title: Scanning electron microscopic observations of 'fractured' biodegradable plates and screws.
abstract: BACKGROUND
  We encountered two out of 100 cases in which implanted biodegradable plates and screws had fractured within 1 month postoperatively.
  
  
  METHODS
  Failure of the material was confirmed through clinical symptoms, radiographs or CT findings. In addition, four specimens obtained from these two cases were examined with regard to their ultrastructure using scanning electron microscopy.
  
  
  RESULTS
  Several principal patterns of the fractured surface were found: (1) gradual cracking, i.e. 'circular stair' and, (2) tortuous threads, i.e. a wavy line. It is conceivable that the material may not have been hit by major sudden forces but a disproportion between the thread configuration and the drilled hole may have led to screw loosening and torsion. Subsequently, the threads were deformed in a 'wavy' manner, finally leading to cracking and fracture of plates and screws. Fractures of plates and screws due to these instabilities are thought to be distinguishable from material resorption.
  
  
  CONCLUSIONS
  In the application of biodegradable materials, more than two screws per single bone segment should be used as a principle of plate-fixation technique in order to avoid a stability-compromising situation, particularly in the stress-bearing areas of the maxillofacial region. Moreover, three-dimensional fixation using more than two plates is recommended in the facial skeleton e.g. zygomatic tripod. Intermaxillary fixation should also be considered to reinforce initial stability in stress-bearing areas.
authors.affiliation: Department of Plastic and Reconstructive Surgery, Kinki University School of Medicine, Osaka, Japan. kosaka@med.kindai.ac.jp
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kosaka
authors.forename: Fumiko
authors.initials: F
authors.lastname: Uemura
authors.forename: Shoko
authors.initials: S
authors.lastname: Tomemori
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kamiishi
mesh_terms: D020341:Absorbable Implants; D000293:Adolescent; D000328:Adult; D000368:Aged; D001672:Biocompatible Materials / Q000737:chemistry; D001860:Bone Plates; D001863:Bone Screws; D016025:Bone Transplantation / Q000295:instrumentation; D002648:Child; D002675:Child, Preschool; D002680:Chin / Q000601:surgery; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation; D006801:Humans; D007223:Infant; D008297:Male; D008337:Mandibular Fractures / Q000601:surgery; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D011091:Polyesters / Q000737:chemistry; D011475:Prosthesis Failure; D012189:Retrospective Studies; D013314:Stress, Mechanical; D013499:Surface Properties; D014057:Tomography, X-Ray Computed
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; C033616:poly(lactide)