A system for the in situ formation of prostheses between adjacent vertebrae of a patient. The system includes a first mold adapted to be located in an intervertebral disc space between the adjacent vertebrae and at least a second mold adapted to be positioned between adjacent posterior elements. Lumens are fluidly coupled to each of the molds. One or more in situ curable biomaterials are delivered through the lumens to the molds. The at least partially cured biomaterial and the molds cooperate to maintain a desired alignment and spacing of the intervertebral disc space and the posterior elements.