title: Evaluation of Preoperative Implant Placement in Total Shoulder Arthroplasty.
abstract: BACKGROUND
  New technology to assist with glenoid placement in shoulder arthroplasty has evolved to include preoperative planning tools and intraoperative guides. These tools provide surgeons with a more complete understanding of glenoid anatomy prior to surgery. However, there have been no studies identifying the information that most influences surgical decision making. Further, there have been few studies that quantify intraoperative identification of scapular landmarks required to execute a preoperative plan. The purpose of this study is to examine the variables that are considered when making a preoperative plan in shoulder arthroplasty.
  
  
  METHODS
  The first part of this study was a cadaveric lab in which three surgeons identified the neutral axis in surgical simulation. The second part of the study utilized a preliminary software tool in which surgeons were able to place glenoid implants in a set of CT reconstructions utilizing standard pegged glenoid components. In the third part of the study, surgeons utilized a novel planning software that included the ability to view the 3D reconstructed glenoid in all planes simultaneously and place either standard or augmented glenoid implants. The results of these three studies were compared.
  
  
  RESULTS
  The center of the glenoid identified in the cadaver lab was 1.69 mm ± 1.58 mm anterior and 1.99 mm ± 2.49 mm superior to center. The identified neutral axis was tilted 14.2° ± 9.2° superior to the Friedman axis with 11.8° ± 7.9° of retroversion relative to that axis. Using the novel preoperative planning tool, the surgeons placed implants less than 0.5 mm from the center of the glenoid (AP = -0.07 mm ± 0.42 mm, SI = 0.44 mm ± 0.82 mm) with an average retroversion of less than 1° (-0.96° ± 3.04°).
  
  
  CONCLUSIONS
  There was a discernible difference between the neutral axis identified in the cadaveric simulation (aver age of 14.2° superior and 11.8° retroverted) and the implant orientation planned using preoperative software (average of 3.26° superior and 0.96° retroverted). Based on the variability of position and orientation seen cadaverically, it is concluded that additional intraoperative guidance is needed alongside a preoperative plan in order to execute ideal placement of the glenoid component.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Hamilton
authors.forename: Sandrine
authors.initials: S
authors.lastname: Polakovic
authors.forename: Paul
authors.initials: P
authors.lastname: Saadi
authors.forename: Richard B
authors.initials: RB
authors.lastname: Jones
authors.forename: Ira M
authors.initials: IM
authors.lastname: Parsons
authors.forename: Emilie V
authors.initials: EV
authors.lastname: Cheung
mesh_terms: D019643:Arthroplasty, Replacement / Q000295:instrumentation*; D002102:Cadaver; D003198:Computer Simulation; D061165:Glenoid Cavity / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007595:Joint Prosthesis; D011474:Prosthesis Design; D011857:Radiographic Image Interpretation, Computer-Assisted; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D012984:Software; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed