1. SD at cesarean section - This results from excessive lateral upward traction and is not spontaneous. This is soft tissue dystocia from a small incision. This injury is rarely permanent and is always the posterior shoulder. This maneuver deviates from accepted standards of care. When SD at cesarean occurs the uterine and/or abdominal incisions must be enlarged, and/or the anesthesia altered by giving muscle relaxants and/or uterine relaxants.
2. Congenital Erbs - It is speculated that brachial plexus injuries (BPI) may very rarely occur during the course of the second stage of labor before the fetal head has delivered, and thus not under the control of the obstetrician no recognizable by the obstetrician. This "Congenital" brachial plexus injury may occur approximately 1 in 25,000 times compared to brachial plexus injury secondary to inappropriately managed shoulder dystocia which occurs at a frequency of 1 in 600 deliveries. it is postulated that such congenital brachial plexus injury may result from clinical factors which are not evident. One such speculative factor is when the injury is secondary to entrapment of the posterior shoulder against the promontory of the sacrum, arresting the downward descent of the posterior shoulder while the fetal head continues to descend through the pelvis, and the physician pulls on the head, thus resulting in an injury to the brachial plexus. This injury has to involve the posterior shoulder (shoulder directed towards the mother's back) and not the anterior shoulder. Furthermore, when such injury occurs, there must be a great deal of edema and bruising over the posterior shoulder and chest. Such speculation implies that posterior brachial plexus injuries may occur in labor prior to the point in time when shoulder dystocia would have been diagnosed, and occurs when the fetal head delivers but the entrapped shoulders fail to follow. This will only be a result of rapid descent, either spontaneously, or with vacuum or forceps. The presence of trauma to the posterior scapula and/or thorax (chest) are key to this theory. This theory remains unproven.
3. Teratogens or Viral Sepsis - Another scenario which can result in congenital brachial plexus injury is when there has been destruction of the nerve plexus in utero by various Teratogens including viral sepsis. Under such circumstances, the child is born with evidence of atrophic or withered muscles of the upper extremity and the presence of a congenital, and underdeveloped brachial plexus cervical root injury can be easily proven by biopsy of the brachial plexus during the neonatal course of the infant.
4. In-Utero Erbs Palsy - A.K.A. Fetal Maladaption Syndrome. Ref. Dunn DW, Engle WA Pediat. Neurol 1985; 1:367-9. These injuries are a chronic injury associated with an abnormal uterine shape, or a deformation from a mass in the neck, fat necrosis, and/or distortion of the first four ribs. Deformation injuries are the result of unusual or excessive fetal constraint in-utero. the electromyographic study performed soon after birth will be normal (Site-Vanessa Villalobas v. Our Lady of Resurrection Medical Center et al., Cook County (IL) Circuit Court, Case No. 89L-9149. Leonard C. Arnold Chicago, IL). Medical abstract Ann. Neural 1980; 8:228, Koenigsberger MR. This theory relates to chronic malpositioning of an upper extremity in utero such as abduction of the arm and shoulder posterior to the fetal back. Under this clinical scenario, such abnormal posturing would have been evident at the time of delivery in concert with abnormal posturing postbirth.
5. Severe Fetal Depression (asphyxia) - This occurs in a labor resulting in a limp, flaccid, or atonic muscle that may predispose to a plexus injury (Volpe JJ. Neural of the newborn. Philadelphia: WB Saunders, 1981: 585-91). This is a stretch or traction injury.
6. Precipitous labor and delivery - This is a poor causation theory. If the shoulder is rammed into the pubic bone enough to tear, stretch and permanently injury nerves, the shoulder would be swollen and bruised. The uterine wall, bladder, and properitoneal fat and fascia protect the baby. Brachial palsy is not an impact injury in labor. It is a stretch injury. The shoulder does not reach the pubic bone until the head is out. the shoulder/head only move very slightly with a contraction which starts slow and gradual and lasts 45-60 seconds. There are not abrupt start and stop movements. Damage to the plexus will only occur after the nerves have been stretched 25%! Such stretching does not occur during labor.
Meghdari studied the mechanics, the level of damage in brachial plexus palsy and determined the maximum permissible forces. Clinical experiments indicate that the BP must be stretched 20% to cause injury. A shear force of 17.5 Newtons (IN=0.22 pound) is sufficient to create such a length increase and damage the BP. (Meghdari A., Davoodi R., & Mesbah F. Engineering analysis of shoulder dystocia in the human birth process by the finite element method. J. Engineering in Med. 1992, p. 243-250.
