Chapters 37, 38, 39 Musculoskeletal Disorders – Trauma, Degenerative, Infectious & Inflammatory (Comprehensive Exam Notes)

Musculoskeletal System – Structural & Functional Foundations

• Primary roles of bones
– Provide structural support and leverage for movement
– Guard vital organs & soft tissues
– Store minerals: Ca^{2+}, PO_4^{3-}, Mg^{2+}
– Hematopoiesis in red bone marrow

• Bone architecture
– Cortical (compact) bone: dense, solid outer shell
– Trabecular (cancellous) bone: porous inner meshwork → most vulnerable to osteoporosis (femur head/neck, vertebrae, distal radius)
– Each bone has individualized cortical-to-trabecular ratio

• Bone-building & –breaking cells
– Osteoblasts: secrete osteoid → initiate mineralization
– Osteocytes: mature osteoblasts, maintain nutrient/waste exchange, non-dividing
– Osteoclasts: acidify & dissolve matrix → resorption
– The coordinated osteoblast–osteoclast cluster is called the Basic Multicellular Unit (BMU)

• Modeling vs. Remodeling
– Modeling = growth/enlargement (osteoblast activity predominates)
– Remodeling = simultaneous formation & resorption after skeletal maturity
– Net balance dictates skeletal mass & fracture healing
– After age 30: osteoclastic resorption > osteoblastic formation → gradual bone loss

Bone Physiology – Calcium & Hormonal Control

• Adequate bone formation requires
– Serum calcium
– Parathyroid hormone (PTH) – raises serum Ca^{2+} via osteoclast stimulation
– Vitamin D (calcitriol) – kidney-activated; enables GI Ca^{2+} absorption
– Calcitonin (thyroid) – inhibits osteoclasts when Ca^{2+} high
– Sex steroids (estrogen, androgens) – promote bone preservation
– Weight-bearing stress strengthens bone; immobility accelerates loss

• Vitamin D pathway
– Skin (UV) → liver → kidney activation
– Deficiency ⇒ hypocalcemia ⇒ ↑ PTH ⇒ osteoclastic bone breakdown

Musculoskeletal Soft Tissues

• Skeletal Muscle
– Composed of myofibrils (sarcomere bundles) under somatic control
– Hypertrophies with overload; atrophies with disuse, ischemia, or denervation

• Connective tissue
– Tendons: muscle ↔ bone
– Ligaments: bone ↔ bone → form joints
– Both collagen-rich, prone to rupture/tear/degeneration → heal with scar tissue

Trauma-Related Disorders

Sprains & Strains

• Sprain = overstretched/torn ligament (most common: ankle)
– S/S: pain, swelling, bruising, painful ROM; may sublux joint
• Strain = overstretch/tear muscle or tendon (common: lumbar, hamstring)
– S/S: pain, limited ROM, muscle spasm

• R-I-C-E protocol
– Rest 24–48 h
– Ice 20 min qh × 48 h
– Compression (splint/ACE)
– Elevation > heart level
– NSAIDs/acetaminophen for analgesia

Fractures – Classification

• Open (compound): bone pierces skin → soft-tissue damage & infection risk; Tx = ORIF
• Closed (complete, non-displaced): fragments beneath skin; Tx = cast or ORIF
• Incomplete: cortical breach not through entire bone (greenstick in children)
• Compression: crushing of cancellous bone (vertebrae)
• Stress (fatigue): microfracture from repetitive load
• Transverse: straight horizontal line
• Comminuted: >1 fracture line; bone shattered
• Avulsion: tendon/ligament pulls off bone fragment

Management Principles

• Reduction – realign fragments
– Closed (external manipulation/external fixator)
– Open (ORIF with plates/screws/pins)
– Early stabilization of long bones ↓ fat embolism risk
• Immobilization – cast, traction, splint

Bone-Healing Phases

  1. Fracture & Inflammatory: hematoma forms within hours–days

  2. Granulation tissue: fibrovascular growth

  3. Callus (soft) formation: osteoblasts + chondroblasts create woven bone ext{≈ 6 weeks}

  4. Lamellar deposition: hard bone (lamellae) replaces callus

  5. Remodeling: BMU sculpts along stress lines; strength returns 3–6 mo

Complications of Trauma

• Neurovascular injury/bleeding
• Compartment syndrome: intracompartmental P > tissue perfusion P → ischemia
– Disproportionate pain, tense edema, pallor, paresthesia, pulselessness
– Diagnostic pressure >30 \text{ mm Hg}
• Infection (open Fx, surgery) → osteomyelitis
• DVT/PE (venous stasis)
• Fat embolism: marrow globules enter circulation → lung/brain ischemia
• Delayed union, malunion, non-union
• Post-traumatic arthritis
• Avascular necrosis (femoral head, humerus)

High-Yield Fracture Sites

• Hip (proximal femur)
– Usually from fall + osteoporosis; risk non-union & AVN
• Vertebral compression
– Osteoporotic trabecular collapse → height loss, kyphosis, radiculopathy
• Femoral shaft
– MVC; massive bleeding; non-weight-bearing
• Tib-fib
– Common sport/MVC; often open, both bones

