Essentials of Paediatric Orthopaedics N De Mazumder
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1General Aspects of Paediatric Orthopaedics2

Anatomical Consideration: Growth and Development of a Child1

N De Mazumder
 
A BABY IN THE MOTHER's WOMB
Starting from a fertilised ovum the development of a baby in the mother's womb takes place in two phases. The first phase is the embryonic phase of about two months, when the fertilised ovum multiplies from a single cell into different tissues and structures. The rest of the seven odd months is the time for the foetus to grow and mature into a fully formed baby. By and large the embryonic development follows a time frame and the embryo takes a recognisable human form by the end of the second month. After a little more than nine months of the onset of development as a fertilised ovum, a baby is born in an immature form and takes many months for the hands and feet to achieve maturity for adopting adult functions. The hands become chief tactile organs after many months and till then the lips are used for feeling. The locomotor activity of the lower limbs begins when the child learns walking at about one year of age.1
The single cell of fertilised ovum divides and forms a cluster of cells known as the morula. The central cells of this mass, devoid of nutrition from the surface, form cystic space and thus transforming into a blastocyst. The implantation into the uterine mucosa takes place at this stage, about nine days from the date of fertilisation. The outer layer of this blastocyst forms the ultimate placenta and soon becomes a syncytium known as trophoblast. The other cells within the blastocyst congregate at a place to form an inner cell mass, which is surrounded by a large cystic cavity known as extra embryonic coelom. Two other cavities known as amnion and yolk sac develop within this inner cell mass separated by a mass of cells forming an embryonic plate. The tissues and organs of the embryo will differentiate from this plate. There are three types of cells in this embryonic plate, the ectodermal cells on the ammiotic aspect and the endodermal cells towards the yolk sac part with the primary mesodermal cells in between.
The nervous system of the body develops from the ectodermal tissues – a groove on it transforming into a tube by the union of its edges forming the neural tube. A row of cells develops from the ectoderm towards the endoderm form the notochord. The neural tube and the notochord have alongside them the mesoderm in three long strips. The mesoderm nearest to the midline or the paraxial mesoderm is segmented into mesodermal somites. The somite producing the sclerotome surrounds the neural tube and notochord producing future vertebrae and dura mater, and the outer cells of somite placed laterally form the myotome or muscle plate, which are the precursor of the muscles of the body wall.
The intermediate strip of mesoderm is again segmented and forms the intermediate cell mass projecting ventrally between the outer two strips. From this develops the future uro-genital system. The outer strip of mesoderm is unsegmented and is known as the lateral plate. The ventrally placed yolk sac is ultimately enclosed by the lateral plate and its mesoderm is split into two layers, the inner lining covering the yolk sac becomes the future gut and an 4outer layer. In between the layers is the coelomic cavity.
The limb buds grow from the lateral plate mesoderm. The muscles of the upper limb migrate for a considerable distance to gain attachment to the trunk. The innervation once developed for a muscle remains the same even after migration, the examples are the latissitums dorsi and trapezius. The limbs are connected to the trunk by means of bones of the pectoral and pelvic girdles. The muscles of the limb buds although develop from unsegmented lateral plate mesoderm, the nerve supply to them is from well arranged limb plexuses from the spinal cord with a definite segmental pattern.
 
THE GROWTH AND DEVELOPMENT OF ANEONATE
This depends much on its perinatal anatomical positions and physiological functions. An important non development is the unmedullated character of the cerebro-spinal tracts. The foetal circulation also differs from adult circulation as the blood is oxygenated in the placenta and not in the lungs. Blood goes from venous circulation to the left and right heart both and then into the arterial stream bypassing the liver and the lungs through three structures-the ducts venosus, the foramen ovale and the ductus arteriosus. Both the sides of the heart, the right and the left, pump blood equally to the tissues and the placenta. The ductus venosus, placed between the layers of lesser omentum in the inferior surface of the liver, carries placental oxygenated blood directly to the inferior vena cava bypassing the capillaries of the liver. After birth the nonfunctioning ductus venosus becomes a fibrous cord and is known as ligamentum venosus. The foramen ovale circulates blood directly to left atrium from the right one and is closed after birth leaving a shallow depression, the fossa ovalis. The stream of venous blood in the right atrium brought through the superior vena cava rarely mixes with the stream of oxygenated blood brought by the inferior vena cava, crosses it and enters the pulmonary trunk via the right ventricle. The nonfunctioning lungs are short circuited by the passage of blood from the pulmonary trunk through the ductus arteriosus into the aorta. The deoxygenated blood is circulated from the aorta through the umbilical arteries into the placenta for oxygenation. After birth ductus arteriosus becomes cord like and is known as ligamentum artriosum. The circulation through the lungs is then established.
The features of the newborn in general show a better developed cranium and upperlimbs than the pelvis and lower limbs. There is almost a nonexistent neck with the chin touching the chest and the shoulder. The vertical height of the face is smaller than the horizontal length due to noneruption of teeth and non development of maxillary sinuses. The cheeks, thus become prominent. The hand does not have any tactile sensation but the grasping reflex is very strong. Most of the viscera remains in the abdomen because of lesser development of the pelvis.
 
