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Background: The aim of this study is a clinical evaluation of the center of rotation (COR) placement towards a patient's recovery with respect to daily living ability and mobility. In past experiments based on three-dimensional (3D) models, medialization of the COR in total hip arthroplasty (THA) showed a negative influence on muscle strength of the abductors and reaction force of the hip joint. This contradicts paradigms, where reduced hip loading forces are claimed to increase functional outcomes. Methods: The plain X-rays of 110 patients who underwent THA after a femoral neck fracture between January 2019 and January 2021 were retrospectively evaluated. A Barthel Index on discharge was obtained in 69 cases. 47 patients were available for a follow-up interview concerning the Barthel Index, Parker mobility score (PMS), and pain levels (NRS) 6 and 12 months after surgery. Results: Medialization of the COR had a significantly negative effect on the need for care (Barthel Index) at patient discharge (Spearman correlation 0.357, p = 0.013). The effect on the PMS is still existent at 6 and 12 months (Spearman correlation 0.471, p = 0.009 at 6 months; 0.472, p = 0.008 at 12 months). Mann–Whitney U tests showed that the groups with medialized COR performed significantly worse than the lateralized groups. This was seen for the Barthel Index at discharge and at 6 months after surgery and for the PMS at 6 and 12 months. The accurately reconstructed CORs showed no significant differences from the lateralized rotation centers in need of care and mobility. The superior COR placement group showed significantly reduced mobility at 12 months in contrast to the inferior COR placement group (p = 0.008), and the group of accurately reconstructed rotation centers showed significantly less pain than the inferior COR placement group (p = 0.007 after 6 months, p = 0.026 after 12 months). Especially the combination of both (superomedialization) leads to reduced mobility (Spearman correlation 0.67, p = < 0.001). Conclusions: COR superior displacement, COR medialization, and the combination of both (superomedialization, Spearman p = < 0.001) lead to reduced mobility while inferior displacement showed increased pain. According to our results, we recommend an exact vertical COR restoration, while horizontal medial displacement needs to be avoided. Level of evidence: III. [ABSTRACT FROM AUTHOR]

Background: Femoral neck fractures (FNF) are among the most common fractures in Germany and are often treated by hemiarthroplasty (HA). The aim of this study was to compare the occurrence of aseptic revisions after cemented and uncemented HA for the treatment of FNF. Secondly, the rate of pulmonary embolism was investigated. Methods: Data collection for this study was performed using the German Arthroplasty Registry (EPRD). HAs after FNF were divided into subgroups stratified by stem fixation (cemented vs uncemented) and paired according to age, sex, BMI, and the Elixhauser score using Mahalanobis distance matching. Results: Examination of 18,180 matched cases showed a significantly increased rate of aseptic revisions in uncemented HA (p < 0.0001). After 1 month 2.5% of HAs with uncemented stems required an aseptic revision, while 1.5% were reported in cemented HA. After 1 and 3 years' follow-up 3.9% and 4.5% of uncemented HA and 2.2% and 2.5% of cemented HA needed aseptic revision surgery. In particular, the proportion of periprosthetic fractures was increased in cementless implanted HA (p < 0.0001). During in-patient stays, pulmonary emboli occurred more frequently after cemented HA [0.81% vs 0.53% in cementless HA (OR: 1.53; p = 0.057)]. Conclusion: For uncemented hemiarthroplasties a statistically significantly increased rate of aseptic revisions and periprosthetic fractures was evident within a time period of 5 years after implantation. During the in-hospital stay, patients with cemented HA experienced an increased rate of pulmonary embolism, but without statistically significant results. Based on the present results, with knowledge of prevention measurements and correct cementation technique, cemented HA should be preferred when using HA in the treatment of femoral neck fractures. Trail registration: The study design of the German Arthroplasty Registry was approved by the University of Kiel (ID: D 473/11). Level of Evidence: Level III, Prognostic. [ABSTRACT FROM AUTHOR]