Bones and Joints

Question 1

What are the functions of bone cells?

Answer 1

Osteoblasts form new bone, whereas osteoclasts remove and remodel old bone under the influence of hormones.

Question 2

Define epiphysis, metaphysis, and diaphysis and explain why a knowledge of these anatomic terms is important for pathology.

Answer 2

epiphysis = above the growth plate

diaphysis = the central part of long bones

metaphysis = the growth plate and adjacent terminal diaphysis which represent the most metabolically active segment of the long bones

Question 3

Compare endochondral and intramembranous ossification.

Answer 3

endochondral ossification
osseous transformation of the cartilage in the growth plate

• ceases by the end of puberty (but can still occur during healing of bone fractures)

intramembranous ossification

bone formation that results from direct transformatio of fibrous matrix into osteoid, followed by mineralization

• accounts for subperiosteal bone formation of long bones
• continues through the normal life span

Question 4

What are the main functions of bones?

Answer 4

1. Mechanical support for the muscles, which makes possible the movement of limbs
2. Protection of internal organs, such as the ribs forming the thorax or the skull protecting the brain
3. Support of hematopoiesis, which occurs in the _bone marrow _
4. Storage of calcium and phosphate salts

Question 5

What is the basic structure and function of joints?

Answer 5

A joint is a junction between two or more bones, designed to provide support and structureal firmness and to allow movement.

**1) moveable diarthrodial or synovial joints: **knee, etc

2) limited mvmt synarthoses: head, trunk

Question 6

What is achondroplasia?

Answer 6

Autosomal Dominant mutation in gene encoding fibroblast growth factor receptor 3.

Adversly affects endochondral ossification and growth of long bones = dwarfism.

Question 7

What is osteogenesis imperfect?

Answer 7

Various mutations involving the encoding of collagen I.

Range of ages affected from in utero to later in life. Symptoms are not limited to the bones, and may have thin skin, thin dental enamel, defective heart valves, bluish hue to sclera.

Question 8

What are the main causes of osteomyelitis?

Answer 8

Most common: staph aureus

Drug addicts: mixed flora hematogenous infections

Sickle cell: salmonella

Pott’s disease: mycobacterium, chronic osteomyelitis of the spine

Question 9

Describe the principal pathologic feature of osteomyelitis.

Answer 9

The bacteria reach the metaphysis through the nutrient artery. Bacterial growth results in bone destruction and formation of an abscess.

From the abscess cavity, the pus spreads between the trabeculae into the medulla, through the cartilage into the joint, or through the haversian canals of the compact bones to the outside.

These sinuses traversing the bone persist for a long time and heal slowly. The pus destroys the bone and sequesters parts of it in the abscess cavity. Reactive new bone is formed around the focus of inflammation.

Question 10

What are the possible causes of aseptic bone necrosis?

Answer 10

Sudden onset of ischemia caused by disruption or complete interruption of blood flow.

May be related to trauma, emboli, radiation, or drugs.

A disease of growing children, but also elderly

Question 11

Describe the typical clinical features of aseptic bone necrosis.

Answer 11

Carpal bones are especially vulnerable because of their complex blood supply.

In elderly: most important site is head of the femur

Question 12

What are the causes of osteoporosis?

Answer 12

**Primary: **disease of elderly

**Secondary: **can occur at any age

• hormone disturbance
• dietary insufficiency or malabsorption
• immobilization
• drugs
• tumors

Question 13

Discuss the pathogenesis of osteoporosis.

Answer 13

*Bone resorption outpaces bone formation resulting in net bone loss. *

Question 14

What are the complications of osteoporosis?

Answer 14

• Type 1: trabecular bone loss predominates, mostly in the vertebrae and distal radius

Major complications = crush fractures of vertebral bodies and distal end of radius

• Type 2: proportional loss of cortical and trabecular, head of femur, wedge fractures of vertebrae

Question 15

What is osteomalacia?

Answer 15

Inadequate mineralization of the organic bone matrix, caused by disturances of either vitamin D or phosphate metabolism.

Osteomalacia of growing bones = rickets

Question 16

Explain the role of vitamin D in calcium homeostasis.

