title: Optimal baseplate rotational alignment for locking-screw fixation in reverse total shoulder arthroplasty: a three-dimensional computer-aided design study.
abstract: BACKGROUND
  Baseplate loosening in reverse total shoulder arthroplasty (RTSA) remains a concern. Placing peripheral screws into the 3 pillars of the densest scapular bone is believed to optimize baseplate fixation. Using a 3-dimensional computer-aided design (3D CAD) program, we investigated the optimal rotational baseplate alignment to maximize peripheral locking-screw purchase.
  
  
  METHODS
  Seventy-three arthritic scapulae were reconstructed from computed tomography images and imported into a 3D CAD software program along with representations of an RTSA baseplate that uses 4 fixed-angle peripheral locking screws. The baseplate position was standardized, and the baseplate was rotated to maximize individual and combined peripheral locking-screw purchase in each of the 3 scapular pillars.
  
  
  RESULTS
  The mean ± standard error of the mean positions for optimal individual peripheral locking-screw placement (referenced in internal rotation) were 6° ± 2° for the coracoid pillar, 198° ± 2° for the inferior pillar, and 295° ± 3° for the scapular spine pillar. Of note, 78% (57 of 73) of the screws attempting to obtain purchase in the scapular spine pillar could not be placed without an in-out-in configuration. In contrast, 100% of coracoid and 99% of inferior pillar screws achieved full purchase. The position of combined maximal fixation was 11° ± 1°.
  
  
  CONCLUSIONS
  These results suggest that approximately 11° of internal rotation is the ideal baseplate position for maximal peripheral locking-screw fixation in RTSA. In addition, these results highlight the difficulty in obtaining optimal purchase in the scapular spine.
authors.affiliation: University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery and Biomedical Engineering, Memphis, TN, USA.
authors.forename: Byron F
authors.initials: BF
authors.lastname: Stephens
authors.affiliation: University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery and Biomedical Engineering, Memphis, TN, USA.
authors.forename: Casey T
authors.initials: CT
authors.lastname: Hebert
authors.affiliation: University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery and Biomedical Engineering, Memphis, TN, USA.
authors.forename: Frederick M
authors.initials: FM
authors.lastname: Azar
authors.affiliation: University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery and Biomedical Engineering, Memphis, TN, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Mihalko
authors.affiliation: University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery and Biomedical Engineering, Memphis, TN, USA. Electronic address: tthrockmorton@campbellclinic.com.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Throckmorton
mesh_terms: D001168:Arthritis / Q000000981:diagnostic imaging / Q000601:surgery*; D019643:Arthroplasty, Replacement / Q000009:adverse effects / Q000379:methods*; D001860:Bone Plates; D001863:Bone Screws; D003198:Computer Simulation; D017076:Computer-Aided Design; D006801:Humans; D021621:Imaging, Three-Dimensional; D012399:Rotation; D012540:Scapula / Q000000981:diagnostic imaging / Q000601:surgery*; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed
keywords: Reverse total shoulder arthroplasty; baseplate; locking screws