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Unit XII
MUSCULOSKELETAL FUNCTION
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Structure and Function of
Skeletal System Framework for attachment of muscles, tendons,
and ligaments
Protects and maintains soft tissues in properposition Provides stability for body Maintains bodys shape
Storage reservoir for calcium Contains hematopoietic connective tissue to form
blood cells
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Cartilage
Firm but flexible connective tissue consisting of cells and intercellular fibers embedded inamorphous gel-like material; smooth, resilientsurface and weight-bearing
Essential for growth before and after birth Postnatal, cartilage plays a role in growth of long
bones and persists as articular cartilage Elastic(ear),hyaline(most abundant,epiphysealplates), fibrocartilage(intervertebral discs)
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BoneIntercellular matrix impregnated with inorganic
calcium salts Organic matter 1/3 Inorganic salts 2/3
Can take up lead andantibiotics
Cancellous(spongy)
Compact(cortical)
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Osteogenic Cells Found in periosteum,
endosteum, epiphysealplate of growing bone
Active during normalgrowth, during fracturehealing, replacement of worn-out bone tissue
Both periosteum andendosteum contribute togrowth and remodeling of bone and are necessary forrepair
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Bone Cells Osteoblasts
Bone building cells are responsible for formation of bone matrix
Two stages include ossification and calcification
Secrete alkaline phosphatase Osteocytes
Mature bone cells actively involved in maintaining thebony matrix
Osteoclasts Responsible for the resorption of bone matrix and
release of calcium and phosphate from bone
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Bone Growth and Remodeling
Growth in diameter occurs in concentric rings Long bones are provide with specializes structure
called epiphyseal growth plate
As long bones grow, deeper layers of cartilagecells in growth plate multiply and enlarge, pushingthe articular cartilage farther away from themetaphysis and diaphysis of the bone
Allows for bone growth without changing shapeof bone or disrupting articular cartilage Cells in growth plate stop dividing at puberty at
which time the epiphysis and metaphysis fuse
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Hormonal Control of Bone
Formation and Metabolism PTH prevents serum calcium
levels from falling below andphosphate levels from rising
above physiologic conditions Calciotonin lowers blood
calcium levels by inhibitingrelease of Ca from bone to ECF
Vitamin D-actually steroidhormones increases intestinalabsorption of Ca and promotesaction of PTH
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Classification of Bones Long(arm), short(ankle),
flat(skull), irregular(jaw) Bone marrow occupies medullary
cavity of long bones andcancellous bone in vertebrae, ribs,sternum and pelvis; compositionvaries with age and site
Red bone marrow containsdeveloping RBC, graduallyreplaced with . . .
Yellow bone marrow composedof adipose tissues
Red persists in vertebrae, ribs,sternum and ilia
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Tendons, ligaments and joints Tendons connect muscles to bone; can appear as
cordlike structures or as flattened sheets calledaponeuroses
Ligaments connect moveable bones of joints Articulations-areas where two or more bones
meet. Prefix arthro means joint Synarthroses lack joint cavity; move little-skull,
rib, symphysis pubis Diarthroses-diarthrodial or synovial joints are
freely moveable Synovium secretes synovial fluid to act as
lubricant
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Diarthroidial Joints
Little movement,sacroiliac
Hinge, interphalangeal Many planes-hip Frequently affected by
rheumatic disorders
Articular cartilage ishyaline and healsslowly(diffusion)
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Blood supply,innervation, and
bursae Blood supply to synovial membrane rich healingand repair rapid and complete; innervated only byautonomic fibers, relatively free of pain fibers
local anesthesia As a rule, each joint of an extremity in innervated
by all the peripheral nerves that cross thearticulation referral of pain from one joint to
another Synovial membrane can form closed sacs that are
not part of joint-bursae. Prevents friction ontendon. Bunion is inflamed bursa of
metatarsophalaneal joint of great toe
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Injury and Trauma
Contusion - skin intact, ecchymotic Hematoma - large area of local hemorrhage Laceration - skin torn, continuity disrupted
Strain- stretching injury to muscle ormusculotendinous unit from mechanicaloverloading