Answer 16

Activation of vitamin D occurs in the liver and kidneys. Several active metabolites are fromed, of which the hydroxylated 1,25 vitamin D is the most important.

This vitamin D does three things:

1) stimulation of intestinal absorption of calcium and phosphorus
2) deposition of calcium into the osteoid and movilization of calcium from calcified bone; mineralization of osteoid
3) stimulation of teh PTH dependent resorption of calcium in the kidney

Question 17

Compare rickets and osteomalacia.

Answer 17

Rickets

• growing bones
• endochonral ossification severely disturbed
• growth retardation, softening of growing bones (bowlegs), deformities
• *Osteomalacia**
• excess of osteoid around the calcified core of the trabeculae of spongy bone and ont he endocavitary side of compact bones
• often asymptomatic
• muscle weakness

Question 18

How is osteomalacia diagnosed?

Answer 18

Based on

• clinical symptoms
• radiographic evidence of osteopenia
• laboratory: low vit D, calcium and phosphate; elevated PTH
  *but in phosphate deficiency, the serum phosphate is low while calcium and PTH are normal

Question 19

What are the main pathologic features of renal osteodystrophy?

Answer 19

Kidneys cannot excrete phosphorus

= elevated serum phosphate

- hypocalcemia

- hyperPTH

*PTH stimulates bone resorption and release of Ca and phosphate. *

Question 20

Describe the three phases of Paget’s disease.

Answer 20

1: destructive phase, bone resorption

2: mixed phase, bone resorption counterbalanced by new bone formation

3: osteosclerotic phase, normal compact bone is replaced by wide sclerotic dense bone

Question 21

Describe various forms of fracture of long bones.

Answer 21

simple = single fracture line

comminuted = multiple lines and fragments

closed = overlying skin intact

complete = through entire thickenss of bone

incomplete = do not extend from one side to another

complicated = infected

Question 22

Describe the healing of fractures.

Answer 22

Healing first requires immobilization; prevents disruption of scaffolds that can cause additional bleeding into the fracture site.

Large fractures you must remove necrotic tissue.

Compression of two sides of the fracture promotes healing.

Also depends on vitamin C, D, calcium and phosphorus.

• *1. Hematoma
  2. Granulation tissue
  3. Bony callus
  4. Remodeling**

Question 23

What happens during joint dislocation?

Answer 23

Occurs as a result of force or abnormal movement; the bones forming the joint lose contact and become misaligned.

Question 24

Classify bone tumors.

Answer 24

Bone forming cells: osteoma and osteosarcoma

Cartilate cells: ** chondroma and chondrosarcoma**

Osteoclasts: giant cell tumor
Primitive Mesenchymal bone marrow cells: ** Ewing’s sarcoma**

Secondary tumors: outnumber primary 10:1, most common sites are breast, lung, prostate, kidney, thyroid

Question 25

Describe the main pathologic and clinical features of osteosarcoma.

Answer 25

• Most common primary malignant tumor involving bone.*
• most often metaphysis of long bones
• 50% in knee joint
• also jawbone
• young people
• metastases, esp lung

Question 26

Describe the main pathologic and clinical features of chrondrosarcoma.

Answer 26

• Composed of neoplastic cartilage cells.*
• originate in axial skeleton
• and adjacent long bones
• affect adults, peak 35-60
• treatment = surgery, not responseive to chemo

Question 27

Describe the main pathologic and clinical features of Ewing’s sarcoma.

Answer 27

• Small cells with hyperchromatic bluish nuclei and very little cytoplasm, and abundant glycogen.*
• located mostly in diaphysis
• 85% have translocation btw 11 and 22, fusion protein FLI and EWS
• cortical bone invasion
• suburst or onion skin appearance on x-ray
• occurs mostly in the young
• metastasize

Question 28

What are the main pathologic and clinical features of giant cell bone tumor?

Answer 28

Originate in the epiphyses of long bones

Question 29

What is osteoarthritis?

Answer 29

• Most common joint disease
• Possibly a metabolic disorder, or inflammation
• Usually due to stress

Question 30

Compare the facts favoring the wear and tear hypothesis of osteoarthritis with those favoring a metabolic or inflammatory origin for this disease.

