Chapter 44 Objectives 1,2,3,5,6 and Chapter 43 Objective 14
• Describe the pathology associated with osteonecrosis.
o Blood is supplied to the bones through nutrient arteries and perforating arteries. The medularry portion of the bone is supplied by nutrient arteries that reach the marrow, trabecular bone, and endosteal half of the cortex. The perforating arteries extend from the periosteal arteries and connect with the nutrient arteries. The outer cortex of the bone receives its blood supply from surrounding periosteal, muscular, metaphyseal, and epiphyseal vessels that surround it. The site of necrosis depends on the vessels involved. Necrosis of cancellous bone and marrow is common, while necrosis is not common in the cortex because of collateral blood flow. When ischemia happens below the cartilage (subchondral) there is necrosis in a triangular wedge shape reaching from the subchondral bone plate (base) to the center of the epiphysis (apex). When necrosis occurs in fatty marrow, death of bone results in calcium release and necrosis of fat cells to form free fatty acids. This forms an insoluble "soap." Bone can not resolve an infarct so the lesions remain for life.
• Describe the etiology, pathology, clinical manifestations, diagnosis, of Paget disease (osteitis deformans).
o Etiology: Paget disease usually begins during midadulthood and becomes progressively more common with increasing age. It is more common in people with northern European heritage. Men are about twice as likely as women to have the disease. Those with a first degree relative with the disease have a 15-40% chance of getting it. It may be associated with a virus, possibly a paramyxovirus, suggesting that there may be a viral trigger for those who are genetically predisposed. o Pathology: at the onset, there is regions of furious osteoclastic bone resorption, followed by a period of hectic bone formation with increased osteoblasts deposting bone in a chaotic fashion. This makes the bone disorganized and of poor quality. The poor quality contributes to the bowing and fractures that occur in this disease. The bone marrow adjacent to the bone forming site is replaced by loose connective tissue that contains osteoprogenetor cells and numerous blood vessels. The lesions associated with pagets disease may be solitary or occur at multiple sites. They tend to localize to bones such as the skull, spine, and pelvis. The proximal femur and tibia may be involved in widespread forms. The lesions show increased vascularity and bone marrow fibrosis with intense cellular activity giving the bone a mosaic like pattern caused by areas of density outlined by heavy blue lines called cement lines. o Clinical Manifestations: usually asymptomatic and discovered as an incidental radiograph finding. Skeletal expansion may be obvious if the skull, jaw, clavicle, or long bones of the leg are involved. Involvement of the skull causes headaches, intermittent tinnitus, vertigo, and eventual hearing loss. The vertebrae of the spone may enlarge, weaken, and collapse cauing kyphosis and nerve compression. Weight bearing may cause bowing of the femur and tibia. Softening of the femoral neck can cause coxa vara. Which in combination with pelvis involvement can cause waddling gait and secondary osteoarthritis. Mild to moderate deep, aching pain begins late in the course of the disease and persists through the day and at rest and becomes worse at night. There may be warmth of the overlying skin and subcutaneous tissue because of vascularization. Extensive blood flow to the bones and subcutaneous tissue can lead to high-output heart failure or exacerbation of underlying cardiac disease. Tumorlike conditions may develop in the femur, pelvis, and humerus. o Diagnosis and treatment: diagnsosis is based on characteristic bone deformities and x ray changes. Bone scans and bone biopsies, elevated serum alkaline phosphatase and uinary hydroxyproline. Treatment includes the management of pain and adequate vitamin d levels.
• Describe osteomalacia in terms of etiology, pathology, clinical manifestations, diagnosis, and treatment.
