PRACTICAL CONSIDERATIONS : THE HAND BONES. 



319 



between them. They each have one cartilage-covered surface against the bone and 

 are otherwise surrounded by fibrous tissue. A small one on the radial side of the 

 joint of the index-finger occurs in rather less than half the cases, and one on the 

 ulnar side of the little finger in rather more than four-fifths. Pfitzner^ gives the 

 following table of percentages showing the frequency of the various sesamoid bones, 

 combining his work and that of Thilenius : 



Fourth-month fcetus . . 

 Fourteen to ninety y'ears 



Number 

 of Hands. 



30 

 1323 



Thumb. 



Rad. Uln. 



100 100 



99.9 100 



Index. 



R. L. 



46 23 



47.8 O.I 



Middle. 



R. 



30 

 1-5 



L. 



15 

 o 



Ring. 



R. L. 



23 30 

 o 0.1 



Little. 



Rad. Uln. 

 15 63 

 2.3 82.4 



Variations in the number of the fingers are generally regarded as malforma- 

 tions. The most common occurrence is an extra finger, the identification of which 

 is not certain. It seems often as if we should content ourselves with saying that 

 there is an extra finger, but that no particular one has been repeated. Sometimes 

 the thumb has three phalanges. Occasionally any of the terminal phalanges is 

 doubled. A very uncommon condition is that of seven or eight fingers and no 

 thumb. The dissection of such a case revealed the absence of the radius and of the 

 radial side of the wrist, the skeleton of the forearm consisting of two ulnae, and that 

 of the hand of the ulnar sides of two opposite ones fused together. 



PRACTICAL CONSIDERATIONS. 



The Carpus. — Of the carpal bones the scaphoid and semilunar are most fre- 

 quently broken, on account of their more direct relation to the line of transmission 

 of force in falls upon the hand. The diagnosis is difificult, and has been made 

 oft-enest by the help of a skiagraph. There is but little displacement. The other 

 bones of the carpus, on account of their shortness, irregular and rounded shape, 

 and compact union by strong ligaments which yet permit slight movements be- 

 tween the bones, usually escape injury except in cases of crush of the whole hand. 

 They are, however, not infrequently the seat of tuberculous disease, as might be 

 expected from their great liability to traumatism of all grades. Their synovial re- 

 lations (Fig. 342) favor the spread of such disease from one bone to the remainder, 

 and render conservative treatment unsatisfactory. The result, too, is affected by the 

 close proximity of the flexor and extens6r tendons, which become involved in the 

 tuberculous process or bound down by adhesions. 



The Metacarpus. — The first metacarpal bone, which is morphologically a 

 phalanx, is,, like all the phalanges, developed from an epiphysis situated at its 

 proximal end. But one case of disjunction has been recognized during life. It re- 

 sembled a dislocation at the carpo-metacarpal joint, but the seat of abnormal move- 

 ment was below the level of the lower edge of the trapezium. In the remaining 

 metacarpal bones the epiphysis is situated at the distal extremity. 



Falls upon or striking with the closed fist tend to produce forward displace- 

 ment. As the metacarpal bones of the index-, middle, and ring fingers are the 

 longer, their epiphyses are more likely to be separated in this manner. A fall on 

 the extended fingers and metacarpo-phalangeal region may cause backward displace- 

 ment, though this is rarer. 



The diagnosis from dislocation of the proximal phalanges is not easy. It is 



aided by the recognition of " mufifled crepitus" (Poland) and by the great tendency 



of the deformity to recur, due partly to the small articular areas of the separated 



bones and partly to the action of the flexors and the interossei. Skiagraphy will 



'usually establish the diagnosis. 



Fracture of the metacarpal bones is usually the result of a blow with the 

 clenched fist. The metacarpals of the thumb and little finger are therefore rarely 

 broken. On account of the mode of application of the force, the seat of fracture is 



* Zeitschrift fiir Morph. and Anthropol., Bd. ii., 1901. 



