In an attempt to enhance theimmediatestability of posterior interspinous fusion constructs, the authors conducted the following project. Twenty-four adult mongrel dogs underwent a posterior C4–C5 fusion using iliac crest autogenous graft and internal fixation using either ulna struts (12) or metallic struts (12) fixed into position by sublaminar wires. Half of the animals were killed at either 1 week or 3 months postoperatively, and their C4–C5 motion segments were excised and studied radiologically, mechanically, and histologically. Both fusions created immediate and 3-month stability equivalent or superior to normal C4–C5 canine spinal segments. However, three dogs were rendered completely and two dogs incompletely quadriplegic by the surgery. Clinical Relevance: Because of the relatively high rate of neurologic injury associated with these procedures in normal dogs, the authors hesitate to endorse their use in all but complete quadriplegic patients.