THE GROWTH AND DEVELOPMENT OF A CHILD AND SOME OF THE SPECIAL FEATURES WHICH HELP IN THEU DIAGNOSIS OF MANY DISEASES
 
THE BONES
The long bones of the body develop from cartilaginous ossification, which is the ossification of the mesenchymal precursor transforming into hyaline cartilage mode at 6th week of intrauterine life, where centres of ossification develop later. On the other hand, the flat bones like skull bones and the bones of the face and clavicle are from membranous ossification, which means osteoblasts lay down bone in mesenchymal connective tissue. The diaphysis of a bone develop from endochondral ossification which lies at the mid shaft of a long bone. The longitudinal growth of a long bone is form the secondary centre of ossification which forms within the epiphyseal cartilage. The distal femoral epiphyseal centre appears by 40 weeks of intrauterine development of a baby denoting full term of pregnancy. The epiphyseal centres of other bones appear postnatally.
The appearance of different secondary centres of ossification at different times of growth of a child is important to note. This helps in differentiation of a fracture from epiphyseal separation. To name the appearance of a few secondary centres of ossification the important four are those of lower humerus. The capitellar centre appears at 7-12 months, medial epicondyle at 5-7 years, trochlear at 7-10 years and lateral epicondylar at 12-14 years.
For the appearance of an epiphyseal centre of ossification stimulus from a well formed joint is necessary. This is the reason of delayed appearance of capital epiphyseal centre of femur in DDH when the dislocation is not well reduced.
The epiphyseal plate or growth plate is the physis, which is primarily responsive to compression loading forces, whereas appophyseal growth plate is 5responsive to traction or tensile loading forces. There is migration of capsular attachment in the upper and lower ends of the femur in an adult from the attachment along epiphyseal lines in a child (Figs. 1.1 and 1.2).
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Fig. 1.1: The fused epiphysis of the head of the femur becomes intracapsular in an adult due to migration of capsular attachment
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Fig. 1.2: The fused lower epiphysis of the femur in an adult becomes extracapsular due to capsular migration
 
THE SKULL
The cranium is disproportionately large in comparison with the face. Where the box of the skull ossifies in cartilage, the vault of the skull and the face ossify in membrane and at birth are ossified but mobile on each other. The frontal, parietal, occipital and squamous part of temporal bone are attached by fibrous tissue and not by sutures as in the adult. The anterior and posterior fontanelles produced at the lines of separation of the bones in the midline of the vault are of clinical significance in detecting hydration of an infant. The posterior fontanelle closes by one year of age and the anterior by the second year; but clinically the anterior one is usually not palpable after the age of one and a half years. The bones of the vault are compact at birth and do not contain cancellous element with red bone marrow as in the adults.
 
THE FACE
At birth the facial bones like the mandible is developed in two halves, joined together by fibrous joint in the midline (which ossifies at one year of age of the baby), with the shallow, ill developed maxillae having developing teeth and rudimentary paranasal sinuses within them. The angle of the mandible is obtuse with the coronoid process placed at a higher level than the condyle. The blunt-tipped tongue is relatively large and cannot be protruded. The Eustachian orifices are at the same level with the high arched hard palate.
 
THE NECK
The neck of the newborn being short the position of its viscera is at a higher level with the epiglottis and larynx lying nearer the base of the tongue. The left brachi cephalic vein is above the level of sternal notch while crossing the trachea, the latter and the larynx are of small bore. The vertebral bodies are formed from split sclerotome or somite. The sclerotomes are formed from segmentation of condensed mesenchyme at about 5th and 6th week of intrauterine life. Cervical spine is formed similarly. The failure of normal segmentation of condensed mesenchyme results in Klippel-Feil syndrome.
 
THE THORAX
The rib cage shows horizontal position of the ribs causing a short neck and a higher level of the diaphragm; the abdominal volume is thereby increased giving room to many viscera including the pelvic ones. The thymus is very large, occupies the neck, the superior and part of the anterior mediastinum.
 
