Introduction: Minimally invasive techniques are increasingly utilized in adult deformity surgery as surgeon familiarity improves and long-term data is published. Concerns raised in such cases include pseudoarthrosis at levels where interbody grafts are not utilized. Previous studies have not specifically examined the status of the rostral aspect of the surgical construct, which is commonly instrumented without interbody or intertransverse fusion.

Methods: A retrospective analysis was performed on all patients who underwent minimally invasive deformity corrections in two academic spine centers over a ten-year period. Inclusion criteria were at least 2 rostral levels instrumented percutaneously ranging from T8-L2 as upper end of the construct. Fusion assessment was made using computed tomography when possible or dynamic radiographs. Common radiographic parameters and clinical variables were assessed pre and post operatively.

Results: A total of 34 patients fit inclusion criteria. Baseline characteristics included: M:F 14:20, average age of 65.1 years, and BMI 30.2. The number of levels fused on average was 7.4 with an average of 3.4 instrumented percutaneously between T8 and L2, representing a total of 115 rostral levels instrumented percutaneously. Fusion assessment was performed using CT in 70 levels and radiographs in 45 levels. Among the 115 rostral levels instrumented percutaneously robust fusion was seen in 20 (17.4%) with 49 (42.6%) exhibiting some evidence of fusion. Pseudoarthosis was seen in 2 (1.7%) of rostral segments. There were no instances of proximal hardware revision. The number of patients with radiographic PJK was 11 (32.4%). Follow-up imaging was obtained at a mean of 26.7 months. Patients experienced improvements in ODI and VAS comparable to published series.

Conclusions: In the present series of adult scoliosis patients undergoing thoracolumbar deformity correction, rostral segments instrumented percutaneously have a very low rate of pseudoarthorsis (less than 2%) with clear evidence of fusion occurring in >60% of patients.

Patient Care: To our knowledge this is the first series specifically examining the durability and fusion rate in rostral levels instrumented percutaneously as part of a larger scoliosis surgical construct. Presented data strongly suggests that percutaneous fixation techniques can be employed at the rostral segments in adult scoliosis surgery with confidence.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Recognize that percutaneous instrumentation techniques can provide acceptable fusion with very low rates of non-union when employed in scoliosis surgery, 2) Discuss in small groups some of the common reasons for rostral failure of long segment fusions in scoliosis surgery, 3) Describe the incidence and importance of successful fusion at the upper segments in a thoracolumbar scoliosis construct.

References: 1. Etebar S, Cahill DW. Risk factors for adjacent-segment failure following lumbar fixation with rigid instrumentation for degenerative instability. J Neurosurg. 1999;90(2 Suppl):163-169. 2. Ghobrial GM, Eichberg DG, Kolcun JPG, et al. Prophylactic vertebral cement augmentation at the uppermost instrumented vertebra and rostral adjacent vertebra for the prevention of proximal junctional kyphosis and failure following long-segment fusion for adult spinal deformity. Spine J. 2017;17(10):1499-1505. 3. Glattes RC, Bridwell KH, Lenke LG, Kim YJ, Rinella A, Edwards C, 2nd. Proximal junctional kyphosis in adult spinal deformity following long instrumented posterior spinal fusion: incidence, outcomes, and risk factor analysis. Spine (Phila Pa 1976). 2005;30(14):1643-1649. 4. Haque RM, Mundis GM, Jr., Ahmed Y, et al. Comparison of radiographic results after minimally invasive, hybrid, and open surgery for adult spinal deformity: a multicenter study of 184 patients. Neurosurg Focus. 2014;36(5):E13. 5. Lenke LG, Bridwell KH, Bullis D, Betz RR, Baldus C, Schoenecker PL. Results of in situ fusion for isthmic spondylolisthesis. J Spinal Disord. 1992;5(4):433-442. 6. Mummaneni PV, Park P, Fu KM, et al. Does Minimally Invasive Percutaneous Posterior Instrumentation Reduce Risk of Proximal Junctional Kyphosis in Adult Spinal Deformity Surgery? A Propensity-Matched Cohort Analysis. Neurosurgery. 2016;78(1):101-108. 7. Mummaneni PV, Shaffrey CI, Lenke LG, et al. The minimally invasive spinal deformity surgery algorithm: a reproducible rational framework for decision making in minimally invasive spinal deformity surgery. Neurosurg Focus. 2014;36(5):E6. 8. Park P, Wang MY, Lafage V, et al. Comparison of two minimally invasive surgery strategies to treat adult spinal deformity. J Neurosurg Spine. 2015;22(4):374-380. 9. Tan GH, Goss BG, Thorpe PJ, Williams RP. CT-based classification of long spinal allograft fusion. Eur Spine J. 2007;16(11):1875-1881. 10. Uribe JS, Deukmedjian AR, Mummaneni PV, et al. Complications in adult spinal deformity surgery: an analysis of minimally invasive, hybrid, and open surgical techniques. Neurosurg Focus. 2014;36(5):E15. 11. Wang MY, Mummaneni PV. Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus. 2010;28(3):E9.