title: How many radiographs are needed to detect angular stable head screw cut outs of the proximal humerus - a cadaver study.
abstract: BACKGROUND
  Cut out of locking head screws is the most common complication of locking plates in fracture fixation of the proximal humerus with potentially disastrous consequences. Aim of the study was to find the single best and combination of radiographic projections to reliably detect screw cut outs.
  
  
  METHODS
  The locking plate was fixed to six cadaveric proximal humeri. Six different radiographs were performed: anteriorposterior in internal (apIR), in neutral (ap0) and in 30° external rotation (apER); axial in 30° (ax30) and 60° (ax60) abduction and an outlet view. Each head screw (n=9) was sequentially exchanged to perforate the humeral head with the tip and all radiographs were repeated for each cut out. Randomized image reading by two blinded examiners for cut out was done for single projection and combinations.
  
  
  RESULTS
  Interrater agreement was 0.72-0.93. Best single projection was ax30 (sensitivity 76%) and the worst was the outlet view (sens. 17%). Standard combination of apIR/outlet reached a sens. of 54%. The best combination of two was: apER/ax30 (90% sens.), of three: apIR/apER/ax30 (96% sens.) and of four: apIR/ap0/apER/ax30 (100% sens.).
  
  
  CONCLUSIONS
  Standard radiographs (ap/outlet), especially in internal rotation, may miss nearly half of screw cut outs. Single best radiographic projection was an axial view with 30° abduction. To account for all cut outs and correct screw position a combination of four projections was needed. These simple and feasible intraoperative and postoperative radiographs help to detect screw perforations of the locking plate reliably.
  
  
  METHODS
  I (Study of Diagnostic Test).
authors.affiliation: Department of Orthopaedics and Traumatology, Kantonsspital St. Gallen, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Spross
authors.affiliation: Department of Orthopaedics and Traumatology, Kantonsspital St. Gallen, Switzerland. Electronic address: bernhard.jost@kssg.ch.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Jost
authors.affiliation: Department of Orthopaedics, University Hospital Balgrist, Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rahm
authors.affiliation: Department of Forensic Medicine and Radiology, Institute of Forensic Medicine, University of Zurich, Switzerland; Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Winklhofer
authors.affiliation: Department of Orthopaedics and Traumatology, Kantonsspital St. Gallen, Switzerland.
authors.forename: Johannes
authors.initials: J
authors.lastname: Erhardt
authors.affiliation: Department of Orthopaedics and Traumatology, Kantonsspital St. Gallen, Switzerland.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Benninger
mesh_terms: D000369:Aged, 80 and over; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005471:Fluoroscopy; D005593:Fracture Fixation, Internal; D006801:Humans; D058430:Humeral Head / Q000601:surgery*; D010865:Pilot Projects; D012784:Shoulder Fractures / Q000601:surgery*; D014057:Tomography, X-Ray Computed
keywords: Complications; Cut out; Locking head screw; Locking plate; Proximal humerus fracture; Radiographic projections