Impact of Zweymüller Stem Modification on Clinical and Radiological Outcomes

Background. According to the analysis of large arthroplasty registers we have noted the increase in the use of non-cemented implants, because the latter shows the same results of implant survival as well as cemented implants. On the other hand, they can affect the quality of the bone around the implant in different ways. These components differ in shape, length, and surface properties. According to the analysis of the arthroplasty register of the Vreden National Medical Research Center of Traumatology and Orthopedics, a significant decrease of the Alloclassic femoral stem using can be noted. In parallel the use of its SL-PLUS MIA modification has increased significantly. Aims of the study: 1) to determine the influence of changes in the design of the Zweymller-type femoral stem on midterm and long-term outcomes and its survival; 2) to identify the characteristics of adaptive remodeling of periprosthetic bone tissue around these femoral stems; 3) to determine risk factors for aseptic loosening of these femoral stems. Methods. 492 cases of hip arthroplasty using the Alloclassic and SL-PLUS MIA femoral stems were observed, with an average follow-up 78.6 months. The patients were divided into 2 groups according to the type of femoral stem. The assessment the hip articulation condition was carried out using the HHS and OHS. The intensity of the pain syndrome was assessed by VAS, and the level of patients satisfaction. The dynamic analysis of X-rays was also performed visually. Results. A significant improvement in clinical and functional results was observed according to the HHS and OHS in both groups of patients, regardless of the type of femoral stem. Analysis of X-rays over time showed differences in the behavior of these two femoral component models. The radiolucent lines around the femoral stem are absent in SL-PLUS MIA group, in Alloclassic stem group radiolucent lines are present even at a minimal period (12 months). We also found that a tight fit of Zweymller femoral stems in the distal shaft is a risk factor for severe stress-shielding syndrome, especially in the funnel channels. But ceteris paribus, a distal tight fit of SL-PLUS MIA stems despite similar geometry of the distal part does not lead to such frequent manifestation of severe stress shielding. Conclusion. The change in Zweymller stem design from Alloclassic to SL-PLUS MIA improved the nature of adaptive remodeling in the periprosthetic area of the femur. It may improve the long-term results of primary hip arthroplasty, but these differences require closer observation.