“…(Cuéllar et al, 2009;Cuéllar et al, 2010;Pierchon et al, 1994). As we have indicated in previous studies (Cuéllar et al, 2009(Cuéllar et al, , 2010, the best way to demonstrate the existence of instability is by Examination Under Anesthesia (EUA) with X ray control (Fig-4 A,B A,B). Hip resurfacing implants, having larger femoral heads, offer a greater degree of mobility and stability but the ideal ratio between femoral head and neck is hard to achieve and, therefore, they involve a higher risk of impingement with associated instability (Fig-4 B).…”