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Clinical and Histologic Results Related to a Low-Modulus Composite Total Hip Replacement Stem

¹ University Hospitals of Cleveland, 11100 Euclid Avenue, Hanna House 6, Cleveland, OH 44106. E-mail address for V.M. Goldberg: victor.goldberg{at}uhhs.com
² Musculoskeletal Mechanics and Materials Laboratories, Departments of Orthopaedics and Mechanical and Aerospace Engineering, Case Western Reserve University, 11100 Euclid Avenue, Wearn 311, Cleveland, OH 44106

Investigation performed at University Hospitals of Cleveland, Cleveland, Ohio

NOTE: The authors acknowledge Professor Ian Learmonth for the contribution of the forty-eight-month histologic specimen and Patricia Conroy for contribution to the clinical data gathering.

In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from Zimmer (Warsaw, Indiana). None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

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.

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