Braddom Flashcards
Osteoporosis definition
Heterogeneous group of syndromes where bone mass per unit volume is reduced in otherwise healthy bone –> fragile bone that increases fracture risk
Is the mineral/matrix ratio normal in osteoporosis?
Yes; in osteomalacia the mineral content is very reduced
Where does most of the expense of osteoporosis come from?
Hip fractures
Osteoporosis definition by BMD
2.5 SD below peak mean bone mass of young healthy adults (age 35) of same gender
T score vs. Z score
T score: comparing to healthy young person (how we define osteoporosis)
Z score: comparing with people of same demographics (age/sex/race/height/weight)
Normal BMD vs. osteopenia vs. osteoporosis
Normal BMD: T score -1 or higher
Osteopenia: T score between -1 & -2.5
Osteoporosis: T score -2.5 or less
Severe osteoporosis: T score -2.5 or less with a fracture
How much bone is replaced annually by cyclic process of bone remodeling?
20%
Two types of bone cells & functions
Osteoclasts: resorb calcified matrix
Osteoblasts: synthesize new bone matrix
Osteoclast location & origin
Location: on endosteal bone surfaces
Origin: share common precursor with monocytye macrophage; large multi-nucleated cells with 10-20 nuclei
Osteoclast special cell membrane
Has folds that invaginate at interface with bone surface –> ruffled border. At the ruffled border, osteoclasts produce proteolytic enzymes to induce resorption of bone & mineralized bone matrix
Osteoblast origin & function
Origin: derived from mesenchymal cells
Function: mineralization of matrix through budding of vesicles from their cytoplasmic membrane, which are rich in alk phos. Osteoblasts secrete all the growth factors that are trapped in the matrix
Phases of cyclical bone remodeling
Allows maintenance of the bio-mechanical integrity of the skeleton & supports role of bone in the provision of ionic bank for the body & mechanical support:
- Activation: osteoclast activity recruited
- Resorption: osteoclasts erode bone & form a cavity
- Reversal: osteoblasts recruited
- Formation: osteoblasts replace the cavity with new bone
- Quiescence: bone tissue remains dormant until the next cycle starts
What is the process of bone resorption & formation called?
Coupling
Coupling in osteoporosis
Disequilibrium between resorption & formation, favoring resorption –> bone loss
Does trabecular bone or cortical bone have more active remodeling units?
Trabecular bone
Is trabecular bone or cortical bone more metabolically active?
Trabecular bone
Does osteoporosis clinically affect trabecular bone or cortical bone more?
Trabecular bone
Vertebra vs. femoral neck % trabecular bone
Vertebra: 50%
Femoral neck: 30%
Osteoporosis, therefore, occurs in vertebrae before occurring in femoral neck
When is peak adult bone mass achieved?
30-35 years
What is the other name for trabecular bone?
Cancellous bone
Is skeleton comprised mostly of trabecular or cortical bone?
Cortical (80%)
Examples of high-turnover osteoporosis
Hyperparathyroidism, thyrotoxicosis
Why is fracture incidence related to osteoporosis lower in men than women?
Diameter of vertebral bodies & long bones is greater in men at maturity & bone loss is about half that of women throughout life
Most common types of osteoporosis
Post-menopausal or age-related
What is primary osteoporosis?
Rare disorder of idiopathic juvenile osteoporosis, typically occurs before puberty (between 8 & 14). Osteoporosis progresses over 2-4 years with multiple axial or axio-appendicular fractures. Remission occurs spontaneously after 2-4 years. Osteoclast activity is increased while osteoblast activity stays normal. Clinical findings most evident in thoracic & lumbar spine. Radiographic findings may be permanent. Lab values are normal.
Hereditary/congenital causes of osteoporosis
- Osteogenesis imperfecta
- Myotonia congenita
- Werdnig-Hoffmann disease
- Gonadal dysgenesis
Acquired Osteoporosis examples (Generalized)
- Idiopathic (in pre-menopausal women & middle-aged or young men)
- Post-menopausal
- Age-related
- Endocrine disorders: acromegaly, hyperthyroidism, Cushing syndrome (iatrogenic or endogenous), hyper-PTH, T1DM, hypogonadism
- Nutritional issues: malnutrition, anorexia, bulimia, Vit C or D deficiency, Vit OD (A or D), calcium deficiency, high sodium intake, high caffeine intake, high protein intake, high phosphate intake, alcohol abuse
- Sedentary lifestyle, immobility, smoking
- GI disorders: liver disease, malabsorption syndromes, congenital lactase deficiency (alactasia), sub-total gastrectomy, small bowel resection
- Nephropathies
- COPD
- Malignancies: MM, disseminated carcinoma
- Drug use: phenytoin, barbituates, cholestyramine, heparin, excess thyroid hormone replacement, glucocorticoids
Acquired Osteoporosis examples (Localized)
- Inflammatory arthritis
- Fractures & immobilization in cast
- Limb dystrophies
- Muscular paralysis
What hormones can increase rate of bone remodeling?
