PRACTICAL CONSIDERATIONS : THE HUMERUS. 



273 



Fig. 2S8. 



middle) and to imperfect immobilization of the humerus, the elbow being fixed by 

 splints, any motion of the hand or forearm under those circumstances being trans- 

 formed into motion of the upper end of the lower fragment. These may be factors, 

 but the chief reason for non-union is the entanglement of muscular and tendinous 

 fibres of the brachialis anticus and of the triceps between the bony fragments (page 



59°)- 



Descending the shaft it is not difficult to see why a fracture just above the con- 

 dyles ( " at the base of the condyles, " " supracondylar' ' ) should often be met with. 

 The olecranon fossa, the coronoid fossa, the shallower fossa for the radius just above 

 the external condyle, all contribute to weaken the bone at this point. Moreover, in 

 falls upon the elbow (the common cause of this fracture) the tip of the olecranon is 

 frequently driven directly into its fossa and against the very thin lamina at its base, 

 starting a fracture which extends laterally through the supracondylar and supra- 

 trochlear ridges to the border of the bone. If this transverse 

 line of fracture is associated with one running perpendicularly 

 into the joint, it constitutes the so-called " T-fracture" (" inter- 

 condylar' ' ) ; it is produced in the same manner, but usually 

 by a greater degree of force. 



In the so-called "extension" and "flexion" fractures in 

 this region the same mechanism is probably present, though it 

 is easy to imagine the same result (if the capsule and ligaments 

 of the elbow-joint remain intact) without the agency of the 

 olecranon. 



It should be noted that the external supracondylar ridge, 

 the strongest and most prominent, springs from the external 

 condyle, ascends in the line of the shaft, and terminates in the 

 head, so that it is well adapted to receive and distribute force 

 applied through the radius, as in falls on the hand, or in pushing 

 or striking strongly. The external is smaller than the internal 

 condyle because the extensors and supinators arising from it are 

 less powerful muscles than the flexors and pronators connected 

 with the former. This makes it less prominent ; but in spite of 

 these protective conditions it is at least as frequently broken, es- 

 pecially from indirect violence, because of its direct connection 

 with the hand through the radius and capitellum. On account 

 of the dense triceps fascia covering it, and its connection with the 

 ligaments of the elbow-joint, the displacement is slight. The 

 line of fracture usually passes through the radial fossa and enters 

 the joint through the depression between the capitelluin and 

 the trochlear ridge. 



The internal condyle is more often broken by direct violence, 

 or by the wedge-like action of the olecranon starting a fracture 

 which runs through the thin bone of the olecranon and coronoid 

 fossae, and through the trochlear depression. The displacement 

 is usually upward, is the result of the force causing the break, 

 and is but little influenced by anatomical factors. The brachialis 



anticus may elevate the fragment, but the ulna remains attached and prevents much 

 displacement. 



Either epicondyle may be broken. The line of the lower epiphysis runs 

 obliquely across the bone from just above the external epicondyle to a point just 

 below the internal epicondyle. In infancy both epicondyles (as well as the 

 trochlea and capitellum) enter into the epiphysis ; but at the thirteenth year the 

 internal epicondyle is quite distinct, and the trochlea, capitellum, and external 

 epicondyle are welded into the lower epiphysis proper, which by the fourteenth 

 to the fifteenth year (Dwight), sixteenth year (Treves and Stimson), seventeenth 

 year (Poland), is firmly united to the diaphysis. After the thirteenth year, there- 

 fore, separation of the epiphysis will probably leave the internal epicondyle attached 

 to the diaphysis. "The point of junction of the trochlear and capitellar portions 

 of the lower epiphysis at the middle of the trochlear groove at the sixteenth year 



18 



Lines of 

 the humerus, 

 anatomical 



fractures of 

 a, through 

 neck ; b. 



through tuberosities ; c, 

 through surgical neck ; d, 

 through shaft; e, T-frac- 

 ture involving condyles. 



