Joints (Week 1--Metten)

Question 1

How do MSK tissues develop?

Answer 1

Derived from mesoderm, which turns to mesenchyme, which turns to MSK cells (fibroblasts, chondrocytes, osteocytes) to make MSK tissues

Question 2

Development of extremities

Answer 2

Pluripotent cells migrate to limb buds at day 26 to form mass of mesenchyme covered by epidermis

Fibrous tissue and vessels differentiate from mesenchyme

Bone forms at 6th week and muscle mesenchyme attaches to it

Nerves migrate in

Apoptosis of tissue between digits forms hand and foot

Question 3

Fibrous tissue (connective tissue) composition

Answer 3

Fibroblasts produce ECM, which consists of fibers and ground substance

Fibers: collagen and elastic fibers

Ground substance: GAGs, proteoglycans (GAGs + core proteins (neg charge) hold in water and have consistency of egg whites), adhesion glycoproteins (fibronectin)

Question 4

3 skeletal muscle wrappings

Answer 4

Endomycium: delicate loose fibrous tissue that surrounds each muscle fiber and contains capillaries that supply muscle fiber

Perimycium: fibrous tissue wrapping that encloses a fascicle of skeletal muscle fibers

Epimycium: dense fibrous tissue that wraps around entire muscle (is deep fascia of the muscle)

Question 5

Myotendinous junction

Answer 5

Where epimycium and perimycium fuse to form a tendon

Abrupt, vascularized

Question 6

Tendon structure

Answer 6

Produced by tenocytes

Endotenon wraps around bundles of collagen fibers (this is where capillaries are) and tendon is a collection of endotenons

Where the tendon wraps around a bone, it is less vascularized

Question 7

Tendonitis

Answer 7

Acute inflammation of tendon, most often due to overuse injury

Question 8

Tendonosis

Answer 8

Injury that results from microtears in tendon without significant inflammation

From overuse injury, compression injury, degenerative changes

Usually chronic

Question 9

When tendon is injured (prolonged periods of tensile stress), what happens?

Answer 9

Prolonged periods of tensile stress –> collagen breakdown –> Ca2+ deposits

If you see Ca2+ deposits on X-ray means you’ve been injured there before

Question 10

Tendon sheath

Answer 10

Fibrous tissue sheath that surrounds the tendon in certain locations (where high abrasion on tendon)

Inside is lined with synovial membrane (= synovium)

Ex: many tendons in hand are wrapped in tendon sheaths!

Question 11

Tenosynovitis

Answer 11

Inflammation of tendon sheath (lined with synovium = synovial membrane)

Can cause Trigger Finger (inflamed tendon sheath causes nodule to form and can’t move finger because nodule in the way) and DeQuervain Tenosynovitis

Question 12

Two different types of tendon attachment to bone

Answer 12

1) Fibrous: tendon fibers go through periosteum and attach to bone
2) Enthesis: tendons contain fibrocartilage and become more tough before going into bone (this attachment good for tendons that have a lot of pull/force on them); zones are tendon proper, fibrocartilage, mineralized fibrocartilage, bone insertion

Question 13

Where tendons attach to bone, are there nerve endings?

Answer 13

Yes, nociceptors and mechanoreceptors

Question 14

Enthesitis

Answer 14

Inflammation at enthesis

Question 15

Ligament structure

Answer 15

Attach bone to bone

Similar structure to tendon (fibrous or enthesis attachments)

Nerve endings are nociceptors or mechanoreceptors (proprioception)

Have endoligament and epiligament?

Question 16

Ligament pathology

Answer 16

Acute injury (sprain)

Degeneration

Question 17

Bursa

Answer 17

Fibrous tissue sac lined with synovium

Located where muscle and bone or tendon and bone meet

Question 18

Bursitis

Answer 18

Bursa becomes inflamed (actually is synovium inside bursa becoming inflamed)

Question 19

Shoulder Impingement Syndrome

Answer 19

Overuse syndrome –> tendonitis of supraspinatus muscle tendon –> swelling –> ischemia –> tendinosis with tears in muscle tendon –> subacromial bursa becomes inflamed –> bursitis –> deposition of Ca2+ crystals in bursa is calcific bursitis –> lots of pain –> don’t want to use shoulder –> adhesive capsulitis (thickening of shoulder joint capsule)

Question 20

Cartilage

Answer 20

Produced by chondroblast which make fibers and ground substance

Fibers: Type II collagen (hyaline and elastic cartilage), Type I collagen (fibrocartilage), elastic cartilage

Ground substance: GAGs, proteoglycans (GAGs (hyaluronan)+ core protein), adhesion glycoproteins

Question 21

3 types of cartilage

Answer 21

1) Hyaline cartilage: Type II collagen (in joints!)
2) Elastic cartilage: Type II collagen and elastic fibers
3) Fibrous cartilage (fibrocartilage): Type I collagen and someType II collagen (and chondrocytes line up)

Question 22

Proteoglycan aggrecan structure of cartilage ECM?

