To Retain or Sacrifice the PCL…That is the Question

In the normal knee, the ligaments provide stability during movement of the joint. There are four major ligaments in the knee: the medial and lateral collateral ligaments (MCL and LCL), which provide “side to side” stability and the anterior and posterior cruciate ligaments (ACL and PCL) which provide “front to back” stability.

In total knee replacement surgery, the ACL is routinely removed, the MCL and LCL are preserved, but the PCL is either retained or sacrificed. This brings up the obvious question-is it better to retain or sacrifice the PCL in total knee replacement?

There are many reasons why the posterior cruciate ligament may be removed or retained. Both scenarios have been associated with certain advantages and disadvantages.1 In either case, the implants used have specific geometry to account for the presence or absence of the ligament.

Retaining the PCL is believed to aid in proprioception (the ability to sense where parts of the body are in relation to each other) and could make activities like climbing stairs feel more “stable” or “natural”. Also, when the ligament is maintained, it can promote more normal front to back knee motion, possible aiding in deep flexion.

The implant used in these cases (referred to as “cruciate retaining or ‘CR’) is specially designed to allow for the presence of the PCL. However, in order for the PCL to perform it’s intended function, it must be in relatively good, “healthy” condition. Also, it must be properly “balanced” after the have been oriented and implanted by the surgeon. This can sometimes be challenging and can result in less predictable results from patient to patient.

Also, just as the surgeon must balance the PCL if retained, the MCL and LCL must be properly balanced as well. This can be more difficult with the PCL intact. One can imagine that the tibia (shine bone) is like a swing rotating underneath the femur (thigh bone). The MCL and LCL are analogous to the chains or ropes holding the swing. The PCL is like a third chain coming down in the middle. It is easy to appreciate given this model, why the PCL makes creating the proper tension in the MCL and LCL more difficult since the tension in the PCL itself affects the tension in the other structures.

When the PCL is sacrificed, special geometry in the implant components substitutes for the function of the ligament. That is why these “PS” implants are sometimes referred to as PCL Substituting. When the surgeon removes the PCL, the joint space (the space between the prepared femur and tibia) becomes larger, making exposure easier. Also, the MCL and LCL tension can be more easily assessed.

Finally, since the ligament (whose function can be variable from patient to patient), is now replaced by very consistent implant geometry, results tend to be more repeatable (repeatable meaning less variation, not necessarily better overall).

So given all of this, how does long-term performance of these different types of implants and surgical approaches compare? In a recent study by Kolisek et. al., a group of patients receiving a CR implant was compared to a group with the posterior cruciate ligament removed.2 Two surgeons each did about half of the knee replacements in each group. Here is a summary of how the groups compared:

So as can be seen, and as the surgeons concluded, the study did not demonstrate a distinct advantage for one version over the other. Simply stated, PCL retention versus sacrifice is often a matter of surgeon preference and depends upon the “existing pathology of the posterior cruciate ligament” at the time of surgery. In short, the answer to the question on whether it is better to retain or sacrifice the PCL cannot be answered definitively.

References

1 Wheeles Textbook of Orthopaedics. “TKR – Posterior Cruciate Ligament Retaining Prosthesis.” http://www.wheelessonline.com/ortho/tkr_posterior_cruciate_ligament_retaining_prosthesis. Mar 2009

2. Kolisek FR, McGrath MS, Marker D, Jessup N, Seyler TM, Mont MA, Barnes CL. “Posterior-Stabilized vs. Posterior Cruciate Ligament-Retaining Total Knee Arthroplasty” The Iowa Orthopaedic Journal. Vol. 29. p 23-27.

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The Impact of “High-Risk” Sports in Knee Replacement Patients

At the recent meeting of the American Academy of Orthopaedic Surgeons, a study was presented where survivorship of total knee replacements in patients who participated in certain “high-risk” sports was compared to those who did not participate in such activities.1

In this study, a group of 1500 patients that received the identical prosthesis were asked if they participated in certain high-risk activities. These are activities which place excessive load on the implant such as basketball, soccer or football. Within this group, 218 were identified as having participated in such “high-risk” sports. These patients were then “matched” against a control group so other factors such as BMI, age and sex could be eliminated.

What the researchers discovered was somewhat contrary to conventional wisdom. At roughly 7.5 years after surgery, the high-risk group had slightly superior function and slightly lower rates of failure (loosening, wear of the implant etc) compared to the control group. As stated in the study, “At a mean follow-up time of 7.5 years after modern condylar TKA in 218 patients no significant differences in implant durability could be demonstrated between those involved in not-recommended sports activities compared to matched controls.” Only time will tell if differences in implant longevity over longer periods will become apparent, so further study is warranted. Nonetheless, as increasingly younger and more active patients elect to have total knee replacement surgery, the limits on total knee replacement design and longevity will be tested and questioned.

