Osteoporosis and Bone Disease

• Definition: Osteoporosis is a systemic skeletal disorder of compromised bone strength — reduced bone mass plus microarchitectural deterioration — producing fragility fractures from forces that would not break normal bone. Bone is qualitatively normal but quantitatively deficient (mineral and matrix are lost in proportion), which distinguishes it from osteomalacia (adequate matrix, defective mineralization) and Paget disease (excessive, disorganized remodeling).
• Why it matters: Fracture, not low density itself, is the outcome. Hip fracture carries high one-year mortality and frequent permanent loss of independence; vertebral fractures cause chronic pain, kyphosis, restrictive ventilatory impairment, and early satiety. Most fractures occur in patients who have never been screened or treated — the treatment gap is the central public-health problem.
• Epidemiology worth recalling:
• Millions of US adults have osteoporosis by densitometric criteria, and a larger number have osteopenia; the majority are women.
• Peak bone mass is reached in the third decade; women lose bone rapidly in the first several years after menopause, then at an age-related rate shared with men.
• Highest-risk groups: postmenopausal women, men over 70, White and Asian ancestry, low body weight, and anyone on chronic glucocorticoids.
• Men account for a substantial minority of hip fractures and have worse post-fracture mortality, yet are far less often evaluated.
• Related bone diseases tested alongside it: Paget disease of bone (focal, usually asymptomatic, isolated alkaline phosphatase elevation in an older adult), osteomalacia/rickets (vitamin D deficiency), and renal osteodystrophy (CKD–mineral and bone disorder).
• Screening framing: The USPSTF recommends bone density screening for all women 65 and older and for younger postmenopausal women with elevated fracture risk; it considers evidence insufficient to recommend for or against screening men. The screening of men 70 and older reflects the Bone Health and Osteoporosis Foundation and Endocrine Society, not the USPSTF.

Non-modifiable (host) factors

• Advancing age: cumulative remodeling imbalance plus declining osteoblast reserve and renal 1α-hydroxylase activity.
• Female sex and postmenopausal state: estrogen withdrawal is the dominant driver of accelerated loss.
• Race/ethnicity and body habitus: White and Asian ancestry, low body weight, small frame — less peak bone mass and less mechanical loading.
• Family history of hip fracture and prior fragility fracture: prior fracture is the single strongest clinical predictor of the next one.

Modifiable/lifestyle factors

• Smoking: antiestrogenic, directly toxic to osteoblasts.
• Excess alcohol (three or more drinks daily): suppresses osteoblasts and increases fall risk.
• Physical inactivity/immobilization: absent mechanical strain removes the osteocyte signal that restrains sclerostin and RANKL.
• Low calcium and vitamin D intake: drives secondary hyperparathyroidism.
• Low body weight / eating disorders: hypothalamic amenorrhea in the female athlete triad.

Endocrine causes

• Hypogonadism (menopause, anorexia, hyperprolactinemia, androgen-deprivation therapy for prostate cancer).
• Glucocorticoid excess — endogenous Cushing or exogenous steroids; the most common drug cause.
• Hyperparathyroidism, hyperthyroidism (including over-replacement with levothyroxine), type 1 diabetes.

Gastrointestinal/nutritional

• Celiac disease, inflammatory bowel disease, bariatric surgery, chronic liver disease — malabsorption of calcium and fat-soluble vitamin D.

Marrow, renal, and inflammatory

• Multiple myeloma (osteoclast-activating cytokines), systemic mastocytosis, rheumatoid arthritis (IL-1/IL-6/TNF-driven RANKL).
• CKD: impaired calcitriol synthesis and phosphate retention.

Drugs examiners plant in the stem

• Glucocorticoids, aromatase inhibitors, GnRH agonists, antiepileptics (phenytoin, phenobarbital) via CYP-mediated vitamin D catabolism, heparin (long-term), thiazolidinediones, proton pump inhibitors, and SSRIs. The ACR glucocorticoid-induced osteoporosis guideline treats any anticipated long-course steroid as an indication for risk assessment and calcium/vitamin D at minimum.

