Abstract
Purpose
It is generally accepted that the cement mantle surrounding the femoral component of a cemented total hip arthroplasty (THA) should be complete without any defects, and of at least 2 mm in thickness. Radiographic evaluation is the basis for assessment of the cement mantle. The adequacy of radiographic interpretation is subject to debate. Poor interobserver and intraobserver reproducibility of radiographic cement mantle assessment has been reported. In this study, 3D template software was used that allow anatomical measurements and analysis of three-dimensional digital femura geometry based on CT scans. The purpose of this study is to analyze the three-dimensional cement mantle thickness of cemented hip stem.
Materials and Methods
52 hips that underwent THA with Exeter stem (Stryker Orthopaedics, Mahwah, NJ) were enrolled in this study. All surgeries were performed by a single surgeon. There were 49 hips in 49 women and 3 hips in 3 men. The average age at surgery was 73 years (range, 60–88 years). The etiology of the hip lesions were osteoarthrosis in 49, rheumatoid arthritis in 3, and osteonecrosis of the femoral head in 1.
For preoperative and postoperative evaluation, a CT scan of the pelvis and knee joint was obtained and was transferred to 3D template software (Zed hip, Lexi, Tokyo, Japan). We evaluated the alignment for stem anteversion/valgus/anterior tilt angles and the contact of the cortical bone with the cement mantle was evaluated.
Results
Concerning the alignment of the stems, variability was observed in the anteversion; however, the stems were inserted in an almost neutral position in varus-valgus and extension-flexion.
The 3D contact of the stems with a cement mantle of 2 mm added with the cortical bone was evaluated, and it could be broadly classified into three patterns: cases in which the cortical bone was not reamed in the range of 2 mm from the stem, those in which the distal medial part was partially reamed, and cases in which the distal anterior and medial parts of the cortical bone were reamed in a relatively wide range. In this study, there were 17 patients with no reaming, 32 patients with partial reaming, and 3 patients with a relatively large range of reaming.
Discussion and Conclusion
Oversizing of the stem associated with incomplete cement mantles has been suggested to account for early femoral component loosening. In this study, 3 patients whose cortical bone was reamed in a relatively wide range and who had a risk of partial thinning of the cement mantle as a result were observed. The effect of reaming of the cortical bone on the clinical results is still unknown; however, a careful follow-up in the future may be required.
