2.5 Bone Health, Osteoporosis & Metabolic Bone Disease

Bone Health, Osteoporosis & Metabolic Bone Disease

Bone health is a high-yield Domain D topic because rehabilitation patients are disproportionately affected by metabolic bone disease. Immobility, neurologic injury, glucocorticoid therapy, and inflammatory arthritis all accelerate bone loss and elevate fragility fracture risk. The physiatrist must interpret bone densitometry, stratify fracture risk, prescribe or coordinate pharmacotherapy, and design loading exercise that stimulates bone without exceeding fragility thresholds.

DEXA Interpretation & Diagnostic Thresholds

Dual-energy X-ray absorptiometry (DEXA) reports bone mineral density (BMD) as a T-score (comparison to a healthy young adult reference) and Z-score (age-matched comparison). Diagnostic categories apply to postmenopausal women and men >= 50 years:

Z-scores <= -2.0 in younger patients suggest secondary osteoporosis and warrant workup for hyperparathyroidism, hypogonadism, celiac disease, or chronic glucocorticoid exposure.

FRAX Fracture Risk Stratification

The WHO FRAX tool integrates clinical risk factors (age, sex, BMI, prior fracture, parental hip fracture, smoking, glucocorticoids, rheumatoid arthritis, secondary osteoporosis, alcohol) with or without femoral-neck BMD to estimate the 10-year probability of a major osteoporotic fracture and of hip fracture. Pharmacologic treatment is generally recommended when the 10-year hip fracture probability reaches >= 3% or major-osteoporotic-fracture probability >= 20%. Glucocorticoid-induced osteoporosis uses adjusted FRAX thresholds.

Pharmacotherapy

• Bisphosphonates (alendronate, risedronate, zoledronic acid): inhibit osteoclast-mediated resorption; first-line for most patients. Dental clearance is prudent given osteonecrosis of the jaw risk, and drug holidays after 3-5 years reduce atypical femoral fracture risk.
• Denosumab: monoclonal antibody against RANKL; subcutaneous every 6 months; reversible on discontinuation ("rebound" vertebral fracture risk necessitates follow-on antiresorptive therapy).
• Anabolic agents (teriparatide, abaloparatide, romosozumab): stimulate bone formation; reserved for very high fracture risk or multiple fractures; followed by an antiresorptive to consolidate gains.
• Calcium (1000-1200 mg/day) and vitamin D (800-1000 IU/day): foundational supplementation; monitor 25-hydroxyvitamin D levels in deficient patients.

Rehabilitation Relevance

Immobility / SCI / Hemiplegia  ──►  ↑Bone Resorption  ──►  ↓BMD  ──►  Fragility Fracture Risk
      │                                                        │
      └── Weight-bearing & Site-Specific Loading Exercise ◄─── Reverses Trend

Weight-bearing and high-load, low-repetition activity (resistance training, impact loading where safe) osteogenically stimulates bone remodeling. In SCI, standing frames and electrical-stimulation cycling slow but do not fully prevent distal-femur/proximal-tibia demineralization. Fall-prevention programs (balance training, home hazard reduction, vision/medication review) are essential adjuncts because most osteoporotic fractures result from falls.

Secondary & Glucocorticoid-Induced Osteoporosis

Chronic glucocorticoid therapy (>= 5 mg prednisone for >= 3 months) rapidly impairs osteoblast function and increases resorption; the FRAX glucocorticoid correction factor should be applied. Other secondary causes—hyperthyroidism, hyperparathyroidism, hypogonadism, chronic kidney disease, and malabsorption—must be identified and treated.

Falls, Fragility Fractures & Rehabilitation After Vertebral Compression

Fragility fractures most commonly occur at the spine (vertebral compression fractures), hip, distal forearm (Colles), proximal humerus, and pelvis. Vertebral compression fractures present with acute mid-back pain, often after minimal trauma or activities of daily living, and may cause progressive kyphosis with loss of height, restrictive lung impairment, and reduced abdominal space (early satiety, reflux). Most are managed conservatively with a brief period of relative rest, analgesia, early mobilization in a TLSO as needed, and bone-specific pharmacotherapy; vertebroplasty/kyphoplasty are reserved for selected refractory cases.

Hip fragility fractures carry high one-year mortality and disability. Rehabilitation emphasizes early mobilization, weight-bearing per fixation (germ and intertrochanteric fractures fixed with arthroplasty or sliding hip screw often permit early protected weight-bearing), delirium and pressure-injury prevention, VTE prophylaxis, and discharge to inpatient rehab when impairment warrants. Post-fracture, every patient should trigger an osteoporosis workup and treatment to prevent the next fracture.

Pharmacologic Side Effects Relevant to Rehab

Bisphosphonates: esophageal irritation (take upright, with water, remain upright 30 min), rare osteonecrosis of the jaw and atypical subtrochanteric femoral fractures (prodromal thigh pain → image). Denosumab: must not be stopped without follow-on therapy due to rebound vertebral fracture risk. Teriparatide: transient orthostatic hypotension, hypercalcemia monitoring, limited to 2 years followed by antiresorptive. Candidates should recognize the prodrome of atypical femoral fracture (dull thigh pain) and the importance of drug holidays after 3-5 years of bisphosphonate therapy.

Integration With the Rehab Team

Bone health management is interdisciplinary: physiatrist (loading prescription, fall prevention, coordination), endocrinology/rheumatology/primary care (pharmacotherapy), dietitian (calcium/vitamin D, protein), therapy (balance, resistance, posture), and social work (home safety). The physiatrist's unique contribution is converting the osteoporosis diagnosis into a safe loading program that builds bone while preventing falls—the two levers that most reduce fracture events.