Answer 22

Complex proteoglucan molecules (chondroitin sulfate, keratin sulfate)

Hyaluronan

Aggrecans form large aggregates

Question 23

Perichondrium of cartilage

Answer 23

Surrounds cartilage

Contains vessels, nerves

Nutrients diffuse from perichondrium to cartilage b/c no vessels in cartilage

Cushioning effect: when compressed, interstitial fluid moves away from proteoglycan aggregate structure but when compression released, interstitial fluid returns

Question 24

Types of injury to hyaline cartilage

Answer 24

Acute injury: cartilage cannot repair itself because does not have blood supply so no inflammation and no healing

Chronic injury: overuse injury and normal aging causes aggrecan structures to gradually break down and cartilage frays (fibrillation) and erodes (osteoarthritis)

Question 25

2 types of bone

Answer 25

**Cortical**/compact bone **Trabecular**/spongy/cancellous bone

Question 26

2 bone membranes

Answer 26

1) **Periosteum** surrounds/lines **outside** surface of bone and is important because contains blood supply; abundant somatic sensory innervation, lymphatics; thicker in children 2) **Endosteum** lines all spaces **inside** bone

Question 27

Osteoid

Answer 27

Special name for **ECM** of bone **created by osteoblasts**

Question 28

How do you create bone?

Answer 28

**Osteoblasts** produce **osteoid** that becomes mineralized when **minerals from blood** come in and attach to **collagen** **fibers** in osteoid to form **hydroxyapatite** **crystals** Very first bone produced is **woven** bone, then matures to **lamellar** bone

Question 29

Bone composition

Answer 29

**Osteoblast** makes **ECM** called **osteoid**, which contains **fibers** and **ground substance** **Fibers**: **Type I collagen** **Ground** **substance**: **GAGs**, **proteoglycans** (GAGs + core protein, and aggrecan molecules form aggregates)

Question 30

Osteocytes

Answer 30

**Cell bodies** in **lacuna** due to density of matrix **Cell processes** are in **canaliculi** so can communicate with other osteocytes **Haversian system** nourishes osteocytes

Question 31

Haversian canal

Answer 31

Lined by **osteum** **Within osteon** Contain **blood vessels**

Question 32

Osteon

Answer 32

Fundamental unit of compact bone--cylinder surrounding Haversian system **Central rod** **Haversian system** (Haversian canal (contains nerve and blood vessels) and canaliculi) Increased pressure on the bone creates osteons

Question 33

Osteoclasts

Answer 33

Derived from bone marrow in mononuclear phagocyte system (derived from where **monocytes** come from--osteoclasts are **semi-phagocytic**!) Lifetime is several **weeks** **Multinucleated**, large Regulated by **hormones** (calcitonin inhibits activity, PTH indirectly activates) Osteoblasts signal osteoclasts to munch bone

Question 34

How are osteoclasts triggered to munch bone?

Answer 34

**PTH** binds **osteoblasts** and causes them to express **RANKL** which binds to **RANK** on osteoclast and activates it Osteoclast has **ruffled border** and **resorption pit** where releases lysosymes to digest bone --\> **Howship's lacuna** is where bone has been removed by osteoclasts

Question 35

Blood supply of mature bone

Answer 35

**Periosteal arteries** **Nutrient artery** **Epiphyseal** and **metaphyseal** arteries --\> at puberty they unite to form metaphyseal vessels only Arteries branch and course in **Volkmann's canals** --\> **Haversian canals**

Question 36

Bone remodeling

Answer 36

**7 - 10%** of skeleton remodeled every year **Osteoclast** removes bone forming **cutting** **cone** --\> **reversal** --\> **osteoblast** replaces bone

Question 37

Bone pathology

Answer 37

Bone **sclerosis**: bone responds to stress by **remodeling** a more **dense** bone **Osteophyte** formation: **excessive** **remodeling** due to stress **Osteomyelitis**: infection **Fractures** **Tumors**

Question 38

Synarthroses

Answer 38

**Bone** anchored to **bone** by fibrous tissue, resulting in limited to no movement at the joint In functional classification, this is the class called **immoveable joint****s** (note: includes syncondrosis)

Question 39

Syndesmosis

Answer 39

**Fibrous tissue union** In anatomical classification, this is a **fibrous joint** In functional classification, this is a **slightly moveable joint**

Question 40

Synostosis

Answer 40

**Bone union**

Question 41

Synchondrosis

Answer 41

**Cartilage union** In anatomical classification, this is **cartilagenous joint** In functional classification, this is **immoveable joint**

Question 42

Intervertebral disk is what kind of joint?

