Ortho module 1 part C Flashcards
What is a growth site and a growth center?
An area where growth is occurring is a growth site
An growth site that has the ability to grow on its own independently of its surroundings is a growth center.
What is mode and mechanism of growth?
Mode of growth: The way it occurs. In the case of skeletal growth there are 2 possible modes: replacement of cartilage or direct apposition of bone.
Mechanism of growth: How growth changes occur at a higher level such as downward and forward movement of the jaws or expansion of the cranial vault.
What is determinant of growth?
The cause of the observed growth changes and what controls them.
What is suture theory?
A theory developed by Harry Sicher to describe the growth of bone at synchondroses of the cranial base, at the mandibular condyle, and at the sutures of the cranial and facial bones. He theorized that pressures created by formation of new bone at these sites literally pushed the bones apart.
What are sutures in Sicher’s theory?
They are both sites and centers of skeletal growth.
In his view this was also the case for synchondroses, condylar cartilage, and at least to some extent periosteal surfaces
He did not think of mode of growth much because he assumed that the mechanism of growth was bones being pushed away from the site of bone formation.
How accurate was Sicher’s theory?
Sutures and periosteal surfaces are not primary determinants of craniofacial growth and must be considered sites, but not centers, of growth. Growth at sutures does not push bones apart, instead, when sutures are pulled apart growth occurs to fill in the gaps.
What evidence indicates that bone growth does not push the bones apart and instead the gaps are made prior to bone being formed?
2 lines of evidence:
First, when sutures are transplanted at different locations they fail to grow as centers would.
In both animal experiment and humans with growth problems, it can be shown that sutures respond to outside influences. If the cranial or facial bones are pulled apart at the sutures, new bone will fill in and the bones end up bigger than they would have been otherwise and the opposite occurs if the bones are pushed closed to each other.
What was James Scott’s theory?
That main determinant of craniofacial growth is the growth of cartilages. Cartilage growth would push the bones to new positions; in response bone would fill in at sutures and surface remodeling would occur.
What did Scott believe about mandibular growth?
Scott accepted evidence that sutures reacted rather than acted on their own, and so did not push bones apart by growing independently.
He agreed with Sicher about cartilage push by the cartilages of the cranial base and the mandible as a major mechanism for cranial and facial growth
Good way to visualize the mandible:
Considering it as analagous to the diaphysis of a long bone bent into a horseshoe and with the epiphyses removed.
The condylar cartilage represents half an epiphyseal plate on each end of the bone. This representation means the condyle is seen as the growth center.
How is the pace of growth of the maxilla controlled according to Scott?
In the 1950s Scott hypothesized that the cartilaginous nasal septum serves as a “pacemaker” for other aspects of maxillary growth.
What are the potential outcome of growth center experiments?
If growth center:
Transplanting cartilage leads to growth of surrounding tissue
If cartilage removed the growth of surrounding tissues is inhibited.
If it has innate growth potential:
It can grow when transplanted elsewhere
What experimental support is there for epiphyseal plate growth?
When cartilage from an epiphyseal plate is transplanted, it grows very nicely.
What evidence is there of the cranial base synchondroses being centers of growth?
Experimental evidence is hard to get. However, this cartilage is a remnant of original skeelatl cartilages like the epiphyseal plates which indicates its likely.
Mutations prevent growth from taking place in these areas.
What does experimental evidence indicate about nasal septum cartilage and condylar cartilage?
Transplanting cartilage from the nasal septum gives equivocal results. Sometimes it grows reasonably well, sometimes it doesn’t.
When mandibular condyles are transplanted, they hardly grow at all.
Based on this evidence, we have to doubt that the mandibular condylar cartilage could possibly act as a growth center, and we would have some doubts about the nasal septum.
What did removing the nasal septum of a rabbit lead to?
Obviously, losing that little piece of cartilage cost a great deal of growth in the midface. It can be argued that the surgery itself, not the loss of the cartilage, caused the deficient growth, but removing the cartilage decreases growth so much that it looks to most observers as if growth potential was lost along with it.
Humans that deal with trauma that leads to loss of the nasal septum end up dealing with reduced facial growth.
What does achondroplasia reveal about maxillary growth?
The cranial base continues to lengthen by a push of growth at the synchondroses whereas the midface is deficient due to lack of growth at the maxilla.
This doesn’t happen at the maxilla where the sutures are not pushed apart. Instead Scott suggested that the nasal septum is responsible for growth at the maxilla because it exerts a ‘pull’.
Why does the mandible grow more normally in achondroplasia?
The condyle doesn’t appear to be affected by genetic mutations because it isn’t part of the chondocranium and doesn’t arise form primary cartilage. Instead it arises from mesenchyme far way from the primary cartilage. A mutation affecting the primary cartilage might not affect the mesenchymal cartilage.
What is the result of condylar fracture on growth?
The condyle literally has been removed when this happens, and the cartilage is gone. If this occurred at an early age and the cartilage was an important growth center, severe growth impairment would occur.
As recently as the 1960s, standard texts stated that early fracture of the mandibular condyle was a devastating injury because of the growth problems that would follow.
However, there is a 75% chance the condyle would regenerate and mandibular growth will be completely normal again.
What is the functional matrix theory?
A theory proposed by melvin moss which states that the cranium and face grow in response to growth of soft tissue adjacent to skeletal system tissue. In this view, external soft tissues grow and both bone and cartilage react.
What evidence indicates the role of soft tissue on growth of skeletal tissue?
Under normal circumstances, the brain case grows in direct response to the growth of the brain (a small brain leads to microcephaly) The pressure exerted by the growing brain separates the bones at the sutures and new bone passively fills in so that the brain case fits the brain.
In the case of hydrocephaly there is a larger cranium size resulting.
An enlarged or small eye influences the size of the orbit.
What is needed for mandibular condylar growth?
The mandible doesn’t have to be doing anything except opening a reasonable amount with translation and hinge movement.
What causes some people to regenerate after a mandibular fracture worse than others?
Scarring of the capsule around the condyle can impede translation, and it’s the extent of the soft tissue injury that accompanies a condylar fracture, not the extent of injury to the bone, that determines how well it will grow later.
What determines the growht of soft tissue surrounding the bones growing?
Genetic and epigenetic factors.
Soft tissue growth can also be affected by environmental influences such as trauma.
