WRIST-JOINT. (NORMAL ANATOMY). 



1507 



ligament much resembles the one last de- 

 scribed. Arising from the posterior edge of 

 the carpal end of the radius, its fibres pass 

 downwards and inwards to the back of the 

 carpus, where they expand and take an ex- 

 tensive attachment to the three inner bones 

 of the first range. The tendons of the ex- 

 tensor muscles of the fingers are related to 

 the superficial surface of this ligament, which 

 has also in contact with it the posterior carpal 

 arteries from the radial and nlnar trunks. 



The anterior and posterior ligaments are 

 connected, both externally and internally, with 

 the lateral ligaments, so that no portion of 

 the periphery of the articulation is devoid of 

 ligarnentous covering 



c. External Lateral Ligament of the Wrist- 

 Joint. The external lateral ligament v, funi- 

 cular in form, and connects the styloid process 

 of the radius with the scaphoid and trapezium, 

 the two most external of the carpal bones. 

 The direction of its fibres is downwards and 

 backwards. The radial artery crosses ob- 

 liquely over the external surface of this liga- 

 ment, and separates it from the tendons of 

 the extensor ossis metacarpi and the extensor 

 primi internodii pollicis. The synovial mem- 

 brane lines its inner surface. When the hand 

 is fully adducted, this ligament is put upon 

 the stretch. 



d. The internal lateral ligament. This li- 

 gament is larger and longer than the pre- 

 ceding ; for, notwithstanding the greater 

 length of its styloid process, the ulna is more 

 widely separated from the carpus than is the 

 radius. This ligament connects the styloid 

 process of the ulna with the cuneiform bone, 

 giving a fasciculus to the fusiform bone and 

 to the anterior annular ligament. The tendon 

 of the extensor carpi ulnaris is posterior and 

 parallel to th's ligament. The internal lateral 

 ligament limits abduction, so as to render it 

 the least extensive of all the motions enjoyed 

 by the wrist joint. 



III. Synovial Membrane, The synovial 

 membrane of the wrist joint is very extensive, 

 and contains a large quantity of synovia. Its 

 anatomical disposition is so simple as not to 

 require any special notice ; but it may be of 

 practical importance to remember the prox- 

 imity of this structure to the synovial sacs 

 between the lateral articulations of the carpal 

 bones, and also its contiguity to the articula- 

 tion between the trapezium ami the first 

 metacarpal bone. The former circumstance 

 explains the facility with which acute inflam- 

 mation, occurring in the smaller carpal articu- 

 lations as the result of imparonychia, may be 

 propagated to the contiguous wrist joint, 

 where, too frequently, the morbid action thus 

 excited proves destructive to the articulation. 

 The latter circumstance demands our atten- 

 tion, since it teaches that, in amputating at 

 the first carpo-metacarpal articulation a care- 

 less use of the knife may inflict a wound upon 

 the wrist joint itself, from which the most 

 serious consequences may accrue. 



The synovial membrane of the wrist joint is 

 separated from that of the inferior radio- 



ulnar articulation by the triangular interarti- 

 cular cartilage. In .amputating at the wrist 

 joint, if care be taken to leave the inter- 

 articular cartilage uninjured, the motions of 

 pronation and of supination will be left to the 

 forearm, and may therefore be communicated 

 to the artificial substitute for the amputated 

 hand. In this respect, the amputation 

 through the joint offers an advantage which 

 is sacrificed when amputation is performed 

 through the continuity of the bones of the 

 forearm. 



IV. Mechanical Functions. The wrist- 

 joint enjoys every variety of motion included 

 under the head of gliding motions ^Bicliat) ; 

 thus it is capable of flexion, extension, adduc- 

 tion, abduction, and circumduction. In the 

 motions of flexion and of extension, the carpus 

 rolls either forwards or backwards on the 

 lower articular surface of the radius. 1'lcxitui 

 is limited, not only by the posterior ligament, 

 but also by the lateral ligaments which are 

 attached behind the centre of motion of the 

 articulation. Extension is limited by the an- 

 terior ligament only. In adduction and abduc- 

 tion the carpal bones glide from side to side 

 on the surface opposed to them. Of these 

 motions abduction is the more limited, be- 

 cause, probably, the styloid process of the radius 

 and the trapezium come sooner into mutual 

 contact than the corresponding parts at the 

 inner side of the joint do. In circumduclion 

 (a motion compounded of all the preceding 

 ones), the hand moves through a circle re- 

 presenting the base of a hollow cone, the 

 apex of which is at the joint. The free gliding 

 of the carpal bones on each other causes this 

 movement to appear more extensive than it is 

 in reality, whilst it gives all that ease and 

 grace to the movements of the wrist which 

 are in so especial a manner its characteristics. 



The wrist joint thus constituted would not, 

 a priori, be supposed to enjoy that remarkable 

 immunity from accidental luxation which 

 must be conceded to it. In truth, this articu- 

 lation owes its remarkable strength and its 

 freedom from accidental displacements to the 

 mass of tendons which occupy its anterior 

 and posterior surfaces principally, not to its 

 ligamentous connections, nor to the form of its 

 osseous surfaces. Those tendons, like so 

 many vital ligaments kept tense as well by the 

 tonic as by the active contraction of their 

 muscles, and bound down by the annular liga- 

 ments, bear off, in a great degree, all violent 

 shocks from the joint itself, whilst, by their 

 antagonistic resistance to each other, they at 

 the same time maintain the bones in accurate 

 contact. 



But whilst, owing to these circumstances, 

 the impetus of shocks applied to the hand are 

 borne off from the articulation of the wrist, 

 they fall in many instances with resistless 

 force upon the lower end of the radius, 

 which, owing to the thinness of its compact 

 tissue, is ill adapted for opposing an effectual 

 resistance. It has already been shown that 

 the ulna is but indircclly connected \\iili the 

 carpus ; and that a layer of highly-elastic tissue 



5 L) 2 



