1. Embryology of the Hand Tom W Barwick SpR Trauma and Orthopaedics City Hospitals Sunderland

2. Aims Knowledge of early limb development is necessary to understand limb abnormalities Knowledge of early limb development is necessary to understand limb abnormalities Stay awake…. Stay awake….

3. Clinical significance 6% births have anomaly; 3% structural 6% births have anomaly; 3% structural Infant deaths related to congenital anomaly in 20% Infant deaths related to congenital anomaly in 20% Limb deficiency in 3-8 per 1000 births Limb deficiency in 3-8 per 1000 births

4. Congenital anomalies 10% of all anomalies occur in upper limb 10% of all anomalies occur in upper limb Isolated or systemic association (life threatening syndromes) Isolated or systemic association (life threatening syndromes) Most occur in the embryonic period (up to week 8) Most occur in the embryonic period (up to week 8)

6. General terms Congenitalanomaly apparent at birth Congenitalanomaly apparent at birth Developmentaldeviation occurring over time, may not be apparent at birth Developmentaldeviation occurring over time, may not be apparent at birth Malformationstructure wrongly built; failure of embryologic development or differentiation resulting in abnormal or missing structures Malformationstructure wrongly built; failure of embryologic development or differentiation resulting in abnormal or missing structures Dysplasiaabnormal or wrongly constructed tissue due to abnormal development Dysplasiaabnormal or wrongly constructed tissue due to abnormal development

7. General terms Disruptiona structure undergoing normal development that stops developing or is destroyed or removed Disruptiona structure undergoing normal development that stops developing or is destroyed or removed Deformationnormally formed structure that is pushed out of shape by mechanical forces Deformationnormally formed structure that is pushed out of shape by mechanical forces Deformitya body part altered in shape from normal, outside the normal range Deformitya body part altered in shape from normal, outside the normal range

8. Embryogenesis EmbryonicFertilisation to 8 weeks (limb shape is fully formed and differentiation is complete) EmbryonicFertilisation to 8 weeks (limb shape is fully formed and differentiation is complete) Foetal8 weeks to birth (growth and maturation) Foetal8 weeks to birth (growth and maturation)

9. Axial skeleton Skull, vertebrae, ribs and sternum Skull, vertebrae, ribs and sternum Derived from sclerotome of somites Derived from sclerotome of somites Notochordorganising structure of axial skeleton appears @ 15 days Notochordorganising structure of axial skeleton appears @ 15 days Somitesappear either side of notochord Somitesappear either side of notochord (19-32 days) Neural tube closes cranial to caudal by 28 days (vertebral templates (anlage) present) Neural tube closes cranial to caudal by 28 days (vertebral templates (anlage) present)

10. Appendicular skeleton Pectoral and pelvic girdles and limbs Pectoral and pelvic girdles and limbs Limb bud (Wolff’s crest) appears at 28 days Limb bud (Wolff’s crest) appears at 28 days Surface ectoderm thickens to form apical ectodermal ridge (AER) that guides development Surface ectoderm thickens to form apical ectodermal ridge (AER) that guides development Mesoderm = zone of polarising activity (ZPA) and Progress zone (PZ) Mesoderm = zone of polarising activity (ZPA) and Progress zone (PZ)

11. Limb bud

12. Timescale Day 32 hand plate Day 32 hand plate 5 th week cartilage model of bones 5 th week cartilage model of bones Day 41 delineation of rays Day 41 delineation of rays 6 th week hyaline anlage of proximal arm bones 6 th week hyaline anlage of proximal arm bones 7 th weekoutgrowth and rotation 7 th weekoutgrowth and rotation Day 46notched rays/digit Day 46notched rays/digit

13. Limb rotational alignment Embryonic period4 limb/ buds have parallel axes Embryonic period4 limb/ buds have parallel axes Pre-axial bordersCephalad (thumb) Pre-axial bordersCephalad (thumb) Post-axial borders Caudad (little) Post-axial borders Caudad (little) Foetal periodupper limb rotation occurs around axis of long finger Foetal periodupper limb rotation occurs around axis of long finger Upper limb rotates 90 degrees externally Upper limb rotates 90 degrees externally

14. Timescale Day 32 hand plate Day 32 hand plate 5 th week cartilage model of bones 5 th week cartilage model of bones Day 41 delineation of rays Day 41 delineation of rays 6 th week hyaline anlage of proximal arm bones 6 th week hyaline anlage of proximal arm bones 7 th weekoutgrowth and rotation 7 th weekoutgrowth and rotation Day 46notched rays/digit Day 46notched rays/digit

