The year 2010 will see two major milestones for the
Exeter Hip Replacement (Stryker): The 27th of November will be
the 40th anniversary of the first Exeter hip stem implant in a patient; and the
millionth patient, somewhere in the world, will receive an Exeter stem.
The Exeter stem was conceived through collaboration
between Robin S.M. Ling, OBE, MA BM (Oxon), Hon DSc, FRCS, Hon FRCSEd, an
orthopaedic surgeon at the
Princess Elizabeth Orthopaedic Hospital in Exeter, U.K., and
Clive Lee, PhD, a young engineer at the University of Exeter. The collarless
polished tapered cemented hip stem that they designed was unlike any other at
Although Ling and Lee are the first to insist that
serendipity played a significant part in the original design, we now understand
that the remarkable long-term success of this stem is due to this polished
tapered design with its ability to behave like a wedge or self-locking taper.
Because it is polished and collarless, it is free to subside at the stem-cement
interface. The wedged, tapered shape, which is wider proximally than distally,
allows for self-locking and the preferential transmission of loads to the
proximal femur (the
taper slip principle).
Its design was totally contrary to the existing
philosophy for cemented stem fixation at the time — namely to try to bond
the stem as solidly as possible to the bone cement, often by using a collar and
texturing or pre-coating the stem. The Exeter, conversely, is polished and
deliberately not bonded. Rather, it is free to micro-subside at the stem-cement
interface and thus act as a self-locking taper, effectively and continually
tightening step by step throughout the life of the hip. Long-term studies have
shown that this process continues, micron by micron, to a total of 1 mm to 2 mm
over 30 years.
Ling and Lee observed their patients closely and
insisted that the stem only be used in Exeter under their direct supervision
for the first 5 years. There were some early problems associated with the
relatively weak steel that the stem was then made from; therefore, in 1975 the
stem was made heavier in section and from stronger steel. At that time it was
not appreciated how critical the polished surface was to the function of the
stem, and so for cost and fashion reasons the surface was changed from a mirror
finish to a matte surface, while retaining the collarless tapered shape.
The original 1970 Exeter stem (left) and the1988
Exeter Universal modular stem (right) both have a polished surface.
Images: Exeter Hip Unit, Princess
Elizabeth Orthopaedic Hospital
stem loosening and
osteolysis were seen around a number of these matte stems
— something that was almost never seen in the earlier polished version
despite many more years of use. It was realized that this relatively smooth
matte surface was enough to hold the stem up and stop the taper slip process,
preventing self-locking with the associated secure and benign long-term
fixation. In 1986, the Exeter stem reverted back to the original polished
surface; in 1988, the stem was made modular (Exeter Universal) to accommodate
femoral heads of different lengths, sizes and bearing materials.
Worldwide use, success
The use of the Exeter hip system has grown steadily
since that time. There are currently 21 primary and 7 revision stems in the
Exeter line. Not only has the Exeter group reported excellent long-term results
from their own center, these have been reproduced in other units around the
globe. These results, the long-term preservation of bone stock associated with
taper slip loading and the ease of restoration of anatomy due to the
flexibility of the system have resulted in the Exeter stem being one of the
most commonly used hip stems in the world. As a result of this popularity, this
year will see the millionth patient receive an Exeter stem.
The collaboration between Ling and Lee resulted in more
than just the design of a hip stem. As well as observing their patients closely
from the outset and setting up a comprehensive outcomes database, Ling and Lee
also extensively studied the behavior of bone cement and the techniques of hip
arthroplasty surgery. Together with their colleagues and successors in the
Exeter group, this has resulted in a number of advances and innovations in the
use and understanding of these systems in both primary and revision hip
An Exeter hip is
shown at 15 years postoperatively. Note the narrow space above the shoulder of
the stem, showing the typical subsidence of the stem and the preservation of
proximal femoral bone stock.
These innovations include, in particular, techniques and
instrumentation to improve both femoral and acetabular cementing, developments
in surgical technique, education and training and revision hip surgery. Graham
A. Gie, MBChB, FRCS, FRCSEd(Orth), from Exeter, working with Ling and in
collaboration with the Nijmegen group, was the first to undertake the revision
femoral impaction bone grafting; the Exeter group has also
popularized the technique of cement-in-cement femoral revision, demonstrating
reliable long-term fixation with this simple technique.
Education and training have always been key issues for
the Exeter group, and Ling and Lee started the initial Exeter Hip Symposia in
the 1980s. This program has grown steadily over the years. The Exeter Hip Unit
now hosts three full-time specialist training fellowships in hip surgery which
have been undertaken by surgeons from around the globe, with additional
visiting fellowship posts specifically for Scandinavian and Asia Pacific
surgeons. In collaboration with and supported by Stryker, courses in primary
hip arthroplasty, complex and advanced primary surgery and revision
arthroplasty are now run every year in Exeter and many other centers.
The enormous contribution over the last 40 years to hip
arthroplasty surgery by the Exeter group was recently recognized by the award
of a special commendation by the British Orthopaedic Association. A 369-page
book, The Exeter Hip: 40 Years of Innovation in Total Hip Arthroplasty,
has also just been released to coincide with the 40th year anniversary.
With 49 international co-authors, the book covers all of the principles and
practice of hip arthroplasty with particular emphasis on the Exeter system.
- Ling RSM, Lee AJC, Gie GA, et al, eds. The Exeter Hip: 40
Years of Innovation in Total Hip Arthroplasty. Exeter, UK: Exeter Hip
- Matthew Hubble, MBBS, FRCS(Tr&Orth), is from the Princess
Elizabeth Orthopaedic Centre, Exeter, UK. He can be reached at
email@example.com. Hubble is a
member of the Exeter Hip development group which receives funding from Stryker.
Stryker also supports research staff and the hip fellowship at the Princess
Elizabeth Orthopaedic Centre, Exeter, U.K.