Biol 2401

Biol 2401 A&P Lecture Notes Joints Dr. Weis

JOINTS

where two or more components of the skeleton meet, whether it is a bone or cartilage, and referred to as joints or articulations.
May be temporary or permanent (the majority of joints are permanent).

Three major types of joints are :

1. Fibrous immovable synarthrosis

2. Cartilagenous slightly movable amphiarthrosis

3. Synovial movable diarthrosis

1. Fibrous

joints held together by dense fibrous tissue

no joint cavity is present

Three types

a. Synostosis...fibrous tissue replaced by bone. A tight joint formed by the interlocking of bone termed

sutures is seen in the skull

b. Syndesmosis...more fibrous tissue called the interosseous

membrane. Seen in the radius/ulna and tibia/fibula

c. Gomphosis...fibrous tissue creating a short membrane called the periodontal ligament. Seen in fixation of teeth in the mandible and maxilla

2. Cartilagenous

articulating bones united by cartilage

lacking a joint cavity

Two types

a. Synchondrosis...hyaline cartilage at the epiphyseal plates

. Seen during bonegrowth.

This is a temporary joint.

b. Symphyses...the surfaces of opposed bone are covered with sheets of hyaline cartilage and reinforced by fibrocartilage.

Seen in the intervertebral discs and the pubic bones

3. Synovial

Bones held together by an articular capsule

Opposed surfaces are covered by articular cartilage

Contain synovial fluid

The articular cartilage for synovial joints is HYALINE

The joint capsule unites the bone and is a dense fibrous tissue that is a continuation of the periosteum.
Ligaments from this structure are also formed to help in stabilization.

The inner layer of the capsule is lined by a SYNOVIAL MEMBRANE a thin, 1-3 layers of synovial cells
villi are formed due to the folding fo the membrane and form pockets called BURSAE.

This membrane produces synovial fluid, which is a plasma filtrate mixed with hyaluronic acid to form a viscous fluid.
Hyaluronic acid provides lubrication for the joint and nutrition for the cartilage.

SYNOVIAL JOINT STRUCTURE SUMMARY

* articular cartilage (hyaline)

* joint cavity

* articular capsule

* synovial membrane

* synovial fluid

additional structures for synovial joints

> ligaments :: reinforce, strengthen, help direct bone movement

classified as

a. intracapsular (intrinsic)

b. extracapsular

> fat pads :: cushion

> fibrocartilage discs (menisci) :: increase stability

> bursa :: flat synovial sacs that decrease friction

> tendon sheath :: elongated bursa that wrap around a tendon to decrease friction

Stability of Syovial Joints depends on ::

Motion is created by the muscles contracting across a movable joint

so that their insertion (muscle attatchment to a movable bone)

moves toward their orgin (muscle attatchment to a less movable bone).

PLANES OF MOTION :: along the axis formed by the three body planes

(transverse, frontal, midsaggital)

RANGE OF MOTION ::

1. nonaxial

2. uniaxial (one plane)

3. biaxial (two planes)

4. multiaxial (all three planes)

Therefore with the planes and range of motion, we have 3 general types of movement ::

a. Gliding

b. Angular

c. Rotation

a. Gliding :: one fairly flat surface slips over another

e.g. intercarpal, intertarsal, vertebral process

b. Angular :: changing the angle between bones creating the possible motions

flex --> decrease the angle toward 90 degrees

extend --> increase the angle toward 180 degrees

abduction --> away from midline

adduction --> toward midline

circumduction --> circular

c. Rotation :: turning of bone around its own long axis

creates a motions :

pivot ... seen in atlas/axis vertebra

medial/lateral rotation ... appendages

Special Movements by certain synovial joints ::

1. supination/pronation radius/ulna

2. inversion/eversion foot

3. protraction/retraction mandible

4. elevation/depression mandible

5. oppostion thumb

Other ways to classify joints and their movements ::

Plane joints :: gliding motion

Hinge joints :: single plane, flex and extend

Pivot joints :: pivot

Condyloid jnts :: angular motion

Saddle joint :: like condylar, bone surfaces are different

Ball and Socket joints :: multiaxial

SPECIFIC SYNOVIAL JOINTS

I. Shoulder (Glenohumeral joint)

Ball and socket joint --> multiaxial movement

Glenoid fossa of scapula and Head of humerus

Stability ::

a. Primarily due to muscle tendons

* Biceps brachii (mainly)

* Rotator Cuff

tendons of the subscapularis m.

supraspinatus m.

infraspinatus m.

teres minor m.

b. ligaments

coracohumeral

glenohumeral

transverse humeral

c. Very little stability is contributed by the articular surfaces. This therefore allows a very freely movable joint.

Problems :: dislocation

stretching of the rotator cuff

II. Elbow (Cubital joint)

Hinge joint --> flex, extend

Stability

a. Primarily by the articular surfaces of the ulna and humerus

b. ligaments

annular

collateral (medial/lateral)

d. tendons (Biceps brachii, Triceps brachii, Bracialis)

e. capsule

III. Hip (Coxal joint)

Ball and socket ---> multiaxial

Stability

a. Articular surface of acetabulum and head of femur

b. Ligaments : iliofemoral, pubofemoral, ischiofemoral, ligamentum teres

c. capsule

IV. Knee (Stifle joint)

Hinge joint --> flex, extend, some rotation is permitted

Actually three joint in one ::

femoropatellar

medial tibiofemoral

lateral tibiofemoral

Stability

a. Ligaments

* Extracapsular :: prevent hyperextension

* Intracapsular :: help prevent anterior/posterior displacement

anterior cruciate

posterior cruciate

these ligaments are named for their tibial attachment and will extend to the femur

b. Menisci :

medial and lateral semilunar fibrocartilage

cushion and deepen the articular surface between the tibia and femur

shock absorption

c. Muscle tendons ::

Quadriceps group (insert on the patella)

Semimembranous m. (part of the hamstrings)

Summary ::

Joints are usually named for the bone involved, with the bone

most proximal named first, followed by the distal bone.

Examples ::

Some exceptions :

Atlantoccipital joint (the distal bone is named first)

Stifle

Cubital

PROBLEMS ::

Sprains ... ligaments reinforcing a joint are stretched or torn

Cartilage... tearing of articular cartilage can form free floating or "joint bodies"

Dislocations... articular surfaces are forced out of position

subdivisions ::

total dislocation is called a luxation

partial dislocation is called a subluxation

Bursitis / Tendonitis.... caused by excessive strain or friction

Arthritis... inflammatory condition that causes damage to articular cartilage.

Due to several causes :

a. Acute arthritis ... usually due to bacterial infection

b. Chronic arthritis

1. Osteoarthritis / Degenerative Joint Disease (DJD)

wear and tear on articular cartilage that can cause changes in bone

to thicken and create spurs that may restrict joint movement.

Can result in causing secondary inflammation

2. Rheumatoid arthritis

autoimmune disease

cartilage is eventually eroded away --> scare tissue forms,

ossifies and fuses bone ends together

3. Gout

increased blood levels of uric acid can cause urate crystals to be deposited in the soft tissues of the joint