title: 3-dimensional buttocks response to sitting: a case report.
abstract: OBJECTIVE
  The aim of this study was to describe an individual's 3-dimensional buttocks response to sitting. Within that exploration, we specifically considered tissue (i.e., fat and muscle) deformations, including tissue displacements that have not been identified by research published to date.
  
  
  METHODS
  The buttocks anatomy of an able-bodied female during sitting was collected in a FONAR Upright MRI. T1-weighted Fast Spin Echo scans were collected with the individual seated on a custom wheelchair cushion with a cutout beneath the pelvis ("unloaded"), and seated on a 3″ foam cushion ("loaded"). 2D slices of the MRI were analyzed, and bone and muscle were segmented to permit 3D rendering and analyses.
  
  
  RESULTS
  MRIs indicated a marked decrease in muscle thickness under the ischial tuberosity during loaded sitting. This change in thickness resulted from a combination of muscle displacement and distortion. The gluteus and hamstrings overlapped beneath the pelvis in an unloaded condition, enveloping the ischial tuberosity. But the overlap was removed under load. The hamstrings moved anteriorly, while the gluteus moved posterior-laterally. Under load, neither muscle was directly beneath the apex of the ischial tuberosity. Furthermore, there was a change in muscle shape, particularly posterior to the peak of the ischial tuberosity.
  
  
  CONCLUSIONS
  The complex deformation of buttocks tissue seen in this case study may help explain the inconsistent results reported in finite element models. 3D imaging of the seated buttocks provides a unique opportunity to study the actual buttocks response to sitting.
authors.affiliation: School of Applied Physiology, Georgia Institute of Technology, 490 10th Street NW, Atlanta, GA 30318, USA. sharon.sonenblum@coa.gatech.edu
authors.forename: Sharon Eve
authors.initials: SE
authors.lastname: Sonenblum
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Sprigle
authors.forename: John McKay
authors.initials: JM
authors.lastname: Cathcart
authors.forename: Robert John
authors.initials: RJ
authors.lastname: Winder
mesh_terms: D000328:Adult; D002081:Buttocks / Q000033:anatomy & histology* / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging; D011187:Posture / Q000502:physiology*; D003668:Pressure Ulcer / Q000473:pathology / Q000503:physiopathology; D016474:Weight-Bearing / Q000502:physiology*