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Chapter 18
Skeletal & Muscle Pathophysiology
●Significant Points of Normal Skeletal Physiology
-Bone Structure
-Minerals in a collagen framework (like fiberglass)
-Bone is dynamic
-bones don’t “stop growing” after puberty
-they are constantly remodeling and responding to stresses and changes
-Bone anatomy
-articular cartilage, epiphysis, spongy bone (cancellous), compact (cortical bone) periosteum,
etc.
●Genetic Bone Disorders
-Genetic bone disorders are pretty rare- these people end up w/ fractures more often
-Osteopetrosis
-(Also called Albers-Schonberg Disease, Marble-Bone Disease)
-Very heavy but weak bone tissue
-Usually, oseoblasts and clasts work in balance. In osteopetrosis, osteoclasts are deficientperson ends up with severe anemia, compressed brain tissue which results in blindness, short
stature withbonve tissue that is flawed in being brittle and easily fractured, deafness,
paralysis.
Treatment is very high doses of Vitamin D.
-Osteogenesis Imperfecta
-“Brittle-Bone Disease”
-Inherited disease in collagen synthesis, low bone mass, easily fractured (longer healing time)
-faulty ossification, produces osteopenia and brittle bones. Defective tooth formation, an blue
discoloration of the sclerae, and faulty hearing are also often present.
-skeletal abnormalities, pronounced stunting of growth, incomplete ossification, and various
other skeletal defects may be present- for example: long bone shafts of variable thickness or
length and scoliosis.
-Acondroplasia
-lack of cartilage formation at the epiphyseal plates of long bones, which causes ossification
to seal the plates early, so long bones end up shortened from underdevelopment
-Inheritance is dominant (Dd)
-skeletal disproportion, some bones may grow by thickening, even though they can’t elongate
-dominant inheritance, lordosis
●Acquired bone disorders
-Most occur in skull and proximal long bones. Some bones are affected more than others
-Osteoclasts are more active and there is more bone absorption
-Paget’s Disease
-5% of British
-Disorder in bone maintenance: bone absorption=bone depletion
-Heavier, denser bone (but density is patchy) Leads to malformation, and it’s easier to break.
-Leads to hearing and nerve disorders. (bones or the skull, vertebral column, and proximal
portions of the major long bones are most typically involves)
-Microfractures of pagetic bone: b/c bone is weakened, normally trivial stresses may cause the
break…although painful and delayed, healing occurs.
-Osteoporosis
-Most common metabolic disease in N. America
-Ideopathic- gradual loss of bone mass
-There is more breakdown than deposition (little changes over a long time)
-If we all lived long enough, it would happen to everyone
-Type I: more rapid progression, occurs at an earlier age, osteoclasts excessively resorb bone,
causing a loss of bone mass. Genetics
-Type II: most common, called Senile Osteoporosis. Happens mostly in femur, humerus, and
tibia. These people can have spontaneous fractures. As people age, there is a more rapid
breakdown. Slightly reduced degree of bone deposition during normal bone remodeling.
-High Risk Groups- Asians and Caucasians, lighter skin than black skin, sedentary vs. active,
post menopausal women 8:10 ratio, dietary intake calcium and Vitamin D.
-Also, anorexics, sports when being tiny, amenorea, anemia, physical inactivity,
calcium/phosphate/Vitamin D deficiencies, heavy caffeine and alcohol ingestion, and
smoking
-Role of Prevention: start with young people: teens are important! Calcium and vitamin D
supplements, milk, hard cheese, yogurt, weight bearing exercise, avoid cigarettes and heavy
alcohol/caffeine.
-Conditions causing secondary osteoporosis: Table 18.1, p. 491
-loss of bone mass due to an excess of resorption over deposition may also arise as a
result of some other derangement.
-cause may be a nutritional deficiency, a genetic or endocrine abnormality, therapeutic
drugs, certain tumors, or some other disease state
-Rickets
-inadequate minerals but bone matrix is okay.
-result is a softened bone that is subject to malformation or distortion, which causes pain.
-Vitamin D and Calcium deficiency
-found often in kids- shortened, deformed limb: bowed legs, skull, chest, teeth deformities,
increased tendency to bone fractures.
-Osteomalacia
-Rickets in adults, no deformity, weakened/soft bones
-inability to maintain bone deposition during remodeling: usually produces no bone
deformities or other gross indications of the problem. Common symptom of bone pain with
generalized muscle weakness and an increased predisposition to fractures.
-renal disease: impaired absorption of calcium and Vitamin D
-may be due to a GI malabsorption problem, to a renal defect of phosphate retention that
results in hypophosphatemia and defective bone mineralization, or to faulty activation of
cholecalciferol in chronic liver or kidney diseases.
-Osteomyelitis
-bone inflammation, secondary to infection (response restricts circulation)
-infection is difficult to get rid of b/c of: beyond the general effects of ischemia, the
compromised blood flow not only reduces efficiency of the inflammatory response, it also
restricts antibiotic access to the site where it is needed.
-Impaired/no circulation: bone infection that leads to destruction. Hard to get IV to it.
-Secondary to septicemia (can come thru blood or traumatic problem.)
●Bone Tumors
-Secondary metastasis from prostate, breast, thyroid, lung, kidney
-Access to bone is by way of the blood, rather than lymph, and the sites most often involved are the
bones of the axial skeleton (except the skull) and the proximal femur and humerus.
