Embriology

Development

Embryonic Stage:
(first 2 months) differentiation of tissues and formation of structures occurs
Congenital anomalies result from defects in this stage

Foetal Stage:
(remainder) Growth and maturation of these structures

Limb buds grow from the lateral plate mesoderm and their muscles develop in
situ. Articular and skeletal systems develop from mesoderm

4th week
Limb buds appear, upper limb before lower limb
Mesenchyme invaded by ventral rami
5th week
Cartilage first appears
6th week
Flexion creases indicate level of knee and elbow
Long axis of each limb at right angles to the trunk with elbow and knee directed laterally (preaxial border cranially and post axial border caudally)
7th -8th week
Rotation of limbs occurs, and limbs become adducted towards the trunk
Upper limb preaxial border (radial)® laterally
Lower limb preaxial border (tibial)® medially
3rd month
Joint cavities appear
Muscle differentiation occurs
Primary ossification centres appear end of 2nd and beginning of 3rd month in a proximal-distal sequence
4th month
Primary ossification centres of metacarpals, metatarsals and phalanges appear
Joints become mobile
9th month
Secondary ossification centres of knee (distal femur, proximal tibia) and proximal humerus appear.

Embryology of Bone

Membranous Ossification: (skull, maxilla and clavicle)

Condensation of mesenchyme
Intracellular collagen fibres deposited
Osteoblasts differentiation in ossification centres
Formation of osteoid between osteoblasts
Calcium salts deposited in osteoid® primary bone
Increased capillary / blood supply in ossification centre
Periosteum forms surface covering
Trapped osteoblasts become osteocytes and occupy lucunae & Haversian systems develop

Enchondral Ossification

Formation of pre-cartilaginous highly cellular mesenchymal condensations® hyaline cartilage anlage develops
7th week cartilaginous model of bone covered by perichondrium
8th week primary ossification centre evident
Hypertrophy of chondrocytes, increased blood supply® calcification of the matrix
Perichondrium® periosteum
Osteoblasts form in ossification centre and under periosteum
Primary ossification centre extends towards bone ends
Increased length from each end through establishment of a growth plate.
Growth occurs on the diaphyseal side of the plate only.
Appearance of secondary ossification centre within chondro-epiphysis

Zones of growth

  1. Resting Zone (primitive hyaline cartilage)
  2. Proliferative Zone (active mitosies)
  3. Hypertrophic Zone (no mitosies but cells enlarge)
  4. Calcification Zone (Matrix becomes mineralised)
    Increased blood supply & O2 tension
  5. Zone of Retrogression (cartilage cells die)
  6. Zone of Ossification (osteoblasts deposit bone on exposed calcified cartilage
  7. Zone of Resorption (marrow cavity enlarges as bone grows in length)

Joints

Connecting different skeletal elements is avascular mesenchyme which develop into either fibrous joints, cartilaginous joints (synchondrosies) or three layered joints (synovial joints).

1 deg: cartilagenous joints (eg rib costo chondral junction)
2 deg: cartilagenous joints (eg intervertebral disc, symphysis pubis)
Synovial joints

Capsule comes from condensations in vascular mesenchyme outside the inter-zonal mesenchyme.

Synovial mesenchyme forms from vascular mesenchyme to line the capsular and joint surface. Also® ligaments, tendons, discs and menisci. Synovial fluid viscosity due to hyaluronic acid
Capsule originally attaches to the epiphysial line but migration occurs such that in some joints this line is intra or extra capsular.
Capsule and ligaments around joints have a rich nerve supply, the synovium has no innervation.

Vertebral Growth

Vertebral formation at 3-5 weeks with segmentation occurring at 6-8 weeks

Each vertebrae forms from 2 adjacent sclerotomes and so becomes an inter segment structure
Notochord degenerates but between vertebrae it persists to form the nucleus pulposus
During the 6th week chondrification occurs
Two centres in each centrum fuse at the end of the embryonic period resulting in one centre evident in the centrum after this period (defects here® hemi vertebrae)
Centres in the neural arches fuse with each other and the centrum
The two 1/2's of the neural arch usually fuse in the first year and these to the centrum in ~ the 3rd to 6th year
At about puberty five secondary centres appear (upper and lower body, and one in the tip of the TPs and spinous process

Ossification begins in the embryonic period and ends at about 25 years.
Longitudinal growth is via superior and inferior apophysis.

