title: T9 versus T10 as the upper instrumented vertebra for correction of adult deformity-rationale and recommendations.
abstract: BACKGROUND
  Adult spinal deformity correction sometimes involves long posterior pedicle screw constructs extending from the lumbosacral spine to the thoracic vertebra. As fusion obliterates motion and places supraphysiological stress on adjacent spinal segments, it is crucial to ascertain the ideal upper instrumented vertebra (UIV) to minimize risk of proximal junctional failure (PJF). The T10 vertebra is often chosen to allow bridging of the thoracolumbar junction into the immobile thoracic vertebrae on the basis that it is the lowest immobile thoracic vertebra strut by the rib cage.
  
  
  OBJECTIVE
  This study aimed to characterize the range of motion (ROM) of each vertebral segment from T7 to S1 to determine if T10 is truly the lowest immobile thoracic vertebra.
  
  
  METHODS
  This is a prospective, comparative study.
  
  
  METHODS
  Seventy-nine adults (mean age of 45.4 years) presenting with low back pain or lower limb radiculopathy or both, without previous spinal intervention, metastases, fractures, infection, or congenital deformities of the spine, were included in the study.
  
  
  METHODS
  A ROM >5° across two vertebral segments as determined by the Cobb method from radiographs.
  
  
  METHODS
  Lumbar flexion-extension and neutral erect radiographs were obtained in randomized order using a slot scanner. Segmental ROM was measured from T7-T8 to L5-S1 and analyzed for significant differences using t tests. Age, gender, radiographical indices such as standard spinopelvic parameters, sagittal vertical axis (SVA), C7-T12 SVA, T1 slope, thoracic kyphosis (TK), and lumbar lordosis (LL) were studied via multivariate analysis to identify predictive factors for >5° change in ROM at the various segmental levels. There were no sources of funding and no conflicts of interest associated with this study.
  
  
  RESULTS
  In the thoracolumbar spine, significant decreases in ROM when compared with the adjacent caudad segment occurs up to T9-T10, with mean total ROM of 1.98±1.47° (p<.001) seen in T9-T10, 2.19±1.67° (p<.001) in T10-T11, and 3.92±3.21°(p<.001) in T11-T12. The total ROM of T8-T9 (2.53±1.79°) was not significantly different from that of T9-T10 (p=.261). At the thoracolumbar junction, absence of scoliosis (OR 11.37, p=.020), high pelvic incidence (OR 1.14, p=.046), and low T1 slope (OR 1.45, p=.030) were predictive of ROM >5°.
  
  
  CONCLUSIONS
  Lumbar spine flexion-extension ROM decreases as it approaches the thoracolumbar junction. T10 is indeed the lowest immobile thoracic vertebra strut by the rib cage, and the last significant decrease in ROM is observed at T9-T10, in relation to T10-T11. However, because this also implies that a UIV of T10 would mean there is only one level of fixation above the relatively mobile segment, while respecting other factors that influence UIV selection, we propose the T9 vertebra as a more ideal UIV to fulfill the biomechanical concept of bridge fixation. However, this decision should still be taken on a case-by-case basis.
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore. Electronic address: dennis_hey@nuhs.edu.sg.
authors.forename: Hwee Weng Dennis
authors.initials: HWD
authors.lastname: Hey
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore.
authors.forename: Kimberly-Anne
authors.initials: KA
authors.lastname: Tan
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore.
authors.forename: Christabel Shao-En
authors.initials: CS
authors.lastname: Neo
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore.
authors.forename: Eugene Tze-Chun
authors.initials: ET
authors.lastname: Lau
authors.affiliation: Department of Diagnostic Imaging, National University Health System, Singapore.
authors.forename: Denise Ai-Wen
authors.initials: DA
authors.lastname: Choong
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore.
authors.forename: Leok-Lim
authors.initials: LL
authors.lastname: Lau
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore.
authors.forename: Gabriel Ka-Po
authors.initials: GK
authors.lastname: Liu
authors.affiliation: Department of Orthopedic Surgery, National University Health System, Singapore.
authors.forename: Hee-Kit
authors.initials: HK
authors.lastname: Wong
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D016059:Range of Motion, Articular; D012600:Scoliosis / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D013904:Thoracic Vertebrae / Q000601:surgery*
keywords: Adult spinal deformity; Biomechanical; Proximal junctional failure; Range of motion; Thoracolumbar junction; Upper instrumented vertebra