Assessment of primary stability of glenoid bone block procedures used for patients with recurrent anterior shoulder instability - a biomechanical study in a synthetic bone model

Anterior glenoid reconstruction using bone blocks is increasingly recognised as treatment option after critical bone loss. In this study, a biomechanical test setup is used to assess micromotion after bone block augmentation at the glenoid, comparing bone block augmentation with a spina-scapula block to the standard coracoid bone block (Latarjet). Twenty-four synthetic shoulder specimens were tested. Two surgical techniques (coracoid and spina-scapula bone block augmentation) were used on two different types of synthetic bone (Synbone and Sawbone). The specimens were cyclically loaded according to the 'rocking horse' setup defined in ASTM F2028. A mediolateral force of 170 N was applied on the bone block and a complete test comprised 5000 cycles. The Micromotion between bone block and glenoid was measured using a 3D Digital Image Correlation system. The measured micromotion divided into irreversible and reversible displacement of the augmented block. Medial irreversible displacement was the dominant component of the micromotion. The spina-scapula bone block showed a significantly higher irreversible displacement in medial direction compared to the coracoid block, when aggregating both types of synthetic bone (spina: 1.00 ± 0.39 mm, coracoid: 0.56 ± 0.39 mm, <i>p</i> = 0.01). The dominant irreversible medial displacement can be interpreted as initial settling behaviour.