title: Structural integrity of intramedullary rib fixation using a single bioresorbable screw.
abstract: BACKGROUND
  Operative management of flail chest injury is receiving increasing interest. However, we have noticed in our own practice the difficulty in achieving reliable results with posterior rib fracture fixation. In this article, we analyze and model the physiologic forces acting on posterior rib fractures and assess the suitability of an intramedullary screw fixation technique in this site.
  
  
  METHODS
  Computerized finite element analysis (FEA) was used to model a typical sixth rib and analyze the physiologic forces that act on the rib in vivo. A fracture in the posterior aspect of the rib was incorporated into the model, and an intramedullary screw fixation concept was assessed, using both a bioabsorbable polymer screw and a stainless steel screw.The records of 120 consecutive patients with flail chest were reviewed, and 26 patients were identified as having multiple posterior rib fractures with displacement. These patients formed a clinical correlation group by which to assess the FEA model.
  
  
  RESULTS
  FEA modeling of the posterior rib fracture showed likely posterior displacement in response to physiologic forces. Review of the 26 patients with flail chest and displaced posterior fractures confirmed the direction of displacement. Modeling of an intramedullary screw fixation showed significant stresses in the bone/screw contact areas (stainless steel solution) and the prosthesis itself (bioabsorbable polymer solution)
  
  
  CONCLUSIONS
  This FEA model demonstrates that physiologic forces cause posterior displacement at posterior rib fracture sites. Fixation solutions to counteract these forces need to overcome significant stresses at both the bone/prosthesis contact regions and within the prosthetic material itself.
  
  
  METHODS
  Epidemiologic/therapeutic study, level V.
authors.affiliation: CJOB Cardiothoracic Surgery Department, The Alfred Hospital, Perth, Western Australia, Australia. s.marasco@alfred.org.au
authors.forename: Silvana F
authors.initials: SF
authors.lastname: Marasco
authors.forename: Petar
authors.initials: P
authors.lastname: Liovic
authors.forename: Ilija D
authors.initials: ID
authors.lastname: Šutalo
mesh_terms: D020341:Absorbable Implants; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D015331:Cohort Studies; D019245:Compressive Strength; D003198:Computer Simulation; D005260:Female; D020342:Finite Element Analysis; D005409:Flail Chest / Q000000981:diagnostic imaging / Q000601:surgery; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods; D017102:Fracture Healing / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional; D004204:Joint Dislocations / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012253:Rib Fractures / Q000000981:diagnostic imaging / Q000601:surgery*