Horizontal growth is by periosteal apposition
Spinal canal enlarges by growth of the pedicles and posterior elements, enlarging rapidly from birth to five years and more slowly from 5-10 years.
The spinal canal reaches its final dimentsions relatively early compared with the continual growth of the rest of the vertebral structures
The final height of vertebral column is reached
girls by 11 - 13 years
boys by 14 - 16 years
Boys grow ~ 3.5cm and girls 1.5cm after Risser IV

Nervous System

Each spinal nerve divides into anterior and posterior primary rami

Posterior Primary Rami:
Supply extensor muscles of the vertebral column, skull and the skin that overlies them
Divide into a medial and lateral branch but only one supplies skin (in the upper 1/2 of the body the medial and in the lower 1/2 the lateral branch)
C1 has no cutaneous branch

Anterior Primary Rami:
Supply skin of sides and front of the neck and body
Intercostal nerves each have a lateral branch (sides) and terminal branch (front) of the body (these branches are sensory only)
Motor fibres run in the collateral branches
Supply inter vertebral and prevertebral muscles segmentally
1st lumbar nerve (iliohypogastric and ilioinguinal) are the lowest to supply the abdominal wall
Lie between middle and deepest layer of muscle and the nerve lies bellow the artery and always nearer to skin

Sympathetic System:
Every spinal nerve without exception carries un-myelinated grey sympathetic fibres and leaves these fibres only at their final destination

Limb Bud Development:
All limb bud plexuses are formed by anterior primary rami (never posterior)
Anterior primary rami are drawn out with the limb bud and the posterior division of the lateral branch® extensor muscles and skin.
Anterior division of the lateral branch fuses with the terminal branch and supplies flexor muscles and skin.

Myotome:
Amount of muscle supplied by one segment of the spinal cord.

Congenital Malformations

Types
  1. Failure of formation of parts (arrest of development)
  2. Failure of differentiation of parts
  3. Duplication
  4. Overgrowth
  5. Undergrowth
  6. Congenital constriction or band
  7. Generalised skeletal abnormalities

Vater Association

Vertebral defects
Atrial atresia
Tracheo Esophageal fistula
Radial limb dysplasia & Renal abnormalities

Need any three of the five to make the diagnosis
Vertebral defects are the commonest feature and many other abnormalities may be associated eg Klippel Feil, Sprengel shoulder, club feet, CDH etc
The child will survive and have normal intelligence therefore it is worth while to treat.

Atlanto-axial Instability

Distance anterior arch to odontoid more than 5mm in children ( more than3mm adults) or post arch to odontoid less than 14mm
Assoiciated with Downs syndrome, muchopolysaccharideosies etc

Lumbar and Sacral agenesis

Motor loss consistent with missing segments and may be unilateral, symetrical, partial or complete
18% have a diabetic mother and 35% have visceral abnormalities

Congenital Abnormalities of the Upper Limb

Congenital arthrodesis of elbow;
Very rare and usually bilateral and associated with other abnormalities
Rx® osteotomy to a functional position

Radio / Ulna synostosis;
Type I; Headless, long radius, extensive fusion, bilateral
Type II; Dislocated head, other deformities, unilateral
Rx® Correct pronation deformity by osteotomy, but do not try to restore rotation

Congenital dislocation radial head;
Usually associated with other skeletal anomalies or a congenital syndrome and look for it in cases of short congenital below elbow amputation, arthrogryposis, Ehlers-Danlos, nail patella syndrome etc
Rarely do patients have pain or significant functional limitation
Domed head, long radius, hypoplastic capitulum, bowed ulna
Rx® If irreducible open or closed resect at maturity

Radial hemimelia

Incidence; 1/100,000
M:F 1.5:1, usually sporadic
Aetiology unknown
50% complete, 50% bilateral R:L 2:1
Opposite thumb hypoplastic in unilateral cases
Muscle & neurovascular abnormalities in some limbs
MCP & IP joints stiff and associated with other anomalies
Rx® Depends on elbow function, splint until 2-5 years then centralise the carpus +/- pollicization (index to thumb)

Ulna Hemimelia

Usually incomplete +/- missing ulna digits
Radius short, bowed & head dislocated
Hand usually stable but the elbow not and associated with dislocation of radial head
Rx® Excise head, fuse radius and ulna remnant

