Which Total KNEE

WHICH TOTAL KNEE

Contents:

Material combinations for Total knee prostheses

Candidate for an Unicompartmental Knee Prosthesis

Candidate for a Tricompartmental (Total) Knee Prosthesis

"The variability of knee conditions and the myriad choices in prosthesis types make the process of selection and performing the best implantation seem impossible. Furthermore, one can easily become confused while considering all of the options." (Krackow, 2001)

Studies demonstrated that > 90% of patients wished that their surgeon should choose the appropriate model of the total knee prosthesis for them.

The majority of patients wished to have the "best" total knee prosthesis, without respect to the cost of the total knee prosthesis.

The patients also wished to discuss the decision with their surgeon.

Materials for joint surfaces:

You have not much choice when it comes to the material combinations for the total knee joint surfaces.

The reigning combination is a metallic femoral component moving against a polyethylene tibial component.

A Cobalt Chrome femoral component moving on a polyethylene tibial component produces reasonably low quantities of polyethylene wear particles.. The wear of particles from the polyethylene surface in this bearing combination is, however, still large enough to cause concern.

Two manufacturers developed ceramic femoral components. One manufacturer (Kyocera) uses alumina ceramic, the other manufacturer (oxinium- Smith&Nephew) uses oxidized metal Zirconium, which is also a ceramic surface.

In laboratory tests the ceramic-on-polyethylene bearing produced low quantities of polyethylene particles compared with the usual metal-on-polyethylene bearings. As yet, there are no reports about the long-term results of the oxinium total knee prosthesis.

The only one report on the alumina ceramic total knee comes from Japan. The authors of this report point out that these results were observed on Japanese patients and that it is known that the Japanese population has lower body weight.

For more info see also the chapters

Outline of total knee prosthesis

Materials for total knee

Polyethylene wear in total knee

and the website www.oxinium.com

Fixation of the total knee prosthesis to the skeleton

The fixation of the total knee prosthesis to the skeleton may be by means of bone cement - cemented total knee prostheses

or by direct impact onto the skeleton - cementless total knee prostheses.

Use of cementless fixation of the tibial component, according to some reports, increases the risk of total knee failure 1,4 times compared with total knees with cemented tibial components. (Robertsson 2000)

Who should have the unicompartmental knee prosthesis

The operation with unicompatmental knee prosthesis produces excellent results in very strongly selected patients. According to some reports, only 10% of all patients with osteoarthritis of the knee joint are candidates for this type of knee joint replacement.

Requirements:

Only patients with joint damage limited to only one knee joint compartment should have an unicompartmental knee prosthesis.

Only patients with intact ligaments of the knee should have an unicompartmental knee prosthesis.

Only patients without too much deformity and stiffness in the knee joint should have an unicompartmental knee prosthesis.

In practice, only patients with osteoarthritic changes in only one knee compartment as seen on the X-ray pictures are candidates for unicompartmental knee prosthesis.

Even for these patients, however, simple X-ray pictures may not be enough to assess the extent of the knee joint disease. The surgeon may be surprised by the extent of osteoarthritic changes in the whole knee not demonstrated on conventional X-ray pictures.

Studies demonstrate that only about 25 % of all patients operated on with unicompartmental knee replacements fulfilled the above requirements. In these badly selected patients about 15% of all unicompartmental knee joint prostheses failed during the ten postoperative years. (Robertsson 2000)

In carefully selected patients only 5 % of all unicompartmental knee prostheses failed during the ten postoperative years. (Svard 2001)

The advantages of the operation with unicompartmental knee prosthesis

Shorter hospital stay and shorter convalescence

normal gait and stair climbing

No problems with kneecap

Blood transfusion not needed

Lower risk of postoperative complications (risk of postoperative infection is 2,6 times lower than for operations with Total Knee Replacement)

Lower costs

Disadvantage

Risk that the osteoarthritis will develop in the non operated part of the knee and a revision operation with a total knee will be necessary.

Should patients with the disease in only one knee compartment still have a total knee replacement?

Some surgeons believe so. They argue that the failure rate of unicompartmental knee prosthesis is high and that osteoarthritis will eventually develop in the non replaced part of the knee joint.

Studies demonstrate that the higher rates of failure of unicompartmental knee prosthesis have been caused by improper selection of patients for operation. The success of the unicompartmental knee arthroplasty is also dependent on the surgeon’s experience.

The spread of osteoarthritic changes in the rest of knee joint is an infrequent cause of failure.

The most frequent cause of failure in the unicompartmental knees is the wear of the polyethylene component. It has been shown, that the wear of this component depends on the sterilization method used. Irradiation and storage in the air atmosphere are the culprits.

The surgeon should be sure that the polyethylene component of the unicompartmental prosthesis has not been sterilized by irradiation in normal air atmosphere, that it was not stored years after the sterilization, and that the component was stored in an oxygen-free atmosphere.

