Management of Normal and High-Risk Labour during Childbirth

Gowri Dorairajan, Gowri Dorairajan

• Editorial: CRC Press
• Año: 2022
• ISBN:
  9781000554502
• Edición: 1
• Categoría: Medizin
• Categoría: Gynäkologie, Geburtshilfe & Hebammen

This book deals with the management of labour, guiding the readers to recognize problems by keen monitoring, based on anatomical and physiological understanding of labour. In this era of technology, this book revives the fading art of identification of clinical signs and symptoms. The chapters are well-structured, covering different aspects from suspicion to identification of the problems by recognizing subtle warning signals by the fetus and the uterus. Operative deliveries and common obstetric emergencies with their appropriate management are also covered. It provides practical points to prevent, anticipate, recognize, and manage problems during labour.

Key Features

• Helps to identify clinical signs and symptoms that infuses the reader with confidence to identify and manage abnormal situations during labour and childbirth through the feel of their fingers and awakened understanding.

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• A must have book for all postgraduate trainees and practitioners of obstetrics, eager to learn the fundamentals of labour management.

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• Features illustrated cases helpful in learning management of normal labour and pick abnormal labour, at the earliest possible deviation from normalcy.

1 Anatomy of the Pelvis

Vandana Mehta

VMMC & Safdarjung Hospital

DOI: 10.1201/9781003034360-1

Changes in Pelvis during Evolution

Two unique evolutionary developments in humans are the big size brain and bipedal gait. Due to the advent of hip preservation surgery, morphological changes in hip bone have assumed relevance.

The human hip is an integral part of the anatomic construct with the pelvis and lumbosacral spine. We will compare these evolutionary changes in various species.

Terrestrial vertebrates called tetrapods had four limbs, and in phylogeny, this was considered as a unique change. They are considered descendants of crossopterygians that possessed lobed fins with a narrow attachment. Two adaptations were perceived in response to the terrestrial environment during the evolution of primary amphibians from crossopterygians. The first was the change in position of limb-like paddles for support and locomotion on land. In this regard, forelimbs rotated laterally and hind limbs medially. The second was the articulation of the pelvic girdle with the vertebral column, again a unique feature of tetrapods.

In tetrapods, the pelvic girdle only consisted of endochondral elements, pubis, ilium and ischium, which fused into a single innominate (hip) bone.

Fish

The pelvic fins are attached to the pelvic ring, which lacks attachment to the spine. Hence, it is a “free” element. With the progression of land life, these paired fins develop into limbs to accommodate the weight of the animal against gravity.

It is believed that terrestrial life began with sarcopterygian in the Devonian period some 400 million years ago. Molecular genetic studies have supported the findings that differences between fins and limbs are a result of genetic switches and ensuing minor changes.

In tetrapods as compared to fish, the pelvic ring is not an independent element but attached to the vertebral column by sacral ribs.

Fish developed ventral symphysis, and in tetrapods, distinct ischial and pubic elements were identified.

Reptiles

During evolution, the limbs of the reptiles shifted under the trunk. Although they developed from amphibians, unlike the amphibians, they are not dependent on water to breed. They started to walk in a more upright position. Their front and hind limbs are disposed along the long axis of the trunk and thus are nearer to the body axis. This disposition of the hind limbs modified the hip joint, the proximal end of the femur altered from a cam-like shape in amphibians to a more rotund cam or oval shape. Correspondingly, there were changes in the acetabulum.

Dinosaurs are believed to have developed from reptiles approximately 230 million years ago. The vertical limb position and a rounded hip joint imparted a greater stride length. The acetabular forces were redirected from a medial position in the semi-erect to a dorsal one in the erect posture.

One of the dinosaur hip hallmarks is the “open” acetabulum due to the requirement for a strong bony buttress in the medial acetabular margin.

Bipedal gait became conceivable when the hind limbs were placed under the trunk, relieving the forelimbs for feeding and fighting. Therefore, all carnivorous dinosaurs were bipedal, and a slender and long-tail assisted their balance. In addition, a cylindrical femoral head featured the bipedal dinosaurs, and many species also displayed a femoral neck. Subsequently, the lateral aspect of the neck simulated the greater trochanter.

The hip morphology varies greatly in extent among mammals, and two types of hips are observed. These are the sturdy (coxa recta) and mobile (coxa mobilis or coxa rotunda) hips. The roundness of the femoral head is similar in both these hips, but the junction of the head and neck displays a straight section in coxa recta and a rounded section in coxa rotunda. Hence, there are two positions: “set”, which is the position of roundness of the head, and “offset”, which is the gap between the head and neck of the femur and the ratio of the thickness of the neck as compared to the head. A low offset characterises the coxa recta while coxa rotunda has a high offset.

The coxa rotunda increases the scope of impingement-free motion within the acetabulum. There is an inversely proportional relationship between the femoral head roundness and offset. Larger mammals have coxa recta, for example, apes that exhibit a rounded femoral head located more symmetrically on the femoral neck along with a higher offset. Earlier, all mammals had a single epiphysis for the greater trochanter and femoral head. This “conjoined” epiphysis resulted in the coxa recta type of hip. However, in other species, including apes, the epiphysis remains separate, one for the greater trochanter and the other for the femoral head [1].

