Human hands make complex and dexterous movements of pinching, grasping, clamping, lifting, etc., with extremely fine sensations. These complex functions of the hands are closely related to their anatomical structure.
I. Skin
The palm surface of the hand has a thicker keratinized layer of skin, a thicker subcutaneous fat pad, there are many vertical fiber trabeculae, there is a good sense of the entity, only touch the membrane with the hand, you can identify the shape of objects, softness and smoothness or not. The skin texture of the hand is obvious, and there are constant skin lines opposite the palm and interphalangeal joints, which are important markers of the hand incision, and the incision should be parallel to the skin lines to prevent scar contracture.
The dorsal skin of the hand is thin, with little subcutaneous fat and a layer of loose cellular tissue in the public, which has greater mobility. When extending the fingers, the skin on the back of the hand can be pinched and lifted, but when clenching a fist, the skin is stretched tight and becomes locally white on the back of the metacarpophalangeal joint due to increased tension. Therefore, skin defects on the back of the hand should also be covered with skin implants or flaps like the palm of the hand, and should not be reluctantly sutured, affecting finger flexion.
The veins and lymphatic vessels of the fingers and palms return through the back of the hand; therefore, swelling of the back of the hand is obvious in cases of palmar inflammation.
Two, tendon
(A) Flexor tendon
The deep and superficial flexor muscles are attached to the base of the distal and middle phalanges, which flex the distal interphalangeal joint and the proximal interphalangeal joint respectively, and there are triangular-shaped membrane-like tissues near the tendon, which are connected to the tendon and the periosteum, and are short tendons. At the proximal interphalangeal joint there is a band of membranous tissue connected to the tendon, which is the long tendon button. They are the intersection of the synovial layer of the tendon sheath and the wall layer. The tendon button contains the blood vessels that nourish the tendon. When the finger is flexed, the deep tendon and the superficial tendon do not have the same contraction amplitude and there is a relative sliding between them of 0.5-0.75 cm. When there is adhesion between the deep and superficial tendons, the relative sliding is lost and the finger flexion and extension functions are affected. From the metacarpal head to the middle phalanx, the flexor tendons are enclosed in a fibrous bone canal called the tendon sheath. The tendon sheaths of the metacarpal head, the middle of the proximal phalanx, and the middle of the middle phalanx are significantly thickened and are called the tendon sheaths of the tendon sheaths.
When these pulleys are injured, the tendon leaves the phalanges during flexion, forming a “bowstring shape” and preventing full flexion. The radial side of the deep palmar flexor tendon is the starting point of the earthworm muscle of the hand, so when the finger tendon is ruptured, the deep tendon remains in the palm of the hand due to the pull of the earthworm muscle. The long thumb flexor ends at the base of the distal phalanges of the thumb, and there is also a tendon sheath in the thumb, because it and the superficial flexor are not pulled by the earthworm muscle, and after rupture, the proximal end is often retracted to the wrist or even the forearm.
(B) Extensor tendon
The extensor tendon of the dorsum of the hand is covered only by skin and a layer of loose reticular tissue, with a paratendinous membrane outside the tendon, which has good circulation. The index finger and little finger each have an intrinsic extensor tendon, both located on the ulnar side of the common extensor tendon.
The thumb has a long thumb extensor and a short thumb extensor, which are attached to the base of the distal phalanges and proximal phalanges, respectively, and extend the interphalangeal joint of the thumb and the veins of the ventral hand in two deep and superficial layers. The deep veins of the palm of the hand are mostly accompanied by arteries and flow back to the ulnar and radial veins or the venous network of the dorsum of the hand. The superficial vein of the hand is on the dorsal side, far more important than the deep vein, and finally returns to the cephalic vein and noble vein, which is the main blood return channel for replantation of broken fingers or thumb (hand) reconstruction.
Nerve
The hand is mainly innervated by the median nerve and ulnar nerve, and the radial nerve only innervates part of the dorsal sensation of the hand.
The main trunk enters the carpal tunnel at the deep surface of the palmaris longus muscle and divides into the interosseous muscle branch just after the transverse carpal ligament, which innervates the interosseous muscles (except for the thumb adductor muscle, and the deep head of the short thumb flexor muscle is occasionally innervated by the ulnar nerve). After the median nerve exits the carpal tunnel, it sends sensory innervation to the radial three and a half fingers one after another.
The ulnar nerve divides into a sensory branch at the wrist to the dorsum of the hand, which innervates the dorsal ulnar half of the fingers. The main trunk enters the ulnar canal at the radial side of the doughy bone. Within the canal, it divides into a superficial branch and a deep branch. The superficial branch is radial and is primarily a sensory branch, innervating the short palmar muscle, the ulnar side of the palm and one and a half fingers on the ulnar side. The deep branch is a motor branch that travels with the ulnar artery, crosses the lesser trochanter into the palm, and travels with the deep arch of the palm on the deep side of the flexor tendon and the superficial side of the interosseous muscle, along which it emits muscular branches that innervate the lesser trochanter, interosseous muscle, 3 and 4 earth muscles, and finally the thumb adductor muscle and occasionally the deep head of the short thumb flexor. Within the ulnar nerve trunk of the wrist, the deep and superficial branches have a natural division of 5-6 cm, and when anastomosing the nerve at the wrist, the sensory and motor branches can be anastomosed separately according to the natural division.
There are more variants in the innervation of the sensation of the hand. The dorsal aspect of the metacarpophalangeal joint of the thumb and part of the greater interphalangeal area may occasionally be innervated by the terminal branch of the musculocutaneous nerve.
Bone, joint and ligament
The radial carpal joint is composed of the radius, navicular bone, lunate muscle and triangular cartilage disc, the ulna does not directly participate, the radial carpal joint is a ball and socket joint, can make multi-axis movement.
The carpometacarpal joint is the most important joint of the thumb, which is composed of most of the angular bones and the base of the first metacarpal bone, and is a saddle-shaped joint with a loose joint capsule, which can flex, extend, adduct and abduct the thumb, and is the main joint of the thumb to palmar abduction movement.
The metacarpophalangeal joint is composed of the metacarpal head and the base of the proximal phalanges. The metacarpal head of the thumb is flat and less dynamic than the other metacarpophalangeal joints. Each metacarpophalangeal joint is strengthened by the lateral collateral ligaments and the lateral palmar ligaments. The lateral collateral ligaments run obliquely from the proximal dorsal side to the distal metacarpal side on both sides. The ligaments are taut when the joint is flexed, making the joint more stable, and ligaments are relaxed when the joint is extended. Fixation in the extended finger position may cause ligament contracture resulting in limitation of flexion, so it should be fixed in the flexed position when the hand is traumatized. The interphalangeal joint is only flexion and extension, and is also strengthened by collateral ligaments on both sides. The structure is the same as that of the metacarpophalangeal joint. The metacarpophalangeal joint is the main joint of the finger movement, and when it is straight or hyperextended, it is difficult to pinch and grip the thumb, even though the interphalangeal joint is in normal flexion and extension, and its function is severely limited. If the interphalangeal joint can be flexed to 35°-45°, the interphalangeal joint can be used and the function of the hand can be greatly improved.