title: When do anterior external or internal fixators provide additional stability in an unstable (Tile C) pelvic fracture? A biomechanical study.
abstract: OBJECTIVE
  This study aimed at evaluating the additional stability that is provided by anterior external and internal fixators in an unstable pelvic fracture model (OTA 61-C).
  
  
  METHODS
  An unstable pelvic fracture (OTA 61-C) was created in 27 synthetic pelves by making a 5-mm gap through the sacral foramina (posterior injury) and an ipsilateral pubic rami fracture (anterior injury). The posterior injury was fixed with either a single iliosacral (IS) screw, a single trans-iliac, trans-sacral (TS) screw, or two iliosacral screws (S1S2). Two anterior fixation techniques were utilized: external fixation (Ex-Fix) and supra-acetabular external fixation and internal fixation (In-Fix); supra-acetabular pedicle screws connected with a single subcutaneous spinal rod. The specimens were tested using a nondestructive single-leg stance model. Peak-to-peak (P2P) displacement and rotation and conditioning displacement (CD) were calculated.
  
  
  RESULTS
  The Ex-Fix group failed in 83.3 % of specimens with concomitant single-level posterior fixation (Total: 15/18-7 of 9 IS fixation, 8 of 9 TS fixation), and 0 % (0/9) of specimens with concomitant two-level (S1S2) posterior fixation. All specimens with the In-Fix survived testing except for two specimens treated with In-Fix combined with IS fixation. Trans-sacral fixation had higher pubic rotation and greater sacral and pubic displacement than S1S2 (p < 0.05). Rotation of the pubis and sacrum was not different between In-Fix constructs combined with single-level IS and TS fixation.
  
  
  CONCLUSIONS
  In this model of an unstable pelvic fracture (OTA 61-C), anterior fixation with an In-Fix was biomechanically superior to an anterior Ex-Fix in the setting of single-level posterior fixation. There was no biomechanical difference between the In-Fix and Ex-Fix when each was combined with two levels of posterior sacral fixation.
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Trauma Institute, University of California-San Francisco (UCSF)/San Francisco General Hospital, 2550 23rd Str., Bldg. 9, 2nd Floor, San Francisco, CA, 94110, USA.
authors.forename: E
authors.initials: E
authors.lastname: Mcdonald
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Trauma Institute, University of California-San Francisco (UCSF)/San Francisco General Hospital, 2550 23rd Str., Bldg. 9, 2nd Floor, San Francisco, CA, 94110, USA. Alekos.Theologis@ucsf.edu.
authors.forename: A A
authors.initials: AA
authors.lastname: Theologis
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Trauma Institute, University of California-San Francisco (UCSF)/San Francisco General Hospital, 2550 23rd Str., Bldg. 9, 2nd Floor, San Francisco, CA, 94110, USA.
authors.forename: P
authors.initials: P
authors.lastname: Horst
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Trauma Institute, University of California-San Francisco (UCSF)/San Francisco General Hospital, 2550 23rd Str., Bldg. 9, 2nd Floor, San Francisco, CA, 94110, USA.
authors.forename: U
authors.initials: U
authors.lastname: Kandemir
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Trauma Institute, University of California-San Francisco (UCSF)/San Francisco General Hospital, 2550 23rd Str., Bldg. 9, 2nd Floor, San Francisco, CA, 94110, USA.
authors.forename: M
authors.initials: M
authors.lastname: Pekmezci
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws; D016267:External Fixators; D005592:Fracture Fixation / Q000295:instrumentation* / Q000379:methods; D050723:Fractures, Bone / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D016268:Internal Fixators; D008953:Models, Anatomic; D010384:Pelvic Bones / Q000503:physiopathology / Q000601:surgery*; D011475:Prosthesis Failure; D012447:Sacrum / Q000293:injuries
keywords: Biomechanical analysis; External fixation; Internal fixation; Pelvic fracture