Radius of Curvature in Patient-Specific Short Rod Constructs Versus Standard Pre-Bent Rods

Abstract

Background: Recent studies support the need for sagittal alignment restoration when performing lumbar degenerative spinal fusions. The development of patient-specific spine rods (PSSRs) may help maintain or improve sagittal alignment in these surgeries.Methods: A retrospective review was conducted for patients who underwent posterior spinal surgeries involving 4 or less levels. The preplanned PSSR radii of curvature (ROC) was compared with standard prebent rods with a ROC of 125 mm. All surgeries were performed at a single institution by 3 surgeons from September 2016 through October 2018. Data were then compared using a 2-tailed paired t test. PSSR had either 1 or 2 definitive ROCs.Results: For rods with 2 ROCs, the ''cranial'' curve was measured between the upper instrumented level and L4 or L5. The ''caudal'' curve was measured between L4 or L5 and the lower instrumented level. The PSSR with 1 ROC and the caudal portion of the rods with 2 ROCs were significantly smaller than the industry standard ROC.Conclusions: PSSR demonstrate more acute ROC than industry standard rods. In PSRs, the most lordosis occurs between L4-S1 and flattens out at the thoracolumbar junction, mimicking the normal distribution of lumbar lordosis. PSSRs could help achieve or maintain sagittal alignment and prevent the sequela of flat back syndrome.

Pre-Operative Planning in Complex Deformities and Use of Patient-Specific UNiD™ Instrumentation

“…When evaluating PSSRs for degenerative spine cases, the rods were noted to have statistically significant differences in radius of curvature compared to off-the-shelf rods. 13 Further, these differences were similar and consistent from L4-S1 when compared to the upper portion of the lumbar spine (L1-L4). Clinical results, as presented, have also shown improved results over a recently published cohort of degenerative lumbar cases (See Table 4 ).…”

The association of rod curvature with postoperative outcomes in patients undergoing posterior lumbar interbody fusion for spinal stenosis

“…Wanivenhaus et al reported that augmented reality-assisted rod bending could reduce surgery time by 20% and increase the accuracy of rod length [20]. Patient-speci c rods were also employed to help achieve satisfactory sagittal alignment, particularly in spine deformity surgery [5,21].…”

Materials for Implantable Surface Electrode Arrays: Current Status and Future Directions

“…[40,69,212] The spinal cord is just a few mm in diameter and is fairly cylindrical in shape with a Gaussian curvature close to zero. [213,214] Because large amounts of nerve inputs and outputs are processed at the spinal cord, the surface electrode arrays that interface with the tissue are almost always used to stimulate regions of the cord rather than record information. The stimulation tends to be at regions that are damaged with a loss of neuronal bodies, and so electrodes must be able to pass large amounts of current to the spinal cord and are often composed of platinum.…”