7. Phalen's Intraabdominal Shelf Syndrome - Unproven. Maternal fat dystocia, a shelf behind the pubic bone causes nerve damage. Fat tissue is very soft, not encapsulated, and has the consistency of Jello. It cannot exert pressure! The uterine wall is thick, muscular, and protective of the infant and would displace any fat. A "shelf of fat" does not exist in the abdominal or pelvic cavity. The fat in the abdominal wall is external to the abdominal muscles and only causes a "pot belly" in the lower part of the abdominal wall and "love handles" on the sides of the abdominal wall. Obese women undergoing cesarean section for CPD do not have dents, grooves or depressions in the uterine wall. Manual removal of the placenta in obese women has never been associated with any dents, impressions, grooves, depressions or any abnormalities in the anterior uterine wall. the obstetric literature since 1880 has never mentioned, postulated, observed, described or even speculated about a shelf of fat in the abdomen. Fat dystocia does not exist.
Non-Congenital Erbs (Traction SD) A Stretch Injury
Inappropriate excessive traction can deliver 50-75 pounds of pressure to the fetal head as compared to 2-3 pounds delivered to the fetal head by judicious gentle traction, as in normal births.
Maternal pushing with the head out does not cause traction on the head; it causes impaction. The turtle sign (retraction of the head against the pubis) is protective. The shoulder does not get impacted until the head is out. Maternal pushing and labor further impact the shoulder or shoulders. They do not stretch the neck. The shoulders are not at risk for a permanent injury until the head is out. Traction or stretch injuries require a force and a resistance. If the shoulders are stuck in labor the forces of labor do not cause direct traction on the head. Injuries occur when the provider does not recognize that shoulder dystocia involves a disproportion between the infant's shoulders and the inlet of the bony maternal birth canal. Thereby failing to not only release the anterior shoulder which is trapped above the maternal inlet but assuring that the shoulder has been released prior to the point in time when any injudicious traction and/or flexion or extension of the fetal head has occurred.
Literature Review for Causation
Sever studied 500 cases of Brachial Plexus Palsy (BPP) and was able to draw "definite conclusions that force and traction caused these injuries." His subsequent observations have proved that in all cases the essential element in the causation is traction on the nerves. His extensive study including nerve finding, autopsy studies and literature review shows that the traction theory is "definitely" supported by pathologic and clinical evidence.
Sever performed numerous dissections on infantile cadavers and demonstrated that traction and forcible separation of the head and shoulder puts the upper cords, the fifth and sixth cervical roots of the BP under dangerous tension. This tension is so great that the upper two cords stand out like violin strings. Considerable force is necessary to injure the plexus.
Clark in a very large study noted that BP palsy is undoubtedly as old as forcible intervention in obstetric practice. The condition of BP palsy at autopsy was noted to be a lacerating lesion resulting from stretching and great pulling on the head. In twenty dissections he demonstrated that the only factor causing the nerve root damage and laceration was traction. The nerves were found to be frayed over a considerable linear area. he concluded that great force must be employed to cause the lesion. Pathologic examination showed that the nerve roots are pulled apart, the nerve sheath is over-stretched, and the arterioles to the nerves were ruptured. The recognition of the importance of the rupture of the perineural sheath and the resulting hemorrhage into the nerve substance are points of great importance, since they are the determining factors in the production of the ultimate BP palsy lesion. In all of the cases he examined there was evidence of persistent hemorrhage into the tissues. The immediate lesion consisted in the tearing of the perineural sheath surround and supporting the nerve trunk and the tearing of the blood vessels belonging to the nerve. Laurent in over 500 operative explorations of BP injuries observed an avulsion of the nerve rootlets from excessive stretching. Despite these studies Sandmire has concluded that the actual mechanisms responsible for BP injuries is complex, obscure, and usually not controllable by the physician.
Clark concluded that the prevention of this serious lesion of the BP nerves "rests with the Obstetrician, who should not overstretch the child's neck in the process of delivery."
Ouzounian feels that BP palsy in the posterior arm cannot be a traction injury despite the works of Allen, Meghdari, Clark, and Sever. The only basis for their conclusion was speculation, hypothesis, and possible intrauterine malposition. This theory cannot be proven. Acker refutes this theory of impartation and concluded\s that no new evidence has been added to the Obstetric literature.
