When Good Bones Go Bad

Numbers Most of us have 206 bones – Some, however, have extra or missing ribs – Or others have extra or fused bones in the hands and feet – In polydactyly the extra bones can form a partial or full digit

Several factors affect bone development and growth – Nutrition – Exposure to sunlight – Exercise – Hormones A deficiency in any of these can lead to bone deformation

Nutrition Vitamin A – needed for normal osteoclast/blast activity Vitamin C – needed for collagen synthesis Vitamin D – necessary for Ca 2+ absorption in intestines

Exposure to Sunlight Activates vitamin D synthesis

Exercise Stimulates remodeling of the bone – Applied forces lead to thickening & strengthening Called hypertrophy – Lack of forces leads to thinning & weakening Called atrophy

Hormones Kidneys  calcitriol  stimulates osteoblasts Pituitary  growth hormone (GH)  stimulates division of cartilage cells in epiphyseal plates

Hormones Parathyroid  PTH  increases osteoclast activity Thyroid – T3/T4  stimulates release of GH – Calcitonin  stimulate osteoblasts

Sex Hormones Androgens (male) and estrogens (female) both promote formation of bone tissue Estrogen also has a protective effect – Stops enzyme that promotes apoptosis in osteoblasts

Apoptosis Apoptosis = programmed cell death Cell manufactures an enzyme that cuts up DNA – normal end of life stage

Since estrogen plays such a major role in bone health – the loss of it causes the decline of bone strength to occur much faster in postmenopausal women Bones mass peaks at approx. age 35 In the first decade following menopause, 15-20% of spongy bones is lost – This is 3-4x faster than men

Osteoporosis Due to this, osteoporosis is much more common in women. – Osteoporosis, specifically, is large loss of bone volume due to loss of mineral content plus the occurrence of a fragility fracture

Osteoporosis Spaces left behind from spongy bone loss are filled with fibrous and fatty tissues – which do not have the same strength baring ability. Osteoclasts start to outnumber osteoblasts leading to uneven remodeling Additionally, calcium levels fall making bones brittle

The incredible shrinking Granny All of this can lead to a decrease in stature – aka shrinking It’s estimated that shrinking in height begins at age 30 and occurs at a rate of 1/16 th inch per year

Also contributing to shrinking are changes in the vertebral column – Discs between vertebrae are mostly fibrocartilage – These discs shrink with age and become more rigid – shortening height

Vertebral Column Issues Another common problem with age are herniated or slipped discs – Outer fibrocartilage layer breaks, squeezing out central mass causing back pain, numbness, and possible loss of muscular function

Vertebral Column Issues Another problem seen in vertebral columns is associated with young age – Scoliosis is the abnormal lateral curvature – Causes one hip to sit higher than the other

Vertebral Column Issues Fractures in vertebrae are especially dangerous since they protect the spinal cord Interference with nervous system communication through the spinal cord can lead to various levels of paralysis

Fractures Bone fractures are grouped first by cause – Pathologic (also called Spontaneous)  result of disease – Traumatic  result of injury Then by exposure – Compound  bone exposed b/c of skin damage – Closed  protected by uninjured skin

Pathologic Fractures Most common cause is Osteoporosis but both benign and malignant bone tumors and infection can fracture bone as well Patient could be doing normal activities (like standing) and the bone just spontaneously fractures

Traumatic Fractures Greenstick – incomplete at convex bend Stress – incomplete; small, thin crack Fissured – incomplete longitudinal Comminuted – complete and fragmented Transverse – complete at right angle to axis Oblique – complete at angle other than right Spiral – complete; excessive twisting

Healing of Fractures 1.Since blood vessels ruptured, a clot forms – called a hematoma 2.Developing blood vessels & numerous osteoblasts come from periosteum into hematoma 3.Osteoblasts build spongy bone 4.Phagocytes & osteoclasts remove clot and dead/damaged cells

Healing of Fractures 5. Fibrocartilage fills gaps creating a “cartilaginous callus” 6. Replaced by bone via enchondral growth creating a “bony callus” 7. Osteoclasts remove extra tissue which is always inadvertently produced 8. End result looks very similar to original

Healing of Fractures The closer the ends are together, the faster the fracture will heal Reduction realigns for proper healing angles Casting immobilizes to prevent bones from losing the alignment during their weakness

Healing of Fractures New technology in immobilization and alignment – Plates – Screws – Rods – Wires