title: Is there a biomechanical cause for spontaneous pneumothorax?
abstract: OBJECTIVE
  Primary spontaneous pneumothorax has long been explained as being without apparent cause. This paper deals with the effect of chest wall shape and explains how this may lead to the pathogenesis of primary spontaneous pneumothorax.
  
  
  METHODS
  Rib cage measurements were taken from chest radiographs in 12 male pneumothorax patients and 12 age-matched controls. Another group of 15 consecutive male thoracic computerised tomography (CT) were investigated using paramedian coronal and sagittal CT reconstructions to assess apical lung shape. A finite element analysis (FEA) model of a lung apex was constructed, including indentations for the first rib guided by CT scan data, to assess pleural stress. This model was tested using different anteroposterior diameter ratios, producing a range of thoracic indexes.
  
  
  RESULTS
  The pneumothorax patients had a taller chest (P = 0.03), wider transversely (P = 0.009) and flatter (P = 0.03) when compared with controls, resulting in a low thoracic index. Prominent rib indentations were found anteriorly and posteriorly on the lung surface, especially on the first rib on CT. FEA of the lung revealed significantly higher stress (×5-×10) in the apex than in the rest of the lung. This was accentuated (×4) in low thoracic index chests, resulting in 20-fold higher stress levels in their apex.
  
  
  CONCLUSIONS
  The FEA model demonstrates a 20-fold increase in pleural stress in the apex of chests with low thoracic index typical of spontaneous pneumothorax patients. Mild changes in thoracic index, as occurring in females or with aging, reduce pleural stress. Spontaneous pneumothorax occurring in young male adults may have a biomechanical cause.
authors.affiliation: Department of Cardiac Services, Mater Dei Hospital, Msida, Malta Faculty of Medicine, Department of Anatomy, University of Malta, Msida, Malta aaron.casha@um.edu.mt.
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Casha
authors.affiliation: Department of Cardiac Services, Mater Dei Hospital, Msida, Malta.
authors.forename: Alexander
authors.initials: A
authors.lastname: Manché
authors.affiliation: Faculty of Science, Metamaterials Unit, University of Malta, Msida, Malta.
authors.forename: Ruben
authors.initials: R
authors.lastname: Gatt
authors.affiliation: Department of Physics and Astronomy, Uniwersytet Zielonogórski, Zielona Góra, Poland.
authors.forename: Wiktor
authors.initials: W
authors.lastname: Wolak
authors.affiliation: Department of Physics and Astronomy, Uniwersytet Zielonogórski, Zielona Góra, Poland.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Dudek
authors.affiliation: Faculty of Medicine, Department of Anatomy, University of Malta, Msida, Malta.
authors.forename: Marilyn
authors.initials: M
authors.lastname: Gauci
authors.affiliation: Faculty of Medicine, Department of Anatomy, University of Malta, Msida, Malta.
authors.forename: Pierre
authors.initials: P
authors.lastname: Schembri-Wismayer
authors.affiliation: Faculty of Medicine, Department of Anatomy, University of Malta, Msida, Malta.
authors.forename: Marie-Therese
authors.initials: MT
authors.lastname: Camilleri-Podesta
authors.affiliation: Faculty of Science, Metamaterials Unit, University of Malta, Msida, Malta.
authors.forename: Joseph N
authors.initials: JN
authors.lastname: Grima
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology*; D016022:Case-Control Studies; D003371:Cough / Q000503:physiopathology; D006801:Humans; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D011030:Pneumothorax / Q000000981:diagnostic imaging / Q000453:epidemiology; D013902:Radiography, Thoracic; D012272:Ribs / Q000033:anatomy & histology; D013909:Thorax / Q000033:anatomy & histology*; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Biomechanics; Pneumothorax, pathogenesis; Pneumothorax, spontaneous