One embodiment of the present application includes: performing a medical procedure on a segment of a patient's spine. This segment includes two vertebrae each in contact with a spinal disk positioned in an intervertebral disk space. A passage is formed that follows a pathway through the vertebrae and the intervertebral disk space. This passage extends from an extradiscal opening through one of the vertebrae along a path that turns to change direction. The tubular device is inserted in the passage and extends through the intervertebral disk space. A fluid material is introduced into the tubular device to at least partially fill it to provide a spinal prosthetic structure. Other embodiments and inventive aspects include other prosthetic device arrangements, implantation methods, systems, and techniques.