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THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

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detemined by using the photographic method described above, with the<br />

metatarsals held at a 50 degree angle.<br />

Area proportions are 0.406 for MT III, and 0.297 for MT II and MT IV. Using<br />

equation (8), the resulting forces on the metatarsals at 50 degrees are therefore:<br />

F~m1=(37873 N)(0.297)=11248 N<br />

F~m~(37873 N)(0.406)=15376 N<br />

F~~-nv=(37873 N)(0.297)=11248 N.<br />

The force on the distal end of MT III, with it inclined at 50 degrees, is the<br />

important value for this analysis. The vector wmponents of this force (Figure 4.2)<br />

were calculated; these components were input along the z and y ordinate axes in<br />

the finite element program. It was assumed that the proximal end of MT III was<br />

held rigid by its articulations with MT II and MT IV. With boundary conditions set<br />

to zero displacement or rotation at the proximal end of the MT Ill, the finite<br />

eiement program calculated bending moments acting on the metatarsal, in arder<br />

ta arrive at the resulting strains.<br />

2. Mafenal properfies<br />

Finite element modeling can incorporate material properties of objects with<br />

non-homogeneous intemal structure, such as bones with cortical and trabecular<br />

wnstituents, as well as stnicturally homogeneous objects such as ligaments. CT<br />

scans revealed that dense cortical bone is predominant in the G. libratus<br />

metatarsus. Cancellous bone is restricted to narrow bands near the phalangeal<br />

and rnesotarsal articular surfaces, and to srnall regions near the proximal and<br />

distal extremities of the medulary cavities. Unfortunately, the size and shape of

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