DISLOCATIONS OF THE THUMB. 121 



dislocations the two tendons of the flexor brevis pollicis, together 

 with their enclosed sesamoid bones, will occupy a similar position. 

 At the same time one or other lateral ligament, generally the 

 outer, is lacerated. 



It is probable that the difficulty in reduction is due chiefly to 

 the fact that when extension is applied to the proximal phalanx, 

 the torn glenoid ligament is drawn taut, and forms a sheet which 

 prevents the return of the base of the phalanx forwards into its 

 natural position. At the same time the tendons of the flexor 

 brevis, together with the sesamoid bones, grasp the neck of the 

 rnetacarpal bone much in the same way as a button-hole does 

 the shank of a button, and thus still further interfere with 

 reduction. 



In order to overcome this difficulty in reduction, an anaesthetic 

 may be required, and a series of particular manipulations should 

 be carried out. The first manoeuvre is to adduct the metacarpal 

 bone towards the palm of the hand ; the second is to acutely 

 dorsi-flex or hyper-extend the first phalanx, so as to bring its 

 base up on to the head of the metacarpal bone, and thus open up 

 the sides of the " button-hole " and displace the torn glenoid 

 ligament forwards. Then a sudden flexion of the phalanx 

 towards the palm of the hand, whilst its base is steadied by the 

 surgeon's thumb, placed behind it, causes the head of the meta- 

 carpal bone to slip through the button-hole formed by the 

 tendons of the flexor brevis and the sesamoid bones and the base 

 of the phalanx to pass into its normal position. 



Should these manipulations fail, operative interference is 

 necessary. This is best carried out by the open method. A 

 median incision over the protruding head of the metacarpal bone 

 on the palmar aspect will readily show the encircling tendons 

 with their sesamoid bones. If these are hooked on one side and 

 the glenoid ligament drawn forwards, it is usually easy to press 

 the head of the bone backwards through the " button-hole," and 

 so bring the base of the phalanx into position. If a few stitches 

 are inserted so as to hold the torn parts of the ligament together, 

 there is but little chance of a recurrence of the displacement. 



