D236 Notes on Homeostasis & Cellular Responses

D236 Notes on Homeostasis & Cellular Responses

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Western Governors University 

D236 Pathophysiology

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SECTION 2: Musculoskeletal Disorders and Related Conditions

What is Degenerative Disc Disease (DDD)?

Degenerative Disc Disease (DDD) refers to a progressive condition in which the intervertebral discs of the spine undergo structural and biochemical deterioration. These discs normally act as shock absorbers, allowing flexibility and distributing mechanical forces during movement. Over time, aging, repetitive mechanical stress, and reduced nutritional diffusion cause disc dehydration, loss of elasticity, and disc height reduction. As disc integrity declines, the vertebrae may approximate abnormally, leading to spinal instability and altered biomechanics.

This degeneration can result in vertebral misalignment and narrowing of intervertebral foramina, increasing the likelihood of spinal nerve root compression. Consequently, individuals may experience radiculopathy, characterized by radiating pain, sensory disturbances, or motor weakness along the affected nerve distribution. When DDD involves the lumbar or sacral spine, compression of the sciatic nerve may occur, producing sciatica with pain radiating into one or both lower extremities (Huether & McCance, 2020). Early recognition is essential to prevent chronic pain and functional impairment.

What is Paget’s Disease of Bone?

Paget’s Disease of Bone is a chronic skeletal disorder marked by disorganized and excessive bone remodeling. In this condition, osteoclastic bone resorption is followed by rapid and uncoordinated osteoblastic bone formation. The resulting bone is enlarged, structurally weak, and prone to deformity and fracture.

Many individuals remain asymptomatic, and the disease is often discovered incidentally through imaging or elevated serum alkaline phosphatase levels. During active phases, excessive bone turnover may release increased calcium into circulation, occasionally leading to hypercalcemia. Clinical manifestations may include localized bone pain, skeletal deformities, pathological fractures, and neurological complications resulting from compression of adjacent nerves or spinal cord structures (Porter et al., 2021). Long-term complications include osteoarthritis and, rarely, osteosarcoma.

How do Stress Fractures Develop and Where Are They Commonly Located?

Stress fractures arise when cumulative microtrauma from repetitive loading exceeds the bone’s capacity for repair. Unlike acute fractures, stress fractures develop gradually and are commonly seen in athletes, dancers, and military personnel undergoing intense physical training. Patients typically report localized pain that worsens with activity and improves with rest.

Causes	Risk Factors	Common Sites
Repetitive high-impact activities	Vitamin D deficiency, overtraining, inadequate nutrition	Tibia, metatarsals, femur

Early diagnosis through imaging, such as MRI or bone scans, is crucial to prevent progression to complete fractures.

What Are Rickets and Osteomalacia?

Rickets is a pediatric disorder caused by defective mineralization of growing bone, leading to soft, weakened skeletal structures. The most common cause is vitamin D deficiency; however, malabsorption disorders, chronic liver or kidney disease, and limited sun exposure may also contribute. Clinical features include bone pain, delayed growth, craniotabes, bowing of the legs, widened wrists, and a protuberant abdomen.

Osteomalacia represents the adult counterpart of rickets and involves impaired mineralization of mature bone. Patients often present with diffuse bone pain, muscle weakness, gait disturbances, and an increased susceptibility to fractures from minimal trauma. Both conditions highlight the essential role of vitamin D and calcium in skeletal health (McCance & Huether, 2020).

What is Compartment Syndrome and How is it Diagnosed?

Compartment Syndrome occurs when increased pressure within a closed muscle compartment compromises tissue perfusion, leading to ischemia and potential muscle and nerve necrosis. It is considered an orthopedic emergency.