Cleft Hand; (Lobster Claw)

Type I:
One or more central rays absent
Sporadic and usually unilateral
Rx®close cleft if this improves function & cosmesis

Type II:
Only short stiff radial and ulna digits remain
Central part of hand missing, often bilateral and dominant inheritence
Feet may be similarly involved
Rx® Deepen web and rotate digits to improve opposition

Brachydactaly

MC 1 dominant not important
Phalanges - more - not important
MC 3,4, & 5 dominant
MC 4 pseudo hyperparthyroidism, Turners

Reduplication

Especially thumb
Rx® beware of which part to remove (neuro-vasculature) Also tends to destabilise the joint® reconstruct ligaments

Polydactyly

Preaxial if 3 phalanges dominant
postaxial common ~ 20% penetrance dominant

Syndactyly

M:F 3:1
Usually middle & ring or ring & little, may be all three
May be skin only or confluence of bones, tendons & vessels
Rx® Operate early if restricted movement otherwise delay to ~ 5 years. Use flaps to cover one finger and grafts the other

Aperts Syndrome

Acrocephalosyndactyly
Complete syndactyly of all fingers +/- thumb
Rx® Operate early® sacrifice one digit

Camptodactyly

F more thanM
FFD PIP joint usually of little finger
May correct with wrist flexion in children
Usually bilateral
May be transmitted as an autosomal dominant trait or occur sporadically
Type I
Appears in infancy Male = Female
Type II
Affects girls in early adolesence
Rx® controversial
Rarely® functional problem® (cosmetic)
No bony changes® soft tissue procedure
Bony changes® osteotomy® change arch of movement

Clindodactyly

Bilateral radio-volar deviation of little finger distal phalanx, also common in tri-phalangeal thumb
Type I
Minor angulation, normal length
Type II
Minor angulantion but short
Type III
Marked angulation (Delta phalanx, abnormal epiphysis)
30% are familial
Rx® occasionally warrants osteotomy if concerned about appearance

Macrodactyly

Rare (neurofibromatosis)
enlargement of all structures especially nerves
Rx® Soft tissue reduction, epiphyseodesis / shortening

Absent Thumb

Associated with radial club hand
Rx® pollicization in the young (2 - 5 years)

Short Thumb

May be associated with dystrophic dwarfism

Trigger Thumb

Often bilateral
30% resolve spontaneously in the first year
Rx® Release at about 2 years

Congenital contracture of 1st web

Clasp thumb
X-linked recessive usually isolated
Occasionally in mild arthrogryposis® loss of MCP extension
Rx®Stretching splints, soft tissue release +/- EIP transfer

Coxa Vara

Type I:
Present at birth and is rare
Associated with PFFD or other anomalies (Morquios etc)

Type II:
Developmental and is more common
Develops after walking and not associated with other abnormalities
Unilateral : Bilateral 3:1
Results in a painless lurching limp and associated with a defect in the medial neck of the femur (Fairbanks triangle)
Treatment indicated if more than 100o varus® valgus osteotomy to make the defect horisontal

Osteology

Pelvis

Three centres of ossification
Ilium appears first at ~ 2 months foetal life
Ischium at three months and the pubis at 4 months
Ischial and pubic rami fuse at about 7 years and the 'Y' shaped cartilaginous physis of the three bones fuses soon after puberty (15 years)

Femur

Centre for the shaft appears in the 8th week of intra uterine life and the centre of the lower end appears at the end of the 9th month (the time of birth) and unites with the shaft at about 20 years
Centre appears in the head at 1 year of age, the greater trochanter at 3 years and the lesser trochanter at 12 years and fuse with the shaft at about 18 years

Patella

Centre appears at 3 years and ossification is complete soon after puberty

Tibia

The primary centre of the shaft appears at about 8 weeks intra uterine life and the upper epiphysis appears immediately after birth and joins with the shaft at about 20 years
The secondary centre for the tuberosity may appear at about puberty
The distal epiphysis ossifies at the second year and joins the shaft at about 18 years

Fibula

Primary centre appears at 8 weeks foetal life
The centre of the proximal end ossifies at about the 4th year and fuses with the shaft at about 20 years, the lower end at about the 2nd year and fuses with the
shaft at about 18 years

