Bone Screw Models and Specifications
Bone screws are typically made of stainless steel (stainless) or titanium alloys or with Elastic intramedullary nail. These materials can be used for both cortical and cancellous bone.
To increase the anchorage of screws against pull-out from cancellous bone, a larger outer diameter can be chosen. However, a design that also ensures adequate anchorage is necessary.
Material
In orthopaedic surgery, screws are usually made of titanium. The material causes a lot of wear and tear, and after a while, patients need to undergo surgery to remove them.
However, there are new biodegradable materials that promote bone growth and don't leave holes once they degrade. Researchers from IFAM developed a moldable composite that is made of polylactic acid and hydroxylapatite, a ceramic that Philipp Imgrund of IFAM's biomaterial technology department says is the main constituent of bone material.
Magnesium-based bioabsorbable screws are a relatively new member of the family of orthopedic fixation materials. There are a limited number of clinical studies that report functional and radiological outcomes, indications and complications.
Thread Design
When designing bone screws that will be subjected to multiple loading conditions, the thread design is an important consideration. Different thread shapes can affect the contact surface area and shear force development at the screw-bone interface, thereby affecting fixation stability.
To determine the optimal thread design, biomechanical tests were conducted on six pedicle screws in two sizes each. These were tested on three densities of synthetic foam.
Several design features have been proposed in previous studies that influence screw anchorage, such as outer diameter (OD), root diameter (RD), and pitch. However, the interplay of these features has not been thoroughly characterized and the effect of each variable has not been clearly defined.
Core Diameter
The core diameter of bone screws is a key factor in determining screw stability. It determines whether a bone screw is able to withstand high forces.
In a typical bone screw, the core diameter is a constant diameter along the length of the screw. However, this can be adapted for specific applications by varying the taper of the core.
The core thickness is increased toward the head of the screw by increasing the angle between the inferior thread surface and a line normal to the screw axis. This angle is smallest at the screw tip and widest at the head.
Pitch
Bone screws come in a variety of models and specifications to meet specific patient needs such as Clavicular hook compression locking plate. They are designed to provide compression in bone and promote repair of the injured bone by preventing it from breaking apart.
The pitch used in bone screws is based on several factors. These include the type of bone and the number of threads engaging it.
Cortical bones: The outer layer of human bones is called cortex and it makes up about 80% of the body's mass. These smooth, white, solid-looking bones provide support and protection for the internal organs of the body.
These dense bones can be anchored using cortical orthopedic screws that have a fine pitch, with closely spaced, shallow threads throughout their length. They usually have a blunt end and are available in a range of lengths from 0.059" to 0.177".
Cutting Edge
Bone screws are a widely used implant for fixation of fractures and osteotomies. They are made from stainless steel or titanium alloys and come in a variety of thread designs, thread pitches, and thread lengths to suit different surgical needs.
The cutting edge is the most important aspect with Metal bone pin of the bone screw because it determines how the screw will be inserted into the underlying bone. A flat cutting surface provides a stable start into the bone that does not promote wobbling of the screw.
The cutting edge may be formed to a point or a flat surface, and it can be shaped to be received in a drive socket of a driver tool, or it may be headless. In either case, it can be configured to mate with the shank of the bone screw so that the bone screw is driven into the underlying bone by a torque applied by a driver tool during insertion.
