A steerable instrument (10) has an actuator (14； 15) at a proximal side and a bendable zone (16； 17) at a distal side. The actuator (14； 15) controls bending of the flexible zone (16； 17) by means of one or more longitudinal elements. The instrument has a first cylindrical element (204), a second cylindrical element (206) and a third cylindrical element (208). The second cylindrical element (206) has a zone (14； 15； 16； 17) with a longitudinal element portion (274； 282) with a first height in a radial direction of the instrument. Radial spacers (275； 279) are located at mutual sides of the longitudinal element portion (274； 282), which have, at least locally, a second height in the radial direction larger than the first height.