Foot

Bones of the tarsus are ossified at birth, the calcaneus at 6/12, the talus at 7/12 and the cuboid at 9/12 inter uterine life (ossification is medico legal evidence of maturity)
Secondary centres in the calcaneum appear at about 10 years and fuse at about 18 years
The navicular ossifies in the 4th year
Cuneiforms ossify, lateral in the 1st year, medial in the 3rd and intermediate in the 4th years of life
Metatarsals (epiphysis of the 1st is at the base and at the head of the other toes) ossify 2 - 3 years later than those of the hand at about the 5th year, and fuse at about 18 years
Secondary centres may also appear in the lateral tubercle of the talus, the tuberosity of the navicular and the styloid process of the 5th metatarsal

Clavicle

Ossifies in membrane and appears before any cartilage is evident in the body
The first bone of the skeleton with two centres ossifying in the fifth week which rapidly fuse
Elongation occurs at the sternal end and a cartilaginous epiphysis appears late in the teens and fuses a couple of years later

Scapula

Forms by chondrification of mesenchyme in the 6th week and bony centres appear in the 8th week in the glenoid angle
The centre at the base of the coracoid appears at about 10 years and fuses with the glenoid at puberty
At birth the blade and spine are ossified
Secondary centres appear in the acromion, coracoid, medial border and inferior angle at about puberty and are fused by the age of 25 years

Humerus

Cartilaginous at 6/52 with the primary centre of ossification appearing in the 8th week
Secondary centres appear at both ends
Upper end:
Head in the 1st year
Greater tuberosity in the 3rd year
Lesser tuberosity in the 5th year
These fuse together by the 7th year and to the shaft at about 20 years
Lower end:
Capitellum in the 2nd year
(Radial head in the 4th year)
Medial epicondyle in the 5th year
Trochlea in the 12th year
Lateral epicondyle in the 13th year
Union with the shaft occurs at about 18 years

Radius

Appears in cartilage at 6 weeks and the primary centre of ossification appears in the 8th week
The distal end is the growing end and secondary centres appear early in the second year with the centre for the head appearing in the 4th year which fuse with the shaft at about 18 years

Ulna

Cartilage at 6 weeks and the primary centre appears in the shaft at about 8 weeks
The head ossifies at about 6 years and fuses with the shaft at about 20 years. The small olecranon epiphysis appears at about 8 years and fuses at about 18 years (does not involve the articular surface)

Hand

Each carpal bone ossifies from one centre the largest (capitate in the first year and then one each year until the 7th with the pisiform becoming ossified in the 10th year
Capitate: 1st year
Hamate: 2nd year
Triquetral: 3rd year
Lunate: 4th year
Trapezium: 5th year
Scaphoid: 6th year
Trapezoid: 7th year
Pisiform: 10th year

Shafts of metacarpals and phalanges ossify in utero
The epiphysis is at the base of the thumb metacarpal and the phalanges and through the neck of the 2nd, 3rd, 4th and 5th metacarpals
The ungual tuberosities of each distal phalanx ossifies in membrane

Spine

Vertebrae develop from sclerotomes which surround the notochord and neural tube in a sheath of mesoderm

A series of cartilaginous rings appear in the mesodermal sheaths and each ring ossifies in 3 centres, the centrum and two halves of the neural arch

The centre of the centrum is double but the two halves rapidly fuse, failure of formation of one half® hemivertebrae
Each one ossifies by the 8th week and by the third year all these parts are jointed
the epiphysis for the body appears as bony rings soon after puberty and fuse with the bodies in the early twenties

Secondary centres also appear in the tips of the spinous and transverse processes and the mamillary body of T12 which also fuse in the early 20's

Costal elements of the cervical and lumbar vertebrae do not have separate centres of ossification but an occasional centre in C7 or L1® formation of cervical or lumbar ribs

Costal elements form the anterior and lateral margins of the vertebral foramen of cervical vertebrae and in the sacrum form the lateral mass which does have separate ossification centres which appear in the 6th month of foetal life and fuse with the neural arch elements at about 5 years and with each other and the sacral bodies at about 20 years

The lower part of the dens ossified at birth and fuses with the centrum of C2 at 4 years of age. The cartilaginous apex has begun to ossify at this time and fuses with the rest of the dens at 12 years