This time-zero biomechanical study investigates femoral stem stability after extended trochanteric osteotomy (ETO) without fragment refixation, representing a worst-case scenario. ETO is used in complex femoral revisions to improve exposure while preserving soft tissue and neurovascular structures. In the setting of a short ETO, surgeons may choose between standard (STD) and intermediate revision (REV) stems, although their primary stability remains unclear. Clinically, STD are still used after short ETO with low rates of aseptic loosening, aiming for proximal bone loading to reduce stress shielding. We therefore hypothesized that STD would demonstrate non-inferior axial and torsional stability compared with REV in a short open ETO model. A biomechanical model using SYNBONE® femurs and uncemented, collared, fully coated triple-tapered STD and REV 135° CCD was established. A standardized 60mm ETO (vastus ridge to distal end of ETO) was performed and left unrepaired to simulate a worst-case scenario. Four groups (n = 6 each) were tested: (1) STD and (2) REV under axial loading (500 cycles at 20° adduction up to 500N at 1Hz, then static loading to failure), and (3) STD and (4) REV under torsional loading (500 cycles up to 10Nm internal rotation at 1Hz, then failure testing). Axial stiffness (N/mm), torsional stiffness (Nm/deg), and failure load/torque were assessed. REV showed higher axial stiffness (297.5 ± 39.7N/mm) than STD (245.9 ± 33.2N/mm, p = 0.035) and greater axial failure load (1228.1 ± 86.8 vs. 1002.5 ± 114.1N, p = 0.003). Torsional stiffness and peak torque were comparable between groups. Axial failure with REV occurred at the distal stem tip, while STD fractured through the ETO. Torsional failure produced spiral fractures from the distal ETO in both groups. Under time-zero worst-case conditions without ETO refixation, the REV demonstrated higher axial stability, while torsional stability was comparable. The STD provided sufficient primary stability after short open ETO, supporting its potential use when revision stem implantation is not required.