Sprain abnormal or excessive movement of joint
with disruption to ligaments Formation of new collagen within 4-5 days, may
have original strength within 7 weeks, danger atdisruption in healing
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Injury and Trauma
Dislocations-loss of articulation of the bone endsin the joint capsule caused by displacement orseparation(congenital, pathological as well)
Shoulder permits a wide range of motion, a factorthat makes the joint relatively unstable; supportand movement of shoulder joint relies heavily onsupport of four relatively small muscle-tendongroups collectively know as the rotator cuff
Rotator cuff impingement tendonitis and tears arecommon among athletes
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Rotator cuff injury
Commonly injuredduring repetitive
movements that carryarm above shoulder-pitchers, swimmers,weight lifters
Partial-non surgical Full thickness-surgical
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Knee Injuries Subject to abnormal twisting
and compression Menisci are C-shaped plates of
fibrocartilage superimposed on
condyles of tibia and femur;stabilize, lubricate and load bear Cruciate ligament secures femur
to tibia in crossed position.Controls flexion and lateral
rotation. ACL is weaker-ofteninjured. Immediately disabling
Patellar subluxation anddislocation
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Hip Injuries
Ball/socket joint in which femoral head articulatesdeeply in acetabulum; vascular anatomy of
femoral head is critical - viability of femoral headmay lead to avascualar necrosis. Fractures
Major public health problem; falls most common cause Categorized by location; 90% are femoral neck and
intertrochanteric fractures Location important to blood flow
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Fractures
Sudden injury Fatigue or stress Pathological (10-15% of patients with
metastatic disease Classified according to location, type, and
direction or pattern of fracture line (seefigure 42-5)
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HEMATOMAFORMATION
Hematoma facilitatesthe formation of thefibrin meshwork that
seals off fracture siteand serves as aframework for theinflux of
inflammatory cells,fibroblasts, and newcapillary buds.
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FIBROCARTILAGINOUS CALLUS FORMATION
Formation of granulationtissue called procallus.Fibroblasts from theperiosteum, endosteumand red bone marrowproliferate and invadeprocallus. Fibroblastsproduce afibrocartilaginous soft
callus bridge that connectsbone fragments.
NO WEIGHT BEARING YET
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BONY CALLUS FORMATION
Fibrocartilaginouscartilage converted tobony callus. Newlyformed osteoblasts firstdeposit bone on outersurface of bone and thenmove toward fracturesite. Begins 3-4 weeks
after injury.
USUALLY SAFE TO REMOVE CAST
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Factors Affecting Bone Healing
Increased cellularity and vascularity in childsperiosteum improves healing
Fracture displacement, edema, arterial occlusion Type of bone, cancellous bone heals faster Degree of immobilization achieved Infection, malignancy, bone necrosis Amount of bone loss Age, nutrition, meds, diseases Malunion, delayed union, nonunion
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Complications of fractures and
other musculoskeletal injuries Compartment syndrome Tissue compromise from pressure in the
muscle compartment Hallmark symptom is pain out of proportion
to the original injury Five Ps
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Fat Embolism
FES refers to a constellation of clinicalmanifestations resulting from fat droplets in smallblood vessels of lung or other organs after a longbone fracture or other major trauma. Releasedfrom bone marrow or adipose tissue at fracture siteinto venous system; rare
Respiratory failure, cerebral dysfunction and skinpetechiae(does not blanch); symptoms within afew hours to 3-4 days. Initial findings subtlechange in behavior and disorientation
Stabilize fractures early
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Osteomyelitis
Acute or chronic infection Direct contamination, seeding
through bloodstream(hematogenous),vascular insufficiency
Staphylococcus most common-produces a collagen binding adhesionmolecule allowing it to adhere toconnective tissue elements of boneand ability to internalize and survive
in osteoblasts making themicroorganism resistant to antibiotics
Sequestrum-infected dead boneseparated from living bone
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Osteonecrosis
Death of bone segment caused by interruption of blood supply to marrow, medullary bone, orcortex; proximal femur, distal femur and proximalhumerus
Common complicating disorder of sickle celldisease, steroid therapy(5-25%), and hip surgery
