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Published on: October 23, 2015
Comparative results of a distal modular sleeve, circumferential coating, and stiffness relief using the Anatomic
1University of Southern California Center for Arthritis and Joint Implant Surgery, Los Angeles 90033, USA.
Abstract:
One hundred forty-eight primary Anatomic Porous Replacement II (APR-II, Intermedics Orthopaedics, Austin, TX) noncemented total hip arthroplasties were studied at follow-up periods of 2 to 5 years. Because the stem geometry has not changed since 1988, it was possible to study three adjunctive criteria for porous-coated hip arthroplasties. The APR-II stem geometry was used in three groups: APR-II stem in 56 hips, APR-IIS stem with distal sleeve in 44 hips, and APR-IIT stem with circumferential coating and hollow stem in 48 hips. The APR-IIT was followed 2 years; the APR-II and APR-IIS were followed an average of 3.4 years (range, 2-5 years). For comparison of the results within these three groups 2-year results were compared. The results of the APR-II and APR-IIS at the last follow-up examination are also reported. There was no statistical difference within the three groups for any clinical comparison: 82% had excellent results, 14% good, 2% fair, and 2% poor. At the 2-year follow-up examination, radiographic fixation of the APR-IIS was worse than that of the APR-II and APR-IIT (P < .0005). The APR-IIS uses a distal sleeve, which results in an adverse stiffness ratio between bone and stem. Fixation of the APR-IIT was better than that of the APR-II (P < .0005), probably because the APR-IIT had an increased volume and circumferential level of porous coating and was hollowed for stiffness relief. At final follow-up examination, fixation of the APR-IIS was still worse than that of the APR-II (P < .0005). There was no progressive loss of fixation for either the APR-II or APR-IIS between 2 and 5 years. Only 1 of 148 patients was revised for osteolysis. No other stem or acetabular component is loose. The adjunctive use of a modular sleeve seems to have little advantage, whereas stiffness relief of the stem seems to be beneficial. Circumferential porous coating seems the most important factor for durable fixation.