• Normal remodeling: Osteocytes sense mechanical strain and set the tone. Osteoblast-lineage cells secrete RANKL, which binds RANK on osteoclast precursors to drive differentiation and resorption, and osteoprotegerin (OPG), a decoy receptor that blocks RANKL. The RANKL:OPG ratio is the master switch of bone resorption. Osteocyte-derived sclerostin inhibits Wnt signaling and thereby restrains osteoblast bone formation.
• Estrogen withdrawal: Estrogen normally suppresses RANKL, boosts OPG, and promotes osteoclast apoptosis. After menopause the RANKL:OPG ratio rises, osteoclast lifespan lengthens, and resorption outpaces formation. Each remodeling cycle now ends in net loss. Because osteoclasts perforate trabecular plates rather than merely thinning them, trabecular (cancellous) bone is lost first and disproportionately — hence vertebral bodies, femoral neck, and distal radius fracture earliest. Once a trabecular strut is resorbed through, there is no template for refilling, so the architectural loss is irreversible even if density later improves.
• Age-related loss: Declining renal 1α-hydroxylation and reduced dietary calcium lower serum ionized calcium, producing secondary hyperparathyroidism; continuous (not pulsatile) PTH elevation is catabolic, driving cortical bone resorption. Rising sclerostin and diminished osteoblast progenitors compound the deficit.
• Glucocorticoids: induce osteoblast and osteocyte apoptosis, prolong osteoclast survival, reduce intestinal calcium absorption and increase renal calcium wasting, and cause myopathy and hypogonadism — fracture risk rises early and at bone densities higher than expected, because bone quality is impaired.
• Clinical translation: Reduced bone strength means fracture at low-energy loads — a vertebral body crushes under axial load from bending or lifting; the femoral neck fails in a sideways fall. Vertebral wedging shortens the anterior column, producing height loss and thoracic kyphosis.
• Contrast — Paget disease: a focal burst of chaotic osteoclastic resorption followed by frenzied compensatory osteoblastic formation yields expanded, hypervascular bone with a mosaic pattern of lamellar bone — dense but mechanically weak.

• Silent until fracture: Osteoporosis itself produces no symptoms; bone loss is painless. The classic stem is an older woman found incidentally to have low bone density, or presenting after a fragility fracture.
• Vertebral compression fracture: acute mid-thoracic or thoracolumbar back pain after bending, lifting, or even coughing — or entirely painless and discovered on a chest film. Mechanism: axial load exceeds the strength of trabecular-depleted vertebral bodies.
• Progressive height loss (historical loss of more than about an inch and a half from peak height is a red flag) and Dowager's hump thoracic kyphosis from anterior wedging.
• Secondary findings: reduced rib–pelvis distance, protuberant abdomen, early satiety, and restrictive ventilatory pattern from a shortened thorax.
• Hip fracture: an older adult who falls from standing and presents with a shortened, externally rotated, abducted leg and inability to bear weight; the mechanism is a sideways fall onto the greater trochanter in cortically thinned bone.
• Distal radius (Colles) fracture: fall on outstretched hand with dinner-fork deformity; often the earliest fragility fracture, appearing in the perimenopausal decade.
• Demographics the stem names: thin postmenopausal White or Asian woman; a smoker; a patient on long-term prednisone for polymyalgia rheumatica, asthma, or transplant; a woman on an aromatase inhibitor for breast cancer; a man on androgen deprivation therapy.
• Red flags that redirect the diagnosis:
• Bone pain, hypercalcemia, anemia, renal failure in an older adult → multiple myeloma, not simple osteoporosis.
• Diffuse bone pain and proximal muscle weakness with a waddling gait → osteomalacia.
• Bone pain, warmth over a limb, skull enlargement (hat no longer fits), hearing loss, or bowing of the tibia in an older adult → Paget disease of bone, which unlike osteoporosis is often unilateral, focal, and warm to the touch because of hypervascularity.
• Physical exam is otherwise normal in uncomplicated osteoporosis — an important negative.

Step 1 — Identify who to test

• Per the USPSTF, screen all women 65 and older and younger postmenopausal women with elevated risk; the BHOF and Endocrine Society extend testing to men 70 and older, and to any adult over 50 with a fragility fracture, chronic glucocorticoid use, or a condition known to cause bone loss.

Step 2 — Central DXA is the gold standard

• Measure lumbar spine, total hip, and femoral neck; the lowest site defines the diagnosis. Distal radius is used when the hip/spine are uninterpretable or in hyperparathyroidism.
• T-score compares the patient to a young adult reference and applies to postmenopausal women and men 50 and older (WHO criteria; osteoporosis at ≤ -2.5).
• Z-score — comparison with age-matched peers — is the correct metric in premenopausal women, men under 50, and children. A Z-score at or below -2.0 is below the expected range for age and mandates a secondary-cause workup.
• Degenerative facet disease, aortic calcification, prior vertebroplasty, or vertebral fracture falsely raise lumbar spine density — an important artifact.

Step 3 — Diagnose clinically when DXA is not needed

• A hip or vertebral fragility fracture establishes osteoporosis regardless of T-score, as does a T-score in the osteopenic range combined with a FRAX-calculated 10-year risk at or above 3% for hip or 20% for major osteoporotic fracture (BHOF intervention thresholds).
• Vertebral fracture assessment or lateral spine radiographs detect the silent vertebral fractures that reclassify the patient.

