A system of surgery . e as afracture of the oscalcis, of the baseof the skull, or ofsome intermediatebone, from a fallon the feet. Theabsolute and re-lative strengths ofthe bones con-cerned, theamount of forceat work (body-weight x velocity as a rule), the line of force,the positions of the various bones with regard to this line, theeffect of muscular action, the freedom of the various bones tomove on each other, the resistance offered by the surface upon whichthe patient falls—these are some of the points about which exactinformation is indispensable before an accurate calculation of theresul
A system of surgery . e as afracture of the oscalcis, of the baseof the skull, or ofsome intermediatebone, from a fallon the feet. Theabsolute and re-lative strengths ofthe bones con-cerned, theamount of forceat work (body-weight x velocity as a rule), the line of force,the positions of the various bones with regard to this line, theeffect of muscular action, the freedom of the various bones tomove on each other, the resistance offered by the surface upon whichthe patient falls—these are some of the points about which exactinformation is indispensable before an accurate calculation of theresult can be attempted; but inquiry along these lines will oftenlead to a helpful hypothesis. Indirect violence may act by producing one or other of thefollowing effects :—(1) Pure flexion, as when, the lower part of theleg being fixed, the body falls to one or other side. The mechanismis similar when a malleolus is broken off by pressure of the astragalusagainst its tip in extreme supination or pronation of wie -Diagrams illustrating me commoner Results of Flexion.(P. Brans.) CAUSES OF FRACTURES. 733 (2) End-to-end compression of a bone, causing increase of itsnatural curve and fracture at the point of greatest tension andweakness. Thus, in falls on the hand the radius is often com-pressed between the capitellum and the carpus; in falls on the foot,the tibia; in false steps, the femur—the neck being fractured. (3)Compression of a bone, flexion being prevented, results in thecrushing of cancellous bones, and in the splitting up of largeepiphyses by the driving into them of smaller and denser arise many fractures of the femoral neck and trochanter.(4) Force transmitted across a joint through tense ligaments maytear off tbe bone into which the ligaments are inserted. Theanterior radio-carpal ligament is credited by some with this actionin producing Colles fracture. The malleoli, epicondyles, styloidprocesses, and the like are sometimes thus torn off. (5) To
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