Patient-specific Rods for Surgical Correction of Sagittal Imbalance in Adults

Abstract

Study Design: This was an innovative concept and a preliminary prospective series. Objective: The aim of this study was to present the concept and the technical aspects of patient-specific rods (PSR), and compare preoperative and postoperative sagittal parameters (after PSR implantation), with a special focus on the difference pelvic incidence (PI)—lumbar lordosis (LL). Background: Despite established techniques for planning and proven correlations between quality of life and sagittal alignment, some patients do not achieve optimal radiologic outcomes after surgery and are still hypolordotic and imbalanced. We hypothesize that the use of PSR could improve the correspondence between planning and surgical realization. Methods: The planning was based on spinopelvic parameters evaluated on a full-spine x‐ray. The surgical procedure including osteotomies was simulated using a dedicated program to reach the following objectives: PI-LL<10 degrees, a pelvic tilt <20 degrees, and sagittal vertical axis <50 mm. From the virtually corrected spine, the rod curvature and length were defined. Two PSRs were thus precisely manufactured and bent to this specification. Adults with degenerative spinal disorders requiring a construct ≥5 levels were implanted with PSR and prospectively included. We compared ratios through the χ2 test. Results: A total of 60 patients (mean age of 64.4 years old; range, 34–83) were included. Follow-up was carried out over a period of 1 year. Average pedicle screws construct was of 6.4 levels (range, 5–9). Eight patients underwent a pedicle subtraction osteotomy. PI-LL was <10 degrees at baseline in 29/60 patients, and at follow-up in 50/60 (odds ratio=5, P=E-5). Conclusions: The ratio of patients with optimal PI-LL improved significantly from PSR implantation. In comparison with published data for conventional surgery, patients implanted with PSR were 2.6 times more likely to be optimally corrected. The expected benefits of PSR include the optimal execution of the plan, decreased mechanical complications, and reduced operating time, no longer requiring the bending of rods during surgery. A randomized trial on sagittal correction using PSR is ongoing.

Adult Spinal Deformities: Can Patient-Specific Rods Change the Preoperative Planning into Clinical Reality? Feasibility Study and Preliminary Results about 77 Cases

“…Finally, results from our study revealed a low rate of mechanical complications (4%) without rod breakage which is comparable with previous report [ 9 ]; however, our mechanical results must be taken into account cautiously due to the short follow-up (3 months).…”

“…The results presented here are in line with the study of Barton et al [ 8 ] who also reported significant improvement of sagittal parameters using PSR. More recently, Solla et al [ 9 ] reported their experience about 60 patients managed using PSR with a correction of PI-LL mismatch in 66% of the cases, a correction of SVA in 38% of the cases, and a correction of PT in 29% of the cases. According to their results, postoperative PI-LL mismatch was correlated with preoperative PI-LL and performing a PSO; postoperative SVA was correlated with preoperative SVA, performing a PSO, and age of the patient, and postoperative PT was correlated with preoperative PT.…”

Advances in Spinal Fusion Strategies in Adult Deformity Surgery

“…The notion of age-adjusted parameters emphasizes that PI–LL mismatch may change substantially for patients over 74 years old [28]. New technology using the latest advancements in machine learning and predictive analytics may offer substantial clinical advantages in determining unique goals of correction to reduce the rates of pseudarthrosis, revision surgery, and proximal junctional failure [41, 42, 45].…”

Treatment of adult thoracolumbar spinal deformity: past, present, and future

“…Improved means of rod contouring are needed, and the recent introduction of preplanned ma-chine-bent rods may improve fatigue life, thereby extending the time for arthrodesis to occur. 84 In addition, preplanned rods may facilitate achievement of desired spinal alignment which may also enhance fatigue life. Advances are also needed in osteobiologics and other grafting materials in order to improve fusion rates.…”

“…Preplanned machine-bent rods may reduce junctional failures by helping to ensure that desired alignment corrections are achieved, including overall magnitudes of thoracic and lumbar curves, location of LL restoration (e.g., in the lower lumbar levels), and appropriate contouring of the proximal end of the rod. 34,35,84 An overall better definition of individualized alignment objectives, beyond simple age-adjusted objectives, could markedly reduce PJK. 32,36 In the future, more aggressive attention to bone optimization may also reduce junctional fractures.…”