A suture to be used in a procedure applied to tissue, comprising: an elongated suture body including first and second ends; and a plurality of bi-directional retainers spaced apart from one another and extending from said elongated suture body between said first and second ends; wherein each said bi-directional retainer is configured to, prior to being deployed through tissue, be deployable through tissue in both a first direction and a second direction opposite the first direction; and characterised in that: each said bi-directional retainer is configured to be collapsible in either of two directions; each said bi-directional retainer is configured such that if it is collapsed due to the bi-directional retainer being deployed through tissue in the first direction, the bi-directional retainer will substantially yield to motion of the elongated suture body within the tissue when the elongated suture body is drawn in the first direction, and will resist motion of the elongated suture body in the second direction opposite the first direction; and each said bi-directional retainer is configured such that if it is collapsed due to the bi-directional retainer being deployed through tissue in the second direction, the bi-directional retainer will substantially yield to motion of the elongated suture body within the tissue when the elongated suture body is drawn in the second direction, and will resist motion of the elongated suture body in the first direction, wherein each said bi-directional retainer includes grooves that guide how the bi-directional retainer collapses. an elongated suture body including first and second ends; and a plurality of bi-directional retainers spaced apart from one another and extending from said elongated suture body between said first and second ends; wherein each said bi-directional retainer is configured to, prior to being deployed through tissue, be deployable through tissue in both a first direction and a second direction opposite the first direction; and characterised in that: each said bi-directional retainer is configured to be collapsible in either of two directions; each said bi-directional retainer is configured such that if it is collapsed due to the bi-directional retainer being deployed through tissue in the first direction, the bi-directional retainer will substantially yield to motion of the elongated suture body within the tissue when the elongated suture body is drawn in the first direction, and will resist motion of the elongated suture body in the second direction opposite the first direction; and each said bi-directional retainer is configured such that if it is collapsed due to the bi-directional retainer being deployed through tissue in the second direction, the bi-directional retainer will substantially yield to motion of the elongated suture body within the tissue when the elongated suture body is drawn in the second direction, and will resist motion of the elongated suture body in the first direction, each said bi-directional retainer is configured to be collapsible in either of two directions; each said bi-directional retainer is configured such that if it is collapsed due to the bi-directional retainer being deployed through tissue in the first direction, the bi-directional retainer will substantially yield to motion of the elongated suture body within the tissue when the elongated suture body is drawn in the first direction, and will resist motion of the elongated suture body in the second direction opposite the first direction; and each said bi-directional retainer is configured such that if it is collapsed due to the bi-directional retainer being deployed through tissue in the second direction, the bi-directional retainer will substantially yield to motion of the elongated suture body within the tissue when the elongated suture body is drawn in the second direction, and will resist motion of the elongated suture body in the first direction, wherein each said bi-directional retainer includes grooves that guide how the bi-directional retainer collapses.