Date Published: April 10, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Shigeru Nakamura, Noriyuki Arai, Takateru Kobayashi, Takashi Matsushita.
Purpose. The Anatomic Fiber Metal plus stem (Zimmer) is one of the anatomically designed cementless stems to achieve stable fixation by metaphyseal fit. We studied outcomes of cementless total hip arthroplasty using this stem and possible effects of metaphyseal fit on outcomes. Methods. The cementless total hip arthroplasty using this stem was performed for 155 hips. One hundred and thirty-seven hips of 122 patients were followed for 5 to 16 (mean, 9.7) years and entered into the study. The metaphyseal fit was defined as good or poor in an anteroposterior radiograph after surgery. We studied the fixation of the stem and bone reaction on an anteroposterior radiograph at the final followup. Results. Twelve hips had revision, six acetabular components and six acetabular liners. No stem was revised. The biological fixation of the stem was bone ingrown fixation for 136 hips and unstable for one. The metaphyseal fit was good for 83 hips and poor for 54 hips. There were no differences for stem fixation and bone reaction between the two groups. Conclusions. The fixation of the stem was stable at a mean followup of 9.7 years independently from metaphyseal fit.
For cementless total hip arthroplasty (THA), a large variety of femoral component designs have been developed. The Anatomic Fiber Metal plus stem (Zimmer, Indiana, USA) is one of the anatomically designed femoral components to be inserted without cement (Figure 1). The concept of this stem was to achieve stable fixation by metaphyseal fit and fill [1, 2]. It has a configuration matching a medullar canal of a normal femur and circumferential fiber-mesh coating on the proximal one-third. The neck of the stem has an anteversion of twelve degrees.
The cementless total hip arthroplasty using the Anatomic Fiber Metal plus stem was performed for 155 hips of 139 patients between February 1994 and August 2003 at our hospital. Eighteen hips of 17 patients were excluded for the following reasons. Six patients (seven hips) had died during followup, eight patients could not be contacted, and the remaining three patients were contacted by telephone and confirmed to have no revision and to have no hip pain, but did not visit our clinic. One hundred and thirty-seven hips of 122 patients were followed for more than five years and entered into the study of clinical and radiographic outcomes.
Twelve hips including one hip with late infection had revision. The mean duration between total hip arthroplasty and revision was nine (1–16) years. No stem was revised. Six hips had revision of acetabular components, and the remaining six hips had revision of acetabular liners. For all 12 hips, conventional polyethylene liners had been used. Out of six acetabular revisions, three cups were well fixed, and the other three had no bony fixation. Well-fixed three cups were HGP-II cups. Cross-linked polyethylene liners were not available for HGP-II cups. We revised these cups to use cross-linked polyethylene liners. The reasons for liner revision were liner wear for three hips, late infection for one, dislocation for one, and dislodge of liner for one. For one hip of liner revision, bone graft was performed to osteolysis at the zone 1 of the femur.
Several studies [1, 2, 8, 9] on the outcome of THA using the Anatomic stem (Zimmer, Indiana, USA) in Caucasian patients reported that the rates of stem revision due to loosening were low (from 0 to 2.6%). There were two reports on the outcomes in Japanese patients. Harada et al.  reported that five cups and no stem had been revised in 81 hips with a mean followup of 8.4 years. Nakoshi et al.  also reported that four cups and no stem had been revised in 20 hips with a mean followup of 12.8 years. In our study, no stem had been revised and one stem showed loosening in 137 hips with a mean followup of 9.7 years. These results suggest that the biological fixation of this stem is good for 8 to 12 years after surgery not only in Caucasian but also in Japanese patients.
The metaphyseal fit was good only in about 60% of cases, but 10-year survival rate of the stem was 99%. The biological fixation of the Anatomic Fiber Metal plus stem was stable at a mean followup of 9.7 years independently from metaphyseal fit.