KEY NOTES CHAPTER 5: UPPER LIMB - Embryology and Congenital Deformities. Flashcards
Describe the developmental anatomy of the upper limb.
Day 26: upper limb bud appears in flank. Consists of a core of lateral plate mesoderm (differentiates into bone, cartilage and tendon) covered by ectoderm.
• Ectoderm thickens at tip of bud in AP axis (analogous to radio-ulnar axis in adults) to form apical ectodermal ridge (AER).
Day 33: paddle-shaped hand.
Day 36: nerve trunks enter arm.
• Somitic mesoderm invades limb and aggregates into dorsal and ventral masses.
∘ These differentiate into myoblasts that become muscle.
Day 42: digital rays present, hand is webbed.
• Limb bud is initially supplied by a capillary network, which coalesces into a main stem artery that drains into a marginal vein.
∘ Artery becomes subclavian axillary-brachial axis.
∘ Vein becomes basilic axillary-subclavian axis.
• Brachial artery branches into interosseous artery and median artery (main blood supply to hand).
Day 44: median is replaced by ulnar and radial arteries.
7th week: upper limbs rotate 90∘ laterally to bring palm anteriorly, and elbow begins to flex.
• Ossification begins and digital separation occurs by apoptosis of tissue between finger rays.
8th week: upper extremity resembles miniature adult upper limb.
What are the mechanisms of development in the proximodistal axis?
- Controls how limb differentiates into shoulder proximally but fingers distally.
- Critical area = AER. (Resection of AER results in truncated limb). Grafting AER elongates limbs (chick embryos).
- AER produces fibroblast growth factors (mostly FGF 2, 4 and 8).
What are the mechanisms of development in the anteroposterior axis?
• Controls how ulna and little finger develop on one side, radius and thumb on other.
• Critical area = zone of polarising activity (ZPA).
∘ ZPA: cluster of mesenchymal cells in posterior limb bud margin.
∘ Grafting of ZPA cells to anterior limb margin induces mirror image duplication.
• The ZPA produces Sonic hedgehog (Shh).
∘ Higher concentrations of Shh result in more posterior (ulnar) digits.
• Cells of AER and ZPA are interdependent:
∘ FGFs from AER are required for Shh expression.
∘ Shh signal is required to maintain AER integrity.
• This may explain why loss of elements often occurs in both AP and proximodistal axes.
What are the mechanisms of development in the dorsoventral axis?
- Controls how limb differentiates into a dorsal and palmar surface.
- The critical area is non-AER ectoderm.
• Dorsal limb ectoderm expresses WNT7A gene and encodes Wnt-7a protein. (It determines dorsal limb identity, e.g. fingernails).
∘ Wnt-7a activates expression of LIM homeodomain factor Lmx1.
- Ventral ectoderm expresses engrailed-1 (en-1), which inhibits Wnt-7a and restricts its actions to dorsal ectoderm.
- Failure of these systems produces duplicated palms or circumferential fingernails.
Tell me about Swanson’s classification.
FFDOUCG
Give me some examples of failure of formation of parts.
A. Transverse arrest
• Shoulder, arm, elbow, forearm, wrist, carpal, metacarpal, phalanx.
B. Longitudinal arrest
• Radial ray
• Ulnar ray
• Central ray (cleft hand)
• Intersegmental (intercalated) type of longitudinal arrest.
Give me some examples of failure of differentiation of parts.
A. Soft tissue involvement • Arthrogryposis • Cutaneous syndactyly • Camptodactyly • Thumb-in-palm deformity B. Skeletal involvement • Clinodactyly • Osseous syndactyly • Symphalangia • Elbow, forearm and carpal synostosis. C. Congenital tumorous conditions
Give me some examples of duplication.
- Whole limb, humerus, radius, ulna
- Mirror hand
- Radial polydactyly (preaxial polydactyly)
- Central polydactyly
- Ulnar polydactyly (postaxial polydactyly).
Give me some examples of overgrowth and undergrowth.
Overgrowth
• Whole limb
• Macrodactyly.
Undergrowth • Whole limb, whole hand • Brachymetacarpia • Brachysyndactyly, with or without absence of pectoral muscle • Brachydactyly.
