Computer-Assisted Rod Contouring in Deformity Surgery. Is it Worth it?

Introduction: In adult spinal deformity surgery, rod-contouring is a critical step that determines postoperative alignment. While the rod is traditionally contoured manually, novel computer-assisted systems have emerged in the hopes of minimizing operation time and blood loss, and improving accuracy. However, these systems require aggressive bending that may increase risk of rod fractures. Incidence of fracture after computer-assisted contouring versus that after manual contouring has been poorly reported.

Methods: We retrospectively reviewed a prospectively maintained database of consecutive cases at our institution from January 2016 through November 2021. Inclusion criteria were age >18, fusion of ≥5 vertebrae, and rod implantation, and minimum 1 year follow-up with radiographs. Patients were divided into computer-assisted (CA) group and traditional-contouring (TC) groups. Incidence of rod fracture between the groups was determined. Mann-Whitney nonparametric test was used to compare medians between the groups. A P value  0.05 was considered statically significant.

Results: 177 patients were identified, with 32 CA and 145 TC. The most frequent age range was 60-69 years in both groups: CA 46.9% (n=15) and TC 41.4% (n=60). There were no differences between the groups in age, sex or body mass index (p>.05). Rod fracture incidence was 34.4% in the CA group versus 17.9% in the TC group (Z=1.83; p=0.03). The risk of presenting rod fracture in the MIS group was 1.92 times higher than those who underwent open surgery.

Conclusion : The use of computer-assisted rod-contouring in deformity surgery was associated with a higher incidence of rod fractures. This can predispose patients to pseudoarthrosis, postoperative pain, neurologic deficit, and reoperation. Increased risk of fracture may be due to aggressive bending and knotching of the rod that is associated more with computer-assisted systems than with traditional manual systems.