o Etiology: incidence is high among the elderly because of diets deficient in calcium and vitamin d and intestinal malabsorption that accompanies aging. Decreased skin pigmentation and sunscreen decrease the absorption of vitamin d. Osteomalacia may occur in patients on long term treatment with anticonvulsants that decrease the activation of vitamin d in the liver. There is also an increased incidence in colder parts of the world because of decreased sunlight exposure. o Pathology: osteomalacia is caused by 1) insufficient calcium absorption from the intestine because of lack of dietary calcium or a deficiency of or resistance to the action of vitamin d 2) phosphate deficiency caused by increased renal losses or decreased intestinal absorption. A form of osteomalacia called renal rickets occurs in persons with chronic renal failure. It is caused by the inability of the kidneys to activate vitamin d and excrete phosphate and is usually accompanied by hyperparathyroidism, increased bone turnover, and increased bone resorption. Vitamin d resistant rickets is an x linked dominant disorder associated with renal tubular defects that cause excessive phosphate losses. o Clinical manifestations: bone pain, tenderness, and fractures as the disease progresses. In severe cases, muscle weakness is often an early sign. It predisposes to pathologic fractues in the weakened bones, especially the distal radius and proximal femur. It is not a significant cause of hip fractures. May be delayed healing and poor retention of internal fixation devices. Usually accompanied by compensatory or secondary hyperparathyroidism due to low serum calcium. Serum calcium levels are only slightly reduced. o Diagnosis: x ray findings including the development of transverse lines or pseudofractures called looser zones. Laboratory tests, bones scans, and bone biopsy may be done. o Treatment: treat the underlying cause, give calcium and vitamin d supplements or replace deficient hormones.
• Explain how osteoporosis may be prevented.
o Identification of those at risk for the development of osteoporosis is essential. Regular exercise and adequate vitamin d and calcium intake are important, weight bearing exercise, smoking cessation, not drinking alcohol, decrease caffeine intake.
• Describe osteoporosis and identify factors that contribute to its development, including osteopenia.
o Osteoporosis is a metabolic bone disease characterized by decreased bone density and strength in which both the bone matrix and mineralization are decreased. Factors contributing to the development of osteoporosis include: • Osteopenia is characterized by a reduction in bone density that is greater than expected. It can be caused by a decrease in bone formation, inadequate bone mineralization, or excessive bone deossification. • Genetic factors that determine the amount of bone in a given person or peak bone mass. Whie and Asian race are contributing factors as well as smaller body builds. • Lack of estrogen causes increased osteoclast activity causin bone density to decrease. • Male hormone deficiency may contribute to the development of osteoporosis. • Age related factors contribute to the development of osteoporosis such as: decreased osteoblast activity because of reduced replicative and biosynthetic potential, loss of growth factors that stimulate osteoblast activity, and reduced physical activity to stimulate normal bone remodeling. • Secondary osteoporosis is associated with endocrine disorders(hyperthyroidism, hyperparathyroidism, cushing syndrome, diabetes mellitus), malabsorption disorders, malignancies(multiple myeloma), alcoholism, and certain medications(corticosterois, aluminum containing antacids, antiretrovirals). • Premature infants, low birth weight infants with low bone density, children who require treatment with corticosteroids, children with cystic fibrosis, and those with hypogonadal states (anorexia nervosa and female athlete triad) • Premature osteoporosis is being seen more frequently in female athletes owing to an increased prevalence of eating disorders and amenorrhea. The loss of nutrients and estrogen helps contribute to loss of bone mass.
• Compare the anatomical features of typical and osteoporotic bone.
o Osteoporotic changes occur in the diaphysis and metaphysis of the bone. There is loss of trabeculae from cancellous bone and thinning of the cortex to the extent that fractures occur because of minimal stress. • Postmenopausal- in postmenopausal women, increased osteoclast activity affects bone with larger surface area such as the cancellous compartment of vertebral bodies. The trabeculae thin and lose their connections causing microfractures and eventual vertebral collapse. • Senile- the osteoporotic cortex is thinned by subperisoteal and endosteal resorption and the haversian systems are so enlarged that the cortex resembles cancellous bone. Hipe fractures are most commonly associated with senile osteoporosis.
• List the primary and secondary risk factors associated with osteoporosis.
o Primary: advanced age, female, gender ethnicity, small bone structure/low body weight, postmenopausal, family history, sedentary lifestyle, calcium/vitamin d deficiency, high-protein diet, excessive alcohol intake, excessive caffeine intake, smoking o Secondary: aluminum containing antacids, anticonvulsants, heparin, corticosteroids, gastrectomy, cushing syndrome, celiac disease, diabetes mellitus, anorexia nervosa, female athlete triad, hyperthyroidism, hyperparathyroidism, rheumatoid arthritis