PTH, thyroxine, GH, Vit D (1, 25)
What hormones can decrease rate of bone remodeling?
Calcitonin, estrogen, glucocorticoids
What is the major hormone for calcium homeostasis?
PTH
PTH physiology
Secreted by parathyroid glands (located behind thyroid glands.
Secreted based on level of plasma Ca2+
Regulates plasma [Ca2+] in 3 ways:
1. Stimulates bone resorption & release of Ca2+ & phosphate (in presence of active Vit D)
2. Produces calcitriol in the kidneys to increase intestinal absorption of Ca2+ & phosphate
3. Increases active re-absorpion of C12+ ions in renal distal tubule
PTH in relation to calcium & phosphate
Increases serum calcium & decreases serum phosphate (reduces proximal tubular re-absorption of phosphate)
Calcitonin physiology
Secreted by parafollicular cells of thyroid gland
Major stimulus of its production is serum Ca2+ level
Directly prohibits calcium & phosphate resorption through inhibition of osteoclastic activity, lowering serum Ca2+
Vit D physiology
Main regulators of synthesis: serum levels of Vit D, Ca2+, phosphate, & PTH
Can be synthesized through exposure to sun & conversion in liver
PTH is the major driver of production of Vit D in the kidney (via 1-alpha-hydroxylase to turn inactive Vit D to active Vit D)
Active Vit D increases intestinal absorption of Ca2+ & phosphate
Vit D is required for appropriate bone mineralization
Active Vit D stimulates osteoblast activity
Main endocrine function that occurs at menopause
Loss of secretion of estrogen & progesterone from the ovaries
What is the major source of estrogen in post-menopausal women?
Estrone (created in fat cells)
Why can bone mass decrease in elderly men?
In some men, bone mass decreases along with a decline in gonadal function (testosterone decreases with age due to decreased # of Leydig cells in the testes)
Male hypogonadism is typically a/w bone loss
Hyperprolactinemia causing osteoporosis
Failure of the gonadal axis –> substantial loss in bone
Other sex hormone factors causing osteoporosis
- Amenorrheic athletes who exercise excessively with lower than normal body weight –> have lower circulating estradiol, progesterone, and prolactin levels (a/w hypothalamic hypogonadism) –> excessive bone loss that can mostly be reversed
What heavily influences bone growth & remodeling?
Rate of change in strain
What happens to bone in the normal aging process?
Deficit between resorption & formation because osteoblastic activity lags compared to osteoclastic –> bone loss during each cycle of remodeling
Activation is decreased –> low turnover osteoporosis
What happens to Vit D levels as people age?
Decreases by about 50% in both men & women
Growth hormone production during aging process
Decreases
Growth hormone & osteoporosis
GH stimulates renal production of active Vit D
Secretion of GH is decreased in patients with osteoporosis
GH & IGF-1 have positive effects on calcium homeostasis –> osteoblast proliferation, osteoclast differentiation, & bone resorption
Vit K therapy in elderly a/w decrease in rate of bone resorption as demonstrated by this urine marker
Hydroxyproline
Are plasma calcitonin levels higher in men or women?
Men (levels do not change with age)
Do thyroid levels change with age?
No, but if they do, it is a slight decrease
Does PTH change with age?
Increases, probably because of mild hypocalcemia & decreased active Vit D
Why does active Vit D decrease with age?
Decreased consumption of dietary Vit D, decreased exposure to sunlight, decreased skin capacity for Vit D conversion, reduced intestinal absorption, & reduced 1-alpha-hydroxylase activity
Recommended dose of calcium & Vit D in estrogen-deficient women
Calcium: 1,500 mg/day
Vit D: 800 IU/day
Can osteoporotic vertebral fractures go unnoticed?
Yes, often found incidentally on CXR
Most common areas for osteoporotic fractures
Mid-thoracic (T7/8) & upper lumbar spine (L1/2), proximal femur (hip), distal forearm (Colles)
Highest incidence for osteoporotic fractures
White women
Female: male-
Vertebral fx- 7:1
Hip fx- 2:1
Colles- 5:1
Which fracture site is of greatest concern clinically?
Hip fx –> risk of death is 15-20%
Management of osteoporotic spine fracture
Immobilization of the involved vertebral bodies & analgesia (these fractures heal by becoming more condensed)
What should you look for if there is non-union in appendicular fractures?
Osteomalacia or hyperparathyroidism
How to typically manage proximal humerus (surgical neck) fracture in osteoporosis
Conservative, typically
How long can a compression fracture appear normal on XR?
Up to 4 weeks. You need to lose 25-30% of BMD for it to be picked up on XR
How can vertebral fractures from osteoporosis cause chronic pain?
Spinal deformity –> kyphotic postural change
Management of acute pain in patients with osteoporosis
Bed rest (2 days), analgesics (avoid constipating meds), avoidance of constipation, PT (initially cold packs then mild heat & massage), avoidance of exertion, avoidance of excessive spinal strain, back support if needed to decrease pain & expedite ambulation, gait aids as needed
What can increase the possibility of compressing vertebrae in the fragile osteoporotic spine?
