cavity 16 as can be seen clearly from the drawings the subtalar implant 1 for reasons of clarity is not yet assembled in the final position u2014 the circumferential edge 18 still needs to be flanged the anchor portions 2 3 are resilient to illustrate the resilience a gap 20 is indicated in fig2 a which is not provided in reality u2014 in this case there is no expansion just elastic deformation the resilience of the anchor portions 2 3 which are forced to spring radially inwardly in the direction of the longitudinal central axis l can be selected by matching the material thickness in a transition region 21 between the circumferentially closed base portion 4 and the actual surface structured anchor portions 2 3 and by influencing the geometry of the transition portion for example by selection of the radius of curvature of a lateral depression 22 it can be seen from fig1 a that two mutually opposed lateral recesses 23 which are concavely contoured in this instance and extend in the longitudinal direction are provided on the spreading slide 8 which is contoured in cross section in a substantially rectangular manner a corresponding implantation tool not illustrated being capable of engaging in said recesses so as to prevent.