Bone ingrowth

Dannywayoflife · September 27, 2011, 01:15:47 PM

As I the norm for me at the moment ( being a pre op hippy) I am almost constantly thinking about HR and devices and there design. And wondering how designs could be improved. I know both sides if the hybrid/cementless debate but something that I was wondering is why on both kinds of device there's no bone ingrowth material on the stem. Surely the more are that you fix to the better?
Surely the extra are would be of use to both designs? As a cemented device could have both cement and a little biological fixation and cementless could have more area to fix to.
Is this just me being stupid or is this an area devices could be improved?

Pat Walter · September 27, 2011, 01:59:38 PM

Hi

In most cases, as I understand, the stem is only to place the cap properly. The bone growth actually takes place inside the femur cap. They take the femur caps of devices that have failed and cut them in half to study the bone growth. I have seen a number of presentations with photos about problems that caused the failure of the cap to stay tight on the femur. I don't have photos at hand, if I can find them, I will post a few.

Dr. Gross worked with Biomet in developing a special coating inside the femur cap to help the bone growth develop in the cementless devices. If you watch the Nov. 3, 2008 video he discusses this and I have a close up of the femur cap during the interview. http://www.surfacehippy.info/doctorinterviews/grossinterview.php

The medical companies and surgeons are always working on ways to improve the devices. There are studies after studies about changes and types of devices. It boggles the mind if you follow much of it. Many of the articles are way above what I can understand and I am a mechanical engineer. It is very complicated and it takes a great deal of time, studies and tests to find out what works and what doesn't. It often takes years to see what difference a very small change makes. By then, patients could have them in their bodies and find out things are not working as well as the doctors thought. The problem is that eventually someone has to try the device inside the and wait to see the outcome. So if you don't want to take chances, stay with the device with the best track record and the surgeon that is very, very experienced.

Pat

Dannywayoflife · September 27, 2011, 02:38:22 PM

Thanks for the reply Pat. It was just the musings of a very unqualified person! :)

John C · September 27, 2011, 02:58:32 PM

Hi Danny,
I have read a number of conclusions that you do not want any bony attachment to the femoral stem, both with cemented and cementless devices. If the stem starts carrying some of the load, it shields it from the surface of the head and cap, which is where you want the load to transfer. It is somewhat similar to THRs, where they usually no longer coat the distal end of the stem for bone ingrowth, because they want the load to be tranferred as proximally as possible.