A Biomechanical Study of Pull-Out Strength in Fenestrated Pedicle Screws Inserted Into Osteoporotic Cancellous Bone...

Background Osteoporosis is increasingly prevalent in aging populations and remains a major barrier to achieving reliable spinal fixation. Poor cancellous bone quality compromises the bone-implant interface, leading to higher rates of pedicle screw loosening, construct failure, and revision surgery. Cement augmentation improves fixation strength but is associated with volume-dependent complication risk, creating a clinical need for low-volume, mechanically efficient augmentation strategies. Concurrently, modern minimally invasive fixation increasingly relies on Jamshidi needle-guided tract preparation, which may influence cancellous bone compaction and cement containment. Despite these evolving surgical workflows, limited biomechanical data exist evaluating the combined effects of cement delivery technique and low-dose cement volume in Jamshidi-guided screw insertion. This study investigated whether the cement delivery technique exerts a greater biomechanical influence than cement volume when using fenestrated pedicle screws. Methods This in vitro biomechanical comparative study utilized standardized osteoporotic cancellous polyurethane foam blocks. Fenestrated cannulated pedicle screws (6.5 × 40 mm) were inserted using a Jamshidi needle and guidewire technique. Five experimental groups were evaluated (n = 3 per group): Group A (no cement), Group B (0.5 mL cannulated injection), Group C (1.0 mL cannulated injection), Group D (0.5 mL prefill), and Group E (1.0 mL prefill). After cement polymerization, axial pull-out testing was performed using a universal testing machine. Primary outcomes included pull-out strength, axial stiffness, and displacement to failure. Statistical analysis was conducted using the Kruskal-Wallis test with post hoc pairwise comparisons. Results Significant overall differences were observed across experimental groups for all biomechanical parameters (all p = 0.01). Mean pull-out strength increased from 524.42 ± 12.40 N in the control group to 874.05 ± 17.41 N with 0.5 mL cannulated injection and 1030.32 ± 37.05 N with 1.0 mL injection, representing improvements of 66.7% and 96.5%, respectively. Prefill augmentation produced smaller gains, with 595.02 ± 41.74 N (+13.5%) for 0.5 mL and 760.08 ± 39.37 N (+44.9%) for 1.0 mL. Axial stiffness increased from 230.35 ± 1.54 N/mm in controls to 324.15 ± 5.57 N/mm and 336.10 ± 6.04 N/mm in injection groups, while prefill augmentation resulted in more modest improvements. Displacement to failure was highest in injection groups (2.70 ± 0.05 mm and 3.07 ± 0.14 mm), compared with the control (2.28 ± 0.06 mm) and prefill groups. Notably, 0.5 mL cannulated injection consistently outperformed 1.0 mL prefill augmentation across primary biomechanical outcomes. Conclusions In Jamshidi-guided insertion of fenestrated pedicle screws, the cement delivery technique has a greater biomechanical impact than low-dose cement volume. Cannulated cement injection provides superior fixation stability, even at reduced cement volumes, whereas low-volume prefill augmentation offers limited mechanical benefit. These findings support a technique-driven, low-volume cement augmentation strategy for optimizing pedicle screw fixation in osteoporotic bone while potentially reducing cement-related complications.