Fixation systems, kits and methods for vertebral interbody fusions are provided. The fixation systems fix an intervertebral cage in the spine to resist left to right rotation, flexion and/or extension. In one embodiment, the fixation system contains two keels that are insertable into an attachment portion or an anterior wall of an intervertebral cage. Each keel contains a blade with two flanges, in the shape of half of an I-beam. The attachment portion may be one or more pieces that mate to form the attachment portion, such as an I-beam attachment portion. The blades can be straight or curved. Preferably the fixation systems are modular, allowing for parts to be interchanged to suit the patients needs. The fixation systems may be provided in a kit, preferably with more than two keels having different sizes and/or shapes, more than one cage, and/or more than one attachment portion.
