title: Biomechanical evaluation of internal fixation techniques for unstable meso-type os acromiale.
abstract: BACKGROUND
  Several internal fixation surgical techniques have been described for the treatment of symptomatic os acromiale. The purpose of this study was to compare the biomechanical characteristics of different internal fixation techniques for the operative treatment of unstable meso-type os acromiale in a cadaveric model.
  
  
  METHODS
  Testing was performed on 12 matched pairs of cadaveric acromia with simulated meso-type os acromiale. Twelve specimens were prepared with 2 cannulated 4.0-mm screws only (SO group), inserted in the anterior-posterior direction. Contralateral specimens were repaired with screws and a tension band (TB group). An inferiorly directed load to the anterior acromion was applied at a rate of 60 mm/min until failure. Ultimate failure load, stiffness, and fracture pattern were recorded and analyzed.
  
  
  RESULTS
  Ultimate failure load was significantly higher for the TB group (mean, 336 N ± 126 N; range, 166-623 N; P = .01) than for the SO group (mean, 242 N ± 57 N; range, 186-365 N). In contrast, no significant difference in stiffness was found between the SO group (mean, 22.1 N/mm ± 4.7 N/mm; range, 13.0-33.3 N/mm; P = .94)) and the TB group (mean, 22.2 N/mm ± 2.9 N/mm; range, 18.2-26.6 N/mm).
  
  
  CONCLUSIONS
  Surgical repair of simulated unstable meso-type os acromiale by a combination of cannulated screws with a tension band leads to significantly higher repair strength at time zero in a cadaveric model compared with cannulated screws alone.
authors.affiliation: Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, CO, USA; Department of Trauma and Reconstructive Surgery, University of Leipzig, Leipzig, Germany.
authors.forename: Ulrich J A
authors.initials: UJ
authors.lastname: Spiegl
authors.affiliation: Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, CO, USA.
authors.forename: Sean D
authors.initials: SD
authors.lastname: Smith
authors.affiliation: Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, CO, USA.
authors.forename: Jocelyn N
authors.initials: JN
authors.lastname: Todd
authors.affiliation: Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, CO, USA.
authors.forename: Coen A
authors.initials: CA
authors.lastname: Wijdicks
authors.affiliation: Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, CO, USA; The Steadman Clinic, Vail, CO, USA. Electronic address: drmillett@thesteadmanclinic.com.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Millett
mesh_terms: D000174:Acromion / Q000002:abnormalities* / Q000601:surgery; D001696:Biomechanical Phenomena; D001863:Bone Screws; D001864:Bone Wires; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*; D010012:Osteogenesis
keywords: Tension band; cannulated screws; os acromiale