Get it While You Can”

Each year, the American Academy of Orthopaedic Surgeons (AAOS) holds its annual meeting. This year, two presentations highlighted a pending “perfect storm”: the demand for (total knee arthroplasty) will increase dramatically while the supply of Orthopaedic Surgeons trained to do them will decrease sharply.

In a paper entitled, “Joint Replacement Access in 2016: A Supply Side Crisis,” 1 Dr. Thomas K Fehring et. al. stated that “demand for arthroplasty is expected to double in 10 years.” By 2016, this translates into an annual demand of 1,046,000 knee replacement procedures. At the same time, the expected supply of Orthopaedic surgeons is expected to fall such that if they were to work at current rates, they will only be able to perform 287,759 knee replacements, leaving many “waiting in pain”.

In a related presentation, “National Projections of Younger Patient Demand for Primary and Revision Joint Replacement,” 2 Dr. Steven Kurtz, et. al. explained the “demand side” of this equation. Overall demand for knee replacement is growing, but not just because the population is aging (i.e. a greater number of people over 65), but also because the demand for knee replacement in folks under 65 is growing as well. That is, it will become increasingly more common for folks under 65 to be total knee replacement recipients.

Hip replacement was also highlighted in both studies; however the shortfall is not estimated to be as severe. Ultimately, both papers warn that something must be done to alleviate this pending crisis.

References:

1 Odum S.M., Iorio R., Fehring T.K. “Joint Replacement Access in 2016: A Supply Side Crisis” 2009 AAOS Annual Meeting”, Poster Presentation P043

2 Kurtz S., Lau E., Ong K., Kelly, M.P., Bozic K.J. “National Projections of Younger Patient Demand for Primary and Revision Joint Replacement”, 2009 AAOS Annual Meeting, Podium No. 183

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Is One Really Better? Fixed vs. Mobile Bearing Knee Replacement

In our recent post “What’s the ‘Best’ Total Knee Replacement?” it was suggested that more often than not, it “may simply be the one which your experienced surgeon has chosen to utilize”. This sentiment was echoed in a recent publication. 1

In the January 2007 Journal of Orthopedic Surgery and Research article, the authors reviewed two major types of total knee replacements: fixed bearing and mobile bearing designs. The theoretical advantages of the mobile bearing design are discussed and the review is broken down into two main sections, a “Biomechanical Review” and a “Clinical Review” where the results of the two types of designs are compared. (See our section on Mobile Bearing Knee Replacement Here, for a brief description of this type of implant).

In the “Biomechanical Review”, laboratory testing of relative wear rates of the plastic components in each type of design is discussed. Also, studies of knee motion comparing mobile and fixed bearings implanted in both cadaver experiments and in actual patients are summarized. Here, the mobile bearing design seems to have less wear and more natural motion.

In the “Clinical Review”, the results of some earlier clinical studies are examined. In these studies, increased wear rate and subsequent osteolysis (see our section on Implant Wear) in the mobile bearing design was observed. At first, this seems to contradict the previously discussed lab studies on wear (where the mobile bearing was superior). However, as the article goes on to explain the increased wear and osteolysis can be attributed to the presence of the additional wear surface on the underside of the mobile bearing as well as to size of the wear particles. Mobile bearings tend to produce smaller particles which actually result in a greater biologic response and osteolysis. Also, the possibility of tibial insert dislocation or “spinout” in mobile bearings is discussed and some observed cases of insert dislocation are shown.

So at this point in the article, the advantage of one type of design over the other is not very clear. The “Clinical Review” continues on with a review of long term clinical results. Unfortunately, that section concludes with the statement: “So far, the theoretical advantages for mobile bearing design to provide long-term durability have not been demonstrated by any outcome study.” Long term performance simply does not help in differentiating the two designs, with both performing similarly. At the end of the day, the study concludes, (as suggested in the previous post) “For the experienced surgeon, one familiar surgical protocol and instrumentation is suggested rather than implant design, either in fixed bearing or mobile bearing.”

1. Huang CH, Liau JJ, Cheng CK: Fixed or Mobile-bearing Total Knee Arthroplasty. J of Ortho Surg and Res 2007, 2:1

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Total Knee Replacement

, which is also known as Total Knee Arthroplasty, is a surgical procedure where:

  • The worn ends of the bones which make up the knee joint are resurfaced with metal and plastic implants
  • The alignment of the bones of the knee is restored so that the weight which passes through the knee is normally distributed.

Further Reading on Total Knee Replacement:

Knee Replacement Surgery Overview

Knee Replacement Complications

Minimally Invasive Knee Replacement

Computer Assisted Knee Replacement

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