Changes in the loads on an internal spinal fixator after iliac-crest autograft

Spines are often stabilised posteriorly by internal fixation and anteriorly by a bone graft. The effect of an autologous bone graft from the iliac cre st on implant loads is unknown. We used an internal spinal fixation device with telemetry to measure implant loads for several body positions and acti vities in nine patients before and after anterior interbody fusion, With th e body upright, implant loads were often higher after than before fusion us ing a bone graft. Distraction of the bridged region led to high implant loa ds in patients with a fractured vertebra and to marked changes in load in t hose with degenerative instability. Leaving the lower of the bridged interv ertebral discs intact led to only small changes in fixator load after anter ior interbody fusion, A bone graft alone does not guarantee a reduction of implant loads.