Final answer:
The optimal angle for lag screw placement across a fracture is typically 90 degrees to the fracture plane but is often adjusted to be perpendicular plus 25 to 30 degrees to the bone's long axis for long bone fractures.
Step-by-step explanation:
The optimal angle for lag screw placement across a fracture is typically perpendicular (90 degrees) to the fracture plane to maximize compression and stability. However, when placing a lag screw across a long bone fracture, an angle of perpendicular plus 25 to 30 degrees to the long axis of the bone is often recommended. This angle helps to ensure adequate compression of the fracture site while also maximizing the screw's holding power within the bone.
Placement of the screw directly over the fracture is essential, although identifying the pain source can be challenging. The fracture mechanics can vary: they may occur straight across the long axis of the bone, at an angle that is not 90 degrees, be pulled apart by twisting motion, or result in one fragment being driven into another. All these scenarios must be considered when determining screw placement.
Torque also plays a role in the stability of the fixation. Applying the principles of physics, including the calculation of torques and lever arms, can inform the direction and angle at which forces should be applied via the screw to optimize healing.