Give me some examples of congenital constriction band syndrome.
- Constriction band either with or without lymphoedema
- Acrosyndactyly
- Intrauterine amputation.
Give me some examples of generalised skeletal abnormalities.
- Chromosomal abnormalities
* Other generalised abnormalities.
How are some conditions difficult to classify?
Transverse arrest, brachysyndactyly and symbrachydactyly (prev aka atypical cleft hand) can be difficult:
∘ Some consider brachysyndactyly and symbrachydactyly to be the same entity, on a continuum
with transverse arrest, rather than classified as undergrowth.
Swanson noted: ‘Brachysyndactyly could be I or II because of some of its features… Its most obvious failure clinically, however, is hypoplasia or undergrowth, therefore it is in Category V’.
Failure of formation: what is transverse arrest?
• Can occur at any level (Shoulder, arm, elbow, forearm, wrist, carpal, metacarpal, phalanx).
• Most common: junction of proximal and middle 1/3s of forearm.
• Rx: prosthesis (usually discarded by children if unilateral)
• Metacarpal remnants may be amenable to:
∘ Distraction lengthening
∘ Free phalangeal or toe transfer.
Failure of formation: longitudinal arrest: What is radial deficiency? What is the prevalence?
- Spectrum of abnormalities affecting radial side of forearm.
- Radius, radial carpus, thumb, tendons, ligaments, muscles, nerves and blood vessels can all be involved.
- 1 in 55,000 live births.
- Usually hypoplastic / absent radius with radial deviation of hand
What abnormalities are associated with radial deficiency?
- Up to 40% of unilateral and 77% of bilateral cases are syndromal.
- All require paediatrics and genetics assessments.
Associated conditions include:
1) Holt–Oram syndrome
- Cardiac septal defects + upper limb malformations.
- AD
2) VACTERL association
- Vertebral anomalies,
- Anal atresia,
- Cardiac defects,
- Tracheal anomalies (including tracheo-oesophageal fistula),
- Esophageal atresia,
- Renal and radial abnormalities,
- Limb abnormalities.
3) TAR syndrome
- Thrombocytopaenia-Absent Radius
- AR.
– Thumb is usually present.
4) Fanconi’s anaemia
- Rare, AR
- Bone marrow failure.
- Radial deficiency affects 40%;
- Aplastic anaemia ~6 years (fatal without bone marrow transplantation).
- Test: chromosome breakage test/ genetic mutation.
What are the clinical features of radial deficiency?
- Short forearm, bowed on radial side.
- Complete or partial absence of radius (+/- fibrous anlage).
- Radially deviated hand with reduced passive wrist motion.
- Radial skin deficiency + relative excess on ulnar side.
- Hypoplastic or absent thumb.
- Flexion contracture and stiffness of radial digits.
- Elbow stiffness, may be due to synostosis.
- Proximal muscles of arm and shoulder can be affected.
- Bilateral and unilateral equally common, may be subtle and asymmetric.
How is radial deficiency classified?
Bayne and Klug: ∘ Type I: Short distal radius ∘ Type II: Hypoplastic radius ∘ Type III: Partial absence of radius ∘ Type IV: Total absence of radius.
What abnormalities are found in radial deficiency?
The following abnormalities may be found:
∘ Variable deficiencies of radial forearm structures.
∘ Aberrant radial wrist extensors and extrinsic thumb muscles.
∘ Absence of radial artery.
∘ Absence of radial nerve below elbow.
∘ Median nerve is always present - often the most radial structure of the wrist.
What is conservative treatment is recommended for radial deficiency?
Based on age, severity and degree of functional deficit.
Manipulation
• Physiotherapy: BD to elbow and wrist to maintain ROM (sufficient for mildest deformities).
• Splintage: difficult to apply, adds little benefit.
• External fixators: to distract radial soft tissues prior to surgery (median nerve is usually tightest structure).
What is the surgical treatment for radial deficiency?
Centralisation
∘ Extensive soft tissue release.
∘ Carpus is repositioned over ulna and stabilised with pin through 3rd metacarpal → carpus → ulna.
∘ Radial wrist extensors are transposed onto ECU to counter
radial deforming force.
