Joints (Week 1--Metten) Flashcards
How do MSK tissues develop?
Derived from mesoderm, which turns to mesenchyme, which turns to MSK cells (fibroblasts, chondrocytes, osteocytes) to make MSK tissues
Development of extremities
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
Fibrous tissue (connective tissue) composition
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)
3 skeletal muscle wrappings
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)
Myotendinous junction
Where epimycium and perimycium fuse to form a tendon
Abrupt, vascularized
Tendon structure
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
Tendonitis
Acute inflammation of tendon, most often due to overuse injury
Tendonosis
Injury that results from microtears in tendon without significant inflammation
From overuse injury, compression injury, degenerative changes
Usually chronic
When tendon is injured (prolonged periods of tensile stress), what happens?
Prolonged periods of tensile stress –> collagen breakdown –> Ca2+ deposits
If you see Ca2+ deposits on X-ray means you’ve been injured there before
Tendon sheath
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!
Tenosynovitis
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
Two different types of tendon attachment to bone
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
Where tendons attach to bone, are there nerve endings?
Yes, nociceptors and mechanoreceptors
Enthesitis
Inflammation at enthesis
Ligament structure
Attach bone to bone
Similar structure to tendon (fibrous or enthesis attachments)
Nerve endings are nociceptors or mechanoreceptors (proprioception)
Have endoligament and epiligament?
Ligament pathology
Acute injury (sprain)
Degeneration
Bursa
Fibrous tissue sac lined with synovium
Located where muscle and bone or tendon and bone meet
Bursitis
Bursa becomes inflamed (actually is synovium inside bursa becoming inflamed)
Shoulder Impingement Syndrome
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)
Cartilage
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
3 types of cartilage
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)
Proteoglycan aggrecan structure of cartilage ECM?
Complex proteoglucan molecules (chondroitin sulfate, keratin sulfate)
Hyaluronan
Aggrecans form large aggregates
Perichondrium of cartilage
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
Types of injury to hyaline cartilage
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)
2 types of bone
Cortical/compact bone
Trabecular/spongy/cancellous bone
2 bone membranes
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
Osteoid
Special name for ECM of bone created by osteoblasts
How do you create bone?
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
Bone composition
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)
Osteocytes
Cell bodies in lacuna due to density of matrix
Cell processes are in canaliculi so can communicate with other osteocytes
Haversian system nourishes osteocytes
Haversian canal
Lined by osteum
Within osteon
Contain blood vessels
Osteon
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
Osteoclasts
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
How are osteoclasts triggered to munch bone?
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
Blood supply of mature bone
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
Bone remodeling
7 - 10% of skeleton remodeled every year
Osteoclast removes bone forming cutting cone –> reversal –> osteoblast replaces bone
Bone pathology
Bone sclerosis: bone responds to stress by remodeling a more dense bone
Osteophyte formation: excessive remodeling due to stress
Osteomyelitis: infection
Fractures
Tumors
Synarthroses
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 joints (note: includes syncondrosis)
Syndesmosis
Fibrous tissue union
In anatomical classification, this is a fibrous joint
In functional classification, this is a slightly moveable joint
Synostosis
Bone union
Synchondrosis
Cartilage union
In anatomical classification, this is cartilagenous joint
In functional classification, this is immoveable joint
Intervertebral disk is what kind of joint?
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)
Disk degeneration
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
Synovial joints (diarthrosis)
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
Synovium
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
Joint effusion
Increase in synovial fluid in the synovial space
4 zones of articular cartilage (hyaline)
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)
Facet joint is what kind of joint?
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
Sinuvertebral nerve
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
Spine degenerative changes resulting in pain
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)
