Developmental Aspects: Fetal Skull Infant skull has more bones than the adult skull Skull bones such as the mandible and frontal bones are unfused At birth, skull bones are connected by fontanelles Fontanelles Unossified remnants of fibrous membranes between fetal skull bones Four fontanelles Anterior, posterior, mastoid, and sphenoid

Frontal suture Frontal bone Anterior fontanelle Ossification center Parietal bone Posterior fontanelle Occipital bone (a) Superior view Parietal bone Frontal bone Ossification center Sphenoidal fontanelle Posterior fontanelle Temporal bone (squamous portion) Mastoid fontanelle Occipital bone (b) Lateral view Figure 7.35

Developmental Aspects: Growth Rates At birth, the cranium is huge relative to the face At 9 months of age, cranium is ½ adult size Mandible and maxilla are foreshortened but lengthen with age The arms and legs grow at a faster rate than the head and trunk, leading to adult proportions

Developmental Aspects: Spinal Curvature Thoracic and sacral curvatures are obvious at birth These primary curvatures give the spine a C shape Convex posteriorly

Figure 7.37

Developmental Aspects: Spinal Curvature Secondary curvatures Cervical and lumbar—convex anteriorly Appear as child develops (e.g., lifts head, learns to walk)

Developmental Aspects: Old Age Intervertebral discs become thin, less hydrated, and less elastic Risk of disc herniation increases Loss of stature by several centimeters is common by age 55 Costal cartilages ossify, causing the thorax to become rigid All bones lose mass

Ankylosing spondylitis The cause of ankylosing spondylitis is unknown, but genes seem to play a role. The disease most often begins between ages 20 and 40, but it may begin before age 10. It affects more males than females.

Medial tibial stress syndrome (MTSS), tibial periostitis or shin splints pain associated with MTSS is caused from a disruption of Sharpey's fibers that connect the medial soleus fascia through the periosteum of the tibia where it inserts into the bone

Stress Fractures Stress fractures are tiny cracks in a bone. Stress fractures are caused by the repetitive application of force, often by overuse — such as repeatedly jumping up and down or running long distances.

*Disorders associated with Homeostatic Imbalances Osteomalacia and rickets Calcium salts not deposited Rickets (childhood disease) causes bowed legs and other bone deformities Cause: vitamin D deficiency or insufficient dietary calcium

Rickets

*Disorders associated with Homeostatic Imbalances Osteoporosis Loss of bone mass—bone resorption outpaces deposit Spongy bone of spine and neck of femur become most susceptible to fracture Risk factors Lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus

Figure 6.16

*Osteoporosis: Treatment and Prevention Calcium, vitamin D, and fluoride supplements  Weight-bearing exercise throughout life Hormone (estrogen) replacement therapy (HRT) slows bone loss Some drugs (Fosamax, SERMs, statins) increase bone mineral density

*Paget’s Disease Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull Pagetic bone has very high ratio of spongy to compact bone and reduced mineralization Unknown cause (possibly viral) Treatment includes calcitonin and biphosphonates

Rheumatoid Arthritis (RA) Chronic, inflammatory, autoimmune disease of unknown cause Usually arises between age 40 and 50, but may occur at any age; affects 3 times as many women as men Signs and symptoms include joint pain and swelling (usually bilateral), anemia, osteoporosis, muscle weakness, and cardiovascular problems; RA begins with synovitis of the affected joint Inflammatory blood cells migrate to the joint, release inflammatory chemicals Inflamed synovial membrane thickens into a pannus Pannus erodes cartilage, scar tissue forms, articulating bone ends connect (ankylosis) Conservative therapy: aspirin, long-term use of antibiotics, and physical therapy Progressive treatment: anti-inflammatory drugs or immunosuppressants

Osteoarthritis (OA) Common, irreversible, degenerative (“wear-and-tear”) arthritis 85% of all Americans develop OA, more women than men Probably related to the normal aging process More cartilage is destroyed than replaced in badly aligned or overworked joints Exposed bone ends thicken, enlarge, form bone spurs, and restrict movement Treatment: moderate activity, mild pain relievers, capsaicin creams, glucosamine and chondroitin sulfate

Developmental Aspects of Bones Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms At birth, most long bones are well ossified (except epiphyses)

Parietal bone Occipital bone Frontal bone of skull Mandible Clavicle Scapula Radius Ulna Ribs Humerus Vertebra Ilium Tibia Femur Figure 6.17