Step 4 — Exclude secondary causes before treating

• CBC, CMP (calcium, creatinine, alkaline phosphatase, liver enzymes), 25-hydroxyvitamin D, PTH, TSH, 24-hour urine calcium and creatinine; add SPEP/UPEP with free light chains, tissue transglutaminase IgA, and morning testosterone in men.
• Interpretation patterns: osteoporosis has normal calcium, phosphate, and alkaline phosphatase. Osteomalacia shows low/low-normal calcium and phosphate with high alkaline phosphatase and high PTH plus Looser zones. Paget disease shows an isolated markedly elevated alkaline phosphatase with normal calcium and phosphate; confirm extent with radionuclide bone scan and characterize lesions with plain films (osteoporosis circumscripta, cotton-wool skull, blade-of-grass lytic front).

Universal foundation (all patients)

• Weight-bearing and resistance exercise, smoking cessation, alcohol moderation, fall-risk reduction (medication review, vision check, home hazards), and repletion of calcium and vitamin D. Correct vitamin D deficiency and hypocalcemia before starting an antiresorptive — otherwise potent agents precipitate symptomatic hypocalcemia.

First-line pharmacotherapy

• Oral bisphosphonates — alendronate 70 mg weekly or risedronate — remain first-line per the Endocrine Society and BHOF. They are pyrophosphate analogs that adsorb to hydroxyapatite, are internalized by osteoclasts, and inhibit farnesyl pyrophosphate synthase, blocking prenylation of GTPases and triggering osteoclast apoptosis.
• Intravenous zoledronic acid 5 mg annually when oral dosing is not tolerated or adherence is poor; expect a transient acute-phase reaction.

Escalation and alternatives

• Denosumab (RANKL monoclonal antibody), 60 mg subcutaneously every 6 months — preferred in significant renal impairment, where bisphosphonates are avoided.
• Anabolic-first therapy for very high risk (recent fracture, multiple vertebral fractures, very low T-score): PTH/PTHrP analogs teriparatide or abaloparatide (intermittent PTH signaling favors osteoblasts), or romosozumab, a sclerostin antibody that simultaneously builds and blocks resorption. The Endocrine Society and AACE advise following any anabolic course with an antiresorptive, because gains are lost if therapy simply stops.
• Raloxifene (SERM) when breast-cancer risk reduction is also desired; hormone therapy is reserved for recently menopausal women with vasomotor symptoms.
• Glucocorticoid-induced osteoporosis: the ACR recommends calcium/vitamin D for everyone on chronic steroids and an oral bisphosphonate as the preferred agent for moderate- to high-risk patients.

Fracture and Paget management

• Hip fracture: analgesia, early surgical fixation or arthroplasty with orthogeriatric co-management, VTE prophylaxis, and initiation of osteoporosis therapy before discharge.
• Symptomatic Paget disease: single-dose IV zoledronic acid is first-line (Endocrine Society).

Contraindicated/cautions

• Bisphosphonates in severe renal impairment, hypocalcemia, esophageal stricture or achalasia, or inability to sit upright.
• Romosozumab in recent myocardial infarction or stroke (boxed cardiovascular warning).
• Never stop denosumab without transitioning to a bisphosphonate — rebound resorption causes multiple vertebral fractures.

Complications of the disease

• Hip fracture: the dominant cause of osteoporosis-related mortality and institutionalization; mechanism is cortical thinning plus a sideways fall. Post-fracture immobility drives pulmonary embolism, pneumonia, delirium, pressure ulcers, and deconditioning — a suspected PE or fat embolism after femoral fracture is an emergency.
• Vertebral compression fractures: chronic pain, progressive kyphosis, restrictive lung disease, abdominal compression with early satiety and weight loss, and increased future fracture risk. Retropulsion of bone with cord or cauda equina compression is a surgical emergency — new saddle anesthesia, bowel/bladder dysfunction, or leg weakness warrants urgent MRI.
• Fracture cascade: one vertebral fracture markedly increases the odds of another within a year, largely from altered spinal biomechanics.

