A modified VSP screw: two-year experience

A new pedicle screw was designed to address the insertion limitations of the existing VSP and TIMX screws. In the standard VSP insertion technique, the T-handle wrench has an enlarged foot, which contacts the superior facet and interferes with countersinking the fixed nut. The hex of the machine screw may strip in hard bone. The hexagonal design of the fixed nut may make explantation difficult. The evolution of the VSP into the TIMX addresses some of these issues. However, the screw design still has problems. The tapered spacer extends beyond the diameter of the fixed nut and must be applied after the screw is inserted. The flattening of the machine thread requires rotational alignment of the screws before the plate can be inserted. The design does not allow for easy placement of the acorn nut. The modified VSP screw preserves the superior facet, allows for countersinking, permits application of the spacer prior to insertion, and facilitates application of the acorn nut. Rotational alignment of the screw is not required to accommodate the plate. The surgeon can save time and effort inserting and explanting the modified VSP screw.