References
1 Parratte S, Lynn Dahm DL, Stuart MJ, Pagnano MW, Berry DJ, Does Participation in Not-recommended Sports Impact Total Knee Arthroplasty Durability, AAOS Annual Meeting Podium Presentation, 2010

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Introductory Topics

Below are Introductory Topics for those who are interested in learning more about Total Knee Replacement:

Introduction

Total Knee Replacement FAQ’s (Frequently Asked Questions)

Normal Knee Anatomy

The Diseased Knee: Osteoarthritis

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Knee Replacement Complications

(also known as total knee arthroplasty) is generally a highly successful procedure with excellent long-term results. In a recent study, 97% of patients remained “revision-free” at 10 years 1. Despite these favorable outcomes, complications may still occur. Listed below are some of the more common complications of total knee replacement surgery.

Infection

Several steps are taken to prevent infection. For example, antibiotics are often given before, during and after knee replacement surgery. Still, a small percentage of knee replacements become infected. In a recent study of over 3000 replacements, 2.9% experienced “superficial” infections while 0.8% of infections occurred within the joint. An increased rate of infection was observed in patients who experienced complex surgery or who had certain characteristics such as obesity or poor pre-operative health. 2

Loosening

Knee replacement components are affixed to the bone in two ways. In “press-fit” implants, long term fixation relies on the growth of bone into what is typically a porous surface or coating on the underside of the implant. Alternatively, the implants may be “cemented” into place with a strong polymer (PMMA) which is mixed and applied at the time of surgery. Both of these fixation methods can fail over time for a variety of reasons causing the implant to become loose and requiring revision (see Implant Poly Wear)

DVT

Deep Vein Thrombosis (DVT) is a rare but potentially very serious complication. Blood clots (thrombus) can sometimes form in the “deep” veins near the surgical site. This can cause pain, redness and swelling. Sometimes, the clot can become dislodged and travel through the bloodstream and into the lungs where it can become trapped. This is called a pulmonary embolism and can be fatal. Obviously, many, many precautions are taken to prevent this serious complication.

Patellar Clunk Syndrome

This complication involves interaction of the scar tissue at the top of the patella with the femoral component. See our article on Patellar Clunk Syndrome for more information.

Joint stiffness

Obviously, the joint will be soar and relatively stiff immediately after surgery, however, limited flexion after the immediate post-operative period is undesirable. To read more on stiffness following knee replacement surgery, visit our article joint stiffness following knee replacement surgery.

Allergic Reaction

A small number of patients may experience an allergic reaction or hypersensitivity to the metallic elements in the implants. A more detailed explanation of this complication can be found our article on this topic.

1 Barrington JW, SahA, Malchau H, Burke DW. Contemporary cruciate-retaining total knee arthroplasty with a pegged tibial baseplate. Results at a minimum of ten years. JBJS (Am.). 2009;91:874-878.

2. Jämsen E, Varonen M, Huhtala H, Lehto MU, Lumio J, Konttinen YT, Moilanen T. Incidence of Prosthetic Joint Infections After Primary Knee Arthroplasty.  J Arthroplasty.2008 Dec 3.

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Knee Replacement Allergies – Nothing to Sneeze At?

Knee Replacement Allergies – Nothing to Sneeze At?

Each year, hundreds of thousands of knee replacements are performed. In knee replacement, the worn ends of the bones that make up the knee joint are replaced with metal and plastic implants. In most cases, results are excellent, however in rare cases, an immune response may arise and can become problematic. That is, the patient may suffer from an allergy or hypersensitivity to the metallic components of the implant. Symptoms may include warmth or swelling at the knee, a skin rash and even loosening of the implant.1

This phenomenon is so rare, that its very existence has been debated. But at this year’s annual meeting of the American Academy of Orthopaedic Surgeons, a paper was presented documenting what appear to be allergic reactions to knee replacements.2 Dr. Alvin Ong et. al. recorded 19 cases from 2005-2008 where total knee replacement failures were attributed to metal sensitivity. The authors ruled out all other possible causes of implant failure and then performed a special test, the lymphocyte transformation test (LTT) which looks at a patients sensitivity to certain metals. Seventeen of the nineteen patients with failed knee replacements were tested. Ten patients recorded high sensitivity while the remaining seven indicated mild sensitivity.

Following the sensitivity testing, 16 of the patients had a second procedure where the traditional metal was removed and replaced with a non-metallic implant (the ceramic Oxinium implant from manufacturer Smith and Nephew). Following this knee replacement, the authors reported good results and elimination of the inflammation that was present with the traditional metal implant.

So although an allergic reaction to metal knee replacement implants may be rare, it is not unheard of. Unfortunately, diagnostic tests like LTT are relatively expensive and persons testing positive are not always symptomatic.1 In their article, Dr. Ong et. al. suggest that surgeons be mindful of the possibility of metal hypersensitivity especially when failures of implants are noted and cannot be attributed to other factors.

1 Rabin SI, Graf CN, Hopkinson, WJ, Hallab NJ “Immune Response to Implants.” emedicine.medscape.com. 08 Mar. 2009. <http://emedicine.medscape.com/article/1230696-overview>

2 Jafari SM, Della Valle CJ, Orozco F, Ong AC. “Metal Hypersensitivity Following Total Knee Arthroplasty: A Real Phenomenon?” 2009 AAOS Annual Meeting, Poster No. P134

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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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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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