Glenoid baseplate fixation using hybrid configurations of locked and unlocked peripheral screws

Nathan T Formaini,Cooper Wilson,Nathan G Everding,Aniruddh N Nayak,Brandon G Santoni,Jonathan C Levy

doi:10.1007/s10195-016-0438-3

Abstract

BackgroundThe 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.Materials and methodsTwenty-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.ResultsAll 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.ConclusionsHybrid 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.Level of EvidenceN/A/, basic science investigation.

Highlights

Improvements in glenoid baseplate fixation have been critical to the success of the modern reverse shoulder replacement
We aimed to determine if different combinations of locked and nonlocked screws significantly alter acute glenoid baseplate fixation in a laboratory setting
Materials and 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)

Summary

Introduction

Improvements in glenoid baseplate fixation have been critical to the success of the modern reverse shoulder replacement. In combination with improved surgical technique and implant enhancements, baseplate failures are less common [6]. First tested by Harman et al [11], locked screw use significantly enhanced baseplate fixation and minimized micromotion at the baseplate-glenoid bone interface. In a 5-year follow-up series using the same implant with 5.0-mm peripheral locked screws, the baseplate failure rate was reduced to 0% [23]. The use of peripheral locked screws has reduced glenoid baseplate failure rates in reverse shoulder arthroplasty. Baseplate micromotion (lm) was recorded throughout 10,000 cycles for each model

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