Abstract
This biomechanical study aims to assess the different designs of glenospheres in SMR reverse total shoulder replacement in the degree of micromotion following dynamic cyclic loading, and its implication for risk of glenoid component loosening. The eccentric designs of glenospheres allowed greater range of motion from improvement in adduction. The eccentric placement of central fixation peg on the glenosphere has raised concerns of increasing micromotion of the baseplate-bone interface during cyclic loading.
In our method, the four different designs of glenospheres were tested; 36mm concentric (Standard), 36mm eccentric, 44mm concentric and 44 eccentric glenospheres. Each glenosphere underwent a thousand cycles of shear loading at four different positions of humeral abduction. The micromotion of each glenosphere baseplate were measured and compared. The 36mm eccentric glenopshere has overall the highest degree of micromotion; its degree of movement was well below the accepted 150 micrometer as the threshold for bony ingrowth inhibition.
Correspondence should be addressed to Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
