title: When is compensation for lumbar spinal stenosis a clinical sagittal plane deformity?
abstract: Degenerative lumbar stenosis (DLS) patients have been reported to lean forward in an attempt to provide neural decompression. Spinal alignment in patients with DLS may resemble that of adult spinal deformity (ASD). No previous studies have compared and contrasted the compensatory mechanisms of DLS and ASD patients.
  
  
  
  This study aimed to determine the differences in compensatory mechanisms between DLS and ASD patients with increasing severity of sagittal spinopelvic malalignment. Contrasting these compensatory mechanisms may help determine at what severity sagittal malalignment represents a clinical sagittal deformity rather than a compensation for neural compression.
  
  
  
  This is a retrospective clinical and radiological review.
  
  
  
  Baseline x-rays in patients without spinal instrumentation, with the clinical radiological and diagnoses of DLS or ASD, were assessed for patterns of spinopelvic compensatory mechanisms. Patients were stratified by sagittal vertical axis (SVA) according to the Scoliosis Research Society-Schwab [SRS-Schwab] classification.
  
  
  
  Radiographic spinopelvic parameters were measured in the DLS and ASD groups, including SVA, pelvic incidence-lumbar lordosis mismatch (PI-LL), T1 spinopelvic inclination (T1SPi), T1 pelvic angle (TPA), and pelvic tilt (PT).
  
  
  
  The two diagnosis cohorts were propensity-matched for PI and age. Each group contained 125 patients and was stratified according to the SRS-Schwab classification. Regional spinopelvic,lower limb, and global alignment parameters were assessed to identify differences in compensatory mechanisms between the two groups with differing degrees of deformity. No funding was provided by any third party in relation to carrying out this study or preparing the manuscript.
  
  
  
  With mild to moderate malalignment (SRS-Schwab groups "0," or "+" for PT, PI-LL, or SVA), DLS patients permit anterior truncal inclination and recruit posterior pelvic shift instead of pelvic tilt to maintain balance, while providing relief of neurologic symptoms. Adult spinal deformity patients with mild to moderate deformity recruit pelvic tilt earlier than DLS patients. With moderate to severe malalignment, no significant difference was found in compensatory mechanisms between DLS and ASD patients.
  
  
  
  Patients with DLS permit mild to moderate deformity without recruiting compensatory mechanisms of PT, reducing truncal inclination and thoracic hypokyphosis to achieve neural decompression. However, with moderate to severe deformity, their desire for upright posture overrides the desire for neural decompression, evident by the adaptation of compensatory mechanisms similar to that of ASD patients.
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA. Electronic address: aaronbuckland@me.com.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Buckland
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Shaleen
authors.initials: S
authors.lastname: Vira
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Oren
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Renaud
authors.initials: R
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Bradley Y
authors.initials: BY
authors.lastname: Harris
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Spiegel
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Bassel G
authors.initials: BG
authors.lastname: Diebo
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Barthelemy
authors.initials: B
authors.lastname: Liabaud
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Themistocles S
authors.initials: TS
authors.lastname: Protopsaltis
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Schwab
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Errico
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, c/- Spine Research Center, 306 E. 15th St, New York, NY 10003, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Bendo
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000000981:diagnostic imaging / Q000473:pathology; D008161:Lumbosacral Region / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011187:Posture; D011859:Radiography; D012600:Scoliosis / Q000000981:diagnostic imaging* / Q000473:pathology; D013130:Spinal Stenosis / Q000000981:diagnostic imaging* / Q000473:pathology
keywords: Adult spinal deformity; Compensatory mechanisms; Lumbar stenosis; Neural decompression; SRS classification; Sagittal malalignment; Spinopelvic alignment