A new system of operative fixation of thoracolumbar and lumbar spine fractures is presented: the 'fixateur interne' (F.I.). From a posterior approach long Schanz screws are inserted through the pedicles into the body of the two vertebrae just adjacent to the lesion and connected by th threaded F.I. rods. By tightening the nuts the Schanz screws are fixed in all directions. The advantages of the F.I. system are: excellent reposition by the long lever-arm of the Schanz screws, immobilization of only two segments and therefore good mobility of the residual spine, stability against flexion forces better than is obtained with Harrington distraction rods, additional rotational stability, and fixation in lordosis or kyphosis as is desired. The F.I. does not act as a four point bending system like all other dorsal spine instrumentation systems, but provides stability in flexion by itself. Therefore it can be Used independently of the condition of all ligaments (including the anterior longitudinal ligament) and of the posterior wall of the fractured vertebrae, and there is no need to fix more than the two immediately adjacent vertebrae, thus avoiding the often painful and cumbersome iatrogenic loss of lumbar lordosis and of mobility and permitting early mobilization of the patient. Experience with the first 45 patients is very promising.