An examination of the explanted hardware identified damage to both the occipital plate and mating set screws.The id of the set screws contain markings and deviations to the manufactured hexalobe form.The evidence indicates the torque driver may not have been properly aligned which can prevent the driver from completely engaging with the mating set screw.Additionally, there is damage to the od threads indicative of cross threading.The rotating body/tulip of the occipital plate was found to be splayed and contain damage/voids to the internal threads.The print calls out for the distance from tulip to tulip to be.162 +/-.002.The splay measured between.166 on one tulip and.175 on the other.The investigation concluded the most likely cause of this event was non-axial alignment of the set screw to rotating body/tulip during the insertion/tightening process.When performing posterior occipito-cervical fusion cases, often times the occipital plate is mounted far inferior and as close to the fixated cervical level as possible, resulting in upwards of a 90° bend in the rod.This can present a difficult approach.With the avalon plate, there are 3 unique degrees of freedom that allow for movement of the attachment point to the rod.This is intended to help mitigate a sometimes difficult approach.When patient anatomy and/or the extreme contours of the rod cause a straight approach to be difficult, the hexalobe driver can sometime become misaligned during set screw placement.When this occurs, the set screw can become cross threaded causing damage to the plate assembly and/or the set screw.
|