Methods for performing spinal fusions using an injectable calcium phosphate-based bone substitute are provided. The injectable bone substitute is injected into the anterior portion of an interbody space and allowed to solidify in vivo. The injectable bone substitute has a minimum compression strength of 10 MPa after setting for about 30 minutes and preferably solidifies to a compression strength of 25 MPa within 24 hours of injection. Optionally, the posterior portion of the interbody space is fixed using a metallic implant selected from rods and pedicle screws or plates and pedicle screws by attachment thereof to adjacent vertebrae.
