Pilot study of oblique lumbar interbody fusion using mobile percutaneous pedicle screw and validation by a three-dimensional finite element assessment.

The purpose of this study was to try oblique lateral interbody fusion (OLIF) using percutaneous pedicle screws (PPS) with mobility. Twelve patients who underwent single-level OLIF were observed for at least one year. These included 6 patients with conventional PPS (rigid group), and 6 with movable PPS (semi-rigid group). Mobile PPS used cosmicMIA, which is a load sharing system. The anterior and posterior disc height, screw loosening and bone healing period, and implant failure were evaluated at final observation by CT. Moreover, the stress on the vertebral body-cage, on the vertebral body-screw/rod and on the bone around the screw was estimated using a three-dimensional finite element assessment in both groups. There was no significant difference in surgical time, amount of bleeding, JOA score, or low back pain VAS between groups. There were no differences between groups in anterior and posterior disc height, screw loosening, and implant failure at final observation. The bone healing period was significantly shorter in the semi-rigid screw group (18.3 months vs 4.8 months, p = 0.01). The finite element analysis showed that the lower stress on the rod/screw would contribute to fewer implant fractures and that lower stress on the bone around the screw would reduce screw loosening, and that higher compressive force on the cage would promotes bone healing. OLIF combined with a movable screw accelerated bone healing by nearly 75%. We conclude that mobile PPS in combination with OLIF promotes bone healing and can be a better vertebral fusion technique.