A spinal stabilization unit, comprising: a flexible coupler including a flexible body, a pair of arms (30, 40), the arms being located at opposed ends of the flexible coupler, and a range-of-motion limiting mechanism configured to control an amount of bending, an amount of compression, and an amount of extension of the flexible coupler, and an anchoring system including a plurality of bone anchors configured to cooperate with the arms (30, 40) of the flexible coupler to attach the flexible coupler to bone, characterized in that the range-of-motion limiting mechanism comprises an attachable sleeve with a narrowed distal opening residing within the flexible body and a pin comprising an elongated body with an enlarged head region and shoulder region, the pin being configured to be received within and cooperate with the attachable sleeve to form an extension and compression stop within the flexible body, the sleeve extending internally from a first end of the flexible coupler towards a second end of the flexible coupler, and the elongated body of the pin extending internally from the second end of the flexible coupler towards the first end of the flexible coupler, the enlarged head region of the pin being disposed within the sleeve and dimensioned such that the enlarged head region abuts the wall of the narrowed distal opening when the flexible coupler is elongated or bent, and the sleeve abuts the second end of the flexible coupler when the flexible coupler is compressed, wherein at least one of the arms has an adjustable connection to the flexible body that permits relative movement of the arm to the flexible body in order to adjust the overall length of the flexible coupler. a flexible coupler including a flexible body, a pair of arms (30, 40), the arms being located at opposed ends of the flexible coupler, and a range-of-motion limiting mechanism configured to control an amount of bending, an amount of compression, and an amount of extension of the flexible coupler, and an anchoring system including a plurality of bone anchors configured to cooperate with the arms (30, 40) of the flexible coupler to attach the flexible coupler to bone, characterized in that the range-of-motion limiting mechanism comprises an attachable sleeve with a narrowed distal opening residing within the flexible body and a pin comprising an elongated body with an enlarged head region and shoulder region, the pin being configured to be received within and cooperate with the attachable sleeve to form an extension and compression stop within the flexible body, the sleeve extending internally from a first end of the flexible coupler towards a second end of the flexible coupler, and the elongated body of the pin extending internally from the second end of the flexible coupler towards the first end of the flexible coupler, the enlarged head region of the pin being disposed within the sleeve and dimensioned such that the enlarged head region abuts the wall of the narrowed distal opening when the flexible coupler is elongated or bent, and the sleeve abuts the second end of the flexible coupler when the flexible coupler is compressed, wherein at least one of the arms has an adjustable connection to the flexible body that permits relative movement of the arm to the flexible body in order to adjust the overall length of the flexible coupler.