2.0mm locking screws - star drive

The angular security of locking plate systems depends on a rigid interface between screw and plate. This is achieved by the use of interlocking threads. The modulus of bone and stainless steel differs greatly and the ideal screw thread for one will not suit the other. Stainless steel demands fine threads whereas bone needs a relatively coarse thread. If we use a fine thread in the plate and a coarse thread in the bone, when the head of screw engages the plate, the screw moving faster through the bone than the plate would have the effect of pulling the plate towards the bone. This is exactly what we do not want. Some systems compromise by using the same thread in both screw head and bone plate. At Veterinary Instrumentation and in the industry Standard Locking Screw the problem is solved by some ingenious engineering. The threads on the head of our screws are fine as required but have a twin start. The threads taper down the head as a double helix. The pitch (the distance between the tips of the threads) of each individual fine thread is the same as the threads on the bone screw but because of the double helix the number of threads per millimeter of locking thread is double that of the bone screw giving the fine threads required for metal on metal. The screw moves through the bone at the same rate as it moves through the plate maintaining the relative positions of both bone fragment and plate. There is an additional benefit of the double helix. As the screw head approaches the plate a single start thread may have to wait 360 degree rotation before the threads start to engage. In the 3.5 screw this might mean that the plate is pushed around one millimeter before the head of the screw engages. With a twin start thread the screw head will engage within 180 degrees of contact.