Chapter 14

Congenital Hand Disorders

General Embryology

1. Hand development occurs during the 4th to 8th gestational weeks (see Table 14.1).

● 3 to 4 weeks’ gestation: Upper limb bud formation

● 4 to 5 weeks’ gestation: Proximal-to-distal upper limb development

● By week 5, the upper limb is formed without digital separation.

● By week 8, complete development of the upper limb and hand occurs.

Table 14.1

Timing of Hand Formation

Time After Fertilization	Hand Development
27 days	Development of arm bud
28-30 days	Further development of arm bud
34-36 days	Elongation of arm bud
34-38 days	Formation of hand paddle
38-40 days	Early separation of digits
44-46 days	Digits separated
Week 9-10	Formation of fingernails begins

2. Signaling pathways involved in upper limb development (see Table 14.2)

Table 14.2

Signaling Pathways During Embryogenesis

Signaling Center	Responsible Substance	Action	Anomaly
Apical ectodermal ridge	Fibroblast growth factors	Proximal-to-distal limb development, interdigital necrosis	Transverse deficiency
Zone of polarizing activity	Sonic hedgehog protein	Radioulnar limb formation	Mirror hand
Wnt pathway	Transcription factor Lmx-1	Ventral and dorsal limb axis	Nail-patella syndrome, abnormal nail and pulp arrangement

Classification of Congenital Hand Disorders

1. Type I: Failure of formation of parts

● Includes cases of longitudinal or transverse arrest

2. Type II: Failure of differentiation (separation) of parts

● Includes all cases of inadequate separation of parts

3. Type III: Duplication disorders

● Includes all cases of duplication

■ Whole limb duplication and/or mirror hand

■ Polydactyly

■ Triphalangeal thumb

4. Type IV: Overgrowth

● Includes macrodactyly or hemihypertophy

5. Type V: Undergrowth

● Includes brachydactyly

● Thumb hypoplasia

6. Type VI: Constriction band syndrome

7. Type VII: Generalized skeletal deformities

● Includes all generalized syndromes

■ Apert syndrome

■ TAR syndrome

■ Poland syndrome

Radial Deficiencies

1. Deficiencies can range from mild thumb hypoplasia to complete absence of the radius.

2. All forms of radial deficiency warrant systemic evaluation for syndromes or associations (see Table 14.3).

Table 14.3

Syndromes Associated with Radial Deficiency

Syndrome	Characteristics
Holt-Oram	Heart defects; most commonly, cardiac septal defects
TAR	Thrombocytopenia–absent radius syndrome; present at birth but improves over time
VACTERL	Vertebral abnormalities, anal atresia, cardiac abnormalities, tracheoesophageal fistula, esophageal atresia, renal defects, radial dysplasia, lower limb abnormalities
Fanconi’s anemia	Aplastic anemia not present at birth; develops at about 6 years of age. Fatal without bone marrow transplant; chromosomal challenge test now available for early diagnosis

3. Hypoplastic thumb

● Occurs most commonly as part of radial deficiency

● Blauth classification (see Table 14.4)

■ Correlates with degree of deficiency and necessary treatment

Table 14.4

Thumb Deficiency Classification and Treatment Paradigm

Type	Findings	Treatment
I	Minor generalized hypoplasia	Augmentation or no treatment
II	Absence of intrinsic thenar muscles, first web-space narrowing, UCL insufficiency	Opponensplasty, first web release, UCL reconstruction
III	Similar findings as Type II, extrinsic muscle and tendon abnormalities, skeletal deficiency A: Stable CMC joint B: Unstable CMC joint	A: Reconstruction B: Pollicization
IV	“Pouce flottant,” or floating thumb	Pollicization
V	Absence	Pollicization