280 SURGICAL APPLIED ANA TOMY. [Chap. xv. 



would appear to be produced with equal ease by 

 a fall upon either the front or the back of the 

 hand. Bransby Cooper gives the case of a lad who 

 fell upon the outstretched palms of both his hands : 

 both wrists were dislocated, one backwards, the other 

 forwards. 



(2) Some dislocations about tJie liand (os magnum). 

 In forcible flexion of the hand, the os magnum 

 naturally glides backwards, and projects upon the 

 dorsum. In very extreme flexion (as in falls upon, the 

 knuckles and dorsum of the metacarpus), this move- 

 ment of the bone backwards may be such as to lead 

 to its partial dislocation, the luxation being associated 

 with some rupture of ligaments. In one recorded 

 case, this luxation was produced by muscular force. 

 The patient, a lady, while in labour, " seized violently 

 the edge of her mattress, and squeezed it forcibly." 

 Something was felt to give way in the hand, and the 

 head of the os magnum was found to be dislocated 

 backwards. 



Dislocation at the metacarpo-pJialangeal joint oj 

 the thumb. In this luxation, the phalanx is usually 

 displaced backwards, and the lesion is of interest on 

 account of the great difficulty often experienced in 

 reducing the bone. Many anatomical reasons have 

 been given to explain this difficulty, which are well 

 summarised by Hamilton in the following passage ; 

 " Hey believes the resistance to be in the lateral liga- 

 ments, between which the lower end of the metacarpai 

 bone escapes and becomes imprisoned. Ballingall, 

 Malgaigne, Erichsen, and Vidal think the metacarpai 

 bone is locked between the two heads of the flexor 

 brevis, or, rather, between the opposing sets of muscles 

 which centre in the sesamoid bones, as a button is 

 fastened into a button-hole. Pailloux and others 

 affirm that the anterior ligament, being torn from one 

 of its attachments, falls between the joint surfaces, 



