. On modern methods of treating fractures . which a wood screwcan be tightly driven, the latter cannot bury its thread at all,but merely makes a faint groove in the smooth walls of the hole,in which it holds by friction only. Fig. 103 shows this quite clearly ; the two lateral screws inthis specimen had been driven into the bone as firmly as waspossible Avith a large screw-driver, and yet the thread has onlycut the shallowest of lines into the bone. The hold of sucha screw entirely depends then upon the frictional grip, whichis distributed not over a large surface of bone, but merely 200 MODER
. On modern methods of treating fractures . which a wood screwcan be tightly driven, the latter cannot bury its thread at all,but merely makes a faint groove in the smooth walls of the hole,in which it holds by friction only. Fig. 103 shows this quite clearly ; the two lateral screws inthis specimen had been driven into the bone as firmly as waspossible Avith a large screw-driver, and yet the thread has onlycut the shallowest of lines into the bone. The hold of sucha screw entirely depends then upon the frictional grip, whichis distributed not over a large surface of bone, but merely 200 MODERN METHODS OF TREATING FRACTURES over the linear spiral surfaee touched by the edge of the serew-thread. No wonder that the bone ra2:)idly softens before thispressure, and the screw becomes loose. Moreover, as all the screws are in the same plane, they canonly hold the bone by a narrow segment of its thickness. How-ever long such a jolate, and however many screws are used in itsfixation, the whole structure only holds to a piece of the bone. Fig. 103.—Showing the action of wood and metal screws. Thebone has been drilled and screwed by three screws ; the left-hand one,an ordinary carpenters screw ; the right-hand one, a Lanes screw ;and the centre one, a metal screw. The wood screws make only afaint spiral groove in the bone, whilst the metal screw thread lies in adeep slot cut for its reeejation. which is the width of one screw. In a femur, for example, 1 dianaeter, a series of screws ^ in. thick only hold the bone bya twenty-fifth part of its cross-section. Lambottes Plates.—Two of the mechanical defects of Lanesplates have been remedied by Lambotte. He uses a curvedplate, and a metal screw. Lambottes largest plate is 6 , about -^V ii^- thick, and it tapers at each end, the centrebeing 1 in. wide and curved so as to form a third of a 1-in. OPERATIVE TREATMENT OF FRACTURES 201 cylinder. It has no less than seven screw-holes in each half of theplate ; but these h
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