Patho Final

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Disorders of the Musculoskeletal System BONE CELLS 1. Osteoblasts a. Major bone-forming cell b. Becomes osteocytes Osteoclasts c. Cells which break down bone Osteocytes a. Trapped osteoblasts; maintain the bone matrix Osteoclasts a. Cells which break down bone b. Macrophage lineage Osteogenic cells a. Undifferentiated cells that turn into osteoblasts b. Active during normal growth c. Activated in adult with healing of fractures/injuries

2. 3.


Osteoblasts Responsible for shape and structure of the bone o Secrete collagen o Produce osteocalcin & synthesize osteoid o Cause calcium salts & phosphorus from blood to precipitate to bone matrix (mineralization of bone) o Signal osteoclast activity (through RANKL) Respond to parathyroid hormone Secrete Type I collagen for mineralization of bone Alkaline phosphatase is contained in osteoblasts & secreted during osteoblastic activity Osteoblasts also have estrogen receptors o Estrogens can increase osteoblastic activity & collagen & bone matrix production Osteocytes Transformed osteoblast that are surrounded in osteoid as it hardens from deposited minerals Synthesize matrix molecules for bone calcification Osteocytes maintain bones o Play a role in controlling extracellular concentration of calcium & phosphate o Directly stimulated by calcitonin & inhibited by Parathyroid hormone (PTH) Osteoclasts Secrete bone-reabsorbing enzymes, which digest bone matrix o Phagocytic! Like macrophages o Contain lysosomes filled with hydrolytic enzymes Calcitonin signals osteoclast to dis-engage o Sparing loss of calcium from bone Osteoclasts also have estrogen receptors o Estrogens can inhibit their recruitment & decreases osteoclastic activity

BONE MATRIX 1. 2. 3. Collagen fibers a. Make up bulk of bone matrix Proteoglycans a. Strengthen bone and assist bone calcium deposition Glycoproteins a. Sialoprotein, osteocalcin, bone albumin, alpha-glycoprotein b. Control collagen interactions that lead to fibril formation Bone mineralization a. Calcium and phosphate


BONE TISSUE Compact (cortical) bone o 85% of the skeleton o Haversian system Haversian canal, lamellae, lacunae, osteocyte, and canaliculi Spongy (cancellous) bone o Lack haversian systems o Trabeculae Periosteum

LONG BONES 1. 2. 3. 4. 5. Diaphysis Metaphysis Epiphysis a. Epiphyseal plate Medullary cavity Endosteum

BONE RESORPTION CYCLE Human body is constantly removing old bone & replacing it with new bone o Called "bone turnover To perform bone turnover, your bone needs o Minerals (calcium and phosphorus) o Bone protein matrix o Osteoclasts o Osteoblasts

REGULATION OF BONE RESORPTION 1. Parathyroid Hormone (PTH) a. Increase recruitment & activity of osteoblasts and osteoclasts b. Promotes release of calcium from bone c. If PTH secretion is too high, there is an acceleration of the bone turnover Calcitonin a. Secreted by Para-follicular cells of thyroid gland. b. Inhibits release of calcium from bone


*PTH & Calcitonin have opposite effects on Calcium levels 3. Vitamin D a. Vitamin D tends to increase recruitment of osteoclasts b. Plays a part in mineralization of bone matrix. c. Lack of Vitamin D results in osteomalacia (impaired mineralization) d. Too much Vitamin D entails bone loss Estrogen a. Increases osteoblast activity/decreases osteoclast activity


COMPACT VS CANCELLOUS BONE Compact Bone o More dense o Exterior portion of bone Cancellous Tissue o Spongy tissue o Interior portion of bone, more vascular

Which heals faster? Cancellous Tissue LIGAMENTS & TENDONS Tendons o Muscle to bone Ligaments o Bone to bone

STRAINS Tearing or overstretching of muscle or tendons Overstretching or tears of ligament structures DISLOCATIONS-look at picture ROTATOR CUFF INJURIES Rotator cuff made up of 4 muscles & their tendons These combine to form a "cuff" over head of humerus Rotator cuff helps to lift & rotate arm & stabilize ball of shoulder within joint

FRACTURES Break in continuity of bone Pathologic o Break at site of preexisting abnormality Usually osteoporosis, cancer, Pagets disease, infection, metabolic bone disorders Injurious/trauma- trauma to bone Stress fractures (repeated strain) o Fatigue- abnormal stress or torque applied to bone with normal ability to deform & recover New activities: jogging, dancing, skating o Insufficiency or fragility- bones without normal ability to deform & recover from normal weight-bearing activity By force that wouldnt normally produce fracture Arthritis, rickets, Pagets disease


