The present disclosure relates to an insert sleeve (19) designed for being inserted into a through hole (17) of an implant (11), comprising a body (21) with a through hole (23) defining an axial direction (29) for receiving a bone anchoring element (25), in particular a bone screw, said body (21) being made of a material having a first modulus of elasticity and including multiple recesses (27) arranged in circumferential direction around said through hole (23) of said insert sleeve (19) for reducing a stiffness of said insert sleeve (19) in a direction transverse (31, 33) to said axial direction (29). At least one of said recesses (27) is filled with a filler material (41) having a second modulus of elasticity different from said first modulus of elasticity.