Answer 30

Wear and Tear

• develops in weight bearing joints
• prevalence increases with age
• mechanical stress accelerates the disease
• familial component of abnormal CT

Inflammatory

• prominent inflammation
• finger joints can be affected and are not weight bearing joints
• responsive to anti-inflammatory meds

Question 31

Describe the pathology of osteoarthritis.

Answer 31

Fragmentation and loss of cartilage denuge the subchondral bone, which undergoes sclerosis (eburnation) and cystic change. Osteophytes form on the lateral sides and protrude into the adjacent soft tissues, causing irritation, inflammation, and fibrosis.

Question 32

What are the main clinical signs and symptoms of osteoarthritis?

Answer 32

most common symptom = pain

• stiffenss
• reduced mobility
• crepitus (rough articular surfaces
• muscle spasm and contractures

Question 33

What is rheumatoid arthritis?

Answer 33

A disease characterized by systemic inflammation of the joints. An autoimmune disease that primarly involves the synovial joints.

Question 34

What are the roles of hormones, genes, and autoimmunity in the pathogenesis of rheumatoid arthritis?

Answer 34

Hormones: affects w > m

Familial predisposition: HLA loci on chromosome 6

Autoimmunity: increased incidence of autoimmune diseases

Question 35

What is pannus, and how does it evolve?

Answer 35

Pannus is caused by exuberant synovial fronds that transform into granulation tissue. The pannus cover ths articular surfaces like a sheet. It is rich in inflammatory cells that secrete lytic enzymes and various mediators of inflammation.

Question 36

Describe the pathology of rheumatoid arthritis.

Answer 36

Inflammation leads to pannus formation, obliteration of the articular space, and finally ankylosis (collagenous scar). The periatricular bone show disuse atrophy in the form of osteoporosis.

Question 37

Whare are the clinical features of rheumatoid arthritis?

Answer 37

Nonspecific: low-grade fever, fatigue, loss of appetite, anemia

Symmetric polyarthritis

Lymphadenopathy

Rheumatoid subcutanous nodules

Splenomegaly

Ulnar deviation

Hallux valgus

Rheumatoid factor

Raynaud’s phenomenon

Question 38

What are the main causes of infectious arthritis?

Answer 38

Most common = Lyme

pyogenic = staph or strep (rare)

tuberculous

gonococcal

Question 39

What is gout?

Answer 39

Group of diseases characterized by hyperuricemia and the deposition of uric acid crystals in the joints, subcutaneous tissues, and kidneys.

Hyperuricemia (>7mg/dL) is a prerequisite, but only 5% of these patients develop gout.

Question 40

How common is gout in men and women?

Answer 40

95% are male, many have family history

Question 41

Compare primary and secondary gout.

Answer 41

Primary gout: metabolic or renal

Secondary gout: hematopoietic malignant disease, chronic hemolysis, obestiy, alcoholism, kidney disease, drugs (diuretics), lead poisoning

Question 42

How does hyperuricemia lead to podagra.

Answer 42

Most uric acid crystals form deposit as insoluble monosodium urate . . . esp in the joints and periarticular connective tissue.

Tarsometatarsal joint of the big toe in 90%: podagra “foot seizure”

Likely because the feet are colder and reduces uric acid solubility >> crystalization inside joint. Activates complement and recruits leukocytes. Because the crystals are sharp, they pierce the lysosomes and release acid hydrolases.

Question 43

Compare the clinical features of acute and chronic gout.

Answer 43

Acute = joint is swollen, hyperemic, warm, excruciating pain

Chronic = less inflammation, but more bone deformities

Question 44

What are tophi?

Answer 44

Painless subcutaneous deposits of uric acid.

*Most commonly on the ears, extensor sites of the arms, over the olcranon, and patella. *

Encapsulated, birefringent urate crystals, surrounded by macrophages, lymphocytes, and giant cells.

Question 45

What kind of urinary stones are found in persons who have gout?

Answer 45

Uric acid stones

Also predisposes to the formation of calcium stones.