Visual inspection revealed the screw head where the tip of the screwdriver sits was found to be damaged.Marks on screw indicate excessive force used during surgery.Device and complaint history records were reviewed for provided lot number.No relevant manufacturing issues or similar complaints were identified.Sales rep indicated that excessive force was not applied during surgery.Per surgical technique, to lock the outer distraction ring and the implant height, place the head of the screwdriver into the head of the locking screw.Rotate the screwdriver counterclockwise two full turns, which will cause the head of the locking screw to protrude out (back-out) of the implant and contact the outer distraction ring.The locking screw was not designed to provide any tactile feedback during the locking step.The locking screw should back-out of the implant freely with rotation of the screwdriver.The screwdriver was also designed to be low-profile to potentially eliminate unnecessary torque transmission to the locking screw.If the surgeon backs-out the locking screw past two full turns and reaches a point where the screw can no longer back-out, the surgeon should stop rotating the screwdriver.At this point, the implant height is locked and any further rotation of the locking screw may compromise its integrity.Some plausible root causes of the screw fractures are: excessive torque applied during implant expansion in-situ, user applies off-axis loading during expansion, and inserter not assembled correctly to implant.However the exact root cause could not be determined conclusively.
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