Children's orthopaedics Flashcards
LO:
Children’s MSK System
Differences:
- Firstly there are more bones in a child skeleton, it has 270 compared to 206 in adult
- Diagram on right demonstrates a child’s typical musculoskeletal system, and the blue lines you can see within the skeletal structure are the physis or growth plates, and these are the areas from which the long bone growth occur post-natally
- So you can see that most long bones have 2 physis, one at the proximal end and one at the distal end. These are very important when discussing child MSK pathology, either via congenital conditions or trauma related to them.
Bone Development
- Bone development can be broadly differentiated into 2 different pathways: Intramembranous and the other is endochondral.
- Intramembranous ossification is the way that the cranial bones as well as the clavicle is formed
- Endochondral bone development is responsible for the development of all the long bones of the body. This is particularly important in the paediatric skeleton.
YouTube Links for more information
Intramembranous ossification: https://www.youtube.com/watch?v=MZGRiUdg0RA
https://www.youtube.com/watch?v=gh6J2CHR_q4&t=52s
Intramembranous Ossificaiton
Intramembranous Ossification - Development of Flat Bones – cranium and clavicle
4 key stages
- In intramembranous ossification, a group of mesenchymal cells in the central ossification centres differentiate first into preosteoblasts and then into osteoblasts.
- These cells synthesize and secrete osteoid and the osteoblasts further differentiate into osteoclasts
- These cells then collectively create the immature woven trabecular matrix and in turn the immature periosteium.
- After this angiogenesis occurs and Blood vessels incorporated between the woven bone trabeculae will form the future bone marrow.
- Later, the woven bone is remodeled and is progressively replaced by mature lamellar bone.
Intramembranous ossification:
Endochondral Ossification
- During endochondral ossification, the tissue that will become bone is firstly formed from cartilage.
- Responsible for development and growth of all the other long bones. This endochondral ossification occurs in 2 different ways, both at the primary and secondary ossification centres.
- Primary Ossification Centres
Sites of pre-natal bone growth through endochondral ossification from the central part of the diaphysis of the bone.
- Post natally, bone growth occur through the secondary Ossification Centres and these are what we referred to earlier as the physis, where usually each long bone has 2 physis, one at the proximal and one at the distal end of the bones respectively:
Occurs post-natal after the primary ossification centre and long bones often have several (the physis)
YouTube Links
Endochondral Ossification: https://www.youtube.com/watch?v=RpV1t9ZMSxY
Endochondral Primary Ossfication 1)
https://www.youtube.com/watch?v=RpV1t9ZMSxY
1) Perichondrium vascularised by blood vessels. These blood vessels start delivering nutrients that are going to stimulate those mesenchymal cells that remain there to differentiate into osteoblasts. Newly formed osteoblasts gather along the diaphysis wall (the outer edge of long bones) and start depositing osteoid to form a bone collar. Primary ossification centre is starting point for endochondral ossification.
2) Formation of the bone collar will cause chondrocytes that remain within that central cavity, to enlarge and send a signal to the surrounding cartilage to calcify. Calcified matrix causes an impermability of nutrients towards the inner portion of that developing bone. The cells in that area are therefore no longer receiving the nutrients they need for survival so causes cell death. Central clearing forms where cells have died (supported by bone collar). While this is all occuring at the primary ossification centre, there are still going to be healthy chondrocytes further distal towards the ends of the bone that are still producing cartilage matrix and are in charge of elongating of that structure.
Endochondral Primary Ossfication 2)
https://www.youtube.com/watch?v=RpV1t9ZMSxY
3) Periosteal bud invades cavity and causes the formation of spongey bone. The reason it does this is because the periosteal bud consists of an artery, vein, lymphatics, nerves, and it’s also going to deliver osteogenic cells (osteoclasts degrade cartilage matrix while osteoblast deposit new spongey bone. Bone continues to elongate elsewhere as have chondrocytes depositing new cartilage.
4) Primary ossification centre is going to continue to enlarge. Osteoclasts break down the newly formed spongey bone so that the early stages of the medullary cavity can form (where we store fat). Cartilaginous growth now only within epiphyses. Bony epiphyseal surface begins to form (as osteoblasts deposit osetoid here). Secondary ossification may appear after birth at one or both epiphyses of the developing bone (not going to start ossifying until after birth, so will remain as cartilage). Larger bones are more likley to have 2 secondary ossification centres. Short bones more likley to have 1 secondary ossification centre, irregular bones may have several.
Endochondral Primary Ossfication 3)
https://www.youtube.com/watch?v=RpV1t9ZMSxY
5) Cartilage now remains on bone surface eg articular cartilage and at epiphyseal plates (important for growth)
Endochondral
Primary Ossification
Pre-natal bone growth through primary ossification centres.
During endochondral ossification, the tissue that will become bone is firstly formed from cartilage
In primary endochondral ossification the ossification occurs at the primary centres, which is in the middle of the diaphysis of the shaft of the bone, and this occurs in the prenatal period.
The first site of ossification occurs in the primary center of ossification, which is in the middle of diaphysis of the bone - prenatal
a) Mesenchymal Differentiation at the primary centre
b) As this occurs you develop the cartilage model of the future bony skeleton forms
c) The through angiogenesis, capillaries penetrate this cartilage, and you create the primary ossification centre, and spongey bone forms from the middle of the shaft as we described.
