PRACTICAL CONSIDERATIONS: THE FIBULA. 393 



process. It is strongest at and below the middle of the bone. It twists backward 

 and is lost at the back of the malleolus. The poslero-internal border begins at the 

 inner side of the back of the head. It is very strong at about the middle. It ends 

 in the last quarter by joining the interosseous ridge. The latter, or aniero-i^iternal 

 border, begins poorly marked at the inner side of the neck, soon becomes sharp, 

 and descends rather straighter than the others to some three inches above the lower 

 end, where it divides into two lines which, ending at the borders of the articular facet 

 for the astragalus, enclose a rough space for ligaments. The interosseous membrane, 

 being attached to this ridge,, separates the front of the bone from the back. The 

 anterior surface^ between this and the antero-external border, is very narrow. It 

 forms a part of a hollow, of which the membrane is the floor, from which certain 

 extensor muscles arise. The exterjial surface, between the antero-external and the 

 postero-external borders, is a characteristic one, presenting for more than the lower 

 half a shallow groove for the peroneus longus and brevis, which sweeps down to 

 the back of the malleolus behind the subcutaneous space enclosed by the splitting 

 of the antero-external border. The. posterior surface is bounded by the postero- 

 external border and by the postero-internal till that border joins the interosseous 

 ridge, which bounds the surface in its lower part. It faces backward above and 

 inward below. The nutrient foramen, running downward, enters it rather above the 

 middle, usually near the postero-internal border. A roughness on the outer part 

 of this surface is for the origin of the soleus. The internal surface, relatively broad 

 in the greater part of its course, looks inward to the hollow between the two bones. 

 It ends in the last quarter where the oblique ridge joins the interosseous one. 



The lower extremity of the fibula is pointed, forming the outer malleolus,^ 

 which projects downward and a little outward. Its outer surface is a continuation of 

 the subcutaneous triangle, and the greatest prominence near its back is in line with 

 the posterior of the borders of the space. Most of the internal surface is occupied 

 by a triangular articular facet for the astragalus, the upper part of which is nearly 

 vertical, while the lower slants outward. Below and behind this, on the inner side 

 of the greatest projection, is a deep hollow for part of the external lateral ligament. 

 The malleolus is broader behind than in front, presenting a groove in continuation 

 of the external surface for the peroneal tendons. 



Development. — The centre for the shaft appears in the eighth foetal week ; 

 that for the head of the bone, which, according to the usual order of long bones, 

 should develop next, does not come till after that of the malleolus. The latter ap- 

 pears in the second year, the former two or three years later. The lower epiphysis 

 is probably fused with the shaft by eighteen or nineteen and the upper by twenty. 



PRACTICAL CONSIDERATIONS. 



The upper epiphysis has a flat lower surface and is about on a level with the 

 most prominent part of the tibial tubercle. It includes, therefore, all that portion 

 of the head of the fibula into which the biceps tendon and external lateral ligament 

 are inserted. Its line of cartilage at and after the thirteenth year is in close relation 

 with the synovial membrane of the tibio-fibular joint. Its disjunction is favored 

 by its situation on the most exposed aspect of the limb, its subcutaneous position, 

 and the insertion into it of the biceps muscle. The attachment of the external 

 lateral ligament also enables a powerful strain to be brought upon it in over-adduction 

 of the leg. In spite of these favorable circumstances, the protection afforded by 

 the slight overhang of the external tuberosity of the tibia and the fixation given by 

 the strong anterior and posterior upper tibio-fibular ligaments make separation of 

 this epiphysis a very rare occurrence. Boyd says that several cases are known in 

 which it has been pulled off by violent contraction of the biceps in an effort to prevent 

 falling. It is then felt as an easily recognizable fragment the space between which 

 and the diaphysis is increased upon extension of the leg. 



fracture of the shaft of the fibula in its upper two-thirds occurs from direct 

 violence and as a secondary result of fracture of the tibia. In spite of the slender- 

 ness of the bone and its position on the outer aspect of the leg, fracture is not very 

 frequent because of {a) its elasticity, which is marked ; (^b) its protective covering 



^ Malleolus lateralis. 