A simple phylogenetic clarification for these hip types is unavailable. Bodyweight plays a role in the extremes of motion. The lightweight mammals like rodents possess coxa rotunda and a distinct ossification pattern. The larger mammals (elephants) have a fused ossification pattern with a rounded femoral head on a thick and vertical neck (neck-shaft angle is 160°). Therefore, when a broad range of hip motion, especially rotation, is required, a “coxa rotunda” and a “separate” ossification pattern is observed, for instance, in apes.

Coxa recta with a low offset is seen where the highest tensile stress is foreseen. On the other hand, coxa rotunda, with a higher offset, raises the range of impingement-free motion within the acetabulum at the cost of tensile strength of the femoral head–neck junction.

Apes

Apes appeared approximately 25 million years ago, characterised by stiff, short backs. Their ilium wings elongated, and the number of lumbar vertebrae reduced to three or four, thereby approximating the rib cage closer to their ilium. Therefore a stiffer “unibody” provided a biomechanical advantage for the larger apes as they were able to climb and swing through trees. Concomitant with a stiff spine, their hips became more mobile, and they were able to climb trees. Moreover, a shallow acetabulum developed with more rounded femoral heads than their quadruped ancestors.

Three exclusive features of man’s development from apes are bipedal gait, encephalisation and elongation of life phases [2]. Man adopted bipedal gait as the sole mode of transport. Moreover, owing to the increased size of the human head, the birth process had to be contrived, and both these alterations reflected on the pelvis, making it a significant skeletal parameter to study human evolution.

The evolution of bipedal gait led to important modifications in the lumbosacral spine and pelvis. These modifications reflected upon the hip bone and steered significant sex differences in the hips.

Approximately 3 million years ago, the hominid pelvis assumed its shape as is seen in humans today. Functioning abductors and hip kinetics permitted a constant bipedal gait [3]. The human pelvis has a three-dimensional character as compared to the long and flat pelvis of apes.

The ilium curved forwards, thereby relocating gluteus medius and minimus and tensor fascia lata, transforming their role from being extensors in quadrupeds to hip abductors in bipedal walking. The efficiency of these novel abductors is revealed in the bony framework of the femoral neck. Humans have minimal cortical bone on the superior aspect of the femoral neck, whereas apes display a peripheral ring of cortical bone. Since the apes do not possess abductor apparatus, they have a swaying gait. In addition, the compressive forces applied by the anterior gluteal muscles on the superior aspect of the femoral neck negate the tension stresses on this area leading to paucity of cortical bone [4].

The shift to upright posture resulted in a change from a vertical pelvic wall in quadruped mammals to a horizontal pelvic floor in early humans. Likewise, the horizontal abdominal floor of quadrupeds evolved into a vertical abdominal wall in bipeds. Understandably the pelvic floor plays a vital role in the control of continence and reducing the incidence of prolapse in humans [5].

In humans, another important evolutionary development is the attachment of strong sacrospinous ligament and tendinous arch of pelvic fascia to the ischial spines. Childbirth is considered a more unwavering reason for the evolution of the pelvis as compared to bipedal gait.

It is construed that enlargement of the true pelvis led to an increase in brain size in humans. The pelvic diameters of the apes displayed a larger anteroposterior than side to side dimensions. Therefore, the fetus head in apes aligns in the antero-posterior direction.

The ensuing expansion in brain size entailed “intra-pelvic adaptations” at pelvic midplane and outlet levels. The pelvic inlet had already been widened in medial-lateral direction by sacral enlargement.

Biomechanically, the widening of pelvic midplane and outlet mediolaterally spaced out the hip joints, furthermore enhancing the moment arm of body weight, necessitating greater abduction in reparation. Therefore, to maintain an energy-efficient bipedal gait, the femoral neck had to be lengthened.

The enlargement in the pelvic midplane and outlet resulted in forward lengthening of pubic rami and sideway diversion of ischial bones. The latter resulted in an increase in A-P(anteroposterior) direction and the creation of an obtuse subpubic angle.

The ossification in adult humans also deserves special mention as secondary ossification centres do not unite before the end of childbearing age in the third decade.

In humans, this delay in secondary ossification permits continuous lengthening of pubic rami even after growth ceases in the rest of the skeleton [3]. So, the pelvic outlet enlarges in a plane 90° to the largest pelvic inlet diameter.

Consequently, the fetal head rotates 90° through its passage from midplane to outlet. The ischial spines appear as an obstructive feature in the evolution of the pelvis. In quadrupeds, the tail muscles in the ischial spines are of an insubstantial size and are present laterally and dorsally near the sacrum.

In early humans, there was an increase in the size of ischial spines, particularly in the above-mentioned obstructive position of the pelvic midplane. Although they constitute the most menacing bony projections during childbirth, they play a pivotal role in the establishment and resilience of the pelvic diaphragm [6].

In apes, the fetus passes effortlessly through the birth passages, characteristically facing the mother.

In humans, due to rotational birth, the fetus faces away from the mother. This presents difficulty in the airway clearance and removal of the umbilical cord from the neck of the fetus. This disposition of the fetus may result in hyperextension (neck) injuries. Therefore, assisted birth improves the chances of survival in humans [7].

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