In order to acquire good stability of an arthroplasty hip, the proper placement of the implants, which prevents impingement between the stem neck and the socket, is important. In general, the anteversion of the uncemented femoral stem depends on the relationship between the three-dimensional structure of the proximal femoral canal and the proximal stem geometry. The exact degree of the anteversion will be known just after broaching during the operation. If the stem anteversion could be forecasted, preoperative planning of the socket placement would be relatively easy. Furthermore, when a high degree of anteversion is forecasted, a special femoral stem to reduce it, such as a modular stem, could be prepared. However, we experienced that the preoperatively measured anteversion of the femoral neck using computer tomography (CT) was sometimes different from that of the stem measured during the operation. The purpose of this study was to investigate whether the preoperative measurement would be helpful to predict the stem anteversion by examining the relationship between the anteversion of the femoral neck and the stem. A total of 57 primary THAs by one senior surgeon from April 2011 until March 2012 were carried out. Two THAs using a modular stem and one for the hip after previous proximal femoral osteotomy were excluded. The remaining 54 THAs were examined. The used uncemented stems were designed for proximal metaphyseal fixation. CT scans, including the distal femoral condyles as well as the hips, were carried out in all cases preoperatively. The anteversion of the femoral neck was measured as the angle of the maximum longitudinal line of the cross section of the femoral neck to the line connecting the posterior surfaces of both of the distal femoral condyles (Fig. 1). The femoral neck anteversion was measured at three levels (Fig. 1). The stem anteversion was measured just after the femoral broaching during the THA. The relationship between the anteversion angles of the femoral neck and of the stem was examined by using a regression analysis. The institutional review board approved this study.Purpose:
Patients and methods:
Fracture during total hip arthroplasty occurs partly because the acquisition of fixation at the time of stem implantation depends on the operator's experience and sensation due to the absence of definite criteria. Therefore, an objective evaluation method to determine whether the stem has been appropriately implanted is necessary. We clarified the relationship between the hammering sound frequency during stem implantation and internal stress in a femoral model, and evaluated the possible usefulness of hammering sound frequency analysis for preventing intraoperative fracture. Three types of cementless stem were used. Orthopedists performed stem insertion using a procedure similar to that employed in routine operation. Stress was estimated by finite element analysis using the hammering force calculated from the loading sensor as a loading condition, and frequency analysis of hammering sound data obtained using a microphone was performed (Fig. 1). Finite element analysis showed a decrease in the hammering sound frequency with an increase in the estimated maximum stress (Fig. 2, 3). When a decrease in frequency was observed, adequate hammering had already been performed to achieve press-fit stability. Therefore, there is a possibility that the continuation of hammering induces intraoperative fractures that become a problem. Based on the relationship between stress and frequency, the evaluation of changes in frequency may be useful for preventing the development of intraoperative fractures. When a decrease in frequency is observed, the hammering force should be reduced thereafter. Hammering sound frequency analysis may allow the prediction of bone fractures that can be visually confirmed, and may be a useful objective evaluation method for the prevention of intraoperative bone fracture.
