Disorders of Skeletal Function:Developmental and Metabolic Disorders

Development of the Skeletal System
Develops from the mesodermal and neural crest cells of the developing embryo
4th week: development of the vertebrae of the axial skeleton
Late in 4th week: the paddle-shaped limb buds of the lower extremities make their appearance
9th week: ossification begins with the appearance of ossification centers in the lower thoracic and upper lumbar vertebrae
Bone Growth
Occurs at the epiphysis
Separation of the epiphyseal growth plate ruptures the blood vessels that nourish the epiphysis
Causes cessation of growth and shortened extremity length
Alterations During Normal Growth Periods
Torsional deformities
Toeing-in and toeing-out
Tibial torsion
Femoral torsion
Genu varum and genu valgum
Flatfoot

Congenital Deformities
Mild limb deformities (relatively common)
Syndactly: simple webbing of the fingers or toes
Polydactly: the presence of an extra digit
Absence of a bone such as the phalanx, rib, or clavicle
Major limb malformations (relatively rare)
Joint contractures and dislocations
Absence of entire bones, joints, or limbs
Hereditary and Congenital Deformities
Osteogenesis imperfecta
Hereditary disease characterized by defective synthesis of type I collagen
Developmental dysplasia of the hip (DDH)
Abnormality in hip development that leads to a wide spectrum of hip problems in infants and children
Clubfoot, or talipes
Congenital deformity of the foot that can affect one or both feet
Juvenile Osteochondrosis
Definition
A group of children’s diseases in which one or more growth ossification centers undergoes a period of degeneration, necrosis, or inactivity that is followed by regeneration and usually deformity
Types
Legg-Calvé-Perthes Disease
Osgood-Schlatter Disease
Slipped Capital Femoral Epiphysis
Scoliosis
Definition
Lateral deviation of the spinal column that may or may not include rotation or deformity of the vertebrae
Classification
Postural scoliosis: a small curve that corrects with bending
Structural scoliosis: fixed deformity that does not correct with bending.
Classifications of Scoliosis
Congenital scoliosis
Caused by disturbances in vertebral development during the sixth to eighth week of embryologic development
Neuromuscular scoliosis
Develops from neuropathic or myopathic diseases
Idiopathic scoliosis
Structural spinal curvature for which no cause has been established
Types of Bone Remodeling
Structural remodeling
Involves deposition of new bone on the outer aspect of the shaft at the same time that bone is resorbed from the inner aspect of the shaft
Occurs during growth and results in a bone having adult form and shape
Internal remodeling
Largely involves the replacement of trabecular bone
Continuous during adulthood

Major Influences on Equilibrium of Bone Tissue
Mechanical stress
Calcium and phosphate levels in the extracellular fluid
Hormones and local growth factors
Cytokines
Osteopenia
Definition
Deduction in bone mass greater than expected for age, race, or sex
Causes
Decrease in bone formation
Inadequate bone mineralization
Excessive bone deossification
Osteoporosis
Definition
Skeletal disorder characterized by the loss of bone mass and deterioration of the architecture of cancellous bone with a subsequent increase in bone fragility and susceptibility to fractures
Causes
Can occur as the result of an endocrine disorder or malignancy
Most often associated with the aging process
Risk Factors Associated with Osteoporosis
Personal characteristics
White, aging female, small bone structure, postmenopausal, family history
Lifestyle
Sedentary, calcium deficient, high protein diet, excessive alcohol and caffeine intake, smoking
Drug related
Disease related
Disorders Involving Softening of the Bones
Osteomalacia
A generalized bone condition in which inadequate mineralization of bone results from a calcium or phosphate deficiency, or both
Rickets
A disorder of vitamin D deficiency, inadequate calcium absorption, and impaired mineralization of bone in children

Paget Disease
Definition
A progressive skeletal disorder that involves excessive bone destruction and repair
Manifestations
Characterized by increasing structural changes of the long bones, spine, pelvis, and cranium