title: Segmental Pelvic Correlation (SPeC): a novel approach to understanding sagittal plane spinal alignment.
abstract: BACKGROUND
  Lumbar lordosis (LL) correlates with pelvic morphology, and it has been demonstrated that as LL increases, the inflection point and apex of lordosis move cranially. This suggests that each segment of the lumbar spine relates to pelvic morphology in a unique way.
  
  
  OBJECTIVE
  This study aimed to establish whether there is a direct relationship between pelvic morphology and lumbar segmental angulation in the sagittal plane.
  
  
  METHODS
  A retrospective analysis of 41 patient radiographs was carried out.
  
  
  METHODS
  Inclusion criteria included patients with full length standing anterioposterior and lateral radiographs of the spine from base of occiput to proximal femora, with clearly visible vertebral end plates from T12 to S1 and a thoracic kyphosis (TK) and LL within the normal range. Patients were excluded if they had a coronal spinal deformity affecting the lumbar spine, chronic back pain, spondylolisthesis, spondylolysis, congenital scoliosis, or skeletal dysplasia.
  
  
  METHODS
  Spinopelvic radiographic parameters of pelvic incidence (PI), LL, TK, and segmental angulation at each level from L1 to the sacrum were the outcome measures.
  
  
  METHODS
  Forty-one lateral whole spine radiographs with normal sagittal profiles from the spinal deformity clinic were retrospectively reviewed. Pelvic incidence, LL, TK, and segmental angulation at each level from L1 to the sacrum were measured (from end plate to end plate), distinguishing the vertebral body and intervertebral disc contribution. Pearson correlation coefficients were used to analyze any relationship between pelvic parameters and segmental angulation.
  
  
  RESULTS
  A strong correlation was found between PI and LL. Pelvic incidence correlated strongly with the L1 and L2 motion segments (p=.0001, p=.03), notably at the intervertebral discs but not the L4 and L5 motion segments. The proportion of total LL contributed at L4-L5 and L5-S1 reduced as PI increased.
  
  
  CONCLUSIONS
  Pelvic incidence can predict segmental angulation. Although the majority of LL is produced at the L4 and L5 motion segments, cephalad lumbar segments sequentially become increasingly important as PI increases. This describes a continuum where the L1 and L2 motion segments crucially fine-tune total LL according to PI. This allows segmental abnormalities to be identified when compensation in adjacent segments maintain normal total LL. It also paves the way for anatomical segmental reconstruction in degenerative adult deformity based on pelvic morphology.
authors.affiliation: Spinal Deformity Unit, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
authors.forename: Hanny A
authors.initials: HA
authors.lastname: Anwar
authors.affiliation: Spinal Deformity Unit, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK. Electronic address: josephsbutler@hotmail.com.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Butler
authors.affiliation: Spinal Deformity Unit, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
authors.forename: Tejas
authors.initials: T
authors.lastname: Yarashi
authors.affiliation: Spinal Deformity Unit, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
authors.forename: Karthig
authors.initials: K
authors.lastname: Rajakulendran
authors.affiliation: Spinal Deformity Unit, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
authors.forename: Sean
authors.initials: S
authors.lastname: Molloy
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D008141:Lordosis / Q000000981:diagnostic imaging*; D008161:Lumbosacral Region / Q000000981:diagnostic imaging*; D008297:Male; D010388:Pelvis / Q000000981:diagnostic imaging*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D013168:Spondylolisthesis / Q000000981:diagnostic imaging*
keywords: Lumbar lordosis; Pelvic incidence; Sagittal balance; Sagittal profile; Segmental angulation; Segmental pelvic correlation