Calcification at the primary ossification centre – spongy bone forms
Perichondrium transforms into periosteum
d) This spongey bone then continues to form up the shaft and as it does so cartilage and chondrocytes continue to grow at ends of the bone
e) Secondary ossification centres develop with its own blood vessel and calcification at the proximal and distal end of these long bones– calcification of the matrix (this blood supply then begins to calcify the previously uncalcified matrix into immature spongey bone)
f) So what your left with is cartilage at the proximal and distal ends of the bone and the epiphyseal growth plate, which will then be the point of secondary endochondral ossification in the postnatal period. (Cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage.)
Endochondral
Secondary Ossification
YouTube Links
Endochondral Ossification: https://www.youtube.com/watch?v=rzuCav3xTyU&t=3s
Secondary Endochondral ossification
So by the time the fetal skeleton is fully formed and in the children’s skeleton ie by the time the child is born, cartilage remains at the joint surface as articular cartilage and between the diaphysis and epiphysis as the epiphyseal plate (aka physis)
It are these physis that is responsible for the futher growth of bones ‘Secondary ossification sites’.
The physis has various zones – and again the youtube link will describe secondary enchochondral ossification in more details’ but the zones each have a role in the growth of the long bones
This is again by the proliferation of chondrocytes and the subsequent calcification of the extracellular matrix into immature bone that is then subsequently remodelled.
What is key however is that it is the physis that is responsible for the skeletal growth of a child. So any congenital malfunction to this area or acquired insult – whether it is traumatic/infective or otherwise will therefore have a subsequent impact on growth of the child
Children’s Skeleton differs to that of an adult:
4 key ways: RESP
- The bone structure itself is different, in the material properties, principally that it is more elastic.
- Children’s musculoskeletal system is constantly developing and growing, particularly at secondary ossification centres, the physis.
- As a result of the continual growth, the speed of healing is vastly different in children compared with adults.
- As a result of the increased speed of healing there is a big difference in the remodelling potential, ie the amount of deformity that can be corrected as a result of the growth that the child is going through.
Elasticity
- Children’s bones can bend more as have increased density of Haversian canals (microscopic tunnels within the cortex of the bones that circulate the blood supply).
- Children have more Haversian canals, due to the fact that their bones are more metabolically active, at the virtue of them continuously growing.
- As bones more elastic, get more plastic deformity, so when an energy is dissipated through the bone, it can bend more before it actually breaks, and this will give different types of fracture patterns when children sustain injuries.
- One of these is known as a buckle fracture. So when a child may fall onto their outstretched hand, instead of the bone fracturing, it can actually buckle in on itself, and create this Torus like structure, which is named after the old Roman columns. Torus or buckle fracture: This occurs when only one side of the bone is compressed and buckles but does not break all the way through, creating a bulge.
- Another way that children’s bones can be injured differently, is that they can be predisposed to getting Greenstick injuries. This is described like an immature tree, as if you find an immature sapling and try and break it, instead of being able to snap it in half, you’ll find that one side snaps, but the other side buckles.
Physis
- Children have physis, adults don’t.
- Closure of physis is dependent on various factors, these include: Puberty, Menarche in girls, Parental height and certain other genetic factors.
- But generally speaking 15-16 years old for girls and 18-19 years old for boys.
- Traumatic injuries of the physis can cause premature failure of growth. And the traumatic injuries are classified by the Salter-Harris classification.
- If there is significant injury to the physis, it can cause growth arrest and the problem is growth arrest may not just across a whole physis itself, but part of it, and this can cause deformities. One part of the bone will continue to grow but the other will have stopped.
Speed and Remodeling
- Dependent on age and location
- Younger child is growing more rapidly and therefore they have the ability to heal more quickly than an older child and an adult.
- Rate of growth at physis vary from site to site.
- Eg in upper limb for instance, it’s extremes of the upper limb so the shoulder and the wrist that have the most growth, whereas in the lower limb it’s around the knee, so the distal femur and the proximal tibia grows more, as opposed to the proximal femur or the ankle itself.
- So injuries where there is most growth, in the younger child has firstly the fastest healing, but secondly the largest modelling potential.
- Here can see series of radiographs (X-rays) in a child, and they’ve sustained a midshaft humerus fracture, and as you can see, within 2 weeks, there’s huge amounts of new bone formation, and by 6 months you can barely notice that the child has had any injury at all. Now the rate of healing in these radiographs is much more accelerated than that of an adult and actually we know that children can tolerate huge amounts of angulation and deformity in most of the planes due to the fact that they are continuously healing so quickly.
Remodeling
Set of images demonstrating how significant remodelling potential in a child can be, that is simply not available in an adult:
- This is a young girl age 9 who was involved in a road traffic incident and broke both of her proximal humeri. As you can see there is significant displacement of both the fractures.
- But because this is an area of rapid growth, being at the proximal humerus, her age being favourable, you can see in the next series of radiographs at the bottom, that within 2 years, the fracture had fully healed and actually that significant deformity had fully remodelled, to the point where actually there was no visible deformity and no functional restrictions. And this was all as a result of being managed non-operatively and conservatively in a sling.
Common Children’s Congenital
Conditions
There are countless more examples, but these are the most common.