Description
Embryology
The clinician involved in the care of children with congenital anomalies must possess a basic understanding of embryogenesis, limb formation, and inheritance patterns. The sequencing of the human genome and investigation into the molecular basis of limb development have provided new information regarding the causes of limb malformation. Advances in genomic and proteomic research have outlined the relationship between underlying gene(s) abnormalities and limb malformation. Genetic evaluation is quickly becoming part of the standard evaluation. In the future, genetic manipulation may prevent certain limb deformities and offer hope to families afflicted with genetic idiosyncrasies.
Embryogenesis of the upper extremity refers to formation of the limb 4 to 8 weeks after fertilization. The majority of upper extremity congenital anomalies occur during this 4-week period of rapid limb development. Limb bud development is initiated by outgrowth of the underlying mesoderm along the axis of the embryo into the overlying ectoderm. A thickened layer of ectoderm (apical ectodermal ridge) condenses over the limb bud and acts as a signaling center to guide the underlying mesoderm to differentiate into appropriate structures. The limb develops in a proximal to distal direction and the apical ectodermal ridge (AER) is responsible for this process. Loss of the AER during embryogenesis results in limb truncation and congenital amputation (Fig. 1). The AER also secretes proteins that influence the development of the underlying tissues. As the hand develops, the AER fragments around the hand paddle, which results in longitudinal interdigital necrosis between the digits. Failure of the AER to separate is the most prevalent explanation for syndactyly.
A second signaling center, the zone of polarizing activity (ZPA), which is responsible for anterior to posterior (radioulnar) development resides within the posterior margin of the limb bud. The hedgehog pathway is located within the ZPA and the signaling molecule necessary for limb orientation is the Sonic hedgehog compound. Duplication of the ZPA into the anterior portion of the limb bud of chick embryos yields digital replication of the ulnar digits along the radial side of the hand, similar to a mirror hand anomaly (Fig. 2). A third signaling center, the Wnt pathway (Wingless type) resides in the dorsal ectoderm
P.2
and secretes factors that induce the underlying mesoderm to adopt dorsal characteristics. This process mediates the development of dorsal to ventral axis configuration. Mice lacking this pathway have duplicated palms. The AER, ZPA, and Wnt pathway all function in a coordinated effort to ensure proper limb patterning and growth during embryogenesis. Abnormalities of these crucial areas directly affect limb formation and indirectly prohibit adequate functioning of the remaining signaling centers.
Table of Contents
1 – Embriology
2 – Anatomy
3 – History
4 – Physical Examination of the Hand
5 – History and Physical Examination of the Child
6 – Anesthesia for Hand Surgery
7 – Casting and Splinting
8 – Distal Radius Fractures
9 – Carpal Fractures
10 – Acute Carpal Dislocations and Ligamentous Injuries
11 – Chronic Carpal Instability
12 – Carpal Metacarpal Fractures and Dislocations
13 – Fractures and Dislocations of the Metacarpals and Phalanges
–
14 – Soft-Tissue Injuries and Lacerations
15 – Extensor Tendon Injuries
16 – Flexor Tendon Injuries
17 – Nerve Injuries
18 – Arterial Injuries
19 – Vascular Disorders
20 – Dermatologic Disorders
21 – Infections
22 – Compartment Syndrome
23 – Tumours
24 – Arthritis
25 – Tendonitis of the Wrist and Hand
26 – Burns
27 – High-Pressure Injection Injuries
28 – Bites
29 – Dupuytren’s Disease
30 – Congenital Anomalies
31 – Amputations
32 – Nail Bed and Fingertip Injuries
33 – Foreign Bodies
34 – Complex Regional Pain Syndromes
35 – Clenched Fist Syndrome, Factitious Limb Edema, and Self-Inflicted Injury
36 – Emergency Room Assessment
37 – The Operating Room in Hand Surgery
38 – Aftercare of the Injured and Operated Hand