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Chapter 9

Joints

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• Joint = point of contact – between 2 bones– between cartilage and bone– between teeth and bone

• Joints hold bones together but permit movement

• Arthrology = study of joints• Kinesiology = study of motion

INTRODUCTION

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I. Classification of Joints

• Structural classification based on:– presence or absence of a synovial (joint) cavity– type of connective tissue– three structural classifications

• fibrous– do not have synovial cavity– held together by fibrous C.T. (lots of collagen)

• cartilaginous– no synovial cavity– bones held together by cartilage

• synovial – bones forming joint have a synovial cavity– dense irreg. C.T. & accessory ligaments of articular

capsule holds bones together

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• Functional classification based on degree of movement allowed by joint:

1) Synarthrosis = immovable

2) Amphiarthrosis = slightly movable

3) Diarthrosis = freely movable

I. Classification of Joints

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II. A. Fibrous Joints

• No synovial cavity

• Articulating bones held closely together by fibrous C.T.

• Allow limited movement

• 3 structural types– sutures– syndesmoses– gomphoses

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Sutures• Thin layer of dense fibrous connective tissue uniting bones

of the skull

• Irregular/interlocking edges give added strength & prevent fracture

• Synarthrosis because immovable

• Synostosis = suture that has fused completely & been replaced by bone

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Syndesmoses• Greater distance btwn articulating bones & more fibrous

C.T. than sutures

• Arrangements of C.T.– bundles = ligament– sheets = inteross. memb.

• Amphiarthrosis: limited movement

• Examples– Anterior tibiofibular joint– Interosseous membranes in forearm and leg

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Gomphoses

• Dentoalveolar joints: cone-shaped pegs in bony socket

• Synarthrosis

• Only example = teeth in alveolar processes of maxillae and mandible

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B. Cartilaginous Joints

• Lack a synovial cavity

• Allows limited movement

• Articulating bones tightly connected by fibrocartilage or hyaline cartilage

• 2 types– synchondroses– symphyses

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Synchondrosis

• Connecting material = hyaline cartilage

• Synarthrosis

• Examples:– epiphyseal plates– articulation of first rib w/ manubrium of sternum– become synostoses when bone replaces cartilage

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Symphysis

• Ends of articulating bones covered w/ hyaline cartilage

• Thin disc of fibrocart. connects bones

• All occur in midline of body

• Amphiarthrosis • Examples:

– intervertebral disc– pubic symphysis

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C. Synovial Joints• Synovial cavity separates articulating bones

• Freely moveable (diarthroses)

• Articular cartilage covers articulating bones– reduces friction– absorbs shock

• Three structural components:– Articular capsule– Synovial membrane/fluid– Accessory ligaments/discs

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Structural Components: Articular Capsule

• Surrounds joint, encloses synovial cavity, & unites articulating bones

• Two layers– outer fibrous capsule

• usually dense irregular C.T.• attaches periosteum of articulating bones• flexibility permits considerable movement, but

tensile strength prevents dislocation • forms ligaments (dense CT) when arranged in bundles

– inner synovial membrane • secretes a lubricating synovial fluid• sometimes contains articular fat pads

– EX: infrapatellar fat pads

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• Synovial fluid– Mixture of hyaluronic acid secreted by synovial

membrane & interstitial fluid

– Lubricates joints & absorbs shock

– Provides nutrients to/removes wastes from articular capsule

– Phagocytes remove microbes

– Immobility of joint increases viscosity, activity decreases viscosity

Structural Components, ctd

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Structural Components, ctd

• Accessory ligaments & articular discs/menisci– extracapsular ligaments lie outside joint capsule

– intracapsular ligaments lie within capsule

– articular discs (menisci) = pads of fibrocartilage btwn bones

• attached to capsule• allow 2 bones of different shape to fit tightly• maintain stability of joint

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Nerve and Blood Supply of Synovial Joints

• Nerves to joints are branches of nerves that supply muscles that move joint

• Many nerve endings distributed to articular capsule & accessory ligaments– sense pain– relay information about degree of stretch/movement

• Many components are avascular but arteries can penetrate ligaments/capsule – deliver nutrients to joint– veins remove CO2 & wastes

• pass from chondrocytes to synovial fluid to vein• pass directly from all other joint structure to vein

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Bursae and Tendon Sheaths• Bursae

– Fluid-filled saclike structures that alleviate friction in some joints

– Resemble joint capsules• Walls consist of C.T. & synovial membrane

– Fluid similar to synovial fluid

– Located between:• Skin/bone• Tendon/bone or ligament/bone• Muscle/bone

• Bursitis = chronic inflammation of a bursa

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Bursae and Tendon Sheaths

• Tendon sheaths = tubelike bursae that wrap around tendons that experience large amounts of friction

– where tendon enters synovial cavity• Biceps brachii @ shoulder

– where many tendons come together in small space• Wrist/ankle

– where there is considerable movement• Fingers/toes

• Bursae & tendon sheaths reinforce the articular capsule

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Types of Movements at Synovial Joints