Linear a. Runs parallel to axis of bone 2. Oblique a. Occurs at oblique angle to shaft of bone 3. Spiral a. Encircles bone b. Twisting injury c. Torque injury d. Unstable and may move after reduction 4. Transverse (closed) a. Straight across bone b. Usually simple to reduce 5. Comminuted a. Bone broken into >2 pieces b. Probably needs surgery 6. Greenstick a. Torus or buckle fracture b. Cortex buckles but does not break c. Typically in children d. Incomplete fracture e. May be parallel to bone 7. Bowing a. Longitudinal force applied to bone b. Common in children c. Involves tibia/fibula or radius/ulna i. One bone in pair breaks and forces bows other bone 8. Open Fracture a. Open to environment b. Increased risk for infection c. Increased bleeding 9. Compression a. Usually in vertebrae b. Can be due to osteoporosis 10. Impacted a. Fragments wedged together

HEALING OF FRACTURES Direct or primary healing o Similar to intramembraneous bone formation when adjacent bones cortices contact one another o Most often with surgical fixation o No callus formation Indirect or secondary healing o Similar to endochondral bone formation o Involves formation of callus & remodeling of solid bone 1. 2. Inflammatory phase a. Hematoma formation Reparative Phase a. Cell proliferation/callus formation b. Ossification Remodeling


Inflammatory Phase: HEMATOMA FORMATION 48 - 72 hours (Inflammatory Phase) o Torn vessels in bone & soft tissues forms hematoma o Fibroblast arrives at the site of injury Initiates healing process Fibrin meshwork forms Granulation tissue begins to form Reparative Phase: CELL PROLIFERATION & CALLUS FORMATION nd th 2 - 6 week of healing (Reparative Phase) o Osteoblast & chondrobalst differentiate (periosteum) o Proteins produced by osteoblasts & chondroblasts begin to consolidate into what is known as cartilogenous soft callus o Ossification Begins Bone begins to calcify Mature bone replaces soft callus (Bony Callus) Fracture completely bridged, ends firmly united May remove cast at this point Remodeling Phase Resorption of excess bony callus by osteoclasts Directed by weight bearing Occurs after healing process HEALING TIMES 1. 2. 3. Children a. 4-6 weeks Adolescents a. 6-8 weeks Adults a. 10-18 weeks

FACTORS INFLUENCING BONE HEALING Systemic Factors o Age o Nutrition o Systemic Disease o Hormones Local Factors o Type of bone o Degree of trauma o Vascular injury o Degree of immobilization o Intraarticular fractures o Separation of bone ends o Infection/ local pathology

COMPLICATIONS OF FRACTURES 1. 2. Infection Osteomyelitis a. Usually caused by Staphylococcus Aureus b. May be due to: Direct contamination (surgical or injury) Hematogenic source Chronic Acute infection recurs Compartment Syndrome a. Increased pressure in limited anatomic space b. Compromises circulation Result from increase pressure in the tissue compartment Compromises circulation Nerve impingement c. The 5 Ps: Pain Pallor Paresthesias Pulses Paralysis d. May require fasciotomy Osteonecrosis a. Death of a segment of bone b. Not uncommon (r/t ischemia) c. Thrombosis/emboli, vascular compression, vessel injury d. Causes/Risk factors: Long term treatments with steroids Excessive alcohol use Sickle cell disease, radiation therapy, DM, gout, atherosclerosis Dislocation or fractures around a joint




Fat Emboli Syndrome a. Usually after fracture of long bones or pelvis Fat released by bone marrow or adipose tissue at fracture site Results in fat emboli in lungs (PE) b. Manifestations: Tachypnea Dyspnea Use of accessory muscles Wheezing Inspiratory stridor Petechial rash-neck, upper chest, shoulder, axillary and buccal membranes HA Drowsiness Irritability Memory loss Confusion Rapid pulse Apprehension Fever

BENIGN NEOPLASMS OF THE BONE 1. 2. 3. 4. Osteoma a. small bony tumor on surface of long bone Chondroma a. Hyaline cartilage tumor (hands or feet) Osteochondroma a. Most common, grows only during skeletal growth, made of bone & cartilage Giant cell tumor/osteoclastoma a. Aggressive/metastatic; knee/wrist/shoulder metaphyseal regions

METASTATIC NEOPLASMS 1. Osteosarcoma- children & elderly a. Most common malignant bone-forming tumor b. Formation of immature bone by malignant osteoblasts; aggressive & undifferentiated Ewings Sarcoma- common bone tumor in childhood a. Young males, highly malignant; immature bone marrow cells become malignant (does not make bone) b. Femur, pelvis, humerus; metastasizes fast Chondrosarcoma- middle-aged & older adults (men) a. Common primary malignant tumor of cartilage



CARPAL TUNNEL SYNDROME swelling in compartment in wrist that contains wrist & finger muscles, nerves, & blood supply Swelling puts pressure on nerve that travels in this compartment or "tunnel Pressure on median nerve causes numbness, weakness, & pain in wrist & hand

METABOLIC BONE DISEASES Osteopenia (fewer bone cells) Condition in all metabolic bone diseases Osteomalacia (adults)/Rickets (children) Inadequate & delayed mineralization in bone Softening of bones Vitamin D, C