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When cancellous bone screws are used for bone plate fixation, the following key points should be noted:
Screw type selection: Cancellous bone screws come in two types: semi-threaded and fully threaded. Semi-threaded screws can function as tensile screws. When used as tensile screws, semi-threaded screws should be selected and all the threads should be located within the contralateral bone block and not along the fracture line; otherwise, it will affect the compressive effect of the tensile force. Full-thread screws are used for the fixation of the epiphyseal end.
Operating specification: The cancellous bone screw can open a path by itself in the cancellous bone, and no tapping is required after drilling. Stronger grip can be obtained if the double-layer leather can be passed through. When in use, if a 6.5mm pine bone screw is employed, first drill a hole of the required length with a 3.2mm fine drill bit. Then, use a 4.5mm drill bit to expand the bone hole of the proximal fracture block to make it equal to or slightly larger than the diameter of the proximal stem of the screw. Next, use a 6.5mm tap to remove the thread. Finally, tighten the screw. For patients with osteoporosis, the tapping length should be slightly shorter than the screw length or the distal cancellous bone should not be tapped, and the cancellous bone screw should not penetrate the contralateral cortical bone.
Fixation method: Generally, when fixing a fracture, a Kirschner’s needle is used first. If the fixation screw is used later, the Kirschner’s needle needs to be removed. At this time, the fracture may be displaced. However, a hollow compression screw can solve this problem. When using cancellous bone screws for bone plate fixation, the appropriate fixation method can be selected based on the fracture condition. For example, it is recommended that at least three screws be screwed into each side of the fracture end of the lower extremity. Screwing the screws at the farthest and nearest ends into one side of the cortex can disperse the stress.
When used in conjunction with bone plates: When cancellous bone screws are used in conjunction with bone plates, it is necessary to ensure the compatibility between the screws and the bone plates, as well as the correct position of the screws in the screw holes of the bone plates, to achieve a stable fixation effect. For instance, when using a bone plate, if a compression screw is placed to exert pressure on the fracture line between bone fragments, it can either be placed in the bone through the holes on the bone plate or used independently of the bone plate. When placing, it is best for the screw to be perpendicular to the fracture line.