290 Palm of Hand 



In amputating a metacarpal bone its base should, if possible, be 

 left, as to remove it would be to open up a considerable extent of 

 synovial membrane (p. 286). But this remark does not apply to 

 the first metacarpal, which has an isolated joint with the trapezium. 

 In amputating this bone, however, the utmost care must be taken 

 lest, in attacking its base, the radial artery be wounded as it is pass- 

 ing to the root of the first space, as shown in the fig. on p. 287. 



Amputation of the thumb at its joint with the trapezium may be 

 performed by a racket-shaped incision, the ' handle part ' of which 

 runs from the root of the metacarpal bone and down the dorsum, 

 whilst the ' loop part ' encircles the head of the bone. The three ex- 

 tensor tendons are cut, and the abductor, opponens, flexors brevis and 

 longus, and the adductor. The root of the first dorsal interosseous 

 muscle is detached. The radial artery must be very carefully guarded, 

 but its branches, the two dorsales and the princcps, must needs be 

 severed. 



In amputating a finger or a phalanx a difficulty may arise in hit- 

 ting the articulation unless the finger be first 

 _ bent. The knife should be passed so as to strike 

 the middle of the head of the metacarpal bone, 

 not its dorsal aspect. The joint being traversed 

 from behind, a flap is cut from the flexor aspect. 

 It is important to remember that the prominence 

 of the knuckle is made by the head of the meta- 

 carpal bone or of the phalanx, and ,not by the 

 base of the phalanx ; unless this be understood, the operator may be 

 expending his time in useless cuts against the head of the metacarpal 

 bone or phalanx. 



Ampliation through the first inter-phalangeal joint is apt to leave 

 the phalanx stiff and unmanageable, because it receives no insertion 

 either from the flexor or the extensor tendons. It is preferable, 

 therefore, to amputate through the middle of the second phalanx, 

 as the stump then retains the slips of the superficial flexor and of 

 the common extensor. But when only the first phalanx is left the 

 tendons may still find a cicatricial insertion and render the stump 

 extremely useful. 



The metacarpal bones have a centre of ossification for the shaft 

 which appears at the eighth week of fcetal life, and one for the head 

 which appears in the third year ; they coalesce at manhood 2Oth 

 year. The phalanges are developed on the same plan, except that in 

 them the epiphysis is at the base instead of the head. 



The first metacarpal bone, let it be noted, has its epiphysis at its 

 base ; thus, developmentally, it is a phalanx. 



Occasionally \hzfirst metacarpal bone is dislocated at its saddle- 

 shaped joint with the trapezium ; sometimes its epiphysis is detached, 

 in which case the appearance is a good deal like that of dislocation : 



