Background: Osteolysis secondary to stress shielding in patients
with a total hip arthroplasty has been attributed to greater stiffness of the
prosthetic femoral stem compared with the stiffness of the femur. This concern
led to the development of a composite femoral stem implant with a structural
stiffness similar to that of the native femur. The stem consists of a
cobalt-chromium-alloy core surrounded by polyaryletherketone and titanium mesh
for bone ingrowth. The purpose of this study was to determine the
intermediate-term clinical, radiographic, and histologic results of the use of
Methods: Twenty-eight patients (nineteen men and nine women) with an
average age of 51.3 years underwent primary total hip arthroplasty with the
Epoch stem and were followed for an average of 6.2 years. Harris hip scores
were determined and radiographic studies were performed preoperatively,
postoperatively, and at two-year intervals thereafter. In addition, dual x-ray
absorptiometry scans were made up to two years postoperatively to evaluate
osseous resorption. Two femora obtained at autopsy thirteen and forty-eight
months after surgery were analyzed for bone ingrowth and ongrowth.
Results: The Harris hip scores averaged 56 points preoperatively and
improved to 97 points at the time of the last follow-up. Dual x-ray
absorptiometry scans demonstrated the greatest decrease in mean bone density
(27.5%) in Gruen zone 7 at two years. Radiographs demonstrated no instances of
migration, and only one hip had osteolysis. All stems had stable osseous
fixation. Histologic evaluation of the two femora that had been retrieved at
autopsy at thirteen and forty-eight months showed the mean bone ingrowth (and
standard deviation) along the entire length of the stem to be 49.62% ±
13.04% and 73.57% ± 8.48%, respectively, and the mean bone ongrowth to
be 54.18% ± 7.68% and 80.92% ± 6.06%, respectively.
Conclusions: Intermediate-term follow-up of hips treated with the
Epoch stem indicated excellent clinical success, radiographic evidence of
osseous integration, and histologic findings of osseous ingrowth and ongrowth.
Although the implant has been associated with excellent results in both the
short and the intermediate term, longer follow-up will be necessary to assess
the long-term function of the implant.
Level of Evidence: Therapeutic Level IV. See Instructions
to Authors for a complete description of levels of evidence.