A&P Chapter 9: Joints and Articulations

Joint Design and Movement - Overview

Overview

• the adult human body has 206 bones, and all are connected together (except hyoid)

• because bones are inflexible, movement can only occur at articulations or joints, where two bones connect

• each joint reflects compromise between need for strength and mobility = differ in amount of movement permitted (range of motion/ROM)

• anatomical structure of a joint determines type and amount of movement that may occur

Structural Classification of Joints

structural classification is based on anatomical components that make up joint

• fibrous joints: held together by fibrous connective tissues but lack cartilage and possess no cavity between bones. they are either SYNARTHROTIC or AMPHIARTHROTIC

• cartilaginous joints: held together by fibrous connective tissues such as ligaments, but also possess hyaline/fibrocartilage. cartilaginous joints lack a joint cavity and are either SYNARTHROTIC or AMPHIARTHORIC

• synovial joints: held together by fibrous connective tissues, hyaline cartilage and/or fibrocartilage, and possess a joint cavity. all synovial joints are DIARTHORTIC. they are complex in structure + the most numerous joint type. they permit greatest range of motion.

Functional Classifications of Joints

functional classifications are based on range of motion allowed

• synarthrosis: NO MOVEMENT IS PERMITTED. the body edges are close together/interlocking. these strong joints are located where movement between bones must be prevented.

  • sutures, gomphoses (teeth), synchondroses

• amphiarthrosis: SLIGHT MOVEMENT IS ALLOWED. permits more movement than synanthrotic joints, but is much stronger than freely moveable joints

  • intervertebral discs, pubic symphysis, tibiofibular joint, sternomanubrial joint

• diarthrosis: FREELY MOVEABLE JOINT (aka synovial joint). provide wide range of motion, typical in appendages

  • shoulder/hip, elbow/knee, atlantoaxial, wrist/knuckles, carpal bones

Axis of motion

axis of motion: the movements of diarthrotic joints are divided along the three planes: frontal, transverse, and sagittal

• non-axial motion: LINEAR movements where bones SLIDE (vertebrocostal joints, sacroiliac joint, and intercarpal joints)

• uniaxial motion: movement in ONE planes (interphalangeal joints, elbow, knee)

• biaxial motion: movement in TWO planes (metacarpophalangeal joint, occipital condyles to atlas)

• multi-axial motion: movement in THREE planes (shoulder + hip joint)

[Fibrous Joints]

Sutures

• synarthrotic joint located only between the bones of skull

• edges of bone are interlocked + bound together at the suture by dense fibrous connective tissue

• in newborns/infants: areas of connective tissue is wider and called fontanelles (soft spots)

• in adulthood: sutures of skull transform to synostoses (where bones have fused together + tissue turned to bone)

• abnormal fusion of bones = synostosis that shouldn’t exist (ex: premature ossification of cranial sutures limits growth of brain) (ex 2: radio-ulnar synostosis)

[Fibrous Joints]

Syndesmosis

• bones are connected by ligaments or broad/sheet-like membrane called an interosseous membrane

• they are amphiarthrotic

• most common example: distal articulation between the tibia and fibula called the tibiofibular joint

• example: middle radio-ulnar joint, but NOT THE proximal/distal ends of the radius and ulna because those are synovial/diarthrotic

[Fibrous Joints]

Gomphosis

• found in the maxillae and mandible where teeth are fixed securely in sockets of the alveolar margins

• fibrous connective tissue between a tooth and its socket is a periodontal ligament

• a synarthrotic joint is sometimes called a “peg-in-socket” joint

[Cartilaginous Joints]

Synchondrosis

• rigid, hyaline cartilage bridge units the bones

• example: cartilaginous joint found between ends of the first pair of ribs + manubrium of the sternum (all other ribs are synovial joints)

• example: epiphyseal plate found holding the epiphysis of a long bone to the diaphysis

[Cartilaginous Joints]

Symphysis

• articulating bones are separated by a wedge or pad of fibrocartilage

• example: between vertebrae where thick pad of fibrocartilage forms the intervertebral disc

• example: two pubic bone (pubic symphysis)

• it is an AMPHIARTHROTIC joint = slight movement

[Synovial Joints]

