Armrest assembly for a seat structure comprising: a support member having a passage extending upwardly curved mandrel element having a first defined curvature; a shaft which is slidably disposed on the carrier element and comprises a curved portion having a second defined curvature corresponding to the first curvature of the mandrel portion and coincide with this, the curved portion of the shaft is slidably assembled with the curved portion of the mandrel portion; an armrest that is carried by the shaft; and a ratchet mechanism which can be moved between at least one engaged position and a disengaged position, wherein the latch mechanism comes into the engaged position at least on the shaft or on the support member engage to prevent movement between them, and wherein the shaft relative to movable carrier element when the latch mechanism is in the disengaged position.