Bone Development In Children
There is a delicate interplay of mechanical and biological forces that give a bone shape and strength
The bone is a dynamic living tissue which forms the framework for muscle attachment and protects the visceral organs. It is also the most commonly injured tissue in children and needs to be presented to an orthopaedic surgeon for treatment.
Bone tissue comprises of a collagen material and a mineral which are finely intertwined to give it strength and resilience, much like cement filled around a steel frame in a concrete pillar. There is a delicate interplay of mechanical and biological forces that give a bone shape and strength.
When the biochemical composition of the bone is altered due to any cause, its strength may get affected, making it vulnerable to mechanical forces even during normal activities.
Bone Types
There are two main types of bones – compact and spongy. The compact bone gives the structural support while the spongy bone is the site of bone metabolism. Like any other living tissue, the bone is in a constant state of flux and undergoes remodelling due to interaction between osteoblasts and osteoclasts.
There is also new calcium deposition regularly known as mineralization on the bone fibres called collagen which gives bones their strength. Bones contain 60 per cent organic matrix and 40 per cent minerals. New bones are constantly laid down in response to physical forces and abnormal or dead bones are removed by osteoclasts.
Bone Development In Children
In children, the most unique feature of bone development is the growth plate or physis which contributes to the longitudinal growth of the bone. The physis and its adjacent area called the metaphysis is the most active part of the growing bone in children. Physiological and biochemical interactions take place mainly in the metaphysis and physis and contribute to the development of bones. Any disorders in these areas can impact bone development.
Metabolic Bone Disorders These are a group of conditions where there is a disturbance in the biochemical composition of the bone, thus affecting its integrity and strength. Deficiency of bone vitamins (vitamin D3), calcium insufficiency and hormonal disturbances during childhood affect the mineral part of bone composition, Tissue disturbances (collagen framework) are seen in osteogenesis imperfecta or fragile bone disease, fibrous dysplasia and other collagen disorders also affect bone development.
In osteogenesis imperfecta or fragile bones, the tissue matrix (steel part) is weaker and less durable, resulting in collapse or breakage of the bone under trivial stress. Children born with these disorders are rarely diagnosed and often treated only for a fracture rather than the underlying disorder.
The causative mechanism for this disorder in unknown but there are different varieties of fragile bone diseases. The disorder can also affect two or more members of the same family. Some children have a mild disease and it is hard to distinguish this from a normal fracture. Others may present with fractures about three-four times a year and the incidence of fractures decreases towards adolescence.
Osteogenesis Imperfecta (Fragile Bones)
Although osteogenesis imperfecta has been around for centuries, it is only in the last two decades that knowledge about it has increased sufficiently to be able to use both medical and surgical therapy for this rare yet debilitating condition.
There are not many statistics about its prevalence, but it is certainly not uncommon in India to see children who have been left undiagnosed and thus untreated. Estimated occurrence of the ailment is about one per 20,000 live births. As there is no cure for this disease, treatment focuses on minimizing fractures, reducing bone fragility and also by preventing and treating bone deformity by surgery.
Vitamin D3 Deficiency
The most common metabolic disorder seen in children is vitamin D3 deficiency which impacts bone and muscle development. There are several types of rickets, but most children are afflicted by the nutritional type wherein either poor intake or poor absorption of vitamin D3 occurs. In severe cases, bone development is delayed and children exhibit deformities in the lower limb like bow legs or knock knees. Even lack of parathyroid hormone and thyroid hormones can cause faulty bone development but there is preponderance of other symptoms causing a delay in diagnosis.
Skeletal Dysplasia Or Congenital Disorders
These cause particular type of developmental defects in the bone leading to short stature, deformities of limb and spine and visceral manifestations. Thus, normal bone development is regulated by inherent growth factors and external forces on the body. Any pathology that interferes with this delicate interplay will lead to developmental disorders in the bones.