Abstract: A collapsable reamer assembly and method of reaming a cavity into a bone are described. The reamer assembly comprises a base having a housing and an underside presented toward a surface of the bone in use. A collapsable reamer is rotatably mounted in the housing for rotation about a reaming axis directed away from the underside of the base. The collapsable reamer comprises at least one reaming component, supported for movement along the reaming axis from a collapsed state of the reamer to an extended state of the reamer to ream at least partially along the axis into the bone.