THE
COMPOSITE HIP: EPOCH
Frank C. Smith, CH.B,
F.R.C.S.(C) Associate Professor, McMaster University, Hamilton, Ontario The modern hip arthroplasty is generally a successful procedure with good survival and patient acceptance. However, for the patient
with a wide intramedullary canal there is a significant risk of developing
thigh pain. There is also a greater incidence of bone resorption around the
stem from stress relief. This is thought to be due
in part to the greater stiffness of the larger stems and is seen especially
in non-cemented implants. It is also seen in cemented stems but is generally
held to be less severe due to the relative malleability of
polymethylmethacrylate cement at body temperature. The composite stem, EPOCH,
has been developed to examine whether a stem with an elastic modulus very
close to live bone will be effective in relieving the problems of thigh pain
and stress relief when using large stems. The EPOCH stem consists of a
cobalt-chrome core encased in a polymer, polaryl-ether-ketone-ketone, bonded
to an outermost layer of titanium mesh. It is much less stiff than a
conventional stem. It is implanted without cement. An international
multicentre study is being conducted to evaluate the EPOCH stem. The stem has
been available for implantation since 1996 and has been used in Canada since
April 1997. Thirty-two hips have been
replaced in thirty patients at the Hamilton site to date. The results have
been satisfactory with some initial minor complications leading to technical
modifications of instrumentation. One female patient has
dislocated twice and one male has developed greater trochanteric pain
unaffected by weight bearing. No infections have been identified. There have
been no proximal venous thrombi or pulmonary emboli. Two patients have an
EPOCH stem in one femur and a different stem in the contralateral femur. One
prefers the EPOCH; the other has trochanteric pain at rest but is pain free
when walking. All patients are being
followed carefully and indefinitely. The complete international enrolment
will be reported in due course. |
