title: Glenoid baseplate fixation using hybrid configurations of locked and unlocked peripheral screws.
abstract: BACKGROUND
  The use of peripheral locked screws has reduced glenoid baseplate failure rates in reverse shoulder arthroplasty. However, situations may arise when one or more non-locked screws may be preferred. We aimed to determine if different combinations of locked and non-locked screws significantly alter acute glenoid baseplate fixation in a laboratory setting.
  
  
  METHODS
  Twenty-eight polyurethane trabecular bone surrogates were instrumented with a center screw-type glenoid baseplate and fixated with various combinations of peripheral locked and non-locked screws (1-, 2-, 3- and 4-locked con). Each construct was tested through a 55° arc of abduction motion generating compressive and shear forces across the glenosphere. Baseplate micromotion (μm) was recorded throughout 10,000 cycles for each model.
  
  
  RESULTS
  All constructs survived 10,000 cycles of loading without catastrophic failure. One test construct in the 1-locked fixation group exhibited a measured micromotion >150 μm (177.6 μm). At baseline (p > 0.662) and following 10,000 cycles (p > 0.665), no differences were observed in baseplate micromotion for screw combinations that included one, two, three and four peripheral locked screws. The maximum difference in measured micromotion between the extremes of groups (1-locked and 4-locked) was 29 µm.
  
  
  CONCLUSIONS
  Hybrid peripheral screw fixation using combinations of locked and non-locked screws provides secure glenoid baseplate fixation using a polyurethane bone substitute model. Using a glenosphere with a 10-mm lateralized center of rotation, hybrid baseplate fixation maintains micromotion below the necessary threshold for bony ingrowth.
  
  
  METHODS
  N/A/, basic science investigation.
authors.affiliation: Holy Cross Orthopedic Institute, 5597 North Dixie Highway, Fort Lauderdale, FL, 33334, USA.
authors.forename: Nathan T
authors.initials: NT
authors.lastname: Formaini
authors.affiliation: Holy Cross Orthopedic Institute, 5597 North Dixie Highway, Fort Lauderdale, FL, 33334, USA.
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Everding
authors.affiliation: Holy Cross Orthopedic Institute, 5597 North Dixie Highway, Fort Lauderdale, FL, 33334, USA. jonlevy123@yahoo.com.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Levy
authors.affiliation: Phillip Spiegel Orthopaedic Research Laboratory, Foundation for Orthopaedic Research and Education, Tampa, USA.
authors.forename: Brandon G
authors.initials: BG
authors.lastname: Santoni
authors.affiliation: Phillip Spiegel Orthopaedic Research Laboratory, Foundation for Orthopaedic Research and Education, Tampa, USA.
authors.forename: Aniruddh N
authors.initials: AN
authors.lastname: Nayak
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of South Florida, Tampa, USA.
authors.forename: Cooper
authors.initials: C
authors.lastname: Wilson
mesh_terms: D000072228:Arthroplasty, Replacement, Shoulder / Q000295:instrumentation*; D001860:Bone Plates; D001863:Bone Screws; D019544:Equipment Failure Analysis; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D008953:Models, Anatomic; D012785:Shoulder Joint / Q000601:surgery*
keywords: Glenoid baseplate; Glenosphere; Hybrid screw fixation; Micromotion; Reverse shoulder arthroplasty