A clinical RSA study using the Symax stem

Cementless hip arthroplasty is one of the most successful orthopaedic
techniques. Still the survival of hip implants is not indefinite. One of the
causes for implant failure in loosening and osteolysis as a consequence of
particulate wear and stress shielding.
The Symax hip used in this study is designed to optimize stability, fixation
and preservation of bone stock, to prevent loosening. By way of measurements of
micromotion in the first years after implantation a long term prediction can be
made of prosthetic loosening. A very accurate way to measure micromotion is
roentgen stereophotogrammetric Aanalysis (RSA).

The goal of this clinical investigation is to assess the early migration of the
Symax stem and the precision of the RSA measurements done at this hospital.
Also clinical outcome and patient satisfaction will be assessed.

This is a prospective clinical follow up study with a group of 26 patients who
will receive a RSA Symax hip stem. The selection of a control group was not
possible since there are no RSA hip stems of comparable hip prosthesis.

The study population will get a cementless RSA Symax hip arthroplasty. To do
the symax measurements correctly a number of tantallum markers will be inserted
into the femur during surgery. This will lead to a minor lengthening of
operating time. A few days after surgery and during the follow up period
thereafter a number of RSA X-rays will be made.

During this study a number of RSA X-rays will be made. At some follow ups these
X-rays will replace the normally made X-rays to minimize the radiation load of
the patients. Patients will also be asked to fullfill two questionnaires at
regular intervals.
The measurements of early migration will benifit the patient and has to be
researched in this catagory of patients.