15. 6 week foetus

16. Timescale Week 8digits short and webbed Week 8digits short and webbed Week 12Primary ossification centres Week 12Primary ossification centres Week 34-38Secondary oss. Centres Week 34-38Secondary oss. Centres Vessels present in mesoderm by week 3 Vessels present in mesoderm by week 3 Primary axial artery; brachial Primary axial artery; brachial Innervation follows and muscle diffn Innervation follows and muscle diffn

17. What controls growth? Homeobox (Hox genes) convey body plan or position information (Hox A/D) Homeobox (Hox genes) convey body plan or position information (Hox A/D) Sonic hedgehog (Shh) genes and proteins are involved in limb development Sonic hedgehog (Shh) genes and proteins are involved in limb development Retinoic acid regulates cells that produce shh; hox is an intermediate Retinoic acid regulates cells that produce shh; hox is an intermediate Shh and hox genes regulate BMP expression Shh and hox genes regulate BMP expression Conservation across species Conservation across species

18. Limb bud

19. Apical Ectodermal Ridge (AER) Columnar epithelium Columnar epithelium Needed for sustained outgrowth of limb bud Needed for sustained outgrowth of limb bud Organisational region Organisational region Proximal to distal positional information Proximal to distal positional information Hox genes may control mass and local mesenchymal condensation Hox genes may control mass and local mesenchymal condensation ?Radical fringe gene regulation ?Radical fringe gene regulation

20. Apical Ectodermal Ridge FGF produced by AER FGF produced by AER Apoptosis of webbing to form digits (syndactyly) Apoptosis of webbing to form digits (syndactyly) AER Loss leads to amelia AER Loss leads to amelia Duration of AER induction/ amount of mesoderm available/ interaction/ local growth factors = normal growth Duration of AER induction/ amount of mesoderm available/ interaction/ local growth factors = normal growth

22. Zone of Polarizing Activity

23. Posterior mesoderm in limb bud Posterior mesoderm in limb bud Sonic hedgehog gene control Sonic hedgehog gene control Retinoic acid mimics its effects Retinoic acid mimics its effects Stimulates FGF production from AER Stimulates FGF production from AER Positive feedback Positive feedback (Putting ZPA on chick abdomen leads to formation of normal wing (Putting ZPA on chick abdomen leads to formation of normal wing Transplant ZPA onto pre-axial border leads to duplication of distal elements of limb) Transplant ZPA onto pre-axial border leads to duplication of distal elements of limb)

24. Progress zone Mesoderm beneath AER Mesoderm beneath AER Undifferentiated cells Undifferentiated cells Orientation and progression Orientation and progression Skeletal positioning Skeletal positioning Loss of PZ leads to truncation of limb Loss of PZ leads to truncation of limb Thalidomide: abnormal progress zone cells Thalidomide: abnormal progress zone cells Excision leads to normal growth Excision leads to normal growth

25. Limb bud

26. Wingless type (Wnt) signalling centre Located in dorsal ectoderm Located in dorsal ectoderm Wnt-7 gene mediates dorsal to ventral axis configuration of mesenchyme Wnt-7 gene mediates dorsal to ventral axis configuration of mesenchyme Muscle/ tendon derived Muscle/ tendon derived Note that muscle and tendon develop separately and connect later Note that muscle and tendon develop separately and connect later Coordination of signalling centres Coordination of signalling centres

28. Classifications Numerous Numerous Swanson, Barsky and Entin Swanson, Barsky and Entin Based on embryological failures (7) Based on embryological failures (7) Inclusive Inclusive

29. Swanson Classification 1. Failure of formation –Transverse deficiencies-any level –Longitudinal deficiencies; pre-axial, central, post- axial, intercalatory 2. Failure of differentiation –Soft tissue; syndactyly, trigger finger, Poland Syn, camptodactyly –Skeletal; synostoses and carpal coalition –Tumours; neurovascular

31. 3. Duplication: thumb,triphalangism/hyperphalangism, polydactyly, mirror hand 4. Overgrowth: limb, macrodactyly 5. Undergrowth 6. Congenital constriction band syndrome 7. Generalised skeletal abnormalities Swanson Classification

32. Take home messages……… 10% congenital anomalies occur in upper limb 10% congenital anomalies occur in upper limb Embryonic period up to week 8 vital in normal development Embryonic period up to week 8 vital in normal development Importance of apical ectodermal ridge Importance of apical ectodermal ridge Homeobox / Sonic hedgehog genes Homeobox / Sonic hedgehog genes Swanson classification Swanson classification

33. ?