Objective: Total hip arthroplasty (THA) is a very useful procedure for the treatment of degenerative arthritis. In Japan, cementless stems are used in approximately 75% of all THA procedures. Therefore, research on the outcomes obtained with cementless stems are important. The objective of our research was to study the factors associated with remodeling of periprosthesis bone.
Methods: Ninety-six patients who underwent cementless THAs in our hospital were recruited for our study. The patients were divided in two groups according to the position of the cementless stem observed from radiographs taken immediately in the postoperative period, namely the ‘center’ group and the ‘varus’ group, respectively. We retrospectively compared the outcomes in each group, i. e., the Japanese Orthopaedic Association score, postoperative bleeding, canal flare index, stress shields, cortical hypertrophy, radiolucent line, and spot welds.
Results: Postoperatively the position of the stem included 77 ‘center’ cases and 19 ‘varus’ cases. Patient characteristics were not dissimilar between the two groups, and clinical outcomes did not differ significantly either. Cortical hypertrophy was observed in 30 and 13 cases in the ‘center’ and ‘varus’ groups, respectively. In addition, the radiolucent line was observed in 36 cases (46.7%) in the ‘center’ group and in 14 cases (73.7%) in the ‘varus’ group. These phenomena were significantly more frequent in the ‘varus’ group.
Conclusion: The position of stem insertion influenced the remodeling of the periprosthesis bone. Varus positioning of the stem may cause distal stem micromotion. Although no clear differences were noted in the clinical outcome in this study, it is important to consider the long-term stability of THA prostheses. This study revealed that cortical hypertrophy and a radiolucent line were more frequently observed in association with varus stem insertion of THAs.
