Objective: Intersegmental shear is a key factor in degenerative lumbar spondylolisthesis. The effects of external loads on the lumbosacral spine under different spinopelvic parameters on segmental shear mechanisms remain unclear. Therefore, this study aims to investigate the effects of inclined axial compressive force and flexion moment on the anterior or posterior shear stiffness of the lumbosacral joint. Methods: Six fresh-frozen human cadaveric L5?S1 joints were tested under three progressive structural conditions: Intact, a 4mm bilateral facet joint gap, and a n anterior discectomy anteriorly with Nucleus Pulposus Removal and circumferential release of the inner annular fibers (NPR). A 300N axial compressive force was applied vertically downward and with a 10°/20° anterior inclination through the disc's center of shear. Anterior (0 to +250N) and posterior (0 to ?50N) shear tests were performed using an electromagnetic-servo-controlled material testing machine. These tests were repeated under an 5Nm flexion moment. Relative motion between L5 and S1 was measured using an NDI Optotrak Certus 3D motion capture system. A repeated measures ANOVA was utilized to analyze the effects of axial compressive force inclination and flexion moment on shear stiffness across the three structural conditions. Results: In the intact state, axial compressive force inclination did not significantly alter anterior or posterior shear stiffness, but a flexion moment increased anterior shear stiffness by 49.3%. Progressive structural damage, from the intact state to the NPR condition, resulted in incremental increases in anterior-posterior shear translation and corresponding reductions in stiffness. Notably, under the combined loading of axial compression and a flexion moment, anterior stiffness decreased from 939N/mm (Intact) to 224N/mm (NPR), while posterior stiffness decreased from 572N/mm to 217N/mm. Within the low-load range, no significant differences in shear stiffness were observed across any structural conditions, irrespective of axial compressive force inclination or the presence of a flexion moment. Conclusion: Axial compressive force inclination does not appear to significantly influence the shear stiffness of the lumbosacral joint. In contrast, a flexion moment enhances anterior shear stiffness. In the low-load range, anterior and posterior shear stiffness is not significantly affected by either axial compressive force inclination or a flexion moment across the tested structural conditions. This study supports the clinical view that retro-inclination of the plevis is a compensatory mechanism to enhance the segmental shear stability. However, this capacity gradually diminishes and ultimately fails as spinal degeneration progresses.