The device for protecting adjacent stages Vc of a spinal segment Sr of a vertebral column previously instrumented by an osteosynthesis device (1) is constituted of fixation elements (110) formed of connectors (111) immobilized in translation and in rotation on the corresponding connection rod (4) of osteosynthesis device (1), a support block (130; 180) in which is housed the spinous process Ve of superjacent vertebra Vc found just above the instrumented spinal segment Sr and at least one ligament (150, 170, 190) allowing spinous process Ve of superjacent vertebra Vc to be joined to support block (130; 180) and the support block (130; 180) to be joined to connectors (111).