Complications of treatment

• Oral bisphosphonates: pill esophagitis and erosive ulceration — the reason for upright posture and a full glass of water; and hypocalcemia if vitamin D is unrepleted.
• Zoledronic acid: acute-phase reaction (flu-like illness within 1–3 days from γδ T-cell activation), and renal deterioration if infused too rapidly or into a dehydrated patient.
• Osteonecrosis of the jaw: rare with osteoporosis dosing, far more common with oncologic dosing; presents as exposed necrotic mandibular bone after dental extraction. Complete invasive dental work before starting therapy.
• Atypical femoral fracture: transverse or short-oblique subtrochanteric/diaphyseal fracture with lateral cortical beaking, preceded by weeks of prodromal thigh or groin pain from severely suppressed remodeling. Prodromal pain requires imaging before the bone completes the break — a limb-threatening near-emergency. The ASBMR task force supports a drug holiday after roughly five years of oral or three years of IV therapy in patients no longer at high risk.
• Denosumab discontinuation: rebound multiple vertebral fractures; also hypocalcemia in CKD, which can present with tetany, paresthesias, and QT prolongation — an emergency.
• Teriparatide/abaloparatide: hypercalcemia and orthostatic hypotension.
• Paget disease complications: high-output heart failure from hypervascular bone, cranial nerve VIII hearing loss, spinal stenosis, and rarely osteosarcoma — signaled by new severe pain, a soft-tissue mass, and a rising alkaline phosphatase in previously stable disease.

• Normal labs define osteoporosis: calcium, phosphate, and alkaline phosphatase are all normal. An isolated elevated alkaline phosphatase with normal calcium and phosphate in an older adult is Paget disease until proven otherwise; low calcium and phosphate with high alkaline phosphatase and high PTH is osteomalacia.
• Best next step after a fragility fracture is to treat, not to wait for a T-score. A hip or vertebral fracture from a fall from standing height diagnoses osteoporosis regardless of DXA, and the fracture itself is the strongest predictor of the next one.
• Check and correct 25-hydroxyvitamin D before starting an antiresorptive — the classic vignette punishes giving zoledronic acid or denosumab to a vitamin D–deficient patient, who then develops perioral paresthesias and carpopedal spasm from hypocalcemia.
• T-score versus Z-score: T-score for postmenopausal women and men 50 and older; Z-score for premenopausal women, men under 50, and children — a Z-score at or below -2.0 mandates a secondary workup.
• Prodromal thigh pain in a patient on years of alendronate = impending atypical femoral fracture; image the femur. The characteristic radiographic clue is lateral cortical beaking with a transverse subtrochanteric lucency.
• Never stop denosumab cold: rebound osteoclast activation causes multiple vertebral fractures; transition to a bisphosphonate.
• The steroid association: chronic glucocorticoids fracture patients at higher bone densities than expected because they impair bone quality — the ACR advises calcium, vitamin D, and a bisphosphonate for moderate- to high-risk users rather than waiting for a T-score of -2.5.
• Paget buzzwords: cotton-wool skull, osteoporosis circumscripta, blade-of-grass lytic front, mosaic pattern of lamellar bone, increasing hat size, hearing loss, high-output heart failure, and osteosarcoma as the feared malignant transformation; IV zoledronic acid is treatment.
• Common distractor: attributing bone pain plus hypercalcemia, anemia, and renal failure to osteoporosis — that combination is multiple myeloma, and osteoporosis does not cause hypercalcemia.

• Osteoporosis = low bone mass (T-score ≤ -2.5 on DEXA) with increased fracture risk; osteopenia = T-score -1 to -2.5
• Most common cause of fractures in elderly; hip, spine, and wrist are typical sites
• Postmenopausal women and men >70 are highest risk groups
• DEXA scan is gold standard for diagnosis; screening recommended for all women ≥65 and men ≥70
• Fragility fractures (trauma from fall <10 feet or spontaneous) warrant workup even if DEXA normal

• Asymptomatic elderly woman with kyphosis, height loss, or vertebral compression fractures on imaging
• Hip fracture from minor fall in postmenopausal woman
• Young patient with fragility fracture → screen for secondary causes (hyperthyroidism, malabsorption, chronic corticosteroid use)
• Dowager's hump (thoracic kyphosis) from multiple vertebral fractures

1. 1.Assuming normal DEXA = no fracture risk: A fragility fracture warrants treatment regardless of T-score; consider secondary osteoporosis workup
2. 2.Forgetting vitamin D screening: Many "osteoporotic" patients have vitamin D deficiency (25-OH vitamin D <20 ng/mL) driving secondary hyperparathyroidism; this must be corrected first
3. 3.Not screening secondary causes in young patients: Age <50 with osteoporosis demands workup for thyroidism, hypogonadism, malabsorption, and multiple myeloma

• Lifestyle: Weight-bearing exercise, smoking cessation, limit alcohol, calcium intake 1000-1200 mg/day, vitamin D 800-2000 IU/day
• Pharmacotherapy:
• Bisphosphonates (alendronate, risedronate) = first-line; inhibit osteoclasts; requires upright posture 30 min post-dose, no food
• Vitamin D/calcium supplementation if deficient
• Hormone therapy (estrogen/progestin) if recent menopause (cardiovascular/thromboembolism risk limits use)
• Denosumab (RANKL inhibitor) if bisphosphonate intolerant
• Teriparatide (PTH analog) for severe osteoporosis or bisphosphonate failure (stimulates osteoblasts)