Disproportionate weakness in back extensor musculature relative to body weight or spinal flexion strength
Why is development of kyphotic posture bad?
Can lead to postural back pain & predispose to falls
What can spinal pain related to osteoporosis be from?
Caused by deformity from vertebral wedging & compression, as well as by secondary ligamentous strain
What happens to inter-vertebral disks as we age?
Increase in number & diameter of collagen fibrils in the disk –> progressive decrease in disk resilience –> loss of distinction between nucleus pulposus & annulus fibrosis
Therapy for chronic back pain 2/2 osteoporosis
Back extensor resistance training –> studies show less amount of vertebral fractures long-term compared to controls with osteoporosis
What else can chronic pain in back from osteoporosis be from?
Micro-fractures, only visible on bone scan
What position is recommended for back strengthening exercise in osteoporosis?
Prone –> improves horizontal trabecular connections; needs to be progressive, resistive, & non-loading to avoid vertebral compression fracture
Vertebroplasty & kyphoplasty
Vertebroplasty: Injection of acrylic cement (such as polymethylmethacrylate) into a partially collapsed vertebral body
Kyphoplasty: balloon dilation catheter to restore vertebral height
Unclear if either actually helps based on studies
Why does kyphotic posture lead to instability?
Places center of gravity closer to limit of stability
What are two general types of hip fracture?
Intra-capsular (femoral neck) or extra-capsular (trochanteric)
Which hip fracture has a high surgical failure rate?
Femoral neck fractures repaired by internal fixation
Most surgeons prefer arthroplasty for this reason (hemi-arthroplasty of femoral head & neck for older, frailer patients with a prognosis of limited mobility)
Operative treatment choice for trochanteric fracture
Internal fixation
When do patients get a NWB status after hip fracture?
Severely comminuted or fractures where the operative result was non-satisfactory
Hip pads for fracture ppx
Questionable benefit but may work for some who are compliant
Landing on buttocks is less traumatic to hips than landing on greater troch –> teaching this may be more beneficial than hip pads
Sacral insufficiency fractures
Pelvic fractures are common in osteoporosis
Fractures of pubic rami/sacrum can occur with minimal strain (most patients cannot recall a traumatic event
Treated conservatively typically
Wheeled walker recommended initially –> crutches/cane
WB is as tolerated
Who should be getting a BMD evaluation?
Estrogen-deficient women with risk factors, women 65 or older, women in post-menopausal stage who have at least 1 risk factor for osteoporosis, people who have a vertebral abnormality indicative of bone loss, taking medication like Prednisone, T1DM, liver/kidney disease, thyroid disease, family history of menopause, & women who underwent early menopause.
May also want to include alcohol abusers/smokers
When should follow-up BMD testing be done?
After 2 years or longer, depending on baseline T-score & patient risk factors
Bone markers
Bone formation: calcium, phosphorus, PTH, bone-specific alk phos, serum osteocalcin, pro-collagen type I, C, & N pro-peptides
Resorption: 24-hour urine hydroxyproline/calcium excretion (corrected by creatinine excretion)/pyridinium cross-links
These markers are clouded in patients with osteoporosis because many variations among people exist. Indices of bone turnover have seasonal & circadian variations
Evaluation studies for osteoporosis
- H&P (FH of osteoporosis, general dietary calcium intake), level of physical activity, height/weight
- CXR, Spine XR (r/o lymphomas, rib fractures, compression fractures, etc)
- BMD eval (at menopause & every 2 years for high-risk patients, 5 years for low-risk patients)
- CBC (r/o anemias a/w malignancy)
- Chemistries (alk phos which may be increased in osteomalacia, Paget disease, bony mets/fracture, intestinal malabsorption, Vit D deficiency, chronic liver disease, alcohol abuse, Phenytoin use, hypercalcemia of hyperparathyroidism, hypophosphatemia of hyperparathyroidism & osteomalacia, malabsorption, or malnutrition)
- ESR & SPEP (MM or other gammopathies)
- Total thyroxine (increase may be a cause of osteoporosis because of increased bone turnover)
- Immunoreactive PTH (hyperparathyroidism with hypercalcium)
- Vit D (inactive & active) (GI disease, osteomalacia)
- UA & 24-hour urine (check for proteinuria caused by nephrotic syndrome & for low pH from RTA; 24-hour urine can r/o hypercalciuria)
- Optional: bone scan, iliac crest biopsy
Radiographic findings of osteoporosis
Increased lucency of vertebral bodies with loss of horizontal trabeculae, increased prominence of the cortical end plates, vertically oriented trabeculae, reduction in cortex thickness, & anterior wedging of vertebral bodies
What is the degree of wedging that indicates a true fracture?
15-25% reduction in anterior height relative to posterior height of the same vertebra