A Biomechanical Comparison of Facet Screw and Pedicle Screw Fixation

· (a – NuVasive, Inc.; d – NuVasive, Inc.)

PURPOSE: To compare the short-term and long-term stability of lumbar motion segments instrumented with either a pedicle screw or a facet screw construct.

METHODS: Short-term: Specimens were tested intact for 6 cycles (compression, flexion, extension, lateral bending, torsion) and then instrumented with interbody allografts and either pedicle screw instrumentation or facet screws. The testing sequence was repeated. Long-term: 12 specimens were instrumented in a similar manner and loaded to 6Nm of flexion bending for 180,000 cycles.

RESULTS: After 6 cycles, facet screw specimens were significantly stiffer than pedicle screw specimens in flexion. Over repetitive cycling, no decreases in stability were detected and no differences were observed between fixation systems.

CONCLUSIONS: The stabilization achieved by facet screw fixation is comparable to that of pedicle screw fixation even after long-term repetitive cycling.

· If noted, the author indicates something of value received. The codes are identified as: a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options.