Boettcher, Julius M.Julius M.BoettcherSellenschloh, KayKaySellenschlohPardos, Ana CruzAna CruzPardosHuber, GerdGerdHuberOndruschka, BenjaminBenjaminOndruschkaMorlock, MichaelMichaelMorlock2025-12-092025-12-092025-11-27Clinical Biomechanics 131: 106723 (2026)https://hdl.handle.net/11420/59545Background: Cortical contact of the stem is a key determinant for primary stability in cementless revision hip arthroplasty. This matched-pair cadaveric study evaluated whether implant designs that increase cortical contact improve primary fixation of cementless revision stems Methods: Ten paired femora received either a tapered monoblock RECLAIM™ stem with advanced spline (RAS) geometry or an identically sized prototype solid stem. Axial seating and rotation were recorded using dynamic image correlation during implantation. Specimens were cyclically loaded up to 200 % body weight, after which torque-to-failure was measured Findings: Both designs showed mean micromotion <50 μm during cyclic loading, consistently favourable for osseointegration. However, solid stems rotated more during implantation than RAS stems (3.6 ± 5.0° vs. 0.5 ± 0.6°, p = 0.088). The cortical contact area of the solid stems was 43.6 % larger than RAS stems (p < 0.001) without an impact on superior fixation: Axial subsidence and rotation during cyclic loading did not differ significantly between the designs but two solid-stem specimens fractured under high loading. Torque-to-failure of the RAS stems was 38.7 ± 7.5 nm, exceeding that of solid stems by 24.3 % (p = 0.032) Interpretation: These findings suggest that maximising circumferential contact by implant design alone cannot compensate for irregularities of the femoral canal. Whereas solid stems wedge firmly only at the cost of positioning accuracy and increased fracture risk, the thin splines of the RAS design engage the cortex progressively, guide the implant to the planned depth, and augment torsional resistance without excessive press-fit. Tapered stems with cortex-indenting splines improve primary stability in cementless revision hip arthroplasty more effectively than increasing contact area alone.en1879-12712025Elsevierhttps://creativecommons.org/licenses/by/4.0/Biomechanical cadaver studyCementless revision hip arthroplastyHip revision stemImplant designIn-vitro experimentPrimary stabilityTechnology::617: Surgery, Regional Medicine, Dentistry, Ophthalmology, Otology, AudiologyTechnology::620: Engineering::620.1: Engineering Mechanics and Materials ScienceJournal Articlehttps://doi.org/10.15480/882.1628110.1016/j.clinbiomech.2025.10672310.15480/882.16281Journal Article