Answer 42

**Synchondrosis** (**cartilage** union) Has **nucleus** **pulposus** (mass of proteoglycans, 70 - 90% water), **annulus** **fibrosus** (fibrocartilage rests on **vertebral** **endplate** and outer edges attach to anterior/posterior longitudinal ligaments), vertebral endplate (**hyaline cartilage** that gradually ossifies)

Question 43

Disk degeneration

Answer 43

1) **Annulus fibers tear** (due to OA or degenerative disk disease) --\> **nucleus pulposus escapes** thru tear (herniated disk) --\> **neuropathic** **pain** (**myelopathy** if impingement on spinal cord; **radiculopathy** if impinges on spinal roots), **nociceptive pain** (from nociceptors on **sinuvertebral nerve** responding to irritated dura, ligaments, other soft tissues in spinal canal) 2) **Proteoglycans** break down in nucleus pulposus and it becomes **dehydrated** and dense, narrowing intervertebral space

Question 44

Synovial joints (diarthrosis)

Answer 44

In anatomical classification, this is **synovial joint** In functional classification, this is **highly moveable joint** **Joint capsule**: continuous with periosteum of articulating bones **Synovium** (synovial membrane): fibrous tissue membrane lining inside of joint capsule **Articular** cartilage: **hyaline** cartilage **Periarticular** **tissue**: soft tissue surrounding joint

Question 45

Synovium

Answer 45

**Intima**: cells are **synoviocytes** (**Type A** are **macrophage**-like; **Type B** are **fibroblast**-like and produce **hyaluronan**) **Subsynovium**: where **capillaries** are, blends with joint capsule **Synovial** **fluid**: pale yellow, clear, consistency of **egg** **white**; lubrication/reduce friction, nourishes superficial layers of articular cartilage; sources are (1) **capillaries** in subsynovium and (2) **Type B synoviocytes** that secrete hyaluronan; has **few WBCs**, **no neutrophils**

Question 46

Joint effusion

Answer 46

Increase in **synovial fluid** in the synovial space

Question 47

4 zones of articular cartilage (hyaline)

Answer 47

1) **Superficial** zone 2) **Middle** zone 3) **Deep** zone Tidemark 4) **Calcified** cartilage zone (gradually ossifies with age) **Subchondral bone** (provides blood supply for calcified cartilage zone; bone layer just deep to cartilage; can form osteophytes)

Question 48

Facet joint is what kind of joint?

Answer 48

**Synovial joint** Superior and inferior articular processes articulate and are supported by ligaments and deep back muscles Bears less weight than intervertebral disk Joint capsule innervated by sinuvertebral nerve Reacts to trauma with pain, stiffness, deep back muscle spasm

Question 49

Sinuvertebral nerve

Answer 49

Nerve fibers innervate: **Posterior longitudinal ligament** **Ligamentum flavum** Peripheral fibers of **annulus fibrosis** **Facet joint capsule** **Smooth muscle in vessels** **Dura mater** **Periosteum** Branch of spinal nerve that contains **nociceptive** fibers from soft tissues in spinal canal and tells you that you have back pain

Question 50

Spine degenerative changes resulting in pain

Answer 50

1) Outer **annulus fibrosis tears** in ID (OA) --\> interrupted blood supply, activate **sinuvertebral nerve** --\> **nociceptive** **pain** (dull, poorly localized w/o paresthesia) 2) **Breakdown** of **proteoglycan** molecules in **nucleus** **pulposus** --\> dehydration --\> **decrease intervertebral space** --\> spine **malalignment** --\> **laxity** **of ligaments** --\> **facet joint takes on greater load** --\> **articular cartilage injury** --\> **OA** (**nociceptive** **pain**) 3) Bone **sclerosis** --\> **osteophytes** --\> **impingement** of nerve roots in spinal canal --\> **neuropathic** **pain** (sharp, well-localized with paresthesia-**radiculopathy**)