Structural features of a synovial joint

• joint cavity: space between articulating bones

• joint capsule: layers of connective tissue enclose the cavity to house the fluid

  • articular capsule: thick outer layer = strength/stability

  • synovial membrane: inner soft tissue, leak plasma to produce synovial fluid

• synovial fluid: derived from blood + egg consistency. small amount of liquid. three primary functions:

  • lubrication: reduces friction, called weeping lubrication

  • nutrient distribution: provides nutrients/waste disposal for chondrocytes. circulates when joint moves

  • shock absorption: provides cushion against shock

• articular cartilages: line the surfaces of articulating bones; composed of hyaline cartilage. provides slick, smooth surface = less friction

• accessory organs (in complex synovial joints like the knee)

  • ligaments: support, strengthen, reinforce (intrinsic: parallel bundles within the joint capsule) (extrinsic: separate from joint capsule, can pass outside or inside joint capsule)

  • bursa: small, fluid-filled pocket inside connective tissue. contains synovial fluid + lined by membrane. form where tendon/ligament rub against each other = shock absorbers and reduce friction

  • tendon sheath: smaller bursa, where tendon crosses a joint

  • fat pads: localized masses of adipose tissue. protects articular cartilages + packing material

  • meniscus: pad of fibrous cartilage between opposing bones withina joint. can channel flow of fluid.

[Types of Synovial Joints]

Pivot Joints

rounded end of one bone protrudes into a sleeve or ring composed of bone/ligament; uniaxial

• proximal radio-ulnar joint, neck or dens of axis to atlas

[Types of Synovial Joints]

Hinge Joints

cylindrical projection of one bone fits into a trough-shaped surface on another bone; uniaxial

• elbow joint (this is both a pivot and hinge), knee joint, ankle joint, and interphalangeal joints

[Types of Synovial Joints]

Saddle Joints

articular surfaces have a concave area on one that fits with the convex area of the other; biaxial

• first carpometacarpal joint in the thumb

[Types of Synovial Joints]

Plane Joints

AKA gliding joints

articular surfaces are flat and only allow for short gliding movements; multi axial

• intercarpal and intertarsal joints, sacro-iliac joint, vertebrocostal joint, acromioclavicular and sternoclavicular joints, and between superior/inferior articulating processes of vertebrae)

[Types of Synovial Joints]

Condyloid Joints

AKA ellipsoid joint

oval articular surface of one bone fits into a complementary depression in another; biaxial

• metacarpophalanges 2-5 (knuckles), radiocarpal joints, and metatarsophalangeal joints

[Types of Synovial Joints]

Ball and Socket Joints

the spherical end of one bone articulates with cup-like socket of another bone; multi-axial

• shoulder joint and hip joints

How does joint movement correlate to joint strength?

• a joint cannot be both highly mobile and very strong

• the greater the range of motion —> the weaker it becomes

  • a synarthrotic joint, the strongest type of joint, permits no movement

  • a diarthrotic joint (ex: shoulder), is far weaker, but permits a broad range of motion

[Body Movement]

Flexion

bending a joint to decrease the angle

• detail: basically going upwards with a limb. happens in the anterior-posterior plane (front-to-back)

• example: lifting a dumbbell in a biceps curl

[Body Movement]

Extension

straightening a joint to increase the angle

• detail: basically going backwards or back down with a limb. in the anterior-posterior plane (front-to-back)

  • in anatomical position, all major joints (except ankle) are at full extension

  • example: lowering a dumbbell back down after a bicep curl

[Body Movement]

Lateral Flexion

tilting your upper body or head to the side

• detail: bending the neck or body to the left or right

[Body Movement]

Hyperextension and Hyperflexion

moving a joint too far past its normal limit

• detail: moving it past the anatomical position. they are a common cause of injury in the joints like the knee or elbow

• example: looking up at the stars hyperextends the neck

[Body Movement]

Abduction

moving a body part outward, away from your center line

• detail: happens in the lateral-medial plane (side-to-side). moves away from the longitudinal axis (center line)

• example: raising arms for a jumping jack, spreading fingers, or cocking the wrist

