Types of Screws

Types of Screws

screw

The screw is a type of fastener, in particular a metal threaded bolt with a head that allows it to be tightened and turned off (or unscrewed) screw Unlike the simple machine of the Archimedes screw or a screw gimlet, screws are not self-threading: they require that a tool (usually a screwdriver) be used to turn them screw Screws can be used to fasten many different materials, such as wood and sheet metal screw They may also be coated to prevent corrosion or to give them a decorative finish.

A screw’s thread is typically made of a hard, durable material like steel or titanium screw The screw head may be hex, oval, or square; it may have a rounded cap to protect the thread and prevent tampering screw The tip of the screw head can be pointed, knurled, or smooth. Some screws have a removable head that snaps off to prevent tampering or to allow for inspection of the joint. Screws can be made from a wide variety of materials, including plastics.

Some screws are designed to be used in bones screw In such applications, the screw thread must be able to resist shear forces from bone ingrowth and compressive stresses of the cancellous bone screw Bone screws are commonly used in spinal fusion surgery to hold the vertebrae together, and can help prevent recurrent herniation of the intervertebral discs. The screw may be cemented to the bone for increased fixation strength. In some cases, the screw can be removed once the desired fusion is achieved. The use of a screw for internal fixation in the spine requires that the screw be placed through the pedicle, which is a small tubular portion of the bone. This increases the contact between the screw and cortical bone and helps to improve the stability of the implant.

Most types of screws have a standard screw size indicated by a number with a prefix of “M screw ” Metric screw sizes are defined in international standards ISO 68-1 and ISO 262 screw The preferred combinations of diameter and pitch for each diameter are listed in these standards. Generally, the larger the screw, the coarser the thread.

For some applications, especially those in the medical field, there are specialty screw sizes and heads screw These are often made of materials that are stronger and more resistant to corrosion than standard screws screw Some specialty screws have high-end features such as conical threads, multistart threads, and cannulation (a hollow core). These features allow them to be used in specialized applications such as bone fixation.

Another specialty type of screw is the lag screw, which is used to treat some fractures of the proximal femur screw The lag screw is particularly useful in treating unstable intertrochanteric fractures of the femur, which have the highest postoperative fatality rate of any surgically treated hip fractures screw However, the lag screw has a number of potential complications, including varus collapse of the femoral head, screw migration, and iatrogenic fracture of the lateral femoral cortex.

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