THE FOREARM AND WRIST.
139.Ulna.—The edge of the ulna can be felt subcutaneous from the olecranon to the styloid process (in supination). Any irregularity could be easily detected. The styloid process of the ulna does not descend so low as the styloid process of the radius, or it would impede the free abduction of the hand. Its apex is on a level with the radio-carpal joint. The head of the ulna is plainly felt and seen projecting at the back of the wrist, especially in pronation of the forearm. It then lies between the tendons of the extensor carpi ulnaris and extensor minimi digiti. There is often a subcutaneous bursa over it.
140.Radius.—The upper half of the shaft of the radius is so covered by muscles that we cannot feel it; the lower half is more accessible to the touch, especially just above and just below the part where it is crossed by the extensors of the thumb. Its styloid process is readily felt, and made allthe more manifest by being covered by the first two extensor tendons of the thumb. It descends lower, and lies more to the front than the corresponding process of the ulna. The relative positions of these styloid processes can be best examined by placing the thumb on one and the forefinger on the other.
Feel for the little bony pulley on the back of the radius near the wrist, which keeps in place the third extensor tendon of the thumb. This and the bone just above it is the place which we examine for a suspected fracture (termed Colles’s) near the lower end of the radius.
141.Carpus.—Below the styloid process of the radius, just on the inner side of the extensors of the thumb, we feel the tubercle of the scaphoid bone. Between the styloid process and the tubercle is the level of the radio-carpal joint. A little lower we feel the trapezium.
Just below the ulna on the palm of the hand we feel the pisiform bone; and on the inner side of this, the cuneiform.
There are several transverse furrows on the palmar aspect of the wrist. The lowest of these, which is slightly convex downwards, corresponds with the upper edge of the anterior annular ligament and the intercarpal joint. The line of the radio-carpal joint, as already stated, is on a level with the apex of the styloid process of the ulna.
In forcible flexion of the wrist, the tendon of the flexor carpi radialis and that of the palmaris longus come up in relief. On the outer side of the first-named tendon we feel the pulse, the radial artery here lying close to the radius.
The tendon of the palmaris longus runs near the middle of the wrist, and close to its inner border runs the median nerve. In letting out deep-seated matter near the wrist, the incision should be made close to and parallel with the inner edge of the radial flexor tendon, so as to avoid injury to the median nerve.
We can feel the tendon of the flexor carpi ulnaris for some distance above the wrist. It overlies the ulnar artery, and somewhat masks its pulsation.
142.Pulse.—The ‘pulse at the wrist’ is felt just outsidethe tendon of the flexor carpi radialis. In feeling the pulse it should be remembered that, in some cases, the superficialis volæ arises higher and is larger than usual. In such cases it runs by the side of the radial artery, and gives additional volume to the pulse. The old writers call it ‘pulsus duplex.’ When in doubt, therefore, it is well to feel the pulse in each wrist.
143.Great carpal bursa.—The great synovial sheath under the annular ligament common to the flexor tendons of the fingers and the long flexor of the thumb, extends, upwards, about an inch and a half above the edge of the ligament, and, downwards, as low as the middle of the palm. This general synovial sheath communicates with the special sheaths of the thumb and the little finger; not with that of the index, middle, and ring fingers.
144. ‘Tabatière anatomique.’—On the outer side of the wrist we can distinctly see and feel, when in action, the three extensor tendons of the thumb. Between the second and third there is deep depression, at the root of the thumb, which the French humorously call the ‘tabatière anatomique.’ In this depression we can make out—1, the relief of the superficial radial vein; 2, the radial artery, in its passage to the back of the hand; 3, the upper end of the metacarpal bone of the thumb.
145.Tendons on back of wrist.—The relative positions of the several extensor tendons of the wrist and fingers, as they play in their grooves over the back of the radius and ulna, can all be distinctly traced when the several muscles are put in action. The length of their synovial sheaths should be remembered. They vary from one inch and a half to two inches and a half. The longest of all are those of the extensors of the thumb. When these sheaths are inflamed and swollen, the motion of the tendons becomes painful and gives rise to a feeling of crepitus, called ‘tenalgia crepitans’ by some writers. It is said to be met with sometimes in pianists.
146.Lines of arteries.—The course of the radial artery corresponds with a line drawn from the outer border of the tendon of the biceps at the bend of the elbow down the frontof the forearm to the front of the styloid process of the radius. In the upper third of its course the artery is overlapped by the supinator longus. To make allowance for this, the incision for the ligature of the artery in this situation should be made, not precisely in the line of its course, but rather nearer the middle of the forearm.
The line of the ulnar artery runs from the middle of the bend of the elbow (slightly curving inwards) to the outer side of the pisiform bone. The radial and ulnar arteries can, in most cases, be effectually commanded by pressure well applied at the wrist, in wounds of the palmar arch.
Before we make incisions along the forearm, it is always desirable to ascertain whether the ulnar artery, which usually runs under the superficial muscles, may not run abnormally over them; in which case its pulsations can be felt all down the forearm.