Robotic-assisted navigation with patient-specific implants vs. modified Stoppa and MIPPO in Tile C pelvic fractures: a multicenter cross-sectional observational study with osteoporosis subgroup analysis

Tile C pelvic fractures present significant therapeutic challenges, especially in obese and osteoporotic patients, where traditional techniques (Modified Stoppa approach, minimally invasive percutaneous plate osteosynthesis [MIPPO]) are limited by poor precision and high complication rates. Robotic-assisted navigation (RAN) with patient-specific implants (PSI) may improve outcomes, but gaps remain in understanding its performance in multicenter settings (e.g., surgeon skill variability), nonlinear BMI effects on functional recovery, and cost-effectiveness stratified by BMI-bone mineral density (BMD) interactions. This study aimed to compare RAN + PSI with traditional methods in operative efficiency, functional outcomes, and cost-effectiveness, while addressing multicenter bias and validating the optimal BMI for functional recovery. This was a multicenter prospective observational cohort study conducted at tertiary trauma centers in China (January 2022-2025), enrolling 220 patients with Tile C pelvic fractures. Patients were stratified by center and fracture subtype (Tile C1/C3) before allocation to three groups: RAN + PSI (n = 110), Modified Stoppa (n = 55), and MIPPO (n = 55)-this stratification minimized bias from intercenter surgeon skill differences and uneven case distribution. For RAN + PSI, preoperative CT scans generated 3D pelvic reconstructions to design custom implants and plan screw trajectories; intraoperative robotic calibration (TianJi Robot system) ensured submillimeter precision. Traditional techniques followed standardized protocols (Modified Stoppa: open anterior pelvic exposure with precontoured plates; MIPPO: fluoroscopy-guided percutaneous plate/screw placement). Primary outcomes included Matta reduction grade, Majeed Pelvic Score (12 months), and cost-effectiveness (incremental cost-effectiveness ratio [ICER], Chinese RMB/quality-adjusted life-year [QALY]). Polynomial regression modeled nonlinear BMI effects, and stratified analyses validated BMI-BMD interactions. RAN + PSI outperformed traditional methods in key metrics: (1) Implant precision: mean deviation 1.2 ± 0.5 mm vs. 2.7 ± 1.1 mm (Modified Stoppa) and 2.4 ± 0.9 mm (MIPPO, p < 0.001); (2) Operative efficiency: 98 ± 22 min vs. 145 ± 35 min (Modified Stoppa) and 138 ± 30 min (MIPPO, p < 0.001); (3) Complications: 10% vs. 25.5% (Modified Stoppa) and 23.6% (MIPPO, p = 0.003). Polynomial regression identified a peak Majeed Score (89.2 ± 5.8) at BMI ~ 26.5 kg/m² (p = 0.041), with declining outcomes in underweight (BMI < 18.5) and obese (BMI ≥ 30) subgroups. Obese osteoporotic patients (BMI ≥ 30 + BMD T ≤ -2.5) had a 2.9-fold higher risk of screw loosening (p < 0.001) and higher ICER (¥250,000/QALY), though RAN + PSI remained more cost-effective than traditional methods (¥400,000-500,000/QALY). Stratified allocation by center ensured balanced case distribution across techniques (no single center dominated RAN + PSI cases), eliminating intercenter skill bias. RAN + PSI surpasses Modified Stoppa and MIPPO in precision, efficiency, and functional recovery for Tile C pelvic fractures. The optimal BMI for functional outcomes is ~ 26.5 kg/m², and BMI-BMD interactions necessitate personalized strategies (e.g., bone cement augmentation for obese osteoporotic patients). Multicenter stratification by center and fracture subtype effectively mitigates bias from surgeon skill variability, confirming the reliability of results. RAN + PSI is most cost-effective in normal-weight, nonosteoporotic patients and remains clinically valuable in high-risk subgroups.