Paediatrics Flashcards
When does growth occur?
Growth runs from infancy to adolescence (embryonic to adult life)
What makes up the soft tissues and hard tissues?
Soft tissues • Muscles • Neurovascular structures • Joint capsules and ligaments Hard tissues • Bones • Joints
How can we diagnose growth plate limb deformities in children early?
Diagnosis:
Starts antenatal (early): • USS – relative limb length • Amniocentesis • CVS • Genetics testing of foetus and maternal blood samples
Describe the process of Intramembranous bone formation such as flat bones in the skull
- Ossification within membranes such as the cranial bones of the skull and clavicle
- An ossification centre appears in the fibrous connective tissue membrane
- Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification centre
- Bone matrix (osteoid) is secreted from the fibrous membrane
- Osteoblasts begin to secrete osteoid which is mineralised within a few days
- Trapped osteoblasts become osteocytes
- Woven bone and periosteum form
- Accumulating osteoid is laid down between embryonic blood vessels, which form a random network. The result is a network (instead of lamellae) of trabeculae
- Vascularised mesenchyme condenses on the external face of the woven bone and becomes the periosteum
- Bone collar of compact bone forms and red marrow appears
- Trabeculae just deep to the periosteum thicken, forming a woven bone collar that is later replaced with mature lamellar bone
- Spongy bone, consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow
Describe endochondral bone ossification
• From cartilage o Hyaline cartilage o Primary ossification centre in diaphysis o Secondary ossification centre in epiphysis o Epiphyseal plate (growth plate) • 5 phases o Phase 1 and 2: In utero Hyaline cartilage template Osteoblasts begin depositing bone Bone collar forms around diaphysis Cartilage cells in centre die which leaves a cavity Primary ossification centre forms o Phase 3 In utero Blood vessels penetrate into the centre of the cavity Fibroblasts enter through the blood Fibroblasts convert to osteoblasts Spongy bone forms along shaft o Phase 4 At birth Elongation of diaphysis Secondary ossification forms in epiphysis Medullary (marrow) cavity forms o Phase 5 Growth and maturation Complete ossification of epiphyses Hyaline cartilage remains at: • Epiphyseal growth plate • Articular surface
What is the growth plate?
- Characteristic layered structure – unchanged by age or site
- Endochondral ossification – organised conversion of cartilage to bone
- Allows rapid longitudinal growth
- Growth timings is variable
- Metaphysis at bottom and epiphysis at top
What are the two types of growth plate?
Discoid • Primary growth plates of long bone • Apophyses • Tension or compression forces Spherical • Secondary centre ossification • Carpel or tarsal bones
What is the growth plate divided into?
The growth plate is divided into multiple zones (Figure 8). These zones include the reserve zone, proliferative zone, and the hypertrophic zone. The reserve zone is the area closest to the secondary center of ossification. It has epiphyseal vessels the pass through this area but do not provide it with oxygen and keeps the oxygen tension low in this area. It has no known function with respect to longitudinal growth.
What are the growth plate zones
On image
What does the reserve zone do and where it located?
Closest to the surface (ie, nearest the epi- physis) is the reserve zone. The cells in this zone produce cartilaginous matrix, primarily in the form of type II collagen, which is used for eventual ossification into bone. These cells do not actively divide, nor are they very metabolically active; accordingly, they have the poorest blood supply.
- Germinal cells of stem cell origin
- Area of low oxygen tension responds to circulating hormones
- Contributes towards secondary centre of ossification and discoid physis
What does the proliferative zone do?
Below the reserve zone, moving toward the metaphysis, is the proliferative zone. Within this zone, the cells are stacked in columns. These columns of cells synthesize proteoglycans, thereby contributing to the extra- cellular matrix. This region, characterized by synthesis and cell division, has the most ex- tensive blood supply within the growth plate. This blood supply provides nutrition, of course, but also allows hormonal signals to reach their targets in the growth plate effectively.
- Chondrocytes thin discs
- Cells palisade
- High oxygen tension
- Cell number correlate with growth rate
What does the hypertrophic zone do?
The third zone of the growth plate, the hypertrophic zone, lies closest to the calcified bone of the metaphysis. The cells in this zone are unusually large and plump; hence, the name “hypertrophic.” This zone of the growth plate is highly active metabolically, even though it has a poor blood supply. It therefore relies on anaerobic metabolism and uses stored glycogen as its source of energy. It is also the region that participates in mineralization of the cartilage. Calcium is stored in the cells in the upper levels of the hyper- trophic zones. In the lower levels of the hypertrophic zone, these cells liberate their calcium in order to assist in matrix mineralisation.
- Proliferation changes to hypertrophy
- Less extracellular matrix
- Matrix mineralisation
- Osteoconductive septa
- Cell death
What is the zone of transformation?
- Vascular invasion from metaphysis
- Chondroclasts
- Osteoblasts
- Matrix ossification
- It is remodelling as primary bone is replaced
What happens between the hypertrophic zone and the metaphysis
The actual process of matrix mineraliza- tion occurs at the interface between the hy- pertrophic zone and the metaphysis: the zone of provisional calcification. Within this area, vascular invasion allows osteoblasts to arrive and replace the calcified cartilage with bone. This bone is a primitive, less-organized form called woven bone. In time, this tissue will be replaced by mature lamellar bone via the process of bone remodeling. The distinction between woven and lamellar bone is one of material orientation: the fibers of woven bone are haphazard, whereas lamellar bone aligns the structure in the direction of load. Blood does not flow easily through the physis; the intramedullary blood supply does not reach the epiphysis or secondary centers of ossification. Accordingly, in children, whose growth plates are open, the main blood supply to the epiphysis is a direct epi- physeal artery. This artery loses its promi- nence once the growth plates close at skele- tal maturity.
Numerous circulating hormones affect growth plate activity. Thyroid hormone (thy- roxine), growth hormone, parathyroid hor- mone (PTH), calcitonin, and testosterone are among the hormones used to regulate growth plate physiology. These hormones can stim- ulate matrix synthesis, cell division, and cal- cification (and thus growth plate closure). The precise method and zone of action of these hormones are beyond the scope of this text. Even without entirely understanding their mechanisms of action, however, it is clear that abnormalities of these hormones can significantly affect the development of the human skeleton
Are the growth mechanisms known?
What 2 factors can influence growth?
- Exact mechanisms unknown – we don’t know when a bone wants to stop growing
- We only know how much of each bone contributes towards growth. Lower limb is mostly grown by knees, upper limb is from the humorous
- Systematic factors
- Local factors