Other Musculoskeletal Injuries

• Lumbar strain/sprain: L4–L5 weight load; r/o herniated disc (straight-leg raise)
• Rotator cuff tear/tendonitis: pain, weak shoulder; rest → surgery if needed
• Brachial plexus trauma: shock-like radiating pain; diminished pulses; neck/head injury association

Degenerative Disorders

Aging Effects

• Osteoclast activity > osteoblast
• \downarrow Vit D/Ca intake, GH, estrogen
• Sedentary lifestyle, \downarrow muscle mass
• Meds (chronic steroids) & comorbidities exacerbate loss

Osteoporosis / Osteopenia

• Porous bone ⇒ fragility Fx (hip, vertebrae, wrist)
• Patho: Imbalance → resorption > formation
• Primary (negative Ca balance, estrogen loss, inactivity, sunlight deficit)
• Secondary (hyperparathyroidism, celiac, IBD, corticosteroids)
• “Silent” until fracture; hip Fx ↑ mortality
• Risks: aging, post-menopause, small frame, smoking, caffeine excess, Ca/Vit D/protein deficits, mobility ↓, endocrine disorders

Osteoarthritis (OA)

• Progressive cartilage wear → bone exposure + osteophytes
• Weight-bearing joints (knee, hip, spine, hands)
• S/S: deep ache post-use, morning stiffness <30 min, crepitus, swelling, altered gait; Heberden’s nodes (DIP)

Rheumatoid Arthritis (RA)

• Chronic autoimmune (type III): synovitis → cartilage & bone destruction → permanent deformity
• Symmetrical tender swollen joints; morning stiffness; systemic fatigue/fever; classic swan-neck & Boutonnière; lung nodules

Rickets & Osteomalacia

• Rickets (children): failed osteoid calcification; vit D deficiency or hypophosphatemia
– Age 4–12 mo; widened growth plates, bowed femur, sternum protrusion
• Osteomalacia (adults): vit D deficiency (renal, malabsorption, low sunlight)
– Diffuse bone pain (lumbar, sternum, tibia), muscle weakness

Degenerative Disc Disease (DDD)

• Disc dehydration → collapse; herniation compresses nerves → radiculopathy
• Osteophytes narrow canal (spinal stenosis)
• S/S: back pain, limb weakness/numbness; risk ↑ with heavy lifting, obesity

Infectious & Inflammatory Conditions

Osteomyelitis

• Bone infection (commonly Staphylococcus\ aureus)
• Routes
– Hematogenous (vertebrae; rapid onset)
– Contiguous (post-op, trauma, diabetic foot)
– Chronic (>6–8 wks) → necrosis, sequestra
• Patho: abscess \rightarrow ischemia \rightarrow necrotic bone
• S/S: fever, chills, malaise + localized erythema, edema, pain, poor wound healing
• Tx: 6–8 wk IV antibiotics, debridement, possible prosthesis removal, hyperbaric O_2
• Complications: pathologic Fx, impaired mobility, amputation

Septic (Infectious) Arthritis

• Direct bacterial invasion of joint (often hematogenous or intra-op)
• Monoarticular red, swollen, painful joint with ↓ ROM, fever
• Dx: aspiration + culture; emergent IV antimicrobials to prevent cartilage loss

Gout (Gouty Arthritis)

• Recurrent hyperuricemia ⇒ monosodium urate crystal deposition
• Primary: renal excretion defect; Secondary: obesity, cancer, psoriasis, meds
• Podagra = 1st MTP; tophi after 15–29 yr
• Attacks: intense warmth, tenderness, severe pain ± fever

Psoriatic Arthritis (PsA)

• Autoimmune joint/CT inflammation linked to psoriasis (skin precedes joint in 85\%)
• Patterns: DIP predominant, arthritis mutilans, symmetric, asymmetric, spondylitis
• S/S: joint pain/swelling, fatigue, ocular pain, nail pitting/onycholysis, skin plaques

Vertebral Tuberculosis (Pott’s Disease)

• Mycobacterium\ tuberculosis infection of vertebrae → osteomyelitis + arthritis
• Thoracic vertebrae most affected; no pulmonary S/S
• Compression fractures, severe kyphosis, spinal nerve impingement pain

Lyme Disease

• Deer tick (\textit{B. burgdorferi})
• Early localized: erythema migrans “bull’s-eye” 7–30 d
• Early disseminated (3–12 wks): multiple EM, meningitis, carditis, ocular issues
• Late: large-joint arthritis (knee), neuropathy, encephalopathy months–years later

Ankylosing Spondylitis

• Systemic inflammatory disease ⇒ fusion of spine & sacroiliac joints
• Immune activation by bacteria → chronic inflammation → cartilage replaced by bone
• S/S begin in 20s: low-back stiffness, sacroiliac tenderness, kyphosis progression, ↓ spinal flexion; extra-articular eye/heart/lung/kidney involvement

Therapeutic & Practical Considerations

• Synovial joints poorly perfused → systemic drugs penetrate poorly; intra-articular injections often required
• Prosthetic material lowers resistance → provides bacterial binding substrate → meticulous asepsis & peri-op antibiotics essential
• Chronic corticosteroid therapy, low sunlight exposure, and immobility should prompt proactive bone-health counseling (diet + weight-bearing exercise)