Patient-specific guides for consistently achieving R0 bone margins after resection of primary malignant bone tumors of the pelvis.

Aims: Primary malignant bone tumor of the pelvis is an uncommon lesion, the resection of which via freehand osteotomy is subject to inaccuracy due to its three-dimensional anatomy. Patient-Specific Guides (PSG), also called Patient-Specific Instruments (PSI) are essential to ensure surgical planning and resection adequacy. Our aim was to assess their use and effectiveness.

Methods: A monocentric retrospective study was conducted on 42 adult patients who underwent PSG-based resection of a primary malignant bone tumor of the pelvis. The primary outcome was the proportion of R0 bone margins. The secondary outcomes were the proportion of overall R0 margins, considering soft-tissue resection, the cumulative incidence of local recurrence, and the time of production for the guides. A comparison to a previous series at our institution was performed regarding histological margins.

Results: Using PSGs, 100% R0 safe bone margin was achieved, and 88% overall R0 margin due to soft-tissue resection being contaminated, while the comparison to the previous series showed only 80% of R0 safe bone margin. The cumulative incidences of local recurrence were 10% (95% CI: 4-20%) at one year, 15% (95% CI: 6-27%) at two years, and 19% (95% CI: 8-33%) at five years. The median overall duration of the fabrication process of the guide was 35 days (Q1-Q3: 26-47) from the first contact to the surgery date.

Conclusions: Patient-Specific Guides can provide a reproducible safe bony margin.