ABNORMAL CONDITIONS OF THE HAND. 



511 



tremity. In flexion, the head of the os mag- 

 num, which is somewhat inclined backwards, 

 raises up the thin capsule which surrounds its 

 articulation, and, if this movement be carried 

 very far, the capsule and accessory fibres which 

 support the bone posteriorly are broken, and 

 the os magnum escapes from the cavity in which 

 it is naturally placed ; the dislocation cannot 

 be called complete, yet the os magnum passes 

 somewhat the level of the posterior surface of 

 the other bones of the carpus. The accident 

 is more common in women than in men, no 

 doubt because the ligaments are weaker and 

 the bones enjoy greater motion in the former 

 than in the latter ; the luxation backwards of 

 the os magnum, the only one which can occur, 

 is always the result of a forced and violent 

 flexion of the wrist, such, for example, as a 

 fall on the back of the hand would produce. 



We recognize the luxation of the os mag- 

 num by the history of the accident, and by the 

 deformity produced. We perceive a hard cir- 

 cumscribed tumour which has suddenly ap- 

 peared on the back of the hand in the situation 

 which corresponds to the head of the bone. 

 This tumour becomes more prominent when 

 the hand is flexed, and diminishes when it is 

 extended ; we can make it disappear entirely 

 by a slight compression. This luxation causes 

 but little inconvenience, but the head of the 

 os magnum always remains more salient when 

 the hand is flexed, and forms a tumour more 

 or less marked according to the extent of the 

 displacement. 



We can easily reduce this luxation by ex- 

 tending the hand, or by exercising a slight 

 pressure on the head of the os magnum ; but, 

 although it is easy to make the bone resume 

 its position in the cavity formed for it by the 

 scaphoid and semilunar bones, it is very dif- 

 ficult to maintain it there, and the inconve- 

 nience and deformity resulting from the luxation 

 are so trivial that few persons will submit with 

 patience to the means usually recommended. 



Luxation of the bones of the metacarpus. 

 Luxation of the metacarpal bone of the thumb. 

 The carpal head of the metacarpal bone of the 

 thumb, notwithstanding the range of motion it 

 enjoys, is rarely dislocated. Sir A. Cooper, in 

 his extensive experience, has seen but one spe- 

 cies of this accident, viz. luxation of the meta- 

 carpal bone of the thumb upon the os trapezium, 

 inwards. " In the cases I have seen of this 

 accident," says Sir Astley, " the metacarpal 

 bone has been thrown inwards between the tra- 

 pezium and the root of the metacarpal bone of 

 the fore-finger ; it forms a protuberance towards 

 the palm of the hand; the thumb is bent back- 

 wards, and cannot be brought towards the little 

 finger : considerable pain and swelling are pro- 

 duced by this accident." 



Luxation of the carpal head of the meta- 

 carpal bone of the thumb backwards. Some 

 surgeons seem to doubt that the metacarpal 

 bone of the thumb is capable of being dis- 

 located in any other direction than that in- 

 wards; but the following case is given on the 

 highly respectable authority of the experienced 

 Boyer. Madame De la P luxated the 



metacarpal bone of her left thumb backwards 

 on the dorsum of the trapezium by falling on 

 the external or radial border of her hand ; the 

 luxation was at first mistaken. When Boyer 

 saw it six months after the accident, the su- 

 perior extremity of the metacarpal bone of the 

 thumb formed posteriorly a very remarkable 

 prominence on the trapezium, and this bone 

 and the phalanges of the thumb were inclined 

 towards the palm of the hand. On pressing 

 posteriorly on the prominence formed by the 

 superior extremity of the dislocated bone, it 

 could be made to resume its natural place and 

 the prominence disappeared; so long as the 

 pressure was continued, the bone retained its 

 place and the thumb enjoyed its natural powers 

 of flexion and extension ; but as soon as the 

 pressure was remitted, the bone became dis- 

 placed anew, and the movements of the thumb 

 impossible. The lady was unwilling to sub- 

 mit to any treatment, and the condition of the 

 joint remained unaltered. These luxations of 

 the metacarpal bone of the thumb, whether 

 backwards or inwards, must be rare, as the 

 causes which are calculated to produce them 

 must act through the first phalanx of the thumb, 

 which, it is manifest, will be much more dis- 

 posed to yield than the metacarpal bone. 



Luxation of the phalanges of the fingers. 

 The first phalanx of the thumb as well as the 

 first phalanx of any of the fingers may be 

 luxated backwards ; the luxation forwards of 

 the phalanx is very rare and perhaps impossible, 

 except in the index finger and the thumb. 



The mutual support which the first pha- 

 langes of the fingers afford each other laterally, 

 and the strength of the lateral ligaments render 

 the luxation outwards or inwards very difficult. 

 Luxations of thejirst phalanx of the thumb 

 from the metacarpal bone. The first phalanx 

 of the thumb may be luxated forwards to the 

 palmar surface of the metacarpal bone, but 

 this form of luxation is very rare, while the 

 luxation of the same phalanx on the dorsum 

 of the metacarpal bone is the most common 

 and important displacement of any to which 

 the bones of the hand are liable. We shall 

 therefore consider this accident in detail. 



In some persons the first phalanx of the 

 thumb can at will be dislocated backwards, 

 solely by the contraction of the muscles. The 

 displacement produced by accident, however, 

 is much more extensive than this, which may 

 be termed the voluntary luxation. When the 

 first phalanx of the thumb is in a state of 

 extreme extension, accident may dislocate it 

 on the dorsum of the metacarpal bone. The 

 signs of the injury are so evident that mistake 

 appears impossible; the first phalanx is thrown 

 back as if pulled by its two extensors, and 

 forms nearly a right angle with its metacarpal 

 bone (jig. 226) ; the head of the latter forms 

 a remarkable tumour at the anterior part 

 or palmar aspect of the articulation, while 

 a prominence behind points out the situation 

 of the base of the first phalanx : the last or 

 distal phalanx is (in recent cases) flexed, and it 

 soon becomes difficult or impossible to extend 

 it, or to flex the first phalanx. 



