Biomechanical phenomena occurring at the bone–implant interface during the press-fit insertion of acetabular cup implants are still poorly understood. This article presents a nonlinear geometrical two-dimensional axisymmetric finite element model aiming at describing the biomechanical behavior of the acetabular cup implant as a function of the bone Young’s modulus Eb, the diametric interference fit ( IF), and the friction coefficient µ. The numerical model was compared with experimental results obtained from an in vitro test, which allows to determine a reference configuration with the parameter set: μ*  = 0.3, [Formula: see text], and IF*  = 1 mm for which the maximal contact pressure tN = 10.7 MPa was found to be localized at the peri-equatorial rim of the acetabular cavity. Parametric studies were carried out, showing that an optimal value of the pull-out force can be defined as a function of μ, Eb, and IF. For the reference configuration, the optimal pull-out force is obtained for μ  = 0.6 (respectively, Eb = 0.35 GPa and IF = 1.4 mm). For relatively low value of µ ( µ < 0.2), the optimal value of IF linearly increases as a function of µ independently of Eb, while for µ > 0.2, the optimal value of IF has a nonlinear dependence on µ and decreases as a function of Eb. The results can be used to help surgeons determine the optimal value of IF in a patient specific manner.

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Among the many different procedures available in the treatment of shoulder instability, the Trillat procedure remains indicated in case of recurrent shoulder instability in elderly patient with an irreparable cuff tear or in case of hyperlaxity. Despite the constantly increasing number of arthroscopic assisted techniques, the open procedure remains a simple, reliable and fast surgical procedure with a shorter learning curve than the arthroscopic techniques. It consists in a partial osteotomy of the anterior cortical of the coracoid process which is then tilted and fixed with a screw into the anterior part of the scapula downwards and medially to obtain a re-centering effect due to the conjoint tendon on the humeral head when rotational movement are applied. This article aims to present a stepwise approach for the open surgical technique.