• memory trick: “ABDUCT” means to take away (away from body)

[Body Movement]

Adduction

bringing a body part inward, toward the center line

• detail: opposite of abduction, lateral-medial plane (side-to-side), moves toward the longitudinal axis (center line)

• example: bringing arms down in a jumping jack, bringing fingers together, or snapping the wrist

[Body Movement]

Circumduction

moving a limb so the end of it draws a circle

• detail: moving a limb in a circle creates a cone in space

• example: doing windmill exercises with your arm

[Body Movement]

Medial (internal) Rotation

twisting a limb inward toward your center line

• detail: the anterior (front) surface of the limb turns toward the body’s midline

• example: standing pigeon-toed (toes pointed inward)

[Body Movement]

Lateral (external) Rotation

twisting a limb outward away from your center line

• detail: anterior (front) surface turns away from the midline

• example: a ballerina’s first position (heels together, toes out)

[Body Movement]

Superior and Inferior Rotation (image just shows scapula but doesn’t necessarily match)

tilting your shoulder blade up or down

• details: these are movements of the scapula. they are tracked by the direction the glenoid cavity faces

[Body Movement]

Supination

turning the forearm so the palms face forwards/up

• detail: in anatomical position, the forearm is supinated, the radius/ulna are parallel, and the palms face forward (anteriorly)

• example: holding a bowl of soup

[Body Movement]
Pronation

turning the forearm so the palms face backwards/down

• detail: the radius rotates and crosses over the ulna. the palms face backward (posteriorly)

• example: basketball players pronate to dribble a ball

[Body Movement]

Dorsiflexion

pulling your foot up at the ankle

• details: flexion at the ankle joint that elevates the sole

• example: rocking back onto your heels

[Body Movement]

Plantar Flexion

pushing your foot down at the ankle

• detail: opposite of dorsiflexion, extends the ankle and elevates the heel

• example: standing on your tippy toes

[Body Movement]

Inversion

tilting the bottom of your foot inward

• detail: the sole turns inward, lifting the medial/inner edge of the sole

• example: club foot

[Body Movement]

Eversion

tilting the bottom of your foot outward

• detail: the sole turns outward, lifting the lateral/outer edge of the sole

[Body Movement]

Protraction

pushing a body part forward horizontally

• detail: moving a part anteriorly (forward) in the horizontal plane

• example: sticking your jaw out into an under-bite

[Body Movement]

Retraction

pulling a body part backward horizontally

• detail: opposite of protraction, moving a part posteriorly (backwards) in the horizontal plane

• example: pulling your jaw back into an overbite

[Body Movement]
Depression

moving a body part downward

• detail: structure moves inferiorly/downwards

• example: opening your mouth (the jaw)

[Body Movement]

Elevation

moving a body part upwards

• detail: structure moves superiorly/upward

• example: closing your mouth (the jaw)

[Body Movement]

Excursion

shifting your jaw side-to-side

• detail: specific to the mandible (jawbone)

[Body Movement]

Opposition

touching your thumb to your fingers

• details: moving the thumb towards the palm or the pads of other fingers

• example: snapping your fingers

[Body Movement]

Reposition

putting your thumb back to original position (away from pointer finger)

• detail: returning thumb to original position after opposition

[Anatomy of Selected Synovial Joints]

Vertebral Column

• held together by intervertebral discs + adjacent vertebrae also articulate with each other at synovial joints formed between superior/inferior articular processes called zygapophysial joints

• atlanto-occipital joint is formed by the articulations between the superior articular processes of the atlas and occipital condyles on base of skull

• the atlantoaxial joint is located between the atlas and axis

[Anatomy of Selected Synovial Joints]

Temporomandibular Joint (TML)

the joint that allows for opening (mandibular depression) and closing (mandibular elevation) of the mouth

also side-to-side and protraction/retraction motions of lower jaw

[Anatomy of Selected Synovial Joints]

Shoulder Joint

• the shoulder joint is called the glenohumeral joint

• it is a ball-and-socket joint formed by head of humerus and glenoid cavity of scapula

• glenoid labrum: small lip of fibrocartilage, extends around outer margin and deepens socket

