Influence of Graft Positioning during the Latarjet Procedure on Shoulder Stability and Articular Contact Pressure: Computational Analysis of the Bone Block Effect

SIMPLE SUMMARY: By osteotomizing the coracoid process from the scapula and transferring it, along with the conjoint tendon, to the anteroinferior glenoid rim, the Latarjet procedure treats recurrent anterior glenohumeral (GH) instability in patients with large anterior glenoid bone defects. One key factor affecting its efficacy is the positioning of the graft on the glenoid rim, which impacts not only GH joint stability, through the so-called bone block effect, but also the joint contact mechanics; however, limited data exist on the best graft placement. In this study, finite element models that consider different medial–lateral graft placements for the Latarjet procedure were applied to evaluate GH joint stability and articular contact pressures. The results showed that the contribution of the bone block effect to GH joint stability increased with bone graft lateralization; however, the lateralization of the bone graft was also associated with an increase in peak contact pressures, which raises concerns regarding the risk of osteoarthritis. A trade-off seems to exist between GH joint stability provided by the bone block effect and the risk of osteoarthritis. This study provides valuable information regarding the influence of bone graft placement on the bone block effect of the Latarjet procedure. ABSTRACT: The Latarjet procedure is the most popular surgical procedure to treat anterior glenohumeral (GH) instability in the presence of large anterior glenoid bone defects. Even though the placement of the bone graft has a considerable influence on its efficacy, no clear indications exist for the best graft position. The aim of this study was to investigate the influence of the medial–lateral positioning of the bone graft on the contact mechanics and GH stability due to the bone block effect. Four finite element (FE) models of a GH joint, with a 20% glenoid bone defect, treated by the Latarjet procedure were developed. The FE models differed in the medial–lateral positioning of the bone graft, ranging from a flush position to a 4.5 mm lateral position with respect to the flush position. All graft placement options were evaluated for two separate shoulder positions. Anterior GH instability was simulated by translating the humeral head in the anterior direction, under a permanent compressive force, until the peak translation force was reached. Joint stability was computed as the ratio between the shear and the compressive components of the force. The lateralization of the bone graft increased GH stability due to the bone block effect after a 3 mm lateralization with respect to the flush position. The increase in GH stability was associated with a concerning increase in peak contact pressure due to the incongruous contact between the articulating surfaces. The sensitivity of the contact pressures to the medial–lateral positioning of the bone graft suggests a trade-off between GH stability due to the bone block effect and the risk of osteoarthritis, especially considering that an accurate and consistent placement of the bone graft is difficult in vivo.