Abstract: A medical device containing an inflatable balloon structure for use in minimally invasive surgery and minimally invasive diagnostic and therapeutic procedures are described herein. The device is delivered by a catheter and expanded using gases, liquids or liquids that solidify in situ. The inflatable balloon may be constructed from a wide variety of materials and may be reinforced by supporting structures, when necessary. The device may form an endoprosthesis in a patient. In the preferred embodiment, the device is used in spinal fusion. Optionally, the device may also be used in combination with bone graft materials and bioactive factors.