Results from ischemia but mechanisms vary;steroids unclear may increase intraosseouspressure with vascular compression, sickle cellthrombosis
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Neoplasms Benign include osteoma,
chrondroma, osteochrondroma, andgiant cell
Osteosarcoma-peak during teens,bones with maximum growthvelocity;localized pain and swelling
Ewings sarcoma Metastatic-skeletal metastases are
most common malignancy of
osseous tissue:spine, femur, pelvis,ribs, sternum, humerus, skull
Breast, lung, prostate , kidney andthyroid are most common. 50% of bone must be destroyed beforelesion is visible on plain radiograph
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Metabolic Bone Disease
Bone integrity depends on a process of boneresorption and formation or bone remodelingwhich is continuous thru life
25% of cancellous bone replaced each year and3% or compact bone; proceeds in cycles that cantake 4 months
Osteoclasts resorb old bone and osteoblasts formnew bone
Mechanical stress, extracellular calcium andphosphate levels and hormones, local growthfactors and cytokines influence
RANK ligand may play role as chemicalmessenger
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Osteoporosis Classified as primary(postmenapausal women or elderly) or
secondary(endocrine or genetic disorder) Enhanced bone resorption relative to bone formation; varies
with age, sex, nutritional status and genetic predisposition Maximal bone mass achieved at 30; loss is 1%/year in
menopausal women; AA less prone than caucasians/Asians Greatest losses occur in areas containing abundant cancellous
bone such as spine and femoral neck Alcohol is a direct inhibitor of osteoblasts and may also
inhibit calcium absorption. Prolonged use of medication that increases calcium excretion
such as antacids and anticonvulsants Premature and low birth weight infants at risk Female athletes- poor nutrition, amenorrhea, estrogen lack
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Osteoporosis
Changes occur in the diaphysis and metaphysis of thebone; diameter of bone enlarges causing the outersupporting cortex to thin; resembles porcelain vase
First manifestations are pain accompanied by skeletalfractures-vertebral compression, hip, pelvis, humerus
Fractures represent end stage of disease Wedging and collapse of vertebrae causes height loss
and kyphosis(hump)
Monitor with bone mass density studies Prevention and early detection critical:Regular
exercise and 1500 mg calcium in post menopausalwomen
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Rheumatoid Arthritis Systemic inflammatory disease that attacks joints by
producing proliferative synovitis that leads todestruction of articular cartilage and underlying bone
0.3-1.5% of population; women 2-3X Cause not established; genetic predisposition and
immunologically mediated Pathogenesis is an aberrant immune response that leads
to synovial inflammation and destruction of jointarchitecture
May be initiated by activation of CD+4 helper T cells,release of cytokines and antibody formation
70-80% have rheumatoid factor (RF) autoantibody
Joint and extra-articular manifestations
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Systemic Lupus Erythematosus
Chronic inflammatory disease affecting any organsystem 1 in 2000, higher incidence in females, AA, Latins, and
Asians
Cause unknown but characterized by formation of autoantibodies and immune complexes; B cellhyperactivity and increased antibodies against self
Genetic, hormonal, immunologic andenvironmental(drug induced such as hydralazine andprocainamide)
Great imitator: musculoskeletal, skin, cardiovascular,lungs, kidneys, CNS, RBC and platelets
ANA testing with history and exam
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Osteoarthritis(OA)
-Formerly DJD; most prevalentform and leading cause of disability and pain in elderly
-Primary or secondary-Progressive loss of articularcartilage and synovitis resultfrom inflammation causedwhen cartilage attempts torepair itself -Creates osteophytes or spurswhich cause joint pain,stiffness, and loss of motion
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Pathogenesis of OA Resides in the homeostatic mechanism that maintains
the articular cartilage Plays two roles: (1) smooth weight bearing surface
and (2) transmits the load down to the bonedissipating mechanical stress
Composition and mechanical properties of cartilageare changed
Chemical messengers such as cytokines stimulate
production and release of proteases that aredestructive to joint structure, more injury results andrepair mechanism is inadequate; portions becomecompletely eroded and synovial membrane
inflammation
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Ankylosing Spondylitis, Gout,and Osteomalacia will not be
covered on the exam