1. DEVELOPMENT OF THE LIMBSLG

2. Development of the Limb Bud
Limb development is divided into four stages:
The bud stage (initial outgrowth),
The paddle stage (dorsoventral flattening),
The plate stage (relative expansion of the distal end), and
Rotation stage (rotation around the proximodistal axis). LG

3. Limb Bud
Limbs will not form just anywhere along the body axis. Rather, there are discrete positions where limb fields are generated.
The upper buds develop at the lower cervical and upper thoracic levels C5-C8. The lower buds develop at the lumbar and upper sacral regions L3-L5.
The upper limb buds are visible by day 26 or 27, and the lower limb buds appear 1 or 2 days later. LG

4. Limb Bud…
Each limb bud consists of an outer ecto- dermal cap and an inner mesodermal core.
The ectodermal cells at the end of each limb bud proliferate to form the apical ectodermal ridge (AER). LG

5. Limb Bud…
The AER, however, does not remain passive, for without the AER cells the limb does not develop. Thus, the ectodermal tissue signals the underlying mesoderm. The mesodermal cells closest to the apical ectodermal ridge proliferate, and as this proliferation continues the cells further from the ectoderm begin to differentiate. LG

6. Limb Bud…
The pattern of digit formation is dependent upon a region of posterior limb bud mesoderm located beneath the apical ectodermal ridge. This region is called the zone of polarizing activity (ZPA).
The ZPA determines the polarity of the developing digits in part by influencing the overlying apical ectodermal ridge. The factors that are involved in this activity include sonic hedgehog, which influences both the AER and the ZPA and fibroblast growth factor - fgf2 and fgf4. LG

7. LG

8. Limb Bud…
As the mesoderm within the limb proliferates, the limb elongates and the mesenchyme segregates into superficial, intermediate and deep regions.
Mesenchymal cells aggregate throughout the cores of the elongating limb buds to form the limb skeleton. Chondrification centers appear and initially the entire limb skeleton is cartilaginous.
Osteogenesis, mostly by the endochondral process, begins with the clavicle and extends throughout fetal life and childhood. Primary ossification centers start in the shaft of long bones; an epiphyseal plate of cartilage occurs between the primary and secondary (epiphyseal) ossification centers. LG

9. Hand and footplate
The distal end of each limb bud becomes flattened as paddle-shaped limb plates.
Five mesenchymal condensations, the digital rays, appear in each plate. These eventually chondrify and ossify to form the long bones of the hands and feet
Loose mesenchyme, lying between the digital rays, eventually degenerates, with the overlying ectoderm, leaving interdigital clefts and thus delimiting and defining the fingers and toes.
28 days
36 days days days 52 days days LG

10. Development of the musculature and nerve supply of the limbs
There is evidence that the limb muscles develop from somites and that the cells migrate into the limb bud. Generally, the muscles differentiate on the flexor and extensor sides of the axial skeleton of the limbs, in the proximo-distal direction. LG

11. Rotation of the Limbs
Initially the limb buds extend laterally with the thumb and great toe facing superiorly. The flexor surface faced ventrally. The limbs then shift into a more ventral position with both thumb and great toe still facing superiorly, but the flexor surfaces now facing medially. Both limbs then rotate.
The upper extremity rotates laterally through 90o on its longitudinal axis. As a result the elbow joint is located dorsally and operates in the ventral direction. The flexor and extensor compartments are located ventrally and dorsally respectively. LG

12. Rotation of the Limbs…
In the lower limb, the rotation of almost 90o occurs in the medial direction. The patella comes to lie anteriorly and the knee operates in the dorsal direction. The flexor and extensor compartments are located in the dorsal and ventral aspects of the lower limb respectively. LG
(Fig. 10)

13. LG

14. Anomalies of the limbs • Amelia, absence of a limb
• Meromelia absence of part of a limb.
Suppression of limb bud development during the early part of the fourth week results in absence of the limbs, amelia. Arrest or disturbance of differentiation or growth of the limbs during the fifth week results in various types of meromelia/phocomelia LG

15. Cleft Hand and Cleft Foot
In lobster-claw deformities, there is absence of one or more central digits, resulting from failure of development of one or more digital rays. The hand or foot is divided into two parts that oppose each other like lobster claws. LG

16. BRACHYDACTYLY
Shortness of the digits (fingers or toes) is the result of reduction in the length of the phalanges. This anomaly is usually inherited as a dominant trait and is often associated with shortness of stature. LG

17. POLYDACTYLY
The term supernumerary digits refers to the presence of more than the usual number of fingers or toes. Often the extra digit is incompletely formed and lacks normal muscular development.
If the hand is affected, the extra digit is most commonly medial or lateral rather than central.
In the foot, the extra toe is usually on the lateral side. Polydactyly is inherited as a dominant trait. LG

18. SYNDACTYLY
Syndactyly is the most common anomaly of the hand or foot. Cutaneous syndactyly (simple webbing between digits) is the most common limb anomaly. It is more frequent in the foot than in the hand.
Cutaneous syndactyly results from failure of the webs to degenerate between two or more digits.
Osseous syndactyly LG

19. CONGENITAL CLUBFOOT
A club foot, or congenital talipes equinovarus (CTEV), is a congenital deformity involving one foot or both. The affected foot appears rotated internally at the ankle.
Without treatment, persons afflicted often appear to walk on their ankles, or on the sides of their feet. It is a common birth defect, occurring in about one in every 1,000 live births. Approximately 50% of cases of clubfoot are bilateral. LG

20. =THE END= LG