Development of Upper Limb & Its congenital anomalies Dr Anita Rani Professor Department of Anatomy KGMU !5th October 2014

Development of Limbs The somatic mesoderm layer of the body wall, contributes mesoderm cells for formation of the pelvic and shoulder girdles and the long bones of the limbs. In most bones mesenchymal cells first give rise to hyaline cartilage models, which in turn become ossified by Endochondral ossification .

LIMB BUDS 4th week: limb buds become visible from the ventrolateral body wall Mesenchymal core covered by a layer of cuboidal ectoderm. 5 weeks

HAND & FOOT PLATES / DIGITS

While the external shape is being established, mesenchyme in the buds begins to condense, and these cells differentiate into chondrocytes. By the 6th week of development, the first hyaline cartilage models, foreshadowing the bones of the extremities, are formed by these chondrocytes.

Ossification of the bones of the extremities Endochondral ossification, begins by the end of the embryonic period. Primary ossification centers are present in all long bones of the limbs by the 12th week of development. From the primary center in the shaft or Diaphysis of the bone, endochondral ossification gradually progresses toward the ends of the cartilaginous model.

At birth, the diaphysis of the bone is completely ossified, but the epiphyses, are still cartilaginous. Ossification centers arise in the epiphyses. Cartilage plate (Epiphyseal plate) remains between the diaphyseal and epiphyseal ossification centers. This plate, plays an important role in growth in the length of the bones. Endochondral ossification proceeds on both sides of the plate. When the bone has acquired its full length, the epiphyseal plates disappear, and the epiphyses unite with the shaft of the bone.

Formation of Joints Joints are formed in the cartilaginous condensations when chondrogenesis is arrested, and a joint interzone is induced. Cells in this region increase in number and density, and then a joint cavity is formed by cell death. Surrounding cells differentiate into a joint capsule. Factors regulating the positioning of joints are not clear, but the secreted molecule WNT14 appears to be the inductive signal.

Limbs Rotation Development of the upper and lower limbs is similar except that morphogenesis of the lower limb is 1 to 2 days behind that of the upper limb. During the 7th week of gestation, the limbs rotate in opposite directions. The upper limb rotates 90 degrees laterally. The lower limb rotates 90 degrees medially, placing the extensor muscles on the anterior surface and the big toe medially.

Positional changes of developing limbs

Molecular Regulation of Limb Development

Clinical Correlates Bone Age Radiologists use the appearance of various ossification centers to determine whether a child has reached his or her proper maturation age. Useful information about bone age is obtained from ossification studies in the hands and wrists of children. Prenatal analysis of fetal bones by ultrasonography provides information about fetal growth and gestational age.

Limb Defects Limb malformations occur in approximately 6 per 10,000 live births. 3.4 per 10,000(upper limb). 1.1 per 10,000 (lower limb). These defects are often associated with other birth defects involving the craniofacial, cardiac, and genitourinary systems. Rare Hereditary abnormalities

Mechanical intrauterine factors Causes of Limb anomalies Genetic Chromosomal anomalies (trisomy) Mutant genes Environmental Thalidomide Multifactorial Mechanical intrauterine factors

Amelia complete absence of one or more of the extremities

Meromelia partial absence of one or more of the extremities Phocomelia Sometimes the long bones are absent, and rudimentary hands and feet are attached to the trunk by small, irregularly shaped bones

Teratogen-induced limb defects Many children with limb malformations were born between 1957 and 1962. Many mothers of these infants had taken thalidomide,a sleeping pill and antinauseant. It was established that thalidomide causes absence or gross deformities of the long bones, intestinal atresia, and cardiac anomalies. Since the drug is now being used to treat AIDS and cancer patients, there is concern that its return will result in a new wave of limb defects. Most sensitive period for teratogen-induced limb malformations is the fourth and fifth weeks of development.

Micromelia all segments of the extremities are present but abnormally short

Brachydactyly The digits are shortened

Syndactyly two or more fingers or toes are fused Mesenchyme between prospective digits in hand- and footplates is removed by cell death (apoptosis). In 1 per 2,000 births this process fails, and the result is fusion between two or more digits.

Polydactyly The presence of extra fingers or toes The extra digits frequently lack proper muscle connections. Abnormalities involving polydactyly are usually bilateral

Ectrodactyly Absence of a digit Usually occurs unilaterally

Cleft hand and foot (lobster claw deformity) Consists of an abnormal cleft between the second and fourth metacarpal bones and soft tissues. The third metacarpal and phalangeal bones are absent, and the thumb and index finger and the fourth and fifth fingers may be fused.

Hand-foot-genital syndrome Mutations in HOXA13 Fusion of the carpal bones and small short digits. Partially (bicornuate) or completely (didelphic) divided uterus Abnormal positioning of the urethral orifice Hypospadias A combination of syndactyly and polydactyly (synpolydactyly).

Craniosynostosis–radial aplasia syndrome Congenital absence or deficiency of the radius Absent thumbs Short curved ulna

Amniotic bands Ring constrictions and amputations of the limbs or digits .

MCQs At which week of embryonic age limb buds appear: 4th 5th 6th 8th Which of the following factor is associated with proximodistal growth of limb A) Wnt-7 B) FGF C) Ser-2 D) ZPA

MCQs Amelia refers to: Complete absence of limb Partial absence of limb Shortening of limb Absence of finger Which of the following mesoderm will give rise to bones of the limb A) Extra embryonic B) Paraxial C) Intermediate D) Lateral plate

MCQs Which of the following IUL period is most susceptible for teratogen induced limb deformities: A) First & Second wks B) Second & third wks C) Third & Fourth wks D) Fourth & Fifth wks Secondary ossification centers appear in Diaphysis Epiphysis Metaphysis In both diapysis & epiphysis

Skeletal System The skeletal system develops from paraxial and lateral plate (somatic layer) mesoderm and from neural crest. Paraxial mesoderm forms a segmented series of tissue blocks on each side of the neural tube, known as Somitomeres (head region )and Somites (occipital region caudally) . Somites differentiate into a ventromedial part, the Sclerotome, and a dorsolateral part, the dermomyotome. At the end of the fourth week, sclerotome cells become polymorphous and form a loosely woven tissue, the Mesenchyme, or embryonic connective tissue. Mesenchymal cells migrate and differentiate in to fibroblasts, chondroblasts, or osteoblasts (bone-forming cells).

Development of Limbs At the end of the fourth week of development, limb buds become visible as outpocketings from the ventrolateral body wall . Initially, they consist of a mesenchymal core derived from the somatic layer of lateral plate mesoderm that will form the bones and connective tissues of the limb, covered by a layer of cuboidal ectoderm.

Development of Limbs Ectoderm at the distal border of the limb thickens and forms the Apical ectodermal ridge (AER) . This ridge exerts an inductive influence on adjacent mesenchyme, causing it to remain as a population of undifferentiated, rapidly proliferating cells, the progress zone. As the limb grows, cells farther from the influence of the AER begin to differentiate into cartilage and muscle. In this manner, development of the limb proceeds proximodistally.

6th week Terminal portion of the limb buds becomes flattened to form the hand- and footplates and is separated from the proximal segment by a circular constriction . Later, a second constriction divides the proximal portion into two segments, and the main parts of the extremities can be recognized. Fingers and toes are formed when cell death in the AER separates this ridge into five parts.

Further formation of the digits depends on their continued outgrowth under the influence of the five segments of ridge ectoderm, condensation of the mesenchyme to form cartilaginous digital rays, and the death of intervening tissue between the rays .