DEVELOPMENT OF LIMBS
Aims and Objectives
At the end of lecture, students should be able to:
1. Know and define the site and time of appearance of upper and lower limb bud
2. Define apical ectoderrmal ridge (AER)
3. Understand mesenchymal proliferation under the influence of AER and
differentiation into cartilaginous models of future limb bones
4. Understand and define the source of mesoderm forming the limb muscles
5. Know the hand plate and formation of digital rays resulting into digits
6. Define and understand the rotation of upper limb with final position of flexor and
extensor limb muscles
7. Define common congenital anomalies of limbs
The parts of the vertebrate limb
►
►
►
►
►
►
►
►
►
►
►
The resulting limb is divided into four basic
elements; a root consisting of the scapula and clavicle
in the forelimb and hip bones in the hind limb, a
proximal part consisting of a single
skeletal element called the Stylopod (in the forelimb
this is the Humerus, in the hind limb the femur),
a middle portion, the Zeugopod with two elements
(ulna and radius in the forelimb or fibula and tibia
in the hind limb) and a distal part, the Autopod
composed of a carpus (hand) or tarsus (foot) with a
variable number of digits.
autopod
stylopod
zeugopod
THE DEVELOPMENT OF LIMBS
► The limb bud appear from ventro-lateral body wall during 5th week of
development at the level of lower cervical and first two thoracic segments
► The mesenchymal core was initially derived from somatoplrure of lateral plate
mesoderm
► This mesenchyme give rise to bones & connective tissue covered by a layer of
cuboidal ectoderm
► The ectoderm at tip of limb ,thickened to form Apical Ectodermal Ridges
► Ridges exerts the inductive influence on underlying mesoderm
► The mesenchyme adjacent to AER remains as undifferenciated , rapidly
proliferating cells
► The cells far away from from inductive influence begins to differentiate into
cartilage &muscles
► The development of limb proceeds to proximo-distal direction
► During sixth week the limb bud flattens to form the handplate & footplate
► The first circular constriction separate these plates from proximal segment
► Second constriction divide the proximal segment into two segments
► Fingers & toes are formed when cell death in AER separate ridges into five parts
► The formation of finger is dependent upon their continuing outgrowth under the
inductive influence of five segments of ridge ectoderm ,condensation of
mesenchyme to form cartilaginous digital rays & death of intervening tissue
between rays
► The development of U/L & L/l is similar , morphogens of L/L appear two days
later than U/L
► During 7th week the limbs rotate in opposite direction
► The U/L rotates 90 degrees laterally so that, the extensor muscle lie on lateral and
posterior surface & thumb lie laterally
► The L/L rotates 90 degrees medially ,so that extensor muscles lie anteriorly & big
toe faces medially
► When the external shape is being established , mesenchyme in buds begin to
condense ,by the end of sixth week the first hyaline cartilage model of bones can
be recognized
► Ossification of bones of extremities, the endochondral ossification begins by the
end of embryonic period.
► From primary centres of ossification in shaft or diaphysis ,endochondral
ossification progresses gradually towards the end of cartilaginous “model.”
► At birth diaphysis of bone is completely ossified but the epiphysis remains
cartilaginous,shortly ossification centres appear in epiphysis
► Temporarily the cartilaginous plate remains between diaphysis & epiphysis
► This cartilaginous plate plays an important role in growth in length of long bones
► On both sides of plate , endochondral ossification proceeds, when the bone
acquire a full length , the epiphyseal plate disappear & the epiphysis then join the
shaft of long bone
► In long bones epiphyseal plate is found on both extremeties , whereas in smaller
bones ,it is found only on one extremity
CINICAL COORRELATES
► The bone age of child can be studied by the radiologist to sort out whether the
child has reached his or her proper maturation age
► The ossification centers in hand &wrist of children are studied
► Prenatal analysis of fetal bones by U/S provide information about fetal growth &
gestational age
Anomalies
► Minor congenital limb anomalies are relatively more common than major
anomalies and can be corrected surgically.
► Most of the major defects are caused by genetic factors
► Most critical period for limb development is from day 24 to 36 in which
environmental factors can affect
►
►
►
►
►
MEROMELIA : is partial absence of limbs
AMELIA is total absence of limb
PHOCOMELIA where long bones absent or rudimentary
MICROMEDIA all segments of bones are present but are very short
These abnormalities are may be due to teratogenic insults e.g. thalidomide
(sleeping pills or antinauseant falum during 4-5th week of development may lead
to absence or gross deformities of long bones, intestinal atresia & cardiac
anomalies
► Other category of limb development is presence of extra fingers and toesPOLYDACTLY
► The extra digit lack proper muscular connection excessive number of bones are
present and may be bilateral
► ECTODACTYLY- absence of digit, such as thumb-umblitical
► SYNDACTYLY- abnormal fusion of fingers or toes
► CLEFT HAND AND FOOT (lobster claw deformity, abnormal cleft between 2nd
& 4th metacarpal bones & soft tissues)
► The 3rd metacarpal & phalangeal bones are about always absent, thumb & index
fingers as well as 4-5th fingers may be fused
► The two parts of hands are some what opposed to each other and act like lobster
claw
► CLUB FOOT: is usually present in combination with syndactyly
► The sole of foot is turned inwards, the foot is adducted and planter flexed
►
►
►
►
►
Common in males, hereditary.
Congenital absence of deficiency of radius
Genetic
Associated with craneisyntosis-radial aplasia syndrome
Digital defects along with it are absent thumb and short corner ulna usually
present
► AMNIOTIC BANDS: may cause rung constrictions of limbs or digits &
amputation
► CONGENITAL HIP DISLOCATIONS:
► Consists of underdevelopment of Acetabulum & head of femur
► Common and occurs in female
► Abnormality of bones occur precaudally whereas dislocation may occur after birth
► Baby with breech deliveries are affected.
CONGENITAL TALIPES EQUINAS VARUS