10.2 Osteoporosis and metabolic bone disorders

Osteoporosis and metabolic bone disorders are serious health concerns that affect bone strength and density. These conditions can lead to fractures, pain, and reduced quality of life. Understanding the risk factors, pathophysiology, and clinical manifestations is crucial for early detection and prevention.

Diagnostic tests, prevention strategies, and treatment options play vital roles in managing osteoporosis and related disorders. From bone density scans to lifestyle modifications and medications, a comprehensive approach is essential for maintaining bone health and reducing fracture risk.

Pathophysiology and Clinical Manifestations of Osteoporosis and Metabolic Bone Disorders

Risk factors of metabolic bone disorders

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• Non-modifiable factors increase risk regardless of lifestyle
  • Advanced age accelerates bone loss due to hormonal changes and reduced bone formation
  • Female gender predisposes to osteoporosis, especially after menopause when estrogen levels decline
  • Family history of osteoporosis or fractures suggests genetic susceptibility
  • Caucasian or Asian ethnicity have lower peak bone mass compared to other racial groups
• Modifiable factors can be altered through lifestyle changes
  • Low body weight (BMI < 18.5 kg/m²) reduces mechanical stress on bones, leading to decreased bone density
  • Smoking impairs bone formation and increases bone resorption by altering hormonal balance and blood supply
  • Excessive alcohol consumption (>2 drinks/day) interferes with calcium absorption and vitamin D metabolism
  • Sedentary lifestyle fails to stimulate bone formation through weight-bearing activities
  • Low calcium and vitamin D intake hinders proper bone mineralization and maintenance
  • Prolonged use of certain medications (glucocorticoids, anticonvulsants, proton pump inhibitors) disrupts bone metabolism and increases fracture risk
• Pathophysiology of osteoporosis involves an imbalance between bone formation and resorption
  • Decreased osteoblast activity results in reduced bone formation and inability to replace old or damaged bone tissue
  • Increased osteoclast activity accelerates bone resorption, leading to net bone loss and deterioration of bone microarchitecture
  • Reduced bone mineral density and altered bone microarchitecture compromise bone strength and increase susceptibility to fractures
• Clinical manifestations of osteoporosis are often subtle until fractures occur
  • Often asymptomatic in early stages, making early detection and prevention crucial
  • Fractures in weight-bearing bones (hip, vertebrae, wrist) are common due to reduced bone strength and increased fragility
  • Height loss and kyphosis (forward curvature of the spine) result from vertebral compression fractures, leading to stooped posture and back pain
  • Chronic pain and reduced mobility following fractures can significantly impact quality of life and increase risk of complications (pneumonia, deep vein thrombosis)
• Other metabolic bone disorders include osteomalacia, rickets, and Paget's disease
  • Osteomalacia and rickets are caused by vitamin D deficiency or impaired vitamin D metabolism, leading to softening and weakening of bones
    • Bowing of legs and other skeletal deformities (knock knees, rachitic rosary) are characteristic of rickets in children
  • Paget's disease of bone involves abnormal bone remodeling, resulting in enlarged, deformed, and fragile bones
    • Pain, arthritis, and fractures in affected bones (skull, spine, pelvis, femur) are common complications

Diagnostic Tests, Prevention, and Treatment Strategies for Osteoporosis

Diagnostic tests for bone density

• Dual-energy X-ray absorptiometry (DXA) is the gold standard for measuring bone mineral density (BMD)
  • Measures BMD at the hip, spine, and sometimes forearm using low-dose X-rays
  • Results expressed as T-score and Z-score for comparison to reference populations
    • T-score compares patient's BMD to that of a healthy young adult
      1. T-score ≤ -2.5 indicates osteoporosis
      2. T-score between -1.0 and -2.5 indicates osteopenia (low bone mass)
    • Z-score compares patient's BMD to age- and sex-matched norms to identify unexpectedly low BMD for age
• Quantitative ultrasound (QUS) is a portable and less expensive alternative to DXA
  • Measures bone density at peripheral sites (heel, shin, finger) using sound waves
  • Results not interchangeable with DXA but can help identify individuals at risk for fractures
• Bone turnover markers reflect the dynamic process of bone remodeling
  • Biochemical markers of bone formation (osteocalcin, bone-specific alkaline phosphatase) and resorption (N-telopeptide, C-telopeptide) can be measured in blood or urine
  • Useful for monitoring treatment response and assessing fracture risk in conjunction with BMD measurements

Prevention strategies for osteoporosis

• Lifestyle modifications promote bone health and reduce fracture risk
  • Adequate calcium and vitamin D intake ensures proper bone mineralization
    • Calcium: 1,000-1,200 mg/day for adults, obtained through diet (dairy products, green leafy vegetables) or supplements
    • Vitamin D: 600-800 IU/day for adults, obtained through sunlight exposure, diet (fatty fish, fortified foods), or supplements
  • Regular weight-bearing and resistance exercises stimulate bone formation and improve muscle strength and balance
  • Smoking cessation and limiting alcohol consumption (<2 drinks/day) reduce the negative impact on bone metabolism
• Pharmacological interventions target specific aspects of bone metabolism to increase bone density and reduce fracture risk
  • Bisphosphonates (alendronate, risedronate, zoledronic acid) are first-line treatments that inhibit osteoclast activity and reduce bone resorption
  • Denosumab is a monoclonal antibody that inhibits RANKL, a key regulator of osteoclast differentiation and activation
  • Teriparatide is a recombinant human parathyroid hormone (PTH) analog that stimulates bone formation by increasing osteoblast activity
  • Selective estrogen receptor modulators (SERMs) like raloxifene mimic estrogen's beneficial effects on bone without stimulating breast or endometrial tissue
• Fall prevention measures reduce the risk of fractures in individuals with osteoporosis
  • Home safety assessment and modifications (removing tripping hazards, installing grab bars) create a safer living environment
  • Strength and balance training exercises (tai chi, yoga) improve stability and reduce the likelihood of falls
  • Assistive devices (canes, walkers) provide support and stability for individuals with impaired mobility
  • Medication review to minimize use of drugs that increase fall risk (sedatives, antidepressants, antihypertensives) and optimize bone health

Patient education for bone health

• Calcium and vitamin D intake are essential for maintaining strong bones
  • Dietary sources of calcium include dairy products (milk, yogurt, cheese), green leafy vegetables (kale, collard greens), and calcium-fortified foods (orange juice, tofu)
  • Calcium supplements can help meet daily requirements if dietary intake is insufficient
  • Vitamin D sources include sunlight exposure (15-30 minutes per day), fatty fish (salmon, tuna), fortified foods (milk, cereals), and supplements
• Weight-bearing and resistance exercises stimulate bone formation and improve overall health
  • Examples of weight-bearing exercises include walking, jogging, dancing, tennis, and pickleball
  • Resistance exercises using weights, resistance bands, or body weight help maintain muscle mass and strength
  • Aim for at least 30 minutes of exercise most days of the week, incorporating a variety of activities
• Medication adherence is crucial for achieving optimal treatment outcomes
  • Taking medications as prescribed ensures consistent benefits and reduces the risk of side effects
  • Strategies to improve adherence include using pill boxes or reminders, discussing concerns with healthcare providers, and combining medication with daily routines (taking with meals)
  • Regular follow-up with healthcare providers allows for monitoring treatment response, addressing side effects, and adjusting therapy as needed