Musculoskeletal and Soft Tissue Disorders

Chapter 23 Musculoskeletal and Soft Tissue Disorders



I. Bone Disorders

A. Osteogenesis imperfecta (“brittle bone” disease)

1. Autosomal dominant (AD)

2. Defective synthesis of type I collagen


Osteogenesis imperfecta: AD; defect in synthesis type 1 collagen



3. Clinical findings

a. Pathologic fractures at birth

b. Blue sclera (Fig. 23-1)

image

23-1 Osteogenesis imperfecta. Note the faint blue tint of the sclera representing the reflection of the underlying choroidal veins.


(From Mir MA: Atlas of Clinical Diagnosis. London, Saunders, 1995.)



Blue sclera: reflection of underlying choroidal veins


c. Deafness in some patients

4. Treatment

• Bisphosphonates to increase bone mineralization

B. Achondroplasia

1. Autosomal dominant

2. Pathogenesis


Achondroplasia: AD; mutation in fibroblast growth factor receptor gene


a. Mutation in fibroblast growth factor receptor gene

• Gene mutations increase with paternal age

b. Impaired proliferation of cartilage at the growth plate

3. Clinical findings

a. Normal-sized head and vertebral column

b. Shortened arms and legs


Achondroplasia: normal head/axial skeleton; short arms/legs


c. Normal growth hormone and insulin growth factor-1 levels

4. No treatment

C. Osteopetrosis (“marble bone” disease)

1. Autosomal recessive (severe)

• Autosomal dominant (less severe)

2. Pathogenesis

a. Deficiency osteoclasts

b. Normal balance of osteoblasts making bone and osteoclasts breaking down bone is disrupted favoring increased bone formation.


Osteopetrosis: deficiency of osteoclasts; “too much bone”


c. Overgrowth and sclerosis of cortical bone (“too much bone”)

3. Clinical findings

a. Pathologic fractures


Osteopetrosis: pathologic fractures; visual/hearing loss


b. Anemia

• Replacement of marrow cavity

c. Cranial nerve compression

• Visual and hearing loss

4. No treatment

D. Osteomyelitis

1. Osteomyelitis in children and adults


Osteomyelitis: usually hematogenous spread to bone; metaphysis most common site


a. Most commonly due to sepsis with subsequent spread to bone

b. Metaphysis is the most common site.

• Favors the tibia and fibula in children

c. Most often due to Staphylococcus aureus (90% of cases)


Staphylococcus aureus: most common pathogen causing osteomyelitis


• Other pathogens: Streptococcus pyogenes, Haemophilus influenzae

2. Osteomyelitis in sickle cell disease (refer to Chapter 11)

• Most often due to Salmonella paratyphi


Salmonella paratyphi: osteomyelitis in sickle cell disease


3. Tuberculous osteomyelitis

a. Hematogenous spread from a primary lung focus


Tuberculous osteomyelitis: commonly involves vertebral column (Pott’s disease)


b. Targets vertebral column (Pott’s disease)

4. Pseudomonas aeruginosa osteomyelitis


P. aeruginosa osteomyelitis: puncture of foot through rubber footwear


• Most often due to puncture of foot through rubber footwear

5. Neutrophils enzymatically destroy bone (Fig. 23-2).

a. Devitalized bone is called sequestra.

image

23-2 Chronic osteomyelitis. The solid arrow points to necrotic bone in the center of a draining abscess (sequestrum). The interrupted arrow is a rim of new bone formation (involucrum).


(From Kumar V, Abbas AK, Fausto N, Mitchell RN: Robbins Basic Pathology, 8th ed. Philadelphia, Saunders Elsevier, 2007, p 810, Fig. 21-7.)



Sequestra: devitalized bone


b. Chronic disease produces reactive bone formation in periosteum.

• Called involucrum


Involucrum: reactive bone formation in periosteum


c. Draining sinus tracts to the skin surface often occur.

• Danger of squamous cell carcinoma developing at orifice of sinus tract

6. Clinical findings

• Fever, bone pain

7. Diagnosis

a. Bone biopsy for culture

Draining sinuses: danger of squamous cancer


b. Imaging studies: CT scan or MRI

8. Treatment

a. Surgical débridement

b. Staphylococcus aureus: vancomycin + ceftazidime

c. Salmonella paratyphi (sickle cell): ciprofloxacin

E. Osteoporosis

1. Epidemiology


Osteoporosis: most common metabolic abnormality of bone


a. Most common metabolic abnormality of bone

b. Loss of both organic bone matrix and minerals

(1) Decreased bone mass and density

• Radiograph shows osteopenia (washed out appearance).


