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Item type:Publication, Access status: without files , Estimating the benefit of a collar on uncemented press-fit stems(British Editorial Society of Bone and Joint Surgery, 2026-03); ; ; ; A collar has been shown to be beneficial in reducing peri-prosthetic fractures (PPF) and revisions in uncemented total hip arthroplasty using tapered press-fit stems (revision rate at 15 years 4,8% compared to 6.1% for collarless)1. The purpose of this study was to develop a numerical model to estimate the benefit of adding a collar to an uncemented stem. Materials and Methods Two human cadaveric femurs were implanted with a collared re. collarless CORAIL stem (DePuy Synthes) until failure using a material testing machine (constant velocity 0.1 mm/s). Shear, axial compressive and tangential tensile strains as well as fracture load were recorded using Digital Image correlation and compared between with vs. without collar. A finite element model (FEM) based on a CT scan of one femur was used to numerically estimate the same parameters for three different stem types with vs. without collar (CORAIL, EMPHASIS, ACTIS all DePuy Synthes). Results The collar increased axial compressive strains instead of causing critical excessive tangential tensile strains (hoop strains) that can result in PPF during loading. This results in substantially higher loads required for a fracture. In the experimental part of the study the collar increased the fracture load for the CORAIL stem by nearly 100% (6824N vs. 3465N, ratio 1.96). The results of the FEM model yielded a similar tendency for the CORAIL stem but with a higher benefit ratio (3.37). The EMPHASYS stem showed very similar results (ratio: 3.47), whereas the ACTIS stem showed a smaller benefit (ratio: 1.69). Discussion The ACTIS stem benefits less from the collar due to its fit-and-fill design in the metaphyseal region associated with a larger width compared to the two other stem designs investigated. This approach can be used for any uncemented stem design. Acknowledgement. The study was financially supported by DePuy-SynthesPublicationtype: Conference Paper9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , How does the collar in cementless hip stems work? Comparison of the strain distribution in the cortex of the proximal femur(Elsevier, 2025-12-01); ; ; ; Background: Collared cementless hip stems have demonstrated a reduced incidence of periprosthetic femoral fractures compared to collarless counterparts. Many fractures occur during implantation, when collarless stems are seated to achieve press-fit, causing critical tensile strains in the femur. Collared stems can limit excessive seating and subsidence through calcar-collar contact. This study aimed to explain the clinically observed smaller fracture rates with collared stems by comparing strain distributions during implantation and loading between collared and collarless stems. It was hypothesized that collared stems distribute applied forces through both the collar and stem, increasing compressive axial and shear strains, allowing higher load tolerance. Methods: Seven collared and seven collarless stems were implanted with constant velocity (0.1 mm/s) in porcine femurs until failure. Two human cadaveric femurs were tested as proof of concept. Shear, axial compressive and tangential tensile strains were compared alongside fracture patterns, subsidence and forces. Findings: Collared stems in porcine femurs resisted approximately twice as much force until failure occurred (collared: 4187 N, collarless: 1980 N; p < 0.001), with similar tangential tensile strains (1 % to 1.4 % p = 0.805) and subsidence of 1.6 mm for collarless and 1.1 mm for collared stems at different failure forces (p = 0.288). Axial compressive strain was heavily increased by 1147 % with collared stems (collared: 1.2 %, collarless: 0.1 %; p = 0.026). Human femurs exhibited similar trends. Interpretation: During loading, the collar prevents periprosthetic femoral fractures by increasing axial compressive strains instead of causing critical excessive tangential tensile strains (hoop strains) that can result in fractures.Publicationtype: Journal Article43 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Small design modifications can improve the primary stability of a fully coated tapered wedge hip stem(Public Library of Science (PLoS), 2024-04-17); ; ; ; Increasing the stem size during surgery is associated with a higher incidence of intraoperative periprosthetic fractures in cementless total hip arthroplasty with fully coated tapered wedge stems, especially in femurs of Dorr type A. If in contrast a stem is implanted and sufficient primary stability is not achieved, such preventing successful osseointegration due to increased micromotions, it may also fail, especially if the stem is undersized. Stem loosening or periprosthetic fractures due to stem subsidence can be the consequence. The adaptation of an established stem design to femurs of Dorr type A by design modifications, which increase the stem width proximally combined with a smaller stem tip and an overall shorter stem, might reduce the risk of distal locking of a proximally inadequately fixed stem and provide increased stability. The aim of this study was to investigate whether such a modified stem design provides improved primary stability without increasing the periprosthetic fracture risk compared to the established stem design. The established (Corail, DePuy Synthes, Warsaw, IN, US) and modified stem designs (Emphasys, DePuy Synthes, Warsaw, IN, US) were implanted in cadaveric femur pairs (n = 6 pairs) using the respective instruments. Broaching and implantation forces were recorded and the contact areas between the prepared cavity and the stem determined. Implanted stems were subjected to two different cyclic loading conditions according to ISO 7206-4 using a material testing machine (1 Hz, 600 cycles@80 to 800 N, 600 cycles@80 to 1600 N). Translational and rotational relative motions between stem and femur were recorded using digital image correlation. Broaching and implantation forces for the modified stem were up to 40% higher (p = 0.024), achieving a 23% larger contact area between stem and bone (R2 = 0.694, p = 0.039) resulting in a four times lower subsidence during loading (p = 0.028). The slight design modifications showed the desired effect in this in-vitro study resulting in a higher primary stability suggesting a reduced risk of loosening. The higher forces required during the preparation of the cavity with the new broaches and during implantation of the stem could bare an increased risk for intraoperative periprosthetic fractures, which did not occur in this study.Publicationtype: Journal Article34 53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Stem size and stem alignment affects periprosthetic fracture risk and primary stability in cementless total hip arthroplasty(Wiley, 2024-04); ; ; ; The ideal stem size and stem position is important for the success of total hip arthroplasty, since it can affect early implant loosening and periprosthetic fractures (PPF). This study aimed to investigate how small deviations from the ideal stem size and position influences the PPF risk and primary stability. Six experienced surgeons performed preoperative templating based on which the benchmark size for each femur was determined. Consecutive implantations were performed in six cadaveric femur pairs—one side was implanted with an undersized stem followed by the benchmark size and the contralateral side with a benchmark size followed by an oversized stem (Corail, Depuy Synthes). Moreover, three different alignments (six varus, six neutral, six valgus-undersized) were compared using 18 femurs. Cortical strains during broaching and implantation were measured, and laser scans were used to determine final stem position. All specimens underwent dynamic loading. Primary stability was estimated from stem subsidence and pull-out forces. Templated stem size varied between surgeons (±1 size; p = 0.005). Undersizing increased stem subsidence by 320% (p < 0.001). Oversized stems exhibited 52% higher pull-out forces (p = 0.001) and 240% higher cortical strains (p = 0.056). Cortex strains increased with varus alignment (R2 = 0.356, p = 0.011) while primary stability decreased with valgus stem alignment (p = 0.043). Surgeons should be aware that small deviations from the ideal stem size and malalignments of the stem can significantly alter the mechanical situation and affect the success of their surgery.Publicationtype: Journal ArticleScopus© Citations 3 40 185 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Diskrete-Elemente-Methode in der Endoprothetik - eine Pilotstudie zur numerischen Simulation von Knochenpartikeln(2021-03-22); Publicationtype: Master Thesis121 363