Who should have a tricompartmental (total) knee joint

Patients with destruction of two or all three compartments should have a total ( tricompartmental) knee prosthesis.

The surgeon together with the patient should consider the possibilities of the stabilized or cruciate retaining prostheses

and the option of mobile bearing total knee prosthesis.

For more information see the chapters

Mobile bearing total knee

Posterior stabilized total knee

5

Results of total knee surgery

The results of total knee replacement depend on many factors, such as patient's age, type of knee joint disease, use of bone cement, etc.

Pain relief

The total knee replacement is good to relieve pain as the following figures demonstrate:

Type of activity

Per cent of patients pain-free or with only "some" pain

sitting /lying down 96 %

walking on flat ground 94 %

using stairs 86 %

Satisfaction

Fifteen year after the total knee operation, 82 % of all operated on patients were still satisfied with their total knee prostheses. This figure relates only to patients who have had their original total knee still in place.

In the patient group where the original total knee failed and was replaced with a new total knee joint, only 60 % of patients were still satisfied. (Robertsson 2000)

How long will it last

In large statistics, encompassing patients with different diagnoses and different total knee models, about 1 % to 1,5 % of all operated on total knee prostheses fail annually.

That means that ten years after the operation 85 to 90% of all operated on patients are still going on their total knee prostheses.

In carefully selected patients, operated on by surgeons with extensive experience, the reported success rates are even higher. In such statistics (often encompassing less than 100 patients) there are up to 97 % of satisfied patients and 97% of their prostheses are still in function ten years after the operation.

You may wonder about longer track records than ten years. Yes there are such reports, but these followed older (>10 years old) types of total knee prostheses. And in total knee surgery, fortunately, new is better.

Large statistics demonstrate that the failure rate depends on

patient's age : young patients have had higher rate of failures

diagnosis: patients with knee osteoarthitis have had 1,3 times higher risk that their total knee prosthesis will fail than patients with rheumatoid arthritis. The patients with rheumatoid arthritis, however, have had higher risk of infection of their total knee.

use of cement fixation: patients with uncemented tibial component have had 1,4 times higher risk of total knee failure than patients with cemented tibial components

type of prosthesis: The total knee prostheses in general use have had the average rate of failure of about 1% per year. In a study over 22 400 total knee operations, the less often used and unproven models of total knee prostheses have up to three times higher risk of failure than the most often used models.

How often was the model used
(Per cent of all 22 400 operations)
Risk of prosthetic failure
increased

38 % 1,0 (reference)

2,5 % 2,3 fold

1,5 % 3,1 fold

(Robertsson 2000)

Questions

Should I have a total knee prosthesis which replaces my Posterior Cruciate Ligament (PCL) too?

Statistics demonstrate excellent results achieved with total knee designs of both types. i.e. total knee models that retain PCL and with models that replace it.

See also the chapter Posterior stabilized total knee

Should I have my patella replaced too?

The patella is an enigma to the knee surgeon because of all complications it causes after the total knee replacement. It is the major cause of pain in the total knee.

Patients who have their kneecap not replaced have more pain in front of their total knees, especially in climbing stairs and especially if they are heavier ( >82 kg).

But even the patients who have their kneecap replaced still have frontal pain in their knees.

PAIN IN THE KNEECAP
% patients with kneecap pain

Kneecap replaced 11 %

Kneecap not replaced 16 %

Patients with the kneecap replaced, however, are at higher risk of postoperative infection.

There is no universal agreement as to which design of a total knee prosthesis is best. Each surgeon selects what he believes is the best model, the model he was trained to use.

The most important consideration is that your surgeon should be totally comfortable and familiar with the surgical technique for implantation of the total knee prosthesis he / she selected for you. Each model of the total knee prosthesis needs unique operation technique and experience with unique set of instruments used with the operation. This technique can only be learned by experience with operations on many patients.

Some studies demonstrated that surgeons who perform low numbers of total knee operations have had more postoperative complications in their patients.

Questions to ask your surgeon:

What are the clinical results of this total knee implant you have chosen for my hip replacement operation?

How can I be sure that I’m getting the best available total knee implant?

Were the results of this total knee implant published? May I read about the results?

What are your personal clinical results with this total knee implant? Do you have a personal register about the results? How long back does this register reaches?

What, in your opinion, makes this implant the very best implant available for use in just my case?

May I discuss the results with other patients, operated on by you?

References:

Archibeck MJ, White RE J Bone Joint Surg-Am, 2002; 84-A:1719 - 26

Krackow J Bone Joint Surg-Am; 2002; 84-A: Supplement II, 182

Svard J Bone Joint Surg-Br;2001; 83-B:191- 194

Robertsson Thesis Lund 2000

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