Ph.D.,Dept. of Orthopaedic Surgery, Faculty of Health Sciences, University of the Witwatersrand, 2009. / Total hip replacement (THR) is an effective method of treatment for patients with hip
disability. The procedure is capable of providing long-term functional improvement
with excellent control of pain and restoration of function. Sir J Charnley developed a
concept of low friction arthroplasty, which was based on use of ultra-high molecular
weight polyethylene acetabular and stainless steel femoral components. The
components were attached to bone with the use of polymethylmethacrylate (PMMA)
bone cement. This concept has been very successful, and is considered the gold
standard of THR.
Aseptic loosening of the prosthetic components remains the single most important
reason for failure of THRs. Wear to the ultra high molecular weight polyethylene
(UHMWPE) acetabular cup is a well-known cause of osteolysis and aseptic loosening
of the components. Thus, substantial improvement to the wear resistance of
UHMWPE could extend the clinical life span of total hip replacements. In an attempt
to reduce polyethylene wear and subsequent osteolysis, a method was developed in
the early seventies in South Africa to improve polyethylene quality by means of
gamma ray cross-linking. The acetabular cup was irradiated with 100 Kilogray in an
acetylene environment, which was used as a cross-linking gas material, resulting in
improvement of UHMWPE wear resistance.
Influenced by the world trend and with the advent of a ceramic bearing surface, the
Project of cross-linking was, to a certain extent, forgotten. Patients followed up in the
late 1990s, showed minimal or total absence of wear after 15 years or longer.
3
Based on my preliminary studies, and anticipating the world trend of acceptance of
cross- link UHMWPE, the aim of this research is to consolidate the results from the
largest long term group of patients with acetylene cross-link UHMWPE, to study
polyethylene gamma irradiated in the presence of a cross-linking acetiylene gas and
the effects of it, in vitro, using a hip simulator. I was planning to communicate with as
many patients as possible from the group operated on from 1977 until 1983 in whom
cross-link UHMWPE was used. This group of over thousand patients represents the
largest group of patients with cross-linked UHMWPE acetabular components in the
world, with the longest clinical follow up of over 20 years on average.
The first part of the research is a retrospective study:
The goal was to contact as many patients as possible who were operated on during the
period 1977 to 1983 when cross-linked polyethylene was used. To qualified for the
study each patient had to have an early postoperative and the latest follow up
radiograph.
The radiological study consisted of the radiological measurement of wear. For this
purpose the Hip Analysis Suite program was used. This is a software program
designed by Dr John M. Martell from the University of Chicago, which is widely used
and internationally accepted for
that purpose. Image analysis offers significant improvements in reproducibility and
accuracy when compared to manual analysis.
4
The final results were compared with results of polyethylene wear in patients in
whom conventional UHMWPE was used. For this comparison only patients with
acetabular components made from the same UHMWPE material and from the same
supplier were used. The conventional UHMWPE is a component of the gold standard
of hip replacement surgery. World-wide published follow up studies of 15 years and
longer using conventional UHMWPE were compared to the cross-link UHMWPE
group.
If revision surgery was indicated for whatever reason in patients in with cross-linked
UHMWPE acetabular components, the retrieved prosthesis was analyzed. The
analysis consisted of examination of the articular surface of the cross-linked
acetabular component for micro wear phenomena using a Scanning Electron
Microscope (SEM). In order to perform an objective analysis of the retrieved
components, two independent laboratories were used, namely:
Peterson Tribology Laboratory, Loma Linda University, California, and
Biomechanical Laboratory, Faculty of Engineering, University of Pretoria.
The analyses were possible thanks to collaboration with Dr Ian Clark from Peterson
Tribology Laboratory and Dr NDL Burger in charge of the Biomechanical Laboratory
at the Department of Engineering, University of Pretoria
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/7382 |
| Date | 21 October 2009 |
| Creators | Cakic, Josip Nenad |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf, application/pdf, image/jpeg, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf |
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