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.
The average follow-up period of the study group was 9.7 (5–16) years, and the average age at the surgery was 62 (33–80) years old. The diagnosis was osteoarthritis for 117 hips, osteonecrosis of the femoral head for 18 hips, and rapidly destructive coxarthrosis for two hips.
The indication of the usage of the Anatomic Fiber Metal plus stem was different according to the periods of the surgery. This stem had been used principally for all hips between February 1994 and May 1999 (defined as nonselection period). Between June 1999 and August 2003 (defined as selection period), we had used this stem as a first choice, but selected other stems (straight taper type or modular type) when the Anatomic Fiber Metal plus stem was not fit to the shape of medullar canal in an anteroposterior (AP) radiograph. During this period, we used the Anatomic Fiber Metal plus stem for 48% of all THA cases. Of the 155 hips inserted with this stem, 62 hips were operated in the nonselection period and 93 hips in the selection period.
The acetabular components were cementless spherical cups: HGP-II (Zimmer) for 22 hips and Trilogy (Zimmer) for 115 hips. The modular head was made of cobalt chromium alloy. The polyethylene of the acetabular liner was conventional for 51 hips and cross-linked for 76 hips.
We evaluated the metaphyseal fit on the postoperative AP radiograph and divided all hips into two groups (). The metaphyseal fit was defined as good, if the medial side of the stem was in contact with the endosteum of the medial femoral cortex through the area of proximal fiber-mesh coating. The metaphyseal fit was defined as poor, if the medial side of the stem was not in contact with the endosteum of the medial femoral cortex at any point in the area of proximal fiber-mesh coating. We calculated the canal-filling ratio (CFR) at the distal end of the lesser trochanter and at the distal end of the stem in the poor metaphyseal fit cases to evaluate the stem size.
Figure 2 The metaphyseal fit evaluation in AP radiographs. (a) The medial side of the stem was in contact with the endosteum of the medial femoral cortex through the area of proximal fiber-mesh coating. The metaphyseal fit was defined as good. (b) The medial side (more ...)
We studied the fixation of the components and bone reaction on an AP radiograph at the final followup. The biological fixation of the stem was classified into bone ingrown fixation, stable fibrous fixation, or unstable according to the methods of Engh et al. [4
]. Unstable was defined as loosening. The subsidence of the stem more than four mm was defined as significant. The acetabular component having clear zone of more than 1
mm in all of the three zones of DeLee and Charnley [5
] around the cup or change of inclination angle of more than 4 degrees was defined as loosening. The stress shielding was classified into four degrees according to the method of Engh et al. [4
]. Radiolucent line, spot welds, and osteolysis were evaluated in seven zones of Gruen et al. [6
] in AP radiographs.
The function of the hip was evaluated using the Japanese Orthopedic Association (JOA) hip score [7
], with a full score of 100 points (pain 40, gait 20, range of motion 20, and activity of daily living 20 points).
We studied the revision rates and survival rates of all 155 hips using Kaplan-Meier methods. Chi-square test or Fisher test was used for categorical data, and Mann-Whitney test was used for numerical data. P value less than 0.05 was defined as significant.
This study was approved by the ethics committee of our institute and had been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki.