Injuries to the Median Nerve at the Wrist-Carpal Tunnel Syndrome-Injuries to the Median Nerve at the Elbow-Motor-Sensory-Vasomotor Changes-Trophic Changes-

Injuries to the Median Nerve at the Wrist

■■ Motor: The muscles of the thenar eminence are paralyzed and wasted so that the eminence becomes flattened. The thumb is laterally rotated and adducted. The hand looks flattened and “apelike.” Opposition movement of the thumb is impossible. The first two lumbricals are paralyzed, which can be recognized clinically when the patient is asked to make a fist slowly, and the index and middle fingers tend to lag behind the ring and little fingers.

■■ Sensory, vasomotor, and trophic changes: These changes are identical to those found in the elbow lesions.

Perhaps the most serious disability of all in median nerve injuries is the loss of the ability to oppose the thumb to the other fingers and the loss of sensation over the lateral fingers. The delicate pincer-like action of the hand is no longer possible

Carpal Tunnel Syndrome

The carpal tunnel, formed by the concave anterior surface of the carpal bones and closed by the flexor retinaculum, is tightly packed with the long flexor tendons of the fingers, with their surrounding synovial sheaths, and the median nerve. Clinically, the syndrome consists of a burning pain or “pins and needles” along the distribution of the median nerve to the lateral three and a half fingers and weakness of the thenar muscles. It is produced by compression of the median nerve within the tunnel. The exact cause of the compression is difficult to determine, but thickening of the synovial sheaths of the flexor tendons or arthritic changes in the carpal bones are thought to be responsible in many cases.

As you would expect, no paresthesia occurs over the thenar eminence because this area of skin is supplied by the palmar cutaneous branch of the median nerve, which passes superficially to the flexor retinaculum. The condition is dramatically relieved by decompressing the tunnel by making a longitudinal incision through the flexor retinaculum.

Injuries to the Median Nerve at the Elbow

Motor

The pronator muscles of the forearm and the long flexor muscles of the wrist and fingers, with the exception of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus, will be paralyzed. As a result, the forearm is kept in the supine position; wrist flexion is weak and is accompanied by adduction.

The latter deviation is caused by the paralysis of the flexor carpi radialis and the strength of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. No flexion is possible at the interphalangeal joints of the index and middle fingers, although weak flexion of the metacarpophalangeal joints of these fingers is attempted by the interossei. When the patient tries to make a fist, the index and to a lesser extent the middle fingers tend to remain straight, whereas the ring and little fingers flex. The latter two fingers are, however, weakened by the loss of the flexor digitorum superficialis.

Flexion of the terminal phalanx of the thumb is lost because of paralysis of the flexor pollicis longus. The muscles of the thenar eminence are paralyzed and wasted so that the eminence is flattened. The thumb is laterally rotated and adducted. The hand looks flattened and “apelike.”

Sensory

Skin sensation is lost on the lateral half or less of the palm of the hand and the palmar aspect of the lateral three and a half fingers.

Sensory loss also occurs on the skin of the distal part of the dorsal surfaces of the lateral three and a half fingers. The area of total anesthesia is considerably less because of the overlap of adjacent nerves.

Vasomotor Changes

The skin areas involved in sensory loss are warmer and drier than normal because of the arteriolar dilatation and absence of sweating resulting from loss of sympathetic control.

Trophic Changes

In long-standing cases, changes are found in the hand and fingers. The skin is dry and scaly, the nails crack easily, and atrophy of the pulp of the fingers is present.

Injuries to the Bones of the Hand-Dislocation of the lunate bone-Fractures of the metacarpal bones-Bennett’s fracture-Compartment Syndrome of the Forearm--Volkmann’s Ischemic Contracture

Injuries to the Bones of the Hand

Fracture of the scaphoid bone is common in young adults; unless treated effectively, the fragments will not unite, and permanent weakness and pain of the wrist will result, with the subsequent development of osteoarthritis. The fracture line usually goes through the narrowest part of the bone, which, because of its location, is bathed in synovial fluid. The blood vessels to the scaphoid enter its proximal and distal ends, although the blood supply is occasionally confined to its distal end. If the latter occurs, a fracture deprives the proximal fragment of its arterial supply, and this fragment undergoes avascular necrosis.

Deep tenderness in the anatomic snuffbox after a fall on the outstretched hand in a young adult makes one suspicious of a fractured scaphoid.

Dislocation of the lunate bone
occasionally occurs in young adults who fall on the outstretched hand in a way that causes hyperextension of the wrist joint. Involvement of the median nerve is common.

Fractures of the metacarpal bones
 can occur as a result of direct violence, such as the clenched fist striking a hard object.

The fracture always angulates dorsally. The “boxer’s fracture” commonly produces an oblique fracture of the neck of the fifth and sometimes the fourth metacarpal bones. The distal fragment is commonly displaced proximally, thus shortening the finger posteriorly.

Bennett’s fracture
is a fracture of the base of the metacarpal of the thumb caused when violence is applied along the long axis of the thumb or the thumb is forcefully abducted. The fracture is oblique and enters the carpometacarpal joint of the thumb, causing joint instability.

Fractures of the phalanges are common and usually follow direct injury.

Compartment Syndrome of the Forearm

The forearm is enclosed in a sheath of deep fascia, which is attached to the periosteum of the posterior subcutaneous border of the ulna. This fascial sheath, together with the interosseous membrane and fibrous intermuscular septa, divides the forearm into several compartments, each having its own muscles, nerves, and blood supply. There is very little room within each compartment, and any edema can cause secondary vascular compression of the blood vessels; the veins are first affected, and later the arteries.

Soft tissue injury is a common cause, and early diagnosis is critical. Early signs include altered skin sensation (caused by ischemia of the sensory nerves passing through the compartment),

pain disproportionate to any injury (caused by pressure on nerves within the compartment), pain on passive stretching of muscles that pass through the compartment (caused by muscle ischemia), tenderness of the skin over the compartment (a late sign caused by edema), and absence of capillary refill in the nail beds (caused by pressure on the arteries within the compartment). Once the diagnosis is made, the deep fascia must be incised surgically to decompress the affected compartment. A delay of as little as4 hours can cause irreversible damage to the muscles.

Volkmann’s Ischemic Contracture

Volkmann’s ischemic contracture is a contracture of the muscles of the forearm that commonly follows fractures of the distal end of the humerus or fractures of the radius and ulna. In this syndrome, a localized segment of the brachial artery goes into spasm, reducing the arterial flow to the flexor and the extensor muscles so that they undergo ischemic necrosis. The flexor muscles are larger than the extensor muscles, and they are therefore the ones mainly affected. The muscles are replaced by fibrous tissue, which contracts, producing the deformity. The arterial spasm is usually caused by an overtight cast, but in some cases the fracture itself may be responsible. The deformity can be explained only by understanding the anatomy of the region.

Three types of deformity exist:

■■ The long flexor muscles of the carpus and fingers are more contracted than the extensor muscles, and the wrist joint is flexed; the fingers are extended. If the wrist joint is extended passively, the fingers become flexed.

■■ The long extensor muscles to the fingers, which are inserted into the extensor expansion that is attached to the proximal phalanx, are greatly contracted; the metacarpophalangeal joints and the wrist joint are extended, and the interphalangeal joints of the fingers are flexed.

■■ Both the flexor and extensor muscles of the forearm are contracted. The wrist joint is flexed, the metacarpophalangeal joints are extended, and the interphalangeal joints are flexed.

Vaginal Examination-Injury to the Perineum during Childbirth-Pudendal Nerve Block-Area of Anesthesia-Indications-Transvaginal Procedure-Perineal Procedure

Vaginal Examination

Digital examination of the vagina may provide the physician with much valuable information concerning the health of the vaginal walls, the uterus, and the surrounding structures

Injury to the Perineum during Childbirth

The perineal body is a wedge of fibromuscular tissue that lies between the lower part of the vagina and the anal canal. It is held in position by the insertion of the perineal muscles and by the attachment of the levator ani muscles. In the female, it is a much larger structure than in the male, and it serves to support the posterior wall of the vagina. Damage by laceration during childbirth can be followed by permanent weakness of the pelvic floor.

 Few women escape some injury to the birth canal during delivery. In most, this is little more than an abrasion of the posterior vaginal wall. Spontaneous delivery of the child with the patient unattended can result in a severe tear of the lower third of the posterior wall of the vagina, the perineal body, and overlying skin. In severe tears, the lacerations may extend backward into the anal canal and damage the external sphincter. In these cases, it is imperative that an accurate repair of the walls of the anal canal, vagina, and perineal body be undertaken as soon as possible.

In the management of childbirth, when it is obvious to the obstetrician that the perineum will tear before the baby’s head emerges through the vaginal orifice, a planned surgical incision is made through the perineal skin in a posterolateral direction to avoid the anal sphincters. This procedure is known as an episiotomy. Breech deliveries and forceps deliveries are usually preceded by an episiotomy
.