-Replaces healthy bone tissue with less effective tissue: breaks easily, impaired mobility, anemia.
Some are benign and amputations are common.
●Osteoarthritis
-weight bearing joints
-Review of normal joint structure: Figure 18.11, p. 494
-Pathogenesis of osteoarthritis: Figure 18.12, p. 495
-damage to cartilage: becomes thin, irregular, and frayed. Cracks or fissures then develop in
the articular cartilage and with progression, they fill with synovial fluid and penetrate to the
underlying bone.
-fluid-filled cysts and microfractures can occur. Also bony projections called bone spurs are
the cause of the pain and limitation of joint mobility that are characteristic of osteoarthritis
-Predisposing causes
-sports injuries (more strain), obesity (especially women)
●Rheumatoid Arthritis
-Systemic, Autoimmune disease, primary affect of joints (hands, wrists, ankles, feet) 1% adults in N.
America affected. It’s a systemic disease with prominent involvement of the joints. It initially
affects the synovium, with later effects in articular cartilage and bone. It is an inflammatory
condition that primarily affects the joints of the hands, wrists, ankles, and feet, with systemic effects
involving the heart, lungs, skin, and other organs.
-ideopathic, characterized by immune-mediated destruction of joints. Infection, may be an
autoimmune disorder, also caused by rheumatoid factor.
-Pathogenesis: starts in 20’s and 30’s
-Characteristic Symptoms
-Early phase of Illness (?)
-excess synovial exudates, acute inflammation, then Pannis
-irreversible damage to bone: articular cartilage is eroded and damage to bone continues until
Pannis, which fills the joints and then they become fixed. Synovial membrane inflames and
finger-like projections go into the bones, Pannis: fabric: swelling, stiffness, pain and
disfigurement leads to immobility. Therapy is prevention and delaying progression (?)
-Mid phase of Illness
-End stage disease: fixed joints and immobile
-Figure 18.4, p. 498: possible genetic predisposition
-Table 18.3
●Gout
-Increase in uric acid from excess production or decreased secretion from defective renal handling
-Uric crystals are deposited in joints and if they precipitate, it’s very painful.
-Most often: deficiency in renal excretion
-Treatment: aimed at changing secretion
●Pseudogout
-Same process, different crystal
●Anklosing Spondylitis
-white men most often affected
-Progressive spine disorder, destroys joint and spine straightens (bamboo spine)
●Skeletal Muscle Disorders
-Duchenne Muscular Dystrophy
-progressive degeneration of skeletal muscle. X-linked recessive defect. High serum levels
of creatine kinase.
-most common in men: family history
-mutation (defect in muscle protein called dystrophen) decreased stability in muscle tissue.
-fibrosis, contracture, lordosis, scoliosis, prevents normal chest expansion, resp. insufficiency,
dysrhythmias, and congestive heart failure.
-Myotonic Dystrophy (muscle tone defect)
-autosomal dominant inheritance: abnormal ion channels that are linked to muscle atrophy,
loss of strength, and a characteristic myotonia: delay in muscle relax after contraction
-no channels to move ions in and out quickly enough
-symptoms arise in 20’s the progress (ex: cardiac muscle) slow progression
-some are worse off than others
●Key Concepts
1) Apart from infections and tumors, bone disease derives from abnormalities of bone formation or later
imbalances in the bone remodeling process
2) Apart from infections and tumors, most of the more common bone disorders produce osteopenia, with the
exception of Paget’s disease, which involves both osteopenia and hyperostosis
3) Genetic bone disease are rare and involve various patterns of inheritance of traits that produce defects in
the cartilage template on which ossification depends or in the activities of osteoblasts or osteoclasts
4) Pain, skeletal malformations, and pathological fractures are the principal derangements produced by
acquired bone disorders
5) The most important fact or in preventing the osteopenia that characterizes osteoporosis is the early
development and maintenance of the maximum skeletal mass provided by one’s genetic makeup, to
counter the inevitable loss of bone in later life
6) Osteomyelitis is usually caused by a pyogenic exogenous bacterial infection that arises secondary to bone
trauma, but organisms from previously established infection sites may reach bone via the blood.
7) Most bone tumors are secondary carcinomas from various body sites; of primary bone tumors, 2/3 are
malignant and 1/3 benign.
8) Osteoarthritis, the most common in N. American joint disease, involves the degradation of articular
cartilage, often in response to long-term overloading of the larger weight-bearing joints.
9) Rheumatoid arthritis typically involves the joints of the wrists, hands, ankles, and feel and derives from
inflammatory damage to the synovium, with later effects in articular cartilage and adjacent bone.
10) RA is caused by the immune destruction of joint structures, and has a genetic component to its etiology.
11) Superimposed on its alternating pattern of exacerbation and remission in affected joints, RA exhibits a
range of variable occurring systemic effects.
12) Although essentially a systemic autoimmune disorder, 90% of SLE is accompanied by joint pain and
swelling due to synovitis induced by immune complex deposition.
13) With nerve and blood supply intact, skeletal muscle is remarkably resistant to disease, but with
inadequate neurological stimulus, its cells atrophy and weaken.
14) Duchenne muscular dystrophy is the most common of a group of rare genetic diseases characterized by
progressive degeneration of muscle tissue.