A fixation mechanism of an implantable lead includes a plurality of depressions of an outermost surface of the lead and a relatively flexible sleeve mounted around the outermost surface. The depressions are spaced apart from one another along a length, and each extends circumferentially, wherein a longitudinal center-to-center spacing between each adjacent depression is uniform along the length, and each depression is of substantially the same size. The sleeve has an internal surface in sliding engagement with the outermost surface of the lead, and an external surface, in which suture grooves are formed. A longitudinal center-to-center spacing between adjacent suture grooves may be substantially the same as, or a multiple of, the longitudinal center-to-center spacing between adjacent depressions of the outermost surface of the lead. The sleeve may also include a ridge protruding from the internal surface, aligned with, or offset (by center-to-center spacing of depressions) from, the grooves.