Section 4.3: Bone & Joint Disorders (Fractures, Osteoporosis, Fibromyalgia)

Bone & Joint Disorders

PANCE High-Yield Focus: Chronic bone and soft tissue conditions are major drivers of morbidity in primary care and orthopedics. Key exam themes include interpreting bone mineral density scores (T-scores) and matching them to appropriate treatment thresholds, reinforcing the highly specific administration rules for oral bisphosphonates, identifying key fracture deformities and their neurovascular risks (e.g., radial nerve injury with humeral/wrist fractures, sciatic nerve injury with hip dislocations), and recognizing Fibromyalgia as a diagnosis of exclusion that is managed with non-pharmacologic exercise and neuropathic therapies rather than opioids.

---

Osteoporosis Pathophysiology and Diagnostics

Pathophysiology

Osteoporosis is a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to bone fragility and susceptibility to fractures. It occurs when bone resorption by osteoclasts exceeds bone formation by osteoblasts.

• Postmenopausal Osteoporosis (Type I): Driven by estrogen deficiency. Estrogen normally inhibits osteoclasts and stimulates osteoblasts. Postmenopausal estrogen withdrawal leads to accelerated bone resorption, primarily affecting trabecular (spongy) bone.
• Senile Osteoporosis (Type II): Occurs in both men and women over age 70 due to an age-related decline in osteoblast function and decreased intestinal calcium absorption.
• Secondary Osteoporosis: Most commonly caused by chronic glucocorticoid therapy (>= 5 mg/day of prednisone for >= 3 months). Other causes include hyperthyroidism, hyperparathyroidism, celiac disease, and long-term use of proton pump inhibitors (PPIs) or anticonvulsants.

Diagnostic Criteria (DEXA Scan)

The Dual-Energy X-ray Absorptiometry (DEXA) Scan is the gold standard for measuring bone mineral density (BMD) at the lumbar spine and hip. Results are reported as a T-score (comparing the patient's BMD to a young adult peak bone mass) and a Z-score (comparing BMD to age-matched controls).

• Normal: T-score >= -1.0
• Osteopenia: T-score between -1.0 and -2.5
• Osteoporosis: T-score <= -2.5
• Severe Osteoporosis: T-score <= -2.5 PLUS a history of one or more fragility fractures (fractures from a fall from standing height or less).
• Screening Guidelines: The USPSTF recommends screening for all women aged 65 and older, and in postmenopausal women under 65 who have an increased risk of osteoporosis (determined by a FRAX 10-year risk assessment).

---

Osteoporosis Management and Safety Rules

Nutritional and Lifestyle Measures

All patients require adequate daily calcium (1,200 mg/day for women >50 and men >70) and Vitamin D3 (800-1,000 IU/day) to maintain serum levels > 30 ng/mL. Weight-bearing exercises (e.g., walking, jogging) are critical to stimulate bone remodeling.

Pharmacological Therapies

1. Bisphosphonates (First-line): Alendronate, Risedronate, Ibandronate (oral); Zoledronic acid (IV).
   • Mechanism: Pyrophosphate analogues that bind to bone mineral and are taken up by osteoclasts, inhibiting their activity and inducing apoptosis.
   • Critical Patient Education: Oral bisphosphonates must be taken first thing in the morning on an empty stomach with a full glass (8 oz) of plain water. The patient must remain completely upright (sitting or standing) for at least 30 minutes (60 minutes for ibandronate) and avoid eating or drinking anything else. This prevents severe pill-induced esophagitis and esophageal ulceration.
   • Adverse Effects: Esophagitis, atypical femur fractures (long-term use), and osteonecrosis of the jaw (ONJ) (rare, often linked to invasive dental procedures).
   • Contraindications: Creatinine clearance < 30-35 mL/min, esophageal disorders (stricture, achalasia).
2. Denosumab: A subcutaneous monoclonal antibody that targets and inhibits RANKL, preventing osteoclast activation.
   • Clinical Pearl: Safe for patients with renal impairment. Do NOT discontinue denosumab without transitioning to another therapy, as it can cause a rapid rebound in bone resorption and vertebral fractures.
3. Teriparatide: A recombinant human parathyroid hormone (PTH) that stimulates osteoblast activity (anabolic).
   • Safety Rule: Carries a warning for osteosarcoma. Use is limited to a maximum of 2 years over a patient's lifetime.

