An intervertebral fusion device is disclosed. The intervertebral fusion device comprises a superior component (40), an inferior component (60) and a core component (10). The superior component (40) has a superior component top side and a superior component bottom side and is configured to be received in an intervertebral space between first and second vertebrae whereby the superior component top side abuts against the first vertebra. The inferior component (60) has an inferior component top side and an inferior component bottom side and is configured to be received in the intervertebral space whereby the inferior component bottom side abuts against the second vertebra. The superior component bottom side and the inferior component top side oppose each other when the superior and inferior components (40, 60) are received in the intervertebral space. The core component (10) is configured for insertion between the superior and inferior components (40, 60) whereby a separation between the superior and inferior components is determined. The core component (10) comprises a retention mechanism which moves between a contracted condition and an expanded condition. The core component (10) is insertable between the superior and inferior components (40, 60) when the retention mechanism is in the contracted condition. The retention mechanism inter-engages with the superior component (40) and the inferior component (60) when in the expanded condition and when the core component (10) is received between the superior and inferior components to thereby present resistance to movement of the core component from between the superior and inferior components.