Osteoporosis: loss of mineralized bone + organic bone matrix (osteoid)


(2) Decreased thickness of cortical and trabecular bone

c. More common in women than men

• Men have greater bone mass to begin with; takes longer to develop osteoporosis


Osteoporosis: more common in women than men


d. Osteoporosis-related fractures: 50% in women > 65 years old

e. Osteoporosis-related fractures: 20% in men > 65 years old

f. Classification

(1) Primary

(a) Most common type (80% women, 60% men)

(b) Idiopathic type in children and young adults

(c) Postmenopausal type (most common)

(d) Senile type in men and women


Secondary causes: ↑ cortisol, heparin, hypogonadism, malnutrition, space travel


(2) Secondary

(a) Underlying disease (e.g., hypercortisolism)

(b) Drugs (e.g., heparin)

(c) Hypogonadism (e.g., hypopituitarism)

(d) Malnutrition (e.g., anorexia nervosa)

(e) Space travel

• Lack of gravity reduces bone stress.

2. Postmenopausal osteoporosis

a. Due to estrogen deficiency


Estrogen: inhibits production of osteoclasts; enhances osteoblasts


(1) Increased resorption of bone by osteoclasts

(2) Decreased formation of bone by osteoblasts

b. Clinical findings

(1) Compression fractures of vertebral bodies (Fig. 23-3)

• Most common fracture

image

23-3 Osteoporosis of vertebral column. The vertebral body on the right shows decreased bone mass caused by compression fractures when compared with a normal vertebral body on the left.


(From Kumar V, Fausto N, Abbas A: Robbins and Cotran’s Pathologic Basis of Disease, 7th ed. Philadelphia, WB Saunders, 2004, p 1284, Fig. 26-12.)



Postmenopausal osteoporosis: compression vertebral fractures most common


(2) Colles’ fracture of distal radius


¯ Estrogen: ↑ osteoclastic activity, ¯ osteoblastic activity


(3) Dowager’s hump (Fig. 23-4)

c. Dual-photon absorptiometry

• Noninvasive test that evaluates bone density

image

23-4 Elderly woman with osteoporosis showing the classic Dowager’s hump.


(From Seidel HM, Ball JW, Danis JE, Benedict GW: Mosby’s Guide to Physical Examination, 6th ed. St. Louis, Mosby Elsevier, 2006, p 756, Fig. 21-78.)



Diagnosis osteoporosis: dual photon absorptiometry


d. Prevention

(1) Role of estrogen replacement is being reevaluated.

(2) Calcium and vitamin D supplements

(3) Stop smoking (inhibits osteoblast activity)


Prevention: weight-bearing exercises; calcium, vitamin D; stop smoking


(4) Weight-bearing exercise

(a) Weight lifting; vigorous walking

(b) Excludes swimming, which decreases bone stress

e. Treatment


Rx for osteoporosis: bisphosphonates first-line drug


(1) Bisphosphonates inhibit bone resorption.

• First-line treatment

(2) Calcitonin inhibits osteoclasts.

3. Senile osteoporosis

• Decreased ability of osteoblasts to divide and produce osteoid

F. Aseptic (avascular) necrosis of bone

1. Disruption of microcirculation causes bone infarctions.

a. The term “avascular” is sometimes used because the problem involves the blood supply to the bone.


Aseptic necrosis: disruption of microcirculation causes bone infarctions


b. Causes

(1) Corticosteroids (35%)

(2) Alcohol (22%)

(3) Other causes (43%)

(a) Idiopathic

(b) Fractures

c. Sites of aseptic necrosis


Aseptic necrosis: femoral head most common site


(1) Femoral head and condyle

(2) Humeral head

(3) Scaphoid (navicular) and lunate bones in wrist


Aseptic necrosis: corticosteroids most common cause


(4) Talus bone

• Located between the calcaneus and the tibia and fibula

d. Femoral head aseptic necrosis

(1) Fracture in elderly persons

(a) Pertrochanteric fracture (Fig. 23-5A) is extracapsular and does not compromise blood supply to the femoral head; hence, no aseptic necrosis.

image

23-5 Schematic showing a pertrochanteric fracture (A) and a subcapital fracture (B). See text for discussion.


(From Moore NA, Roy WA: Rapid Review Gross and Developmental Anatomy, 2nd ed. St. Louis, Mosby Elsevier, 2007, p 147, Fig. 5-4.)



Aseptic necrosis: subcapsular fracture disrupts blood supply


(b) Subcapsular fracture (Fig. 23-5B) disrupts blood supply (retinacular arteries from medial circumflex femoral artery); hence, aseptic necrosis occurs.