Pudendal Nerve Block

Area of Anesthesia

The area anesthetized is the skin of the perineum; this nerve block does not, however, abolish sensation from the anterior part of the perineum, which is innervated by the ilioinguinal nerve and the genitofemoral nerve. Needless to say, it does not abolish pain from uterine contractions that ascend to the spinal cord via the sympathetic afferent nerves.

 

Indications

During the second stage of a difficult labor, when the presenting part of the fetus, usually the head, is descending through the vulva, forceps delivery and episiotomy may be necessary
.

Transvaginal Procedure

The bony landmark used is the ischial spine . The index finger is inserted through the vagina to palpate the ischial spine. The needle of the syringe is then passed through the vaginal mucous membrane toward the ischial spine. On passing through the sacrospinous ligament, the anesthetic solution is injected around the pudendal nerve .

Perineal Procedure

The bony landmark is the ischial tuberosity . The tuberosity is palpated subcutaneously through the buttock, and the needle is introduced into the pudendal canal along the medial side of the tuberosity. The canal lies about 1 in. (2.5 cm) deep to the free surface of the ischial tuberosity. The local anesthetic is then infiltrated around the pudendal nerve.

Uterus in the Child-Uterus after Menopause-Uterus in Pregnancy-Role of the Uterus in Labor-Prolapse of the Uterus-Hysterectomy and Damage to the Ureter-Varicosed Veins and Hemorrhoids in Pregnancy-

Uterus in the Child

The fundus and body of the uterus remain small until puberty, when they enlarge greatly in response to the estrogens secreted by the ovaries.

Uterus after Menopause

After menopause because the ovaries no longer produce estrogens and progesterone, the uterus atrophies and becomes smaller and less vascular. These changes occur.

Uterus in Pregnancy

During pregnancy, the uterus becomes greatly enlarged as a result of the increasing production of estrogens and progesterone, first by the corpus luteum of the ovary and later by the placenta. At first, it remains as a pelvic organ, but by the third month the fundus rises out of the pelvis, and by the ninth month it has reached the xiphoid process. The increase in size is largely a result of hypertrophy of the smooth muscle fibers of the myometrium, although some hyperplasia takes place.

 

Role of the Uterus in Labor

Labor, or parturition, is the series of processes by which the baby, the fetal membranes, and the placenta are expelled from the genital tract of the mother. Normally, this process takes place at the end of the 10th lunar month, at which time the pregnancy is said to be at term. The cause of the onset of labor is not definitely known. By the end of pregnancy, the contractility of the uterus has been fully developed in response to estrogen, and it is particularly sensitive to the actions of oxytocin at this time. It is possible that the onset of labor is triggered by the sudden withdrawal of progesterone. Once the presenting part (usually the fetal head) starts to stretch the cervix, it is thought that a nervous reflex mechanism is initiated and increases the force of the contractions of the uterine body. The uterine muscular activity is largely independent of the extrinsic innervation. In women in labor, spinal anesthesia does not interfere with the normal uterine contractions. Severe emotional disturbance, however, can cause premature parturition

Prolapse of the Uterus

The great importance of the tone of the levatores ani muscles in supporting the uterus. The importance of the transverse cervical, pubocervical, and sacrocervical ligaments in positioning the cervix within the pelvic cavity. Damage to these structures during childbirth or general poor body muscular tone may result in downward displacement of the uterus called uterine prolapse. It most commonly reveals itself after menopause, when the visceral pelvic fascia tends to atrophy along with the pelvic organs. In advanced cases, the cervix descends the length of the vagina and may protrude through the orifice.

Because of the attachment of the cervix to the vaginal vault, it follows that prolapse of the uterus is always accompanied by some prolapse of the vagina.

Hysterectomy and Damage to the Ureter

During the surgical procedure of hysterectomy, great care must be exercised to not damage the ureters. When the surgeon is looking for the uterine artery on each side at the base of the broad ligament, it is essential that he or she first identifies the ureter before clamping and tying off the artery. The uterine artery passes forward from the internal iliac artery and crosses the ureter at right angles to reach the cervix at the level of the internal os.

Varicosed Veins and Hemorrhoids in Pregnancy

Varicosed veins and hemorrhoids are common conditions in pregnancy. The following factors probably contribute to their cause: pressure of the gravid uterus on the inferior vena cava and the inferior mesenteric vein, impairing venous return, and increased progesterone levels in the blood, leading to relaxation of the smooth muscle in the walls of the veins and venous dilatation.