• coracohumeral ligament: structural support for the joint, thickenings of articular capsule wall

• glenohumeral ligament: three ligaments, anterior side

• rotator cuff: thickening of capsule formed by fusion of four muscle tendons

• subacromial burse and subscapular bursa: help prevent friction between rotator cuff muscle tendons and scapula

[Anatomy of Selected Synovial Joints]

Elbow Joint

• uniaxial hinge joint formed by the humeroulnar joint

• it is the articulation between the trochlea of the humerus and the trochlear notch of the ulna

• also: humeroradial joint and the proximal radioulnar joint

• on the medial side: ulnar collateral ligament

• on the lateral side: radial collateral ligament

• the annular ligament encircles the head of the radius

[Anatomy of Selected Synovial Joints]

Hip Joint

• multiaxial ball-and-socket joint between head of femur and the acetabulum of the hip bone

• the acetabulum is deepened by the acetabular labrum (fibrocartilage lip)

• ligaments: iliofemoral ligament, pubofemoral ligament, and ischiofemoral ligament (all spiral around head/neck of femur)

• the ligament of the head of femur spans between acetabulum and femoral head

[Anatomy of Selected Synovial Joints]

Knee Joint

the knee joint is the largest joint of the body

• three articulations:

  • femoropatellar joint: between patella and distal femur

  • medial tibiofemoral joint and lateral tibiofemoral joint: between medial and lateral condyles of femur/tibia

• patellar ligament: continuing from patella to tibia

• fibular collateral ligament: lateral side + spans from lateral epicondyle of femur to head of fibula

• tibial collateral ligament: medial knee runs from medial epicondyle of femur to tibia

• anterior cruciate ligament and posterior cruciate ligament: inside the knee, two intracapsular ligaments

[Anatomy of Selected Synovial Joints]

Ankle and Foot Joints

• the ankle is formed by the talocrural joint

• consists of articulations between talus bone of foot and distal ends of tibia/fibula

• deltoid ligament: on the medial side; supports the ankle joint and resists excessive eversion

• anterior talofibular ligament and posterior talofibular ligament: small ligaments, span between talus bone and malleolus of fibula

• calcaneofibular ligament: located between calcaneus bone (heel) and fibula

Development of Joints

• joints form during embryonic development in conjunction with the formation and growth of associated bones

• mesenchyme: the embryonic tissue that gives rise to all bones, cartilages, and connective tissues of the body

[Common Joint Injuries]

Sprain

stretching or tearing of a ligament across the joint capsule

[Common Joint Injuries]

Strain

stretching or tearing of a tendon attaching muscle to bone

[Common Joint Injuries]

Dislocation

• also known as luxation

• reinforcing structures cannot protect a joint from extreme stresses = articulating surfaces are forced out of position

• displacement damages articular cartilages, tear ligaments, and distorts the joint capsule

• even though inside of joints have no receptors, nerves monitor the capsule, ligaments, and tendon = painful

• subluxation: a partial dislocation

[Common Joint Injuries]

Bursitis

inflammation of the bursa

[Common Joint Injuries]

TMJ Disorder

• a type of temporomandibular disorder/TMD

• can cause pain in your jaw joint and in the muscles

• can be due to: genetics, arthritis or jaw injury

• they tend to clench or grind their teeth (bruxism), but doesn’t have to be related

[Common Joint Injuries]

Arthritis

inflammation/degenerative disease of the joint where synovial membranes thicken (pannus) and fluid production decreases = friction and pain

arthroscopic surgery may be necessary to treat injuries + install artificial joints

• osteoarthritis (AKA degenerative arthritis/joint disease): affects individuals 60+ normally. can result from wear and tear or genetic factors (collagen). 25% of women and 15% of men over age 60 show signs of this

• rheumatoid arthritis: an autoimmune disease. can occur at any age but more common in middle age + women. infection, genes, and hormone changes can cause this. usually impacts joints on both sides of body equally. most common parts: wrists, fingers, knees, feet, and ankles.

• gouty arthritis: gout is caused by too much uric acid in the blood = form hard crystals in joints. this causes burning pain, stiffness, and swelling, especially in big toe. more common in men.