Accuracy of Rod Contouring to Desired Angles With and Without a Template: Implications for Achieving Desired Spinal Alignment and Outcomes

Abstract

Study Design: Biomechanical Study. Objective: The search for optimal spinal alignment has led to the development of sophisticated formulas and software for preoperative planning. However, preoperative plans are not always appropriately executed since rod contouring during surgery is often subjective and estimated by the surgeon. We aimed to assess whether rods contoured to specific angles with a French rod bender using a template guide will be more accurate than rods contoured without a template. Methods: Ten experienced spine surgeons were requested to contour two 125 × 5.5 mm Ti64 rods to 40°, 60° and 80° without templates and then 2 more rods using 2D metallic templates with the same angles. Rod angles were then measured for accuracy and compared. Results: Average angles for rods bent without a template to 40°, 60° and 80° were 60.2°, 78.9° and 97.5°, respectively. Without a template, rods were overbent by a mean of 18.9°. When using templates of 40°, 60° and 80°, mean bend angles were 41.5°, 59.1° and 78.7°, respectively, with an average underbend of 0.2°. Differences between the template and non-template groups for each target angle were all significant (p < 0.001). Conclusions: Without the template, surgeons tend to overbend rods compared to the desired angle, while surgeons improved markedly with a template guide. This tendency to overbend could have significant impact on patient outcomes and risk of proximal junctional failure and warrants further research to better enable surgeons to more accurately execute preoperative alignment plans.

Correction of Thoracic Hypokyphosis in Adolescent Scoliosis Using Patient-Specific Rod Templating

“…Various factors have been implicated in thoracic hypokyphosis and reciprocal loss of lumbar lordosis after AIS surgery. They include: The surgeon themselves: Variation in surgeons’ choice of techniques and differences between different surgeons’ techniques, including variation in rod contouring [ 12 , 25 , 26 , 27 , 28 , 29 , 30 ]. Implant density and implant choice: Higher screw density on the concave side with thicker and cobalt chrome rods have been associated with restoration of kyphosis to greater than 20 degrees [ 31 ].…”

“…The surgeon themselves: Variation in surgeons’ choice of techniques and differences between different surgeons’ techniques, including variation in rod contouring [ 12 , 25 , 26 , 27 , 28 , 29 , 30 ].…”

“…Regardless of the technique used to correct scoliosis deformity, the ultimate shape of the spine is dependent on the shape of the rods. Rod contouring plays a crucial role in the correction achieved, and a recent study has demonstrated poor reliability and high variability of free-hand rod bending [ 12 , 29 , 30 ]. The authors [ 29 ] found that even in experienced surgeons, free-hand bending results in overbending rods by a mean value of 18.9°.…”

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

“…In the operating room, rods are bend manually using French benders, which may cause over or under bending of the rods and lead to malalignment. Biomechanical properties of posterior instrumentation and rod contouring are important factors effecting the patient outcomes (6,7). Adequate rod contouring is vital for achieving both global and regional target re-alignments, thus, reinforcing the importance of intra-operative rod bending.…”

“…Recent studies have reported that inappropriate (over or under) bending of spinal rods can affect the postoperative spino-pelvic alignment, leading to inferior patient outcomes (6).…”