∘ +/- transposing redundant skin from ulnar wrist to release radial contracture.
Radialisation
∘ Scaphoid is placed over ulna with a pin through second metacarpal.
∘ Transfer of FCR and FCU to ulnar carpus/ 5th MC decreases radial deforming force.
Risk:
- high recurrence rates.
- damage to distal ulna physis (growth arrest).
How is a severely hypoplastic thumb treated in radial deficiency?
Pollicisation - to reproduce thumb function by shortening and rotating index finger.
1. Radial palmar incision is made, creating skin flaps at base of index finger (for future 1st WS).
2. UDN is mobilised by interfascicular dissection of CDN of index-middle finger web.
3. RDA to middle finger is ligated and divided.
4. Interossei are elevated from index finger metacarpal.
5. Index metacarpal is removed, except for head (= new trapezium).
• Epiphysis is resected to prevent subsequent growth.
6. Metacarpal head is rotated 160∘ (eventually relaxes to 120∘), and secured with K wires in 40∘ of palmar abduction with MCPJ hyperextended.
7. Length of MC removed is measured and similar length of flexor and extensor tendon is excised (not required in children).
8. Intrinsics rebalance is essential:
• First dorsal IO is sutured to radial lateral band → APB.
• First palmar IO is sutured to ulnar lateral band → adductor pollicis.
• EIP → EPL.
• EDC to index → APL.
• +/- Opponensplasty age 5 - 8.
Failure of formation: longitudinal arrest: What is ulnar deficiency? What is the prevalence?
• Prevalence: 1/10th of radial deficiency.
• Spectrum of abnormalities, from hypoplasia of ulnar digits to absence of ulna.
• Hand and carpus are always affected: missing digits, syndactyly, thumb abnormalities.
• It differs from radial deficiency:
∘ The wrist is stable but elbow unstable.
∘ Associated more with musculoskeletal abnormalities than cardiovascular.
∘ Total absence is most common for the radius; partial absence is most common for the ulna.
∘ Less likely to occur as part of a syndrome.
How is ulnar deficiency classified?
Bayne
∘ Type I: hypoplasia of ulna (both proximal and distal epiphyses present)
∘ Type II: partial aplasia of ulna (absence of distal or middle third)
∘ Type III: total aplasia of ulna
∘ Type IV: radiohumeral synostosis.
What is the treatment for ulnar deficiency depending on severity?
- Release of fibrous anlage with realignment of carpus and forearm. (The anlage, present in types II and IV, increases ulnar deviation of hand and ulnar bowing of radius as child grows).
- As required:
- Separate syndactyly
- Deepen first webspace
- Thumb reconstruction: opponensplasty, rotation osteotomy or pollicisation.
• Rotation osteotomy of humerus: improves hand position for some cases of radiohumeral synostosis.
Failure of formation: longitudinal arrest: What is central deficiency?
Aka cleft hand: typical and atypical (symbrachydactyly).
Tell me about a typical cleft hand.
- V-shaped cleft in centre of hand; one or more digits absent.
- Often bilateral; frequently hands and feet.
- Family history common (AD).
- Associated syndromes, e.g. split-hand/split-foot, EEC (ectrodactyly, ectodermal dysplasia, facial clefts).
- First webspace often narrowed.
- ‘Transverse metacarpals’ can widen cleft over time.
- Phalanges may have longitudinally bracketed epiphyses or duplications.
How is typical cleft hand classified?
Manske and Halikis classification (focuses on first webspace):
∘ Type I: normal web
∘ Type IIA: mildly narrowed web
∘ Type IIB: severely narrowed web
∘ Type III: syndactylised web (first webspace is obliterated)
∘ Type IV: merged web (index ray suppressed; first webspace merged with cleft)
∘ Type V: absent web (thumb elements suppressed; first webspace not present).
What surgery may be required for a typical cleft hand?
- Patients usually have good hand function.
- Early surgery (may be required to prevent progressive deformity):
- Syndactyly release between unequal digits, esp thumb-index.
- Remove transverse bones that would worsen cleft.
• Other surgery (after year 1):
1. Release or reconstruction of first webspace.
2. Closure of cleft.
– Snow-Littler technique: palmar-based flap from cleft is transposed to first web.
