WRIST-JOINT (Radio-carpal Articula tion), NORMAL ANATOMY OF TIIE.— The ar ticulation of the wrist results from the union of the bones of the fore-arm with those of the hand, and is constituted by the contact of the lower surfaces of the radius and of the trian gular interarticular cartilage with the sca phoid, lunar, and cuneiform bones of the carpus. The radius and the triangular fibro cartilage accordingly present a uniformly smooth and slightly concave surface, whilst the first three bones of the carpus afford a surface which is as uniformly convex. The transverse measurement of these articular surfaces is greater than the antero-posterior, since the former averages one inch and a half in the adult male, whilst the latter scarcely exceeds three quarters of an inch.
In this joint are found all the anatomical dispositions which characterize other arthro dial articulations : the bones are invested with cartilage, lined by a synovial membrane, and present smooth surfaces which deviate but slightly from being planiform ; and lastly, the ligaments connecting the osseous surfaces are so disposed, as to admit of all the free gliding motions which are indispensable to the hand as an organ of touch and of prehension.
It is proposed in this article to describe, seriatim, the different structures which enter into the composition of the radio-carpal articulation, with their relative anatomy, but for a detailed account of the surgical anatomy of the region of the wrist, the reader is re ferred to the article Hand, where this subject has been fully entered into.
I. The Bones which constitute the wrist-joint.
a. The lower end of the radius, which is of a quadrilateral form, is curved so as to present a concavity ante riorly, and a convexity in the opposite direction. On its different aspects various objects of interest present themselves to view, which may be thus enumerated : — Anteriorly is seen a smooth surface, to which the ten dons of the flexor muscles, surrounded by their synovial sheath, are applied ; posteriorly, a series of depressions and irregular elevations are observable, the former of which indicate the course of different tendons passing to the hand. Of these depressions the most ex
ternal is a broad but shallow groove, which lodges the tendons of the radial extensors of the carpus: to its inner side, but separated from it by a well-marked ridge, is a narrow deep groove, which runs obliquely down wards and outwards, and transmits in this In insects we find a great diversity of beau tifully contrived mechanism for the modula tion of sound, all answering the same end in the economy of these countless myriads of minute beings.
direction the tendon of the extensor secundi internodii pollicis. The remainder of the dorsal aspect of the radius is subjacent to the tendons of the m. extensor digitorum cora munis and the extensor indicis. The outer surface of the lower extremity of the radius is the least extensive, and is furnished with a shallow groove, which affords insertion to the tendon of the supinator longus, and gives passage to the tendons of two of the extensor muscles of the thumb, viz., the extensor ossis metacarpi pollicis and extensor primi inter nodii pollicis. This surface is terminated inferiorly by the styloid process, which lies on a plane a little posterior to the last-mentioned groove : lastly, the inner surface of this por tion of the bone presents a smooth concave surface of oval form, its long axis directed from before backwards, which serves for arti culation with the head of the ulna, and enters into the formation of the inferior radio-ulnar articulation. By its inferior surface, the radius is adapted for articulation with the carpus. The aspect of the surface, owing to the curvature of the radius already indicated, is downwards and forwards, whilst at the same time it is directed slightly inwards, from its external boundary passing lower than the internal.