The Role Of growth plates in Growth of Long bones
The role played by growth plates in bone growth and their closure is misunderstood by many so this topic definitely deserves a mention.
Simply put, the epiphyseal / growth plates are thin layers of cartilage disc entrapped at the distal ends of long bones between the epiphysis (head ) and metaphysis .
Most long bones in the body have at least two growth plates, including one at each end.
Parts of the body with growth Plates
Growth plates are found in the long bones of the body—the bones that are longer than they are wide. Examples of long bones include the femur (thighbone), the radius and ulna in the forearm, as well as the metacarpal bones in the hands.
X – ray showing open and Closed plates.
How Growth takes place at the Epiphyseal Plate.
skeletal growth at the epiphyseal plate is an active and dynamic process.
The epiphyseal growth plate is made of several key aspects including cartilaginous, bony, and fibrous components, which act together to achieve longitudinal bone growth
Growth plates consist of special cells called chondrocytes, which make a cartilage template for the bone to be formed on.
Immature (stem-like) chondrocytes first start proliferating; then maturing (differentiate and enlarge); and finally die, allowing new bone tissue to be formed on the remaining cartilage matrix.
The epiphyseal growth plate, being a highly specialized layer of cartilage where chondrocytes proliferate and differentiate, brings forth longitudinal bone growth.
The exact mechanism of epiphyseal fusion is still not completely understood and experimental studies are complicated by the fact that there is a species difference between humans and rabbits that do fuse their growth plates and rodents that do not.
How about Flat Bones? How do they grow?
The growing skull, jaw and collar bone do not have a cartilage stage. They form directly from osteoblasts (cells that make bone by producing a matrix that then becomes mineralized.) .
A layer of cells which can differentiate into the osteoblasts lines the bone, with a special concentration between the bones of the skull.
These precursor cells turn into osteoblasts which secrete collagen in a haphazard pattern called woven bone. Later osteoclasts resorb (dissolve) the woven bone and new osteoblasts form the mature, lamellar (layered) bone.
Theories Regarding Growth plate maturation and fusion
A nowadays generally accepted hypothesis is that terminally overgrown chondrocytes die by undergoing apoptosis (A form of cell death in which a programmed sequence of events leads to the elimination of cells ) leaving behind a scaffold of cartilage matrix for cells that make bones (osteoblasts) that invade and lay down bone resulting in growth plate fusion.
In specific disorders, timing of epiphyseal fusion is advanced or delayed; for example, in patients with estrogen deficiency it is delayed and in patients with precocious puberty it is advanced.
In case of Precocious puberty, a child’s body begins changing into that of an adult (puberty) too soon.
Puberty that begins before age 8 in girls and before age 9 in boys is considered precocious puberty.
Puberty includes rapid growth of bones and muscles, changes in body shape and size, and development of the body’s ability to reproduce.
Men with a disruptive mutation in the oestrogen resistance gene
or in the aromatase deÆciency gene (estrogen deficiency) who have no pubertal growth spurt may continue to
grow into adulthood due to lack of epiphyseal fusion.
Timing of Growth Plates closure or fusion
According Andre C. Grant, MD an orthopaedic surgeon at Duke Orthopaedics of Raleigh, It is difficult to predict exactly when each growth plate will close because different bones stop growing at different times.
But there is an average time when the growth plates in the long bones should close.
Most children grow an average of two years after they have completed their pubertal growth spurt.
The age at which puberty starts is quite variable depending on many factors including race, gender, and body habitus. On average, females are done growing around age 12 to 14, and boys around age 14 to 16.
Obviously many children continue to gain some height into their late teen years, but the vast majority of growth is over by these ages
Role Played by Growth hormones and Estrogens
The balance between proliferation and differentiation in bone is a crucial regulatory step controlled by various growth hormones acting in the endocrine pathways .
Growth hormone and insulin-like growth factor-I have major effects on the chondrocytes of the growth plate and act upon all bone cells .
Growth hormone , mostly seen in action during the growth spurt in early adolescence, is considered to be the key hormone regulator of linear growth during childhood.
Estrogen action is indispensable for normal pubertal growth and growth plate fusion. Both estrogen receptors , ER-alpha and ER-beta, are expressed in the growth plate in boys and girls throughout pubertal development .
The rise in estrogen levels at menarche in girls is associated with a large reduction in bone turnover markers and reflects the closure of the epiphyseal growth plates, the reduction in periosteal apposition and endosteal resorption within cortical bone.
New Research regarding Bone growth, transformation and remodeling
From above facts regarding growth plates regulation of bone growth, it’s clear why doctors and researchers believe that growing taller after puberty is not possible once the epiphyseal plate is closed.
In contrast however, according to Los Alamos laboratory research, human bones are in fact dynamic organs continually remodeling through processes that remove existing bone and deposit new bone, a young adult’s skeleton replaces one-fifth of its bone tissue each year.
This dynamic remodeling serves both to subtly adjust structure in response to changing stresses and to maintain the proper level of blood calcium, a mineral essential to the functioning of all cells.
Remodeling normally occurs during bone growth, in response to physico-chemical factors such as stresses from exercise, during repair of injuries such as fractures, and during hormonal changes.
Remodeling includes the sensing of environmental changes, the formation of new bone, and the removal of existing bone (“resorption”).
Limb lengthening surgery ( where a huge fracture is created by way of breaking the bone into two, Pins attached with a gap between the two broken parts then the two parts rejoin the gap forming a complete bone with increased length over a period of time ) is an excellent example to prove that bones remodel, re-build, grow, thicken, and lengthen throughout life.
Vigorous exercise and healthful diet with adequate calcium, protein, vitamin D, and supplements may replace the role of epiphyseal plate.
Thus, bone adaptation is forced to occur because stress is exerted and supplements & vitamins continuously supply nutrients and food for bones.
For those whose plates are closed should look to stress factors & vitamins & supplements.
According to J.S.R. Golding, an orthopaedic surgeon from the department of Surgery, University of the West Indies, Kingston, Jamaica
The shape, strength, growth and form of a bone is determined not only by heredity but by the work it has to perform.
References And Further Reading
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