Apparatus for attaching an object to bone, the apparatus comprising: a suture assembly comprising: a first suture having a generally U-shaped configuration comprising a first arm, a second arm and a bridge connecting the first arm to the second arm； a second suture comprising a first arm, a second arm and a bridge connecting the first arm to the second arm； the first arm of the second suture being wrapped around the first arm of the first suture in a first direction, and the second arm of the second suture being wrapped around the second arm of the first suture in a second, opposite direction； the suture assembly being capable of assuming (i) a longitudinally-extended, radially- contracted first configuration, and (ii) a longitudinally-contracted, radially-expanded second configuration； wherein at least one of the first arm and the second arm comprises a hollow tubular structure.