– Miura and Komada method: simpler – palmar and dorsal flaps are redraped.
– 2nd MC is transferred to 3rd MC base and secured with K wires (at level of 2nd MC neck to preserve adductor pollicis origin from 3rd MC).
– Deep transverse MC ligament reconstruction: adjacent A1 pulleys are unfolded towards one another.
3. Creation of thumb (if req).
– Pollicisation or, if no radial ray available, free toe transfer.
4. Foot deformity
– Only if footwear problems.
– Fibular ray is most important for weight bearing and gait.
– Tibial toe can usually be transferred to hand if required.
What is symbrachydactyly?
- aka atypical cleft hand.
- Characterised by short vestigial digits (nubbins) +/- vestigial nails.
- May occur with Poland’s syndrome.
• Symbrachydactyly, in contrast to central ray deficiency:
∘ Unilateral usually
∘ Feet seldomly involved
∘ Usually no family history.
• Swanson’s classification: probably undergrowth > longitudinal central ray deficiency.
How is symbrachydactyly classified?
Blauth and Gekeler (SOMP)
∘ Short finger type – thumb and four short stiff digits
∘ Oligodactylic type – central aplasia – classic ‘atypical cleft hand’
∘ Monodactylic type – thumb and four nubbins
∘ Peromelic type – complete absence of fingers and thumb.
What are the treatment options for symbrachydactyly?
Short finger type
- Usually have excellent function.
- May require syndactyly release or free phalangeal bone transfer.
Oligodactylic type
- Achieve pincer grip with thumb and little finger.
- Metacarpal rotation osteotomy can improve position.
Oligodactylic and monodactylic types
- may be suitable for toe-to-hand transfers if MCs and extrinsic tendons present.
Peromelic type
- difficult to reconstruct due to lack of proximal structures.
What is intercalated deficiency?
- aka ‘Phocomelia’: Greek for ‘seal limb’ (flipper).
- Hand is always present.
- Thalidomide used for hyperemesis gravidarum (1960s). Also leprosy and myeloma.
Frantz and O’Rahilly classification:
∘ Type I: complete – hand directly attached to trunk.
∘ Type II: proximal – forearm and hand attached to trunk.
∘ Type III: distal – hand attached to humerus at elbow.
• A prosthesis may be required if hand cannot reach mouth.
• Surgery, usually to stabilise limb, is rarely indicated.
How do you classify Swanson type II congenital hand defects?
II. Failure of differentiation (separation) of parts
A. Soft tissue involvement • Arthrogryposis • Cutaneous syndactyly • Camptodactyly • Thumb-in-palm deformity
B. Skeletal involvement • Clinodactyly • Osseous syndactyly • Symphalangia • Elbow, forearm and carpal synostosis.
C. Congenital tumorous conditions
What is syndactyly?
- Type of soft tissue failure of differentiation.
- Failure of apoptosis in interdigital tissue.
- 1:2000 live births
• 20% have FHx (AD); 50% bilateral.
• M:F 2:1.
• Most common in Caucasian races.
• Associated with e.g. Apert’s, Poland’s.
How is syndactyly classified?
- Complete – digits fused to tips of fingers.
- Incomplete – fusion does not extend to tips.
- Simple – only soft tissue connections between digits.
- Complex – soft tissue and bony connections between digits.
- Complex complicated – associated accessory digits or phalanges within syndactyly.
- Acrosyndactyly – characterised by fused distal parts of fingers, with fenestrations between digits proximally. Pathogenesis: distal parts of digits re-fuse due to constriction ring syndrome.
What are the clinical features of syndactyly?
Webspaces ∘ Middle-ring 58%. ∘ Ring-little 27%. ∘ Middle-index 14%. ∘ Thumb-index 1%.
• Synonychia (nail fusion) and no paronychial fold suggests synostosis of distal phalanges.
- Associated limb, chest wall and foot abnormalities.
- Radiographs: synostosis, synpolydactyly or other anomalies.
- Complex syndactylies may have associated with tendon, nerve and vessel anomalies.
- Variable vascular anatomy and distal bifurcation of CDA can lead to vascular compromise following separation.
