With the widespread use and development of transpedicular internal fixation techniques, improving pedicle screw placement techniques and improving pedicle screw revision is one of the current topics of discussion, while the internal fixation of lumbar 5-sacral 1 has its own special characteristics and revision is more difficult. With the widespread use of transperineal internal fixation in spinal surgery, the number of cases of internal fixation failure has gradually increased. Moore et al. concluded that the incidence of intraoperative and postoperative screw loosening and withdrawal of degenerative slippage was nearly 5.5%, while the failure rate of internal fixation after spinal fracture was as high as 9%. 1, selection of revision screw size Different sizes of screws present different biomechanical properties, and within the limits of the anatomical morphology of the pedicle and the mechanical needs of internal fixation, increasing the diameter or length of the revision screw enhances the screw-bone bond [3]. The extraction force is related to the surface area of the cylindrical bone and is determined by the outer diameter of the screw and the depth of entry. When large-diameter screws are placed, the cancellous bone in the center of the pedicle is pushed into the peripheral relatively dense layer, and the threads can be placed into the peripheral relatively dense layer; extraction strength tests for pedicle screws of different diameters show that extraction strength is greater for larger diameter screws than for smaller diameter screws, and extraction strength increases with increasing outside diameter. The longer the screw, the greater the fixation strength, and it was found that 60% of the screw fixation strength was within the pedicle, and the strength increased by 15-20% after reaching the cancellous bone of the vertebral body, by 16% when reaching the anterior bone cortex but not penetrating it, and by 20-25% when penetrating the anterior bone cortex. A 1 mm increase in diameter and a 5 ~10 mm increase in length is also a reliable means. However, the method of increasing the diameter of screws to improve stability is strictly limited by the anatomical condition of the pedicle, and the use of larger diameter pedicle screws also increases the risk of nerve root injury and pedicle fracture, and the maximum outside diameter of screws should not exceed 80% of the outside diameter of the pedicle. In the author’s opinion, screw revision is the best option to increase the diameter and length of the screw with accurate access points because the previous nail path has been destroyed. 2. Differences in the holding force of lumbosacral pedicle screws and anatomical characteristics This experiment shows that when lumbar 5 pedicle screws are revised, the holding force of the pedicle screws exceeds the strength of the original screws when the diameter is increased by 1.5 mm and the length is increased by 10 mm; the holding force of sacral 1 screws is generally smaller than that of the lumbar spine, and the result of simple screw revision is also different from that of the lumbar spine, where the holding force only reaches the level of the original screws. The pedicle screw holding force depends on the bonding strength of the thread-bone screw interface, and the quality of the bone around the screw becomes a key factor in determining the screw holding force, and high-quality bone can obtain a greater holding strength. In the lumbar spine, screw screwing compresses the cancellous bone to the strong cortical bone, and the bone density around the screw is relatively high, with a more satisfactory bone quality; the placement of thick screws can even cut into the surrounding bone cortex, increasing the holding strength. In the sacrum, due to the obvious widening of its arch, the cancellous bone content and the lack of strong bone cortex, the bone density around the screw is low and the bone strength is low after screwing, and the holding strength is relatively small, and it is often difficult to obtain satisfactory holding strength by increasing the diameter and length of the screw. Therefore, clinically, there are more methods to improve the internal fixation of sacral arch, such as increasing the length of screws to make them penetrate the anterior bone cortex, changing the direction of needle entry through S1 upper endplate and even L5 lower endplate or adding additional screws in S2. 3, bone cement reinforced fixation revision Clinically, when the arch nail tract is severely damaged or osteoporotic, it is more difficult to revise simply using large diameter screws, often adding biomaterials to strengthen the stability of the arch screw. After reinforcement with bone cement, the holding force is transformed from bone-screw interface to stronger bone-adhesive-screw interface, which can significantly increase the holding force of pedicle screw, and has little relationship with the screw’s own structure, and screw extraction mainly relies on bone cement-bone interface peeling; when using bone cement for revision, the role of the screw is not reflected, and its own structure has become unimportant, so how to allocate and inject bone cement to make it evenly distributed in the pedicle. The key to revision is how to mix and inject the bone cement so that it is evenly distributed in the pedicle and achieves the best combination with the screw. In practice, the situation is often very complicated, such as osteoporosis, serious damage to the nail path, poor access position and need for additional rerouting, etc. It is more difficult to use large diameter screws alone for revision, and biomaterials need to be added to strengthen the stability of the pedicle screws. In particular, the sacral spine has a special anatomical structure, with a wide pedicle and a large cancellous bone content. After the failure of the first screw fixation, the screw loosens and causes cancellous bone extrusion, which makes the nail channel significantly larger than the original screw, and it is difficult to obtain sufficient holding force with the limited increase of the screw diameter and length, so the significance of bone cement reinforced fixation in the revision of the sacral spine is more significant at this time. Since the strength of the bone-adhesive-screw interface exceeds the structural strength of the spine itself, the improvement of biomaterials should focus on controlling the histochemical reaction of the additive, and it is no longer meaningful to increase the adhesive strength of the reinforcement excessively. The clinical application of common bone cement will produce a series of problems, such as polymerization heat to the surrounding tissue (including the spinal cord and nerve roots) damage, long-term retention in the body to produce toxicity and carcinogenic effects, etc., is gradually replaced by new biomaterials. 4, the correlation between pedicle screw holding force and torque moment Most biomechanical experiments to assess the axial extraction force of screw holding strength indicators, recent studies have found that lateral loading is often the main cause of early loosening of the screw, so the combination of holding force and extraction force better reflects the holding strength of the screw. The results of this experiment show that the screw holding force and torque do not show absolute agreement, and the correlation between the holding force and torque differs greatly for different screw bonding interfaces. The correlation between the bonding strength and torque moment at the bone-screw interface alone is obvious, which is consistent with previous studies (correlation coefficients of 0.83-0.925); in practice, physicians are also accustomed to judging the holding strength of pedicle screws by torque moment, which has some clinical utility. Bone cement reinforced fixation is the screw-cement-bone interface, and the torque moment is meaningless when the bone cement has not yet cured at the time of screw placement. When the bone cement is cured, the bone-cement bond is solid, while the screw-cement bond is not tight enough, so the screw can still be twisted easily; the holding force of the screw mainly relies on the anastomosis of the bone cement with the thread inlay after curing, depending on the strength of the bone cement itself and the bone-cement bond strength.