The effect of metaglene lateralization on joint mobility of reverse shoulder arthroplasty: A cadaveric biomechanical study.

INTRODUCTION

Lateralization of the metaglene reduces scapular notching or impingement. However, the effect on joint mobility remains unclear. With increased attention to reverse shoulder arthroplasty over the past years, the aim of this biomechanical study is to analyze the effect of metaglene lateralization on range of motion in reverse shoulder arthroplasty.

METHODS

Reverse shoulder arthroplasty (DeltaXtend; Fa. Depuy/Synthes) was performed in 7 cadaveric shoulders. Lateralization of the metaglene was performed in increments, using spacers of +0 mm (subgroup I), +5 mm (subgroup II), +10 mm (subgroup III). Deltoid muscle (pars clavicularis, acromialis and spinalis), teres minor (TMI), infraspinatus (IF) and subscapularis muslces (SSC) were loaded separately. Range of motion was measured by using a motion capture system (Optotrak Certus) in the sagittal plane (z-axis), coronar plane (x-axis) and transversal plane (y-axis). A custom-made biomechanical test set up was used to test the samples with a constant preload with additional testing load up to 4 kg on each muscle.

RESULTS

Specimens showed a tendency towards increased range of motion in abduction (deltoid, pars acromialis), external rotation (IS/TMI) and internal rotation (SSC) in subgroup II, compared to subgroups I and III, without reaching the level of significance Abduction at maximum used load was 46° (subgroup I), 62° (subgroup II) and 22° (subgroup III). The mean external rotation (ISF) at maximum used load was 25° (I), 28° (II) and 24° (III). Mean internal rotation was 22° (subgroup I), 48° (subgroup II) and 26° (subgroup III).

CONCLUSION

Moderate lateralization of the glenosphere of +5 mm has improved the range of motion in our experimental cadaveric setup. Especially a higher internal and external rotation can be reached with less load.Level of evidence III.