The invention relates to an elastic ring (18), defining an inner opening, an outer contour (42) and an annular bearing surface between the inner opening and the outer contour (42), the ring (18) being deformable between a rest position and an introduction position in which the inner opening has a diameter greater than its diameter in the rest position, the ring (18) being elastically biased towards the rest position. The ring (18) comprises at least three strands (60) passing through the ring (18), each strand (60) comprising a first end (62) and a second end positioned on the outer contour (42), the inner contour of the opening being defined by a portion of each strand (60) and having a pseudo-polygonal shape.