Four main categories of joint movement (Table 9.1)

1) Gliding movements• flat bone surfaces move back and forth & side to side

with respect to one another

• no significant alteration of angle between bones

• limited in range because of structure of capsule/ligaments

• Ex: intercarpal or intertarsal joints (planar joints)

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Types of Movements at Synovial Joints

2) Angular movements• Increase or decrease in angle btwn articulating bones

• Measured with respect to anatomical position

• Covered in lab

• Flexion/extension, lateral extension, hyperextension

• Abduction/adduction, circumduction

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Types of Movements at Synovial Joints

4) Special movements– Occur only at certain joints– 11 different special movements

• Elevation/depression: upward/downward motion• Protraction/retraction: movement in transverse plane• Inversion/eversion: movement of soles medially/laterally• Dorsiflextion/plantarflexion: bending of ankle in direction

of superior/inferior surfaces• Supination/pronation: movement of prox/distal

radioulnar joints which turns palms anteriorly/posteriorly• Opposition: movement of carpometacarpal joint in which

thumb touches fingers of same hand

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Types of Synovial Joints

• ***These will be covered in lab, so they will be minimally discussed in lecture. However the notes may be useful to you in studying for the lab exam.***

• Varying shapes of bones/joints allow numerous movements

• 6 types– Planar– Hinge– Pivot– Condyloid– Saddle– Ball & socket

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1. Planar Joint

• Articulating surfaces flat or slightly curved

• Primarily allow gliding movements

• Rotation prevented by ligaments

• Nonaxial because motion does not occur around axis or along plane

• Examples– intercarpal or intertarsal joints– sternoclavicular joint– vertebrocostal joints

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2. Hinge Joint

• Convex surface of one bone fits into concave surface of another

• Monaxial: allows motion around single axis

– produces angular opening & closing– flexion/extension only

• Examples– Knee, elbow, interphalangeal joints

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3. Pivot Joint

• Rounded/pointed surface of bone articulates with ring formed by 2nd bone & ligament

• Monaxial: rotation around own axis

• Examples– Proximal radioulnar joint

• supination• pronation

– Atlanto-axial joint• nodding head “no”

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4. Condyloid (Ellipsoidal) Joint

• Convex oval-shaped projection articulates with oval depression

• Biaxial: allows motion along two axes– flexion/extension– abduction/adduction/circumduction

• Examples: wrist & metacarpophalangeal joints for digits 2 to 5

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5. Saddle Joint

• Articulating surface of one bone saddled-shaped; other bone fits into “saddle”

• Modified condyloid joint

• Biaxial

– Circumduction allows tip of thumb travel in circle

– Opposition allows tip of thumb to touch tip of other fingers

• Example: carpo/metacarpal joint of wrist/thumb

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6. Ball and Socket Joint

• Ball-like head of long bone fits into a cup-like socket

• Multiaxial: motion around 3 axes & all directions in between– flexion/extension– abduction/adduction– rotation

• Examples:– shoulder joint: humerus in glenoid– hip joint: femur in acetabulum

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III. CONTACT & RANGE OF MOTION AT SYNOVIAL JOINTS

• Range of motion (ROM) = range (measured in degrees of circle) thru which bones of joint can move

• Several factors contribute to keeping articular surfaces in contact & affect ROM:

1) Structure and shape of the articulating bone

2) Strength and tautness of the joint ligaments

3) Arrangement and tension of the muscles

4) Contact of soft parts

5) Hormones

6) Disuse

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IV. ETC…

• Arthroscopy = examination of joint w/ pencil-sized instrument– removes torn knee cartilages & repair ligaments– requires only small incision

• Arthroplasty = joint replacement– hip & knee replacements common

• Dislocation of a joint = luxation – refers to displacement of a bone from a joint– torn tendons, ligaments, capsules accompany dislocation– subluxation = partial dislocation

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ETC…

• Sprain– forcible twisting of joint that stretches or tears

ligaments– no dislocation of the bones– may damage nearby blood vessels, muscles or

tendons or nerves– swelling & hemorrhage from damaged blood vessels– ankle & back are common sprain sites

• Strain– overstretched or partially torn muscle– results from sudden, powerful contraction

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DISORDERS: HOMEOSTATIC IMBALANCES:

• Osteoarthritis– degenerative joint disease commonly known as “wear-

and-tear” arthritis– characterized by deterioration of articular cartilage and

bone spur formation– noninflammatory – primarily affects weight-bearing joints

• Gouty arthritis – sodium urate crystals deposited in soft tissues of joints

causing inflammation, swelling, and pain– If not treated, bones @ affected joints eventually fuse,

rendering joints immobile

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Rheumatoid Arthritis

• Autoimmune disorder: body attacks its own cartilage & joint linings

• Inflammation of synovial membrane

– accumulation of synovial fluid causes swelling, pain & loss of function

– eventually, fibrous tissue in joints becomes ossified joint becomes immovable

• Occurs bilaterally