THE VERTEBRAL COLUMN
The vertebral column consisting of series of vertebral bodies placed one upon another, facilitates the passage of spinal cord due to formation of spinal canal from the fusion with the posterior elements – the neural arch elements. The vertebral bodies formed form sclerotome incorporates a portion of the notochord within, which forms the nucleus pulposus and together with the surrounding sclerotome forms the intervertebral disc. Irregular condensation of mesenchyme of somites leads to formation of hemivertebrae.
Stability of the vertebral column is necessary not only to maintain an erect posture but also to help different movements like flexion, extension, rotation 6and lateral flexion. The stability is maintained by both intrinsic and extrinsic means. The intrinsic stability is helped by the ligaments and muscles attached to spinous processes, laminae and vertebral bodies along with the annulus fibrosus surrounding the intervertebral discs. The additional support of extrinsic stabilisation is by the thoracic cage with its intercostal muscles and ligaments with further help by trunk muscles.
Greater segmental elasticity with increased strength in disc and end-plate effects spread of forces to more levels when a compression fracture occurs in a child. The result is involvement of more number of vertebral bodies but lesser degree, unlike that in an adult.
 
THE ABDOMEN
The size and shape of the viscera in the newborn are different from those in the adults. The liver is quite big; the surface of the kidney is lobulated; the suprarenal glands are very big. The pelvis is small and the fundus of the urinary bladder lies above the level of the symphysis pubis.
 
THE UPPER LIMB
Various types of deformities involving hand and fingers present at birth are due to failure of differentiation of adjacent fingers or simple duplication of a embryonic bud or due to hyper or hypo or no growth of an embryonic bud.
In a better developed upperlimbs than the lower ones in the newborn, the growth in length occurs more at the shoulder and wrist than at the elbow.
 
THE LOWER LIMB
The lower limb has its maximum growth at the knee than at the hip or ankle. The flexed and externally rotated foetal position of the lower limb remains for six months or more after birth.
The neonatal period is the turning point when the rotation or version of the femur and tibia during the gestation reverses completely. Version is the normal twisting of a long bone on its antatomic longitudinal axis. Foetal development of the limbs and their rotation need a short description in order to understand clearly the rotation of the limbs. During the fourth to fifth week of gestation a bud develops on the ventro lateral body wall. Which is the limb bud. The end of this flattens to form a plate. The digits are formed form the condensation of mesenchyme of this plate and dissolution of tissues between the rays. The toes are formed at around 8th week of gestation and the feet are placed in a position apposed to each other, known as ‘praying feet’ position. The great toes thus are placed upwards taking a preaxial position. With further growth of the foetus the lower limbs rotate medially and the feet assume plantigrade position. The thumbs in the hands follow the same. Now rotation takes place in the limb bud; the femur rotating laterally and the tibia medially. The femoral anteversion is 35° at birth, which gradually decreases with age reaching a figure of 8° in an adult male and 14° in a female. The tibiofibular version is interestingly lateral in the gestational period gradually decreasing towards full term and in the newborn thetransmalleolar axis/plane is medially placed with reference to the transcondylar axis/plane. The value of tibial version, on an average, is 2 to 4° lateral at birth and 10 to 20° lateral in the adult. I would like to make out the difference between the term version and torsion.
Version is the normal twisting of a long bone on its anatomic longitudinal axis as said earlier. When this twisting or rotation is increased or decreased giving a measurement greater or lesser than 2 standard deviation (SD) of the mean, the rotational alignment is termed as antetorsion, which is a deformity.
To describe the torsional defects in a long bone like femur and tibia, the inclination or the angle between the axis or plane of the femoral or tibial condyles with the axis of the femoral neck or the transmalleolar axis is measured.
The tibiofibular torsion in the growing foetus was studied by Badelon2 and his associates from the foetal until birth and showed an increased lateral period tibiofibular torsion in the early foetal life gradually changing in the newborn to medial tibiofibular torsion. After birth the tibia rotates laterally.
Normally acetabular anteversion is −2 to 16° (mean 7°)3 and remains almost constant during the first half of gestation and during childhood. There is a reciprocal relationship between the degree of acetabular anteversion and that of femoral anteversion.
REFERENCES
  1. De Mazumder N: Neonatal orthopaedics, Jaypee Brothers Medical Publishers (P) Ltd.  New Delhi,  2003: P5
  1. Badelon O, Bensahel H, Folinais D, Lessale B: Tibiofibular torsion from the foetal period until birth. J pediatr orthop 1989, 9: 169.
  1. Browning WH, RosenKrantz H, Tarquinio T: computed tomography in congenital hip dislocation. The role of acetabular anteversion. J Bone Joint Surg 1982, 64 A: 27.