EXTERNAL DISTRACTOR AND ADJUSTMENT DEVICE FOR USE IN SUCH A DISTRACTOR

External distractor arranged to gradually enlarge the distance between a first bone part and a second bone part, wherein the distractor comprises a first and a second connection device, wherein the first connection device is arranged to be connected to the first bone part with at least one first bone pin and wherein the second connection device is arranged to be connected to the second bone part with at least one second bone pin, wherein the distractor further comprises an adjustment device arranged between the first and second connection devices for adjusting the distance between the first and the second connection devices along an adjustment axis, wherein the adjustment device comprises a tubular base body coupled to the first connection device, an extension tube coupled to the second connection device and an adjustment mechanism for moving the extension tube with respect to the base body along the adjustment axis, wherein the adjustment mechanism comprises a rotatable adjustment ring for moving the extension tube upon rotation of the adjustment ring around the adjustment axis, wherein the adjustment mechanism further comprises a spring member engaging the adjustment ring for preventing unintended activation of the adjustment mechanism.