What Are Bone Screws?

Internal fixation device for fixing fracture site.

Internal fixation device for fixing fracture site.

Chinese name

Bone screw

English name

bone screw

definition

Internal fixation device for fixing fracture site. Use alone or in combination with bone plates. Cancellous bone screws, cortical bone screws, bone plugs and hollow screws are commonly used.

Applied discipline

Materials science and technology (first-level discipline), biological materials (second-level discipline), orthopedic materials (third-level discipline)

The above content was published by the National Science and Technology Terminology Examination Committee.

Chinese name

Bone screw

Foreign name

Bone Screw

Management category

Class III medical devices

Category Name

Implant equipment

Classification of bone screws

1. Self-tapping screws (cancellous bone screws), as shown in Figure 1. For the reduction and correction of limb bones, epiphyses, femoral neck, intertrochanteric, intercondylar, maxillofacial, metacarpal and foot fractures. Wide pitch, thicker thread (strong cutting force), less number of lines, thinner screw, guide hole (rotary head) is slightly thicker than the screw, which is convenient for the screw to cut the screw and screw in; it is not suitable for cancellous bone. Hard cortical bone, strong torque will break the screw; not suitable for use as a tension screw. As shown in Figure 1.

Figure 1 Self-tapping screws (cancellous bone screws)

Figure 1 Self-tapping screws (cancellous bone screws)

2. Non-self-tapping screws (cortical bone screws), as shown in Figure 2. There are more threads, and the pitch is narrower; the threads of the matching taps are exactly the same as the screw threads, and they are sharper than the screws, and the lead-in holes are consistent with the screw cores. The screw torque is small, and the accuracy is high. The original thread is damaged, and it is mostly used for cortical bone, and its holding force is worse than that of cancellous bone screws. as shown in picture 2.

Figure 2 Non-self-tapping screws (cortical bone screws)

Figure 2 Non-self-tapping screws (cortical bone screws)

3. Pull the screws. Also called semi-threaded screw, it does not specifically refer to a certain type of screw. It can be a hollow screw or an ordinary screw. Femoral neck fractures are generally fixed with hollow screws. At the same time, tension is required to compress the bones. The most effective way is to use a tension screw. The direction of the tension screw is perpendicular to the fracture line, which can bring the largest compression between the folds. In most cases, the best function of the tension screw can be achieved. When the screw is not perpendicular to the fracture line, Shear force is generated during tightening to displace the fractured piece. As shown in Figure 3.

Figure 3 Pull screw

Figure 3 Pull screw

4. Hollow compression screw. It may have the function of a tension screw. As shown in Figure 4.

Figure 4 Hollow compression screw

Figure 4 Hollow compression screw

Preparation of bone screws

In the early stage, cortical bones under traumatic amputations were collected according to the bone selection criteria. Later, healthy calf leather bone was selected as raw material for 1-3 years. Cut the saw and wash on the clean machine. The finished product is washed with normal saline, degreased with 95% acetone solution at 20 ° C for 2h, immersed in 3% hydrogen peroxide for 10min, repeatedly rinsed with normal saline, pre-frozen at -30 ° C for 24h, double-layer material bag Packaging, sterilization with 20KG gamma radiation, marking the mouth period of irradiation, and setting at -30 ° C until use. The packaging can be used for 6 months without damage. After 6 months, it can be used again after irradiation. ^[1]

Research Status and Application of Bone Screw Magnesium Alloy Bone Screw

In 1907, pure magnesium plates (the actual purity of which was unknown) were first used to fix fractures of the calf bone with gold-plated steel nails. The result failed because pure magnesium metal rapidly corroded in the body and an excessive amount of gas was generated under the skin in only 8 days. Studies of magnesium alloys and titanium devices for the treatment of rabbit ulnar fractures have shown that bone formation around Mg devices has fully demonstrated that Mg can provide a biomechanical environment for bone healing, and can degrade and promote the formation of new bone.

Magnesium alloy screws can be degraded in vivo. The diameter of 3.64mm and 19.56mm ZK60 magnesium alloy screws. The 2.5mm diameter drill is punched perpendicular to the femoral condyle and screwed into the magnesium alloy cancellous bone screw. The alloy has a yield strength of 285MPa and a tensile strength 335MPa, containing two alloy elements, Zn and Cr, which have the functions of corrosion resistance and providing mechanical properties. They degrade slightly faster in the first 4 weeks of fixation and firm in early fixation. They can induce osteoinduction from 8 to 12 weeks. The surface of magnesium alloy screws degrades. Ca and P elements are gradually deposited to prevent further degradation and match the formation of new bone, which is better used for internal fixation of fractures. ^[2]

Bone Screws Further Reading

[1] Zhang Keyu, Hua Zikai. Failure analysis and strength test of bone screws [J]. Medical Biomechanics, 2018, 33 (03): 280-284.

[2] Tang Li, Li Juan, Xu Jun. Comprehensive nursing of patients with pelvic fractures undergoing percutaneous patella screw fixation [J]. Nursing Research, 2018, 32 (07): 1148-1150.

Bone Screw References

[1] Zhu Lian, Xu Yaozeng, Yang Tongqi, Bao Zhaohua. Bone screw design, biomechanical testing and clinical application research [J]. Journal of Suzhou Medical College, 1998 (06): 551-556.

[2] Zhang Qimei. Structural optimization of Mg-Zn-Y-Nd alloy bone screws based on finite element analysis [D]. Zhengzhou University, 2017.