Three-dimensional printing versus freehand surgical techniques in the surgical management of adolescent idiopathic spinal deformity

Abstract

Background: Three-dimensional (3D) printed guides are finding increasing applications in the field of orthopaedic surgery and more recently spine surgery. This retrospective cohort study compares benefits and costs of 3D printed guides in surgical treatment of adolescent idiopathic scoliosis (AIS) compared to freehand techniques.

Methods: Intraoperative screw placement was conducted either with 3D printed guides (3D cohort) or traditional freehand technique (freehand cohort) for AIS patients undergoing spinal fusion at a single institution. Patient and perioperative data include: screw placement time, length of surgery, blood loss, hospital stay, spinal curvature correction, total implant costs and training level of surgical assist. Multivariate analysis assessed for confounding and effect modification. P-values <0.05 were considered significant.

Results: There were 29 patients included in analyses, 18 in the 3D and 11 in the freehand (FH) cohort, for a total of 263 3D and 307 freehand screws. Between cohorts, there were no significant differences in patient age (P=0.93), gender (P=0.15), height (P=0.18) or weight (P=0.40). The 3D cohort (mean $26,215, SD =$6,374) had significantly higher implant costs than FH (mean $18,660, SD =$5,587, P=0.003) with significantly reduced intraoperative blood loss (mean 559 mL, SD =273 FH; vs. mean 357 mL, SD =123 3D; P=0.01). On multivariate analysis, surgical residents had significantly faster screw placement times when using 3D guides (P<0.001) than when placing screws freehand. There were no significant differences between cohorts in length of postoperative hospitalization, spinal levels fused, or coronal or sagittal curve correction.

Conclusions: At significant cost, 3D printed guides reduce intraoperative blood loss compared to freehand pedicle screw placement and reduce screw placement time for surgical residents.

Keywords: 3D printing; Adolescent idiopathic scoliosis; resident education; scoliosis; screw guide.

Figure 1

Three-dimensional printed anchor placement. Following exposure, the three-dimensional (3D) guide is placed onto the spinal model to determine how the docking points should sit on the inferior facets and transverse processes. In the above figure, the cephalad aspect of the spinal model is closest to the viewer, while the caudal aspect hidden from view.

Figure 2

Three-dimensional printed guide placement on spine. The placement of three-dimensional (3D) guide on thoracic spinal level 7 (T7). The thoracic spinal level 6 (T6) screws are placed and the inferior facets of T6 are removed with a burr. The inferior facets of the transverse processes of T7 must be intact for the 3D guide to dock appropriately and appropriately guide drill hole placement.

Figure 3

Poisson multivariate model for variables affecting screw placement time. A Poisson model was used to account for heteroskedasticity with respect to time per screw placement. Variables are expressed as means with standard 95% confidence intervals. A strong interaction term was observed between the training level of the first surgical assist and time per screw placement, with residents (PGY levels 2-5) benefitting the most from the use of three-dimensional (3-D) guides.