THE EFFECT OF PULSED ELECTROMAGNETIC-FIELDS ON INSTRUMENTED POSTEROLATERAL SPINAL-FUSION AND DEVICE-RELATED STRESS SHIELDING

Study Design. This study was designed to examine stress-shielding effe cts on the spine caused by rigid implants and to investigate the effec ts of pulsed electromagnetic fields on the instrumented spine. Objecti ves. To investigate the effects of pulsed electromagnetic fields on po sterolateral spinal fusion, and to determine if osteopenia induced by rigid instrumentation can be diminished by pulsed electromagnetic fiel ds. Summary of Background Data. Although device-related osteopenia on vertebral bodies is of a great clinical importance, no method for prev enting bone mineral loss In vertebrae by stiff spinal implants has bee n effective. Methods. Twenty-eight adult beagles underwent L5-L6 desta bilization followed by posterolateral spinal fusion. The study was div ided into four groups: 1) Group CNTL: without instrumentation, without pulsed electromagnetic fields, 2) Group PEMF: without Steffee, with p ulsed electromagnetic fields, 3) Group INST: with Steffee, without pul sed electromagnetic fields, 4) Group PEMF + INST: with Steffee, with p ulsed electromagnetic fields. At the end of 24 weeks, the dogs were ki lled, and L4-L7 segments were tested biomechanically without instrumen tation. Radiographs and quantitative computed tomography assessed the condition of the fusion mass. Results. Stress shielding was induced in the anterior vertebral bodies of L6 with the Steffee plates; bone min eral density Was increased with the addition of pulsed electromagnetic fields, regardless of the presence or absence of fixation. A decrease in flexion and bending stiffness was observed in the Group INST; puls ed electromagnetic fields did increase the flexion stiffness regardles s of the presence or absence of fixation, although this was not statis tically significant. Conclusions. Use of pulsed electromagnetic fields has the potential to minimize device-related vertebral bone mineral l oss.