Biomechanics and Related Bio-Engineering Topics

Biomechanics and Related Bio-Engineering Topics

Proceedings of a Symposium Held in Glasgow, September 1964
1965, Pages 41-45
Biomechanics and Related Bio-Engineering Topics

3 - THE DETERMINATION OF OPTIMUM TWIST DRILL SHAPE FOR BONE

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This chapter discusses the determination of optimum twist drill shape for bone. The twist drills used in bone surgery are by no means ideal even when new. In many hospitals, there is also a lack of suitable sharpening facilities which, coupled with the high initial cost of the drills, results in the surgeon often being presented with a drill that is well beyond its useful life. The majority of twist drills used in bone surgery are closely similar to the standard chisel pointed twist drills used in drilling metal. The modifications commonly seen are reduction of the point angle to 90° and removal of the spiral cutting lands. The majority of holes drilled preparatory to the insertion of screws are done so in the shafts of long bones. The shafts of long bones are in effect tubes, there being a hard outer cortex and a central medullary cavity containing marrow. For the screw to engage firmly but not jam, it is essential that the holes through either wall of the tube should be both of accurate size and in line with each other. There are several types of apparatus available for testing twist drills in this manner, but they are all designed for high-end loads compared with the one to two kilograms required in the investigation discussed in the chapter. At this low level of loading, the friction of movement and measurement became proportionately too high to permit accurate readings.

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