---

Major Fractures

Hip Fracture vs. Posterior Hip Dislocation

• Hip Fracture: Common in elderly osteoporotic patients after a fall. The affected leg is shortened, abducted, and externally rotated. The main risk is avascular necrosis (AVN) of the femoral head due to disruption of the medial femoral circumflex artery.
• Posterior Hip Dislocation: Caused by high-energy trauma (e.g., knee striking the dashboard). The affected leg is shortened, adducted, and internally rotated. It is an orthopedic emergency requiring reduction within 6 hours to prevent AVN and sciatic nerve injury.

Colles' vs. Smith's Fracture

• Colles' Fracture: Distal radius fracture with dorsal (posterior) displacement of the distal fragment, producing the classic 'dinner fork' deformity from a FOOSH with wrist extension.
• Smith's Fracture: Distal radius fracture with volar (anterior) displacement of the distal fragment, producing the 'garden spade' deformity from a FOOSH with wrist flexion.

Boxer's Fracture

A fracture of the neck of the fifth metacarpal, typically from punching a hard object. It is critical to assess for rotational deformity (checking if all fingers point toward the scaphoid when flexed; overlap indicates deformity). Treat with closed reduction if angulated >40 degrees, followed by an ulnar gutter splint.

---

Fibromyalgia

Fibromyalgia is a chronic disorder characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and cognitive dysfunction ('fibro fog').

• Pathophysiology: Driven by central sensitization, an amplification of pain processing within the central nervous system, leading to hyperalgesia (increased pain response) and allodynia (pain from non-painful stimuli).
• Clinical Presentation: Widespread, aching pain present for >= 3 months, affecting both sides of the body and occurring both above and below the waist. Physical exam reveals tenderness at specific anatomical sites (tender points) without any signs of joint inflammation.
• Diagnostics: A diagnosis of exclusion. Laboratory markers (ESR, CRP, RF, CBC, thyroid tests) are normal.
• Management:
  • Non-Pharmacologic (Most Effective): Patient education, cognitive behavioral therapy (CBT), and low-impact aerobic exercise (e.g., swimming, cycling, walking).
  • Pharmacologic: Tricyclic Antidepressants (TCAs; e.g., Amitriptyline first-line for pain and sleep), SNRIs (e.g., Duloxetine or Milnacipran), or gabapentinoids (e.g., Pregabalin).
  • Clinical Trap: Avoid opioids and oral corticosteroids; they are ineffective and can worsen central sensitization.

---

Orthopedic Deformity and Injury Summary

Paget Disease of Bone (Osteitis Deformans)

Paget disease is a chronic disorder of disordered bone remodeling, characterized by excessive bone resorption followed by disorganized, weak bone formation.

• Phases: (1) Lytic phase (osteoclastic overactivity); (2) Mixed phase; (3) Sclerotic phase (dense but structurally weak bone).
• Clinical Presentation: Often asymptomatic and found incidentally. Symptomatic patients present with bone pain, joint pain, hearing loss (if skull involved), and bowing of long bones (especially the tibia). Hat size may increase (skull involvement).
• Labs: Markedly elevated serum alkaline phosphatase with normal calcium and phosphate.
• Imaging: X-rays show enlarged, thickened bones with a "cotton wool" appearance of the skull and cortical thickening.
• Complications: Pathologic fractures, hearing loss, spinal cord compression, and osteosarcoma (1% risk — watch for rapidly increasing pain).
• Management: Bisphosphonates (zoledronic acid is first-line) for symptomatic disease or elevated alkaline phosphatase. Calcitonin as an alternative. Pain control with NSAIDs/acetaminophen.