Intervertebral devices

A method of installing an intervertebral fusion device in an intervertebral space defined between first and second vertebrae, the intervertebral fusion device comprising an endplate having a leading end and a trailing end, a core component having a leading end and a trailing end, and a ratchet comprising a pawl and a linear rack defining plural recesses, the pawl comprised in one of the core component and the endplate, the linear rack comprised in the other of the core component and the endplate, the plural recesses spaced apart from each other or one another in a direction of engagement of the core component with the endplate such that the plural recesses extend from near or at one of the leading end and the trailing end of the other of the core component and the endplate towards the other of the leading end and the trailing end of the other of the core component and the endplate, the plural recesses extending by no more than 60% of a distance between the leading end and the trailing end of the other of the core component and the endplate, the method comprising:

• disposing the leading end of the core component adjacent the trailing end of the endplate;
• bringing the core component into engagement with the endplate by moving the core component relative to the endplate in the direction of engagement such that the leading end of the core component moves towards the leading end of the endplate and extent of overlap of the core component and the endplate increases;
• and
• further moving the core component relative to the endplate in the direction of engagement whereby the pawl interlocks with each of the plural recesses of the linear rack in turn until the core component and the endplate have a desired extent of overlap;
• and
• installing the endplate and the core component in the intervertebral space.

An intervertebral fusion device, comprising:

• an endplate configured to be received in an intervertebral space defined between first and second vertebrae, the endplate having a leading end and a trailing end;
• a core component configured to be received in the intervertebral space, the core component having a leading end and a trailing end;
• and
• at least one ratchet, each at least one ratchet comprising a pawl and a linear rack defining plural recesses, the pawl comprised in one of the core component and the endplate, the linear rack comprised in the other of the core component and the endplate, wherein the pawl comprises a finger which defines at least one protrusion at a distal end of the finger, the finger attached at its proximal end at or near one of the leading end and the trailing end of the one of the core component and the endplate, wherein the finger defines plural protrusions towards a distal end of the finger, the finger defining a first number of protrusions and the linear rack defining a second number of recesses, the second number being greater than the first number,
• wherein
• the core component and the endplate are configured to engage with each other by disposing the leading end of the core component adjacent the trailing end of the endplate and then moving the core component relative to the endplate in a direction of insertion such that the leading end of the core component moves towards the leading end of the endplate and extent of overlap of the core component and the endplate increases,
• the plural recesses of the linear rack extend in the direction of insertion and from near or at one of the leading end and the trailing end of the other of the core component and the endplate towards the other of the leading end and the trailing end of the other of the core component and the endplate, the plural recesses extending by no more than 60% of a distance between the leading end and the trailing end of the other of the core component and the endplate, and
• the at least one ratchet is configured such that the pawl starts to inter-engage with the plural recesses of the linear rack as the core component is moved further relative to the endplate in the direction of insertion.