The article by Jennett et all. Jennett RI, Tarbey TJ, Kreinick CJ. Brachial plexus palsy: An old problem revisited. Am J Obstet Gynecol 1992, 166:1673-7) is important because it suggests a role for intrauterine maladaption in brachial plexus impairment. We agree that factors other than birth trauma, mostly in combination with asphyxia have to be considered. One might assume that intrauterine maladaption, and consequently, pressure neuropathy have a better prognosis: this is confirmed by the fact that all the children in the series had a favorable outcome and that there were no lesions of Klumke's type. This experience, however, differs from that in the literature surveys, which estimate the incidence of brachial plexus impairment to be between 0.3 and 3 per 1000 live births in the hospital, with persistent disability in between 5% and 25%. It is a fact that the incidence and severity of obstetric plexus brachial palsy have decreased. In recent years, in all probability because of improved obstetric care and rehabilitation by intensive physiotherapy. It is difficult to reconcile these differences except to point out the difficulty in judging results without uniform tests. in one series of obstetric cases in which the patients were referred to a hospital for evaluation, 86 children were operated on according to the criteria of Gilbert et al., and Hentz and Meyer. Neuromas ruptures or signs of avulsion were found in all these patients. The obstetric history of each patient mentioned risk factors such as shoulder dystocia with extreme lateral traction of the fetal head or a difficult breech delivery, in most cases combined with asphyxia (Sloff).
The seventeenth edition of Williams Obstetrics notes that the BP lesion results from stretching or tearing of the upper roots of the brachial plexus, which is readily subjected to extreme tension as a result of pulling laterally upon the head, sharply flexing it toward one of the shoulders. As traction in this direction is employed frequently to effect the delivery of the shoulders in normal vertex presentations, Erb's palsy may result without the delivery appearing to be difficult. In extracting the shoulders, therefore, care should be taken not to impose excessive lateral flexion of the neck. This observation seems to have lost its importance in recent 1990 textbooks.
Allen et al., found that routine deliveries require 10 pounds of force and shoulder dystocia 28 pounds, and that the faster the force is applied the more vulnerable the BP is to tearing. They showed that the BP stretches about 1 1/2 times more than normal when downward traction is applied. They note that 30 pounds of traction can cause BP nerves to reach their stretchable limit. This is first seen in the BP nerve C5- the nerve most commonly injured.
Bioengineering research supports the view that permanent BP palsy occurs only with applied large forces (excessive), especially during an SD delivery. Neck bending is often significant and can be directed upward (as in cesarean section). This type of force is especially linked to BP trauma. Allen has also reported that a clinician's first reaction to a difficult SD delivery is to exert considerably larger forces than they normally would.
Some authors incorrectly assume that posterior arm injuries are spontaneous. They ignore the well-known fact that 50% of Erb Palsy injuries are associated with unrecorded or undocumented shoulder dystocia. Myographic studies are not reported in these articles. The authors hypothesize and speculate that the Erbs Palsy was possibly a result of normal labor (Ref. Ouzounian, JG, Korst, LM Phelan, JP. Obstet Gynecol 1997; 89: 139-41. Letter to Editor. Ibid 89:797, 1991).
Recognition of warning signs (risk factors) should alert the physician to avert or manage successfully. Ultrasound fetal weight of 4000 grams is a risk factor. Maternal pushing should be avoided. Close attention to the labor curve is important. Prior to Pitocin clinical evaluation of the cause is prudent (Shoulder Dystocia. Strong, TH, Phelan, JP. The Female Patient. 1988; 13:73-93).
A policy of elective cesarean section of infants over 4000 grams (8 lbs 4 oz - 97 percentile) would prevent 44% of SD, increase the CS rate by 2% and half the perinatal mortality (Yeo).
The routine delivery of gestational diabetics at 38-39 weeks using elective induction of labor reduces the incidence of SD ten-fold (Lurie).
Discussion
Shoulder dystocia is characterized as a true obstetrical emergency in that it cannot be diagnosed until it actually occurs. Shoulder dystocia is diagnosed when the infant's head delivers but the shoulders and body fail to follow. During the course of entrapment of the infant's chest and umbilical cord within the birth canal, reduction of fetal oxygenation occurs progressively and therefore, facilitated delivery must occur. Generally, a time framework of five to seven minutes and perhaps as long as ten to twelve minutes exists as a "window" during which time the obstetrician must carry out a series of maneuvers in attempt to decompress the shoulder, assuring the anterior shoulder has entered the pelvis prior to attempting to extract the infant transvaginally. Because of the time framework, all health care providers who are carrying out deliveries must have a structured "plan or drill" for the management of shoulder dystocia should the same occur. Thus, a multiplicity of maneuvers may be carried out and/or repeated in order to effect delivery prior to the point in time when oxygen deprivation occurs.
The deviation in shoulder dystocia is the failure of the physician to properly and gently carry out various maneuvers which are designed not only to facilitate the vaginal delivery but also to significantly reduce the risk of permanent brachial plexus injury. Shoulder dystocia is an obstetrical emergency in that while the infant is trapped within the birth canal, it can neither expand its chest to breathe room air nor can it receive oxygen through the umbilical cord which is also compressed within the birth canal. As noted, it is the anterior shoulder (shoulder pointed towards the maternal abdomen) which is trapped above the pubic bone and being held out of the maternal pelvis, therefore precluding vaginal delivery without brachial plexus injury until the anterior shoulder has been brought into the pelvic inlet.
