title: A new concept: 'Relative position between the external force and the bony prominence' explains location-specific occurrence of superficial injury over an undermining lesion.
abstract: OBJECTIVE
  A pressure ulcer is localized injury to the skin and/or underlying tissue usually over a bony prominence, as a result of pressure, or pressure in combination with shear. Although the external forces and bony prominences differ depending on ulcer location, the way in which these anatomical differences affect pressure ulcer development is not well studied.
  
  
  METHODS
  To clarify the location-dependent factors for pressure ulcer development, we focused on superficial injuries that develop over an undermining lesion, which we have termed them bilayer pressure ulcers. Because it is thought that a deep pressure ulcer is caused by ischemia at the deep lesion and a shallow pressure ulcer is caused by shear force to the superficial skin, a bilayer pressure ulcer can be considered a mixed phenotype, induced by both pressure and shear force. We retrospectively examined the frequency of bilayer pressure ulcers by location in a total of 568 pressure ulcers.
  
  
  RESULTS
  The ratio of bilayer pressure ulcers to deep pressure ulcers staged III or more was significantly larger for pressure ulcers over the sacrum.
  
  
  CONCLUSIONS
  A new concept, the relative position between the external force and bony prominence, could explain the frequency and developmental mechanism of bilayer pressure ulcers. The external forces, shape of the bony prominence, and mobility of the soft tissue may be responsible for this concept.
authors: Department of Nursing & Health, School of Nursing & Health, Aichi Prefectural University, Nagoya, Aichi, Japan.
authors: Yoshiko
authors: Y
authors: Takahashi
authors: Department of Gerontechnology, National Center for Geriatrics and Gerontology, Obu, Aichi, Japan.
authors: Tetsuya
authors: T
authors: Nemoto
authors: Department of Pharmacy, National Center for Geriatrics and Gerontology, Obu, Aichi, Japan.
authors: Fumihiro
authors: F
authors: Mizokami
authors: Department of Pharmacy, National Center for Geriatrics and Gerontology, Obu, Aichi, Japan; Department of Clinical Research and Development, National Center for Geriatrics and Gerontology, Obu, Aichi, Japan.
authors: Katsunori
authors: K
authors: Furuta
authors: Department of Gerontechnology, National Center for Geriatrics and Gerontology, Obu, Aichi, Japan.
authors: Yusuke
authors: Y
authors: Murasawa
authors: Department of Nursing & Health, School of Nursing & Health, Aichi Prefectural University, Nagoya, Aichi, Japan.
authors: Masahiko
authors: M
authors: Yoneda
authors: Division of Dermatology and Connective Tissue Medicine, Department of Advanced Medicine, National Center for Geriatrics and Gerontology, Obu, Aichi, Japan. Electronic address: zenzo@ncgg.go.jp.
authors: Zenzo
authors: Z
authors: Isogai
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005121:Extremities; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D003668:Pressure Ulcer / Q000145:classification / Q000209:etiology* / Q000503:physiopathology; D012189:Retrospective Studies; D012447:Sacrum; D012720:Severity of Illness Index; D012867:Skin / Q000293:injuries*
keywords: Bony prominence; Pressure ulcer; Shear force; Undermining lesion