A collapsible plastic bladder-like prosthesis of the same external form as the nucleus pulposis of an intervertebral disc has a stem through which liquid and/or plastic is introduced to inflate the prosthesis to natural form. The top and bottom have stud-like protrusions which fit into sockets which have been forced through the bony end plates of the bodies of adjacent vertebrae anchoring the prosthesis against slippage. To install the prosthesis, the first step is to insert a transparent tube to the situs with a projecting pin fitting into an adjacent vertebrae to hold the distal end against slippage. A cystoscope may be inserted through the tube to check its location. The degenerated nucleus pulposis of the natural disc is removed in pieces by a forceps inserted through the tube and an incision in the disc wall. The tube provides controlled depth of penetration of this forceps into the disc and acts as a safety feature against injury to blood vessels, nerves and other structures adjacent to the disc. The socket members are inserted through the tube by a specially formed forceps and forced into the adjacent vertebrae. The collapsed prosthesis is then inserted through the stem, the studs pushed into the sockets. Pressure may be adjusted over a period of time; and when finally determined, the stem is severed.