(2) Sickle cell disease (due to vasoocclusive disease; refer to Chapter 11)

(3) Long-term use of corticosteroids

e. Scaphoid bone

(1) Located on the thumb side of the wrist


Scaphoid bone: most common wrist bone fractured; susceptible to aseptic necrosis


(2) Most common bone in the wrist that is fractured

(3) Normally has a poor blood supply

f. Digits

• Dactylitis in sickle cell anemia (refer to Chapter 11)

2. Clinical findings

a. Asymptomatic

b. Localized pain exacerbated by movement


Aseptic necrosis: localized pain


c. Functional limitation of activity

3. Bone shows increased density on radiographs (Fig. 23-6).

a. Magnetic resonance imaging

(1) Early finding—margin of low signal and inner border of high signal produce a “double line sign.”
image

23-6 Radiograph showing avascular necrosis of the femoral head. The interrupted circle highlights an area of increased bone density within which is a fracture site (arrow).


(From Rosai J, Ackerman LV: Surgical Pathology, 9th ed. St. Louis, Mosby, 2004, p 2144, Fig. 24-8A.)



Aseptic necrosis: MRI most sensitive early test for aseptic necrosis


(2) Most sensitive test (75–100%) for early detection of aseptic necrosis

b. CT scan

• Shows central necrosis and area of collapse before regular x-ray

c. Bone scan

(1) Early—shows no uptake (cold area; sensitivity 70%)

(2) Later—increased uptake (result of bone remodeling)

d. X-ray study

(1) Most insensitive test in early phases

(2) Early—may show osteopenia (radiolucency)

(3) Later—flattening, collapsed bone

e. Treatment

• Core decompression; bone graft; joint replacement

4. Osteochondrosis


Osteochondrosis: aseptic necrosis of ossification centers


a. Aseptic necrosis of ossification centers in children

b. Legg-Calvé-Perthes disease


Legg-Calvé-Perthes disease: aseptic necrosis of femoral head ossification center


(1) Aseptic necrosis involving the femoral head ossification center

(2) Occurs most often in boys 3 to 10 years of age

(3) Presents with pain in the knee or a limp

(4) Secondary osteoarthritis is common.

G. Osteochondritis dissecans

1. Variant of osteochondrosis limited to the articular epiphysis


Osteochondritis dissecans: variant of osteochondrosis limited to articular epiphysis


a. Articular epiphyses fail as a result of compression.

b. Trauma is the primary insult.

c. Ischemia is a secondary injury.


Osteochondritis dissecans: trauma primary insult; ischemia secondary injury


d. Portion of cartilage and underlying subchondral bone separates.

2. Occurs between 10 and 50 years of age

3. No sex predilection

4. Most common joint is knee.


Osteochondritis dissecans: distal femur most common site


a. Lateral surface of the medial femoral condyle is the most frequent site.

b. Cartilage may become detached.

5. Other sites

a. Capitellum of humerus

b. Dome of talus bone in foot

c. Shoulder, hip, elbow

6. Clinical findings

a. Localized pain, stiffness, swelling

b. Locking of joint by loose body

c. Tenderness at site of lesion

7. Complication


Osteochondritis dissecans: osteoarthritis late complication


• Osteoarthritis

8. Diagnosis

a. Imaging studies used depend on the site involved.

b. X-ray; spiral (helical CT); MRI

9. Treatment

a. Ice after exercise

b. NSAIDs for pain

c. Immobilization

d. Arthroscopic surgery

H. Osgood-Schlatter disease

1. Affects physically active boys 11 to 15 years of age

2. Painful swelling of tibial tuberosity


Osgood-Schlatter disease: painful swelling tibial tuberosity in boys


• Inflammation of proximal tibial apophysis at insertion of patellar tendon

3. Clinical findings

a. Pain aggravated by

(1) Squatting

(2) Walking upstairs

(3) Extending knee with resistance

b. Permanent knobby-appearing knees


Osgood-Schlatter disease: permanent knobby-appearing knees


4. No effect on bone growth

5. Treatment

a. Ice after exercise

b. NSAIDs for pain

c. Knee splint 2 to 4 weeks in resistant cases

I. Paget’s disease of bone (osteitis deformans)

1. Epidemiology

a. Primarily occurs in men > 50 years of age


Paget’s disease: primarily occurs in men > 50 years old; ? viral etiology


b. Cause unknown (? virus—slow virus, respiratory syncytial virus)

c. Targets the pelvis, skull (enlarged), and femur

2. Pathogenesis

a. Early phase of osteoclastic resorption of bone


Paget’s disease: osteoclastic phase followed by an osteoblastic phase


• Causes shaggy-appearing lytic lesions

b. Late phase of increased osteoblastic bone formation


Paget’s disease: ↑ alkaline phosphatase in osteoblastic phase


(1) Markedly increased serum alkaline phosphatase

(2) Production of thick, weak bone (mosaic bone; Fig. 23-7)

image

23-7 Radiograph of the humerus in Paget’s disease. Note the cortical thickening of the bone and the ragged appearing lytic areas throughout the bone matrix.


