Assessment of Rod Bending Accuracy for Sagittal Spinal Deformity Correction on 3D Printed Moulage

Abstract

Background: One of the most important objectives in the deformity correction surgery of spine is to achieve appropriate sagittal alignment, to improve patient outcome and reduce the risk of junctional failure. Intra-operative rod bending is crucial to achieve desired alignment. Objectives: Assessment of accuracy of rod bending by spine surgeons with or with-out template and/or correction. Methods: Spine surgeons were asked to bend two rods; one in-situ on three-dimensional (3D) printed moulage, designed based on schematic representation of a patient with Kyphoscoliosis, the other rod was asked to bend with correction angles. The differences were measured and correlated with experience and specialty. Results: 21 fellowship trained spine surgeons participated in this study, for in-situ rod, mean thoracic and lumbar bend were 65.2 (P = 0.033) and 49.3 (P = 0.077) degrees, respectively and for the correction rod, mean bend in thoracic and lumbar were 53.8 (P = 0.001) and 51.8 (P = 0.004) degrees, respectively, with significant difference from cut-off point. Each curve was over-bend and it was more pronounce in thoracic, both on in-situ and correction rods, 61.9 and 71.1 %, respectively. Level of experience showed positive correlation with degree of rod bending more than five years in thoracic in-situ bend (P = 0.003) and thoracic bend with correction (P = 0.004). Field of specialty showed positive correlation as well; with orthopedic in-situ bend (P = 0.002) and with correction (P = 0.003). Conclusions: Spine surgeons tend to over-bend rods, when given target angles and when correction is needed. However, when provided with template, a 3D printed moulage in our study, accuracy of rod bending improved significantly.