Time is now October 17, 2017, 8:39 pm

Last Login from 116.93.14.3 on 2012-11-13 02:09:05

Welcome Guest User, Click Register and Post your comments

Knee replacements >> Knee Replacement Surgery Discussion >> Mobile bearing knees vs fixed bearing knees


    Thread Tools

Feb
21

Mobile bearing knees vs fixed bearing knees

admin Online Now | Location: | Joined On:
2009-02-21 17:27:51

Mobile bearing knees are to be introduced shortly. These implants will provide surgeons with extra options. Young and middle aged patients requiring a TKR will do well if a mobile bearing implants is used. The FDA has approved of the Zimmer mobile bearing knee last year. In India, it is going to be introduced in Chennai this month.
In a natural knee, the menisci move a lot during normal knee movements. The mobile bearing knee tries to replicate the natural movements of the menisci.This design has two advantages:

First: the polyethylene bearing plate has a large contact area with the femoral component during the whole range of knee joint movement. Thanks to this large contact area, the stresses on the polyethylene bearing plate are substantially lower than the stresses on the polyethylene plate in the stabile bearing total knee prostheses.

CONTACT AREAS Type of bearing Contact area (square mm)
stabile bearing 200 - 300
mobile bearing 1000 - 1500

(Orthopaedics Today, July/August 1998)

Second: The bearing plate moves free and does not restricts the natural movements of the femoral component. Thanks to the "unrestricted" movements of the plate, the stresses transmitted on the area where the total knee prosthesis is fixed to the skeleton are low and the risk for loosening of the total knee components is low too.

An additional advantage is a more natural gait pattern and a larger range of movement achieved with these total knee prostheses.
one disadvantage

1) The polyethylene mobile plate has two wearing surfaces: one is the surface opposed to the femoral component, the other one is the surface opposed to the polished tibial tray. It is as yet uncertain, how much polyethylene particles this doubling of wearing surface produces.

Who is the candidate for mobile bearing knee joint prostheses

The alleged advantages of mobile bearing knee joint prostheses are increased range of motion in the total knee and low wear of the polyethylene plate with lower risk for loosening. These advantages make this knee prosthesis suitable for young active patients.
The disadvantages of mobile bearing knee joint prostheses

The stability of the mobile polyethylene plate depends on well balanced ligaments and soft tissues around the new knee joint. The precise operation technique is essential for a good result.

The most frequent cause of failure in these prostheses is the accelerated wear, destruction, or dislocation of the mobile polyethylene plate in knees with ligament and soft tissues instability.

The discussion is still ongoing whether the "mobile" polyethylene plate really moves during knee movements, and if it moves, whether it copies the natural movements of the healthy knee parts.

Some studies also claim that the range of movement of mobile bearing total knees is not better than the movement in the conventional stabile bearing total knees. (Archibeck 2002)

4

Results

As yet there are only reports on relatively small number of operations with mobile bearing knees (unicompartmental and tricompartmental) and their results.

These reports show that between 93 and 96 % of tricompartmental mobile bearing total knees were still in function after 10 years.

Satisfaction with the operation was also high, > 90% of the patients were satisfied with the operation.

The same figure of survival applies to unicompartmental knee prostheses.

These reports also show that the postoperative range motion in the mobile bearing total knees improved for patients who have less than 90 degrees of flexion in their knee before the operation (these patients gained 28 degrees of flexion capacity), whereas the patients who had more than 105 degrees of motion before the operation lost 1 degree of motion (on average).

Radiological reports, however, shoved that up to 30 % of mobile bearing total knees have developed "radiolucent lines" around the total knee components. (Hartford 2001)

 

mobile bearing knee

mobile bearing knee


Feb
21

Mobile bearing knees vs fixed bearing knees

administrator Offline Now | Location:India | Joined On:2009-02-21 21:27:41
2009-02-21 22:03:26

yes they are good

 






<< Previous Thread | Next Thread >>

Similar Threads
Sno Topic Name Posted On Total Threads Author
1 Mobile bearing knees vs fixed bearing knees 2009-02-21 17:27:51 2 admin