title: Sacral Bone Mass Distribution Assessed by Averaged Three-Dimensional CT Models: Implications for Pathogenesis and Treatment of Fragility Fractures of the Sacrum.
abstract: BACKGROUND
  Fragility fractures of the sacrum are increasing in prevalence due to osteoporosis and epidemiological changes and are challenging in their treatment. They exhibit specific fracture patterns with unilateral or bilateral fractures lateral to the sacral foramina, and sometimes an additional transverse fracture leads to spinopelvic dissociation. The goal of this study was to assess sacral bone mass distribution and corresponding changes with decreased general bone mass.
  
  
  METHODS
  Clinical computed tomography (CT) scans of intact pelves in ninety-one individuals (mean age and standard deviation, 61.5 ± 11.3 years) were used to generate three-dimensional (3D) models of the sacrum averaging bone mass in Hounsfield units (HU). Individuals with decreased general bone mass were identified by measuring bone mass in L5 (group 1 with <100 HU; in contrast to group 2 with ≥100 HU).
  
  
  RESULTS
  In group 1, a large zone of negative Hounsfield units was located in the paraforaminal lateral region from S1 to S3. Along the trans-sacral corridors, a Hounsfield unit peak was observed laterally, corresponding to cortical bone of the auricular surface. The lowest Hounsfield unit values were found in the paraforaminal lateral region in the sacral ala. An intermediate level of bone mass was observed in the area of the vertebral bodies, which also demonstrated the largest difference between groups 1 and 2. Overall, the Hounsfield units were lower at S2 than S1.
  
  
  CONCLUSIONS
  The models of averaged bone mass in the sacrum revealed a distinct 3D distribution pattern.
  
  
  CONCLUSIONS
  The negative values in the paraforaminal lateral region may explain the specific fracture patterns in fragility fractures of the sacrum involving the lateral areas of the sacrum. Transverse fractures located between S1 and S2 leading to spinopelvic dissociation may occur because of decreased bone mass in S2. The largest difference between the studied groups was found in the vertebral bodies and might support the use of transsacral or cement-augmented implants.
authors.affiliation: AO Research Institute Davos, Davos, Switzerland Department of Orthopaedics and Traumatology, University Medical Center Mainz, Mainz, Germany wagner.daniel@gmx.ch.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wagner
authors.affiliation: AO Research Institute Davos, Davos, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Kamer
authors.affiliation: Department of Orthopedics and Joint Reconstructive Surgery, Toyama Municipal Hospital, Toyama, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sawaguchi
authors.affiliation: AO Research Institute Davos, Davos, Switzerland.
authors.forename: R Geoff
authors.initials: RG
authors.lastname: Richards
authors.affiliation: AO Research Institute Davos, Davos, Switzerland.
authors.forename: Hansrudi
authors.initials: H
authors.lastname: Noser
authors.affiliation: Department of Orthopaedics and Traumatology, University Medical Center Mainz, Mainz, Germany.
authors.forename: Pol M
authors.initials: PM
authors.lastname: Rommens
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D050723:Fractures, Bone / Q000209:etiology* / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D012189:Retrospective Studies; D012447:Sacrum / Q000000981:diagnostic imaging* / Q000293:injuries*; D014057:Tomography, X-Ray Computed; D055815:Young Adult