PLACING A BONE-GRAFT MORE POSTERIORLY MAY REDUCE THE RISK OF PEDICLE SCREW BREAKAGE - ANALYSIS OF AN UNEXPECTED CASE OF PEDICLE SCREW BREAKAGE

Telemeterized internal spinal fixation devices were implanted in a pat ient with degenerative instability and a narrow spinal canal in order to measure the fixator loads during daily activities. Anterior interbo dy fusion was performed three weeks later. During walking, the typical maximum flexion bending moments were 10 N m in the left and 5 N m in the right fixator. On removal of the implants three months later, a fa tigue fracture was found not on the high loaded left side but in the u pper right pedicle screw. The crack started on the caudal side of the cross-sectional area and progressed cranially. Upper vertebral tilting in the sagittal plane must have caused the screw breakage. This would probably have been prevented by a more posteriorly placed bone graft. (C) 1998 Elsevier Science Ltd. All rights reserved.