(From Katz D, Math K, Groskin S: Radiology Secrets. Philadelphia, Hanley & Belfus, 1998, p 311, Fig. 1.)



Paget’s disease: weak, thick, vascular bone


3. Clinical findings

a. Bone pain is the most common complaint.

b. Headaches, hearing loss if it affects skull

c. Increased hat size with skull involvement

4. Complications

a. Pathologic fractures

b. Risk for developing osteogenic sarcomas

c. Risk for developing high-output heart failure (refer to Chapter 10)


Complications: fractures, osteogenic sarcoma, high-output heart failure


• Due to arteriovenous connections in vascular bone

5. Diagnosis

a. Radiographs show thickened bone with shaggy areas of radiolucency.

b. Markedly increased serum alkaline phosphatase with normal serum calcium and phosphorus

6. Treatment

a. Bisphosphonates

b. Calcitonin

J. Fibrous dysplasia

1. Skeletal developmental anomaly

a. Defect in bone-forming mesenchyme with replacement of medullary bone by fibrous tissue


Fibrous dysplasia: defect in osteoblastic differentiation and maturation


• Defect in osteoblastic differentiation and maturation

b. Cysts may develop in the fibrous tissue matrix that manifests as a defect in osteoblastic differentiation and maturation.


Fibrous dysplasia: medullary bone replaced by fibrous tissue with cyst formation


2. May involve single (monostotic; 70–80%) or multiple bones (polyostotic)

3. No sex predilection

4. Occurs between 10 and 30 years of age

5. Most common locations

a. Ribs (28%)


Fibrous dysplasia: ribs most common site


b. Femur (23%)

c. Tibia or craniofacial bones (10–25%)

• In craniofacial bone, it produces cherubism

d. Humerus, vertebra

6. Polyostotic bone involvement is associated with Albright’s syndrome.


Albright’s syndrome: polyostotic bone involvement; café au lait spots; precocious puberty


a. Café au lait spots on skin

b. Precocious sexual development

7. Clinical findings

a. Pain overlying the bone

b. Swelling of bone

8. Complications


Complications: pathologic fracture, osteogenic sarcoma, fibrosarcoma


a. Risk for a pathologic fracture

b. Malignant degeneration in <1%

(1) Osteogenic sarcoma

(2) Fibrosarcoma

9. Diagnose with imaging studies.

10. Treatment is surgery.

K. Neoplastic disorders of bone

1. Metastasis is the most common malignancy of bone (see Figs. 8-7A to D).


Metastasis: most common bone malignancy


• Breast cancer is the most common primary site.

2. Primary malignant tumors of bone, in descending order of frequency

• Multiple myeloma, osteogenic sarcoma, chondrosarcoma, Ewing’s sarcoma

3. Treatment for primary bone tumors is surgery.

4. Summary of bone tumors (Table 23-1; see Fig. 8-1F)


Table 23-1 Tumors of Bone

image


Osteochondroma: most common benign bone tumor



Giant cell tumor: epiphysis distal femur, proximal tibia


II. Joint Disorders

A. Synovial fluid (SF) analysis

1. Routine studies

• WBC count and differential, crystal analysis, mucin clot, culture, Gram stain

2. Crystal identification

a. Monosodium urate (MSU)

(1) Needle-shaped (monoclinic) crystal

(2) Special polarization shows negative birefringence.


MSU crystals: negative birefringence (yellow when parallel to slow ray)


• Crystal is yellow when parallel to the slow ray (Fig. 23-8).

b. Calcium pyrophosphate

(1) Monoclinic-like or triclinic (rhomboid) crystals

(2) Special polarization shows positive birefringence.

image

23-8 Synovial fluid with special polarization. Special red filter causes the background to be red. Crystals are aligned parallel to the slow ray (axis) of the compensator (arrow). If the crystal is yellow when parallel to the slow ray, as in this figure, the crystal demonstrates negative birefringence. If the crystal is blue when parallel to the slow ray, the crystal demonstrates positive birefringence.


(From Henry JB: Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Philadelphia, WB Saunders, 2001, Plate 19-7.)



Calcium pyrophosphate: positive birefringence (blue when parallel to slow ray)


• Crystal is blue when parallel to the slow ray.

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Jun 25, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Musculoskeletal and Soft Tissue Disorders

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