There are approximately sixteen maneuvers to facilitate entrance of the anterior shoulder into the maternal pelvis and therefore allow vaginal delivery to occur and/or facilitate the carrying out of a safe abdominal delivery if the shoulder dystocia cannot be decompressed (i.e., cephalic replacement maneuver). If delivery occurs secondary to excess or injudicious traction and /or excess lateral traction on the fetal head with the anterior shoulder still held out of the pelvis by being wedged against the maternal pubic bone or above the maternal pubic bone, a stretch of the spinal cord cervical roots and/or an avulsion of the roots will occur.
The cervical roots (C5 through C8) as well as the upper two thoracic roots (T1 through T2) of the spinal cord exit at the base of the skull and continue through the neck and into the shoulders to supply the upper and lower arms. When traction on the fetal head persists or is excessive then the movement of the fetal head away from the trapped shoulders results either in a stretch of the brachial plexus or disruption of the blood supply to the brachial plexus (avulsion) with the latter injury generally being permanent whereas the majority of the stretch injuries recover.
Although sixteen maneuvers do not need to be known by all health care providers delivering infants, such professionals must be aware of the common maneuvers. Maneuvers included suprapubic pressure, the modified McRobert's maneuver, the Wood's or corkscrew maneuver, the transabdominal shoulder adduction maneuver, the Hibbard maneuver, the Chavez (shoehorn) maneuver, and/or the cephalic replacement maneuver. I would reiterate the important fact in the management of shoulder dystocia is to utilize serial maneuvers to bring the anterior shoulder of the infant into the bony birth inlet prior to exerting continued or excessive traction to the fetal head and/or excessive lateral traction on the fetal head. As noted, the more common maneuvers include suprapubic pressure which can be directed against the anterior shoulder suprapubically in an anterior posterior direction or towards the lateral posterior quadrants of the abdomen, the McRobert's maneuver which is flexing the mother's thighs on her abdomen to better align the pelvic inlet with the shoulders and therefore facilitate entrance of the shoulder into the maternal pelvic inlet, the Wood's maneuver which is rotating the infant's shoulders through a 180 degree arc counter clockwise and/or clockwise. This maneuver also known as the corkscrew maneuver, substitutes the anterior for the posterior shoulder which has invariably entered the birth canal, thus bringing the anterior shoulder into the birth canal while retaining the posterior shoulder within the birth canal. Extraction of the posterior arm is a maneuver whereby the obstetrician's hand is inserted into the uterine cavity, grasps the infant's posterior hand and then sweeps the posterior arm across the infant's chest in order to deliver the posterior arm and shoulder and thus allowing more room for the anterior arm and shoulder to enter the birth canal. The Chavez or shoehorn maneuver is where the operator forms a shoehorn with his fingers under the symphysis pubis either palm up or palm down. the Hibbard maneuver is displacement of the anterior and posterior shoulder while supporting the vertical alignment of the fetal head to the fetal spine in order to dislodge the entrapped anterior shoulder and then to bring the anterior shoulder into the birth canal. Finally, the cephalic replacement or Zavanelli maneuver is used for severe shoulder dystocias. This maneuver involves repositioning of the fetal head into the vaginal canal then displacing the fetal head above the pelvic inlet, re-establishing the fetal placental umbilical profusion (oxygen supply) and then effecting delivery via cesarean section.
The most important factor in initially managing shoulder dystocia is for the operator to immediately remove his or her hands from the fetal head as soon as the diagnosis of shoulder dystocia is made and exert no further traction to the fetal head until the operator has been assured that one or more of the various maneuvers has brought the anterior shoulder into the maternal inlet prior to continuing with vaginal delivery.
it is the majority opinion that doctors deviate from accepted standards of obstetric practice by failing to carry out appropriate maneuvers to decompress the shoulder dystocia prior to using excessive traction to effect delivery which then result in the permanency of the brachial plexus injury sustained. Even if one were to hypothetically accept statements that suprapubic pressure, the McRobert's maneuver and the Wood's maneuver were utilized then obviously the doctor failed to assure that these maneuvers had decompressed the shoulder dystocia prior to continuing with the vaginal delivery. Assurance that the maneuvers had resulted in decompression of the shoulder dystocia and/or entrance of the anterior shoulder into the birth canal, can be readily attained merely by simple digital examination of subpubic area (palpating the under surface of the symphysis pubis transvaginally). If doctors carry out such prerequisite examination, they would recognize the maneuvers utilized had not decompressed the shoulder dystocia and that the standard of care dictates that they should have employed other maneuvers or repeated the maneuvers prior to completing a vaginal delivery. Most of the maneuvers spoken to can be carried out within a time framework of 30-60 seconds and thus ample time exists for such actions on the part of the doctor.
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