Clinical Signs (6 P’s):

• Pain disproportionate to injury

• Paresthesia

• Pallor

• Pulselessness

• Poikilothermia

• Paralysis (late finding)

Causes	Complications	Diagnostic Criteria
Fractures, crush injuries, burns, tight casts	Tissue necrosis, rhabdomyolysis, nerve injury	Compartment pressure >30 mmHg, CT, MRI, CBC

Immediate intervention, including fasciotomy or removal of constrictive devices, is critical to prevent permanent damage or limb loss.

What is Rhabdomyolysis and Its Classic Presentation?

Rhabdomyolysis is a serious condition characterized by the breakdown of skeletal muscle fibers, resulting in the release of intracellular contents such as myoglobin, creatine kinase, and electrolytes into the bloodstream. Excess myoglobin can precipitate in renal tubules, leading to acute kidney injury.

Classic Triad of Symptoms:

• Muscle pain

• Muscle weakness

• Dark, tea-colored urine

Aggressive intravenous fluid resuscitation and electrolyte management are essential to preserve renal function.

What is a Sequestrum?

A sequestrum is a fragment of necrotic bone that becomes separated from viable bone tissue, typically following trauma or chronic infection. Because it lacks blood supply, it serves as a nidus for persistent infection. Surgical debridement is often required to promote healing and prevent chronic osteomyelitis (Smeltzer et al., 2020).

What are Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE), and How Are They Diagnosed?

Orthopedic trauma, surgery, and prolonged immobilization increase the risk of venous thromboembolism due to venous stasis and endothelial injury.

Condition	Key Features	Diagnostic Tests
DVT	Limb swelling, warmth, tenderness	D-dimer, Doppler ultrasound
PE	Dyspnea, chest pain, hemoptysis	CT pulmonary angiography, V/Q scan

Preventive strategies include early ambulation, compression therapy, and anticoagulation.

What is Fat Embolism Syndrome (FES), and How is It Diagnosed?

Fat Embolism Syndrome occurs when fat globules from bone marrow enter the circulation following long-bone fractures, obstructing pulmonary or cerebral vessels.

Diagnostic Requirement	Major Criteria	Minor Criteria
1 major + ≥4 minor + fat macroglobulinemia	Respiratory distress, cerebral signs, petechiae	Tachycardia, fever, anemia, thrombocytopenia

Supportive care with fluid resuscitation and oxygen therapy is essential.

What is Avascular Necrosis (AVN)?

Avascular Necrosis results from compromised blood supply to bone tissue, leading to osteocyte death and eventual structural collapse. Commonly affected sites include the femoral head, scaphoid, and talus. Patients experience progressive joint pain, stiffness, and reduced mobility. MRI is the diagnostic modality of choice, and treatment ranges from conservative management to surgical intervention.

How Are Delayed Healing Fractures Classified?

Term	Definition	Clinical Implications
Delayed Union	Slower-than-expected healing	Persistent pain
Malunion	Healing in poor alignment	Functional impairment
Nonunion	Failure of fracture healing	Surgical correction required

What Are the Consequences of Prolonged Immobility?

Prolonged immobility adversely affects multiple organ systems:

System	Complications
Skin	Pressure ulcers
Musculoskeletal	Muscle atrophy, osteoporosis
Cardiovascular	Venous thrombosis
Respiratory	Pneumonia, atelectasis
Psychological	Depression, isolation

References

Huether, S. E., & McCance, K. L. (2020). Understanding pathophysiology (7th ed.). Elsevier.

Porter, R. S., Kaplan, J. L., & Homeier, B. P. (2021). The Merck manual of diagnosis and therapy (20th ed.). Merck Research Laboratories.

D236 Notes on Homeostasis & Cellular Responses

Smeltzer, S. C., Bare, B. G., Hinkle, J. L., & Cheever, K. H. (2020). Brunner & Suddarth’s textbook of medical-surgical nursing (15th ed.). Wolters Kluwer.

Grossman, S., & Porth, C. M. (2021). Porth’s pathophysiology: Concepts of altered health states (10th ed.). Wolters Kluwer.