View Full Version : Re: Ball and Socket Assumption

Prof. Joe Mizrahi
08-03-1996, 04:05 PM
On Wed, 31 Jul 1996, Leonard D'Addesi wrote:

> Hello to all,
> I am a masters student and my research involves locating the hip joint
> center. I have a few simple questions that I am confused about:
> 1. I discovered in the biomech-l archives that the hip joint can be
> modelled as a ball and socket joint if the centers of the femoral head
> and acetabulum are the same and the contact surface is spherical. Is
> this a good definition of the center of rotation?
> 2. Does the ball and socket model of the hip joint hold true for patients
> that have neuromuscular diseases such as CP? Has anyone done a study to
> show whether the model holds true?
> I would greatly appreciate any references. I will post a summary of
> replies.
> Thank you.


Concepts of asphericity and incongruence of the human healthy hip have been
suggested in the literature. It is believed that they help in achieving
a progressive load distribution on the contacting surfaces, and improve
lubrication within the joint. Asphericity, however renders a much less
convenient geometry to model and deals with. Nevertheless, if it can be
represented analytically this difficulty can be considerably alleviated.
Based on previously published experimental data, we have attempted to
analytically represent hip asphericity , by approximating the joint as a
tilted solid of revolution. The following two references report our results:
- Mizrahi, J The human femoral head as a tilted solid of revolution. S.
Afr. J. Science, 73, 385-386, 1977.
- Mizrahi, J An axi-symmetrical representation of the human femoral head.
The S. Afr. Mech. Eng., 28, 206-209, 1978.

Prof. Joseph Mizrahi , D.Sc.
Dept. of Biomedical Eng. Technion, Israel Institute of Technology
Haifa 32000, Israel
Phone: +972-4-8294128 Fax: +972-4-8234131
e-mail: jm@biomed.technion.ac.il