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1. Bone screw overview and main structure of the product
Bone screws, also known as fracture fixation screws, are commonly used in orthopedic implants for fixation in clinical practice. Bone screws are usually used to fix internal fractures or dislocations by directly screwing two different bone pieces or internal implants, such as fixed bone plates, to fix the fracture, position the bone and promote its healing. Bone screws are used in a wide range of areas, including shoulders, elbows, hips, knees, and spine. For example, pedicle screw systems are used in spinal fusion, and compression bone screws are often used in foot and ankle surgery or the fixation of fractures in other places under pressure.
2. The structure and classification of bone screws
(1)Screw Cap
The screw cap of the bone screw has three main functions: optimizing the force. The protruding screw cap makes the contact area between the screw and the bone larger, increases the load area, optimizes the local force where the bone screw is driven, and reduces excessive force. Stress causes the risk of bone rupture; the second is the positioning function, the protruding screw cap allows the bone screw to be screwed into a certain depth, preventing the entire bone screw from being completely screwed into the bone; the third function is to provide the force application position, by rotating the force-applying groove at the screw cap, the bone screw moves forward and drives into the bone. Now the force-applying groove is mostly hexagonal, which does not require axial force to keep the driver in the center position, and is suitable for fractures in a wider range. Different shapes of force slots
(2) Screw body
The size of the screw body determines the strength and fatigue resistance of the bone screw. The thicker the diameter of the screw body, the stronger the strength and the better the fatigue resistance. In addition to the diameter of the screw body, the pitch and tooth depth of the screw thread on the screw body are also key parameters in the design of the screw body. Different thread designs have an important impact on the screw’s compression force and occlusal performance. Screw body in several different sizes
(3) Screw tip
Tapping refers to the process of bone screws cutting threads in the bone. According to the shape of the screw tip, bone screws can be divided into self-tapping screws and non-self-tapping screws. The tip of the self-tapping screw is sharper and can be directly screwed into the bone without being pre-drilled. Usually, self-tapping screws are used for cancellous bone, and the bone is compressed when the screw is screwed in so as to locally increase the bone density of the occlusal part and enhance the occlusal effect. When screwing into cortical bone (cortical bone), the screw channel is generally drilled in advance, and the bone screw is screwed in. Usually, self-tapping screws are not directly used to prevent the bone screw from being stuck or damaged due to the cortical bone being too hard.
Structural and Design
Bone screws can be divided into conventional screws, locking screws, headless screws (also called Hubble screws-Herbert screws), and cannulated screws according to different structural designs.
Material
Bone screws can be divided into titanium screws, stainless steel screws, and bio-absorbable screws according to the fixing materials.
Application
According to the application site of bone screws, bone screws are usually divided into cortical bone screws and cancellous bone screws.
Cortical screws are usually fully threaded with a small pitch; cancellous screws are usually partially threaded and usually self-tapping.
Screw Function
Bone screws can be divided into plate screws, lag screws, position screws, interlocking screws, and reduction screws according to the different functions of the screws.
Other commonly used screw classification methods are divided into self-tapping screws, non-self-tapping screws, self-drilling screws, and self-tapping self-drilling screws according to the characteristics of the screws. Bone screws are also divided into screws of different specifications according to diameter and length, like ordinary screws.
3. Innovation of bone screws
Traditional bone screws are mainly made of two materials, stainless steel, and titanium. With the continuous advent of new biodegradable biomaterials, more and more materials are used to make bone screws.
(1) Bio-absorbable screw
Although Chinese companies still mainly promote basic products, new types of degradable bone screws are being actively developed and introduced to the market. In recent years, more bone screws made of absorbable materials have entered the market and achieved good clinical results.
PLA Absorbable Screws and Magnesium Bone Screws
(2) Coated screws
In addition to the overall manufacturing materials, many companies have also begun to devote themselves to the research of screw surface coatings so as to increase the surface wear resistance and hardness of bone screws and reduce the effect of material rejection. For example, Screw PROtect, launched by orthopedic materials giant DePuy Synthes, claims to have the effect of preventing infection.
(3) Biological Screws
The good biocompatibility of the biological bone screw does not need to worry about rejection and does not require a second operation. Researchers at the University of Graz in Austria have developed an allograft orthopedic screw named shark screw, which has been clinically used in 14 hospitals in Austria.