ARTICULATIONS (JOINTS)

An articulation or joint is any interface between two bones.

"Arthr-" is the common prefix or term relating to joints.

*For example: Arthrology, Arthritis, Arthroscope, Arthropod ("jointed foot")

Kinesiology: the study of motion at joints and the interrelationships of bones, muscles and joints.

Classification of Joints

A) Structural Classes

1.Fibrous: fibrous connective tissue binds articulating bones.

2.Cartilaginous: cartilage binds bones.

3.Synovial: synovial cavity is present with ligaments assisting.

B) Functional Classes (based on degree of movement)

1.Synarthroses: immovable.

2.Amphiarthroses: slightly movable.

3.Diarthroses: freely movable.

Synarthroses--rigid and immovable. Tight connection via fibrous tissue or cartilage.

3 subtypes.

1.Sutures: found in skull. Adjacent bones fused. Interface can be convoluted or flat (maxilla & palatine). Fibrous.

2.Synchondroses: temporary joint in growing bones formed between diaphysis and epiphysis. Joint ossifies when adult length is achieved. Cartilaginous.

3.Gomphoses: teeth in bony sockets (alveoli). Fibrous.

Amphiarthroses--semi-movable.

2 subtypes.

1.Symphyses: Flexible connection with pad of fibrocartilage between bones.

For example: symphysis pubis and intervertebral joints. Cartilaginous.

2.Syndesmoses: adjacent bones are held together by collagenous fibers or interosseous ligaments.

For example: distal end of tibia-fibula. Fibrous.

Diarthroses -- freely movable joints. Synovial joint enclosed within joint capsule.

Range of movement limited by bone, muscle and ligament attachments.

Structure: bones with articular cartilages interface within joint capsule.

Synovial fluid between articulating surfaces. Articular cartilage is avascular.

Associated Structures of Synovial Joints:

Meniscus: cartilaginous pads in joint capsule which serve as cushions and guides for articulations.  (See section on knee joint).

Bursa: sac filled with synovial fluid. Cushions muscles. Bursitis is an inflammation of bursa.

Tendon Sheath: modified bursa-- facilitates gliding of tendons.

Example: Tendon sheaths of wrist (carpal tunnel)

Diarthroses Subtypes:

1.Gliding : Simple, flat articulation -- slight movement allowed in many directions (non-axial)

E.g., carpal and tarsal bones.

2.Condyloid (Ellipsoidal): convex-concave articulation. E.g., Metacarpal-phalanx (knuckle) articulation. Biaxial movement possible.

3.Hinge: Convex-concave articulation with bending in one plane of motion. Uniaxial.

E.g., elbow (humerus-ulna), phalanges.

4.Saddle: convex-concave/concave-convex articulation--a modified condyloid.

Only at trapezium and first metacarpal. Allows thumb to be opposable.

5.Pivot: rotation around a central axis. E.g., Atlas/axis articulation--allows rotation of head. Radio-ulnar joint allows pronation and supination of forearm.

6.Ball-and-Socket: modified condyloid.

Femur head - acetabulum; humerus head and glenoid cavity of scapula.

Movements at Diarthroses:

Angular Subtypes:

1.Flexion: decrease the angle of a joint--e.g., bending forearm at elbow.

2.Extension: increase the angle of a joint.

3.Hyperextension: joint angle past 180 degrees.

4.Abduction: body part moves away from main axis of body or appendage.

5.Adduction: body part moves toward the main axis of body or appendage.

Circular Subtypes:

1) Rotation: no lateral displacement. E.g., at pivot & ball and socket joints.

At elbow: pronation & supination.

At hip and shoulder: medial & lateral rotation.

2) Circumduction: appendage moved in cone-forming arc.

Distal end moved, proximal end is pivot. Shoulder, arm, trunk, hip and ankle.

Special Movements:

*Dorsiflexion: flexion at ankle.

*Plantar flexion: extension at ankle.

*Inversion: foot moved inward at ankle.

*Eversion: foot moved outward or laterally.

*Protraction: forward movement parallel to ground--jaw and shoulder.

*Retraction: reverse movement parallel to ground--jaw and shoulder.

*Elevation: body part moved superiorly--jaw and shoulder.

*Depression: body part moved inferiorly -- jaw and shoulder.

SPECIFIC JOINTS

Jaw (Temporomandibular, TMJ)

Shoulder (Glenohumeral; Humeroscapular)

Elbow

Hip (Coxal)

Knee (Tibiofemoral)

Ankle (Talocrural)

Intervertebral

Temporomandibular Joint or Jaw

Articulation between mandibular fossa of temporal bone and the condyle of the mandible.

1) Only movable joint in the skull

2) Combination hinge and gliding joint

*Hinge action: allows elevation and depression of jaw.

*Gliding action: allows protraction and retraction.

Made possible by the articular disk. Allows condyle of mandible to slide or glide forward and backward

(protraction & retraction) and laterally against the articular tubercle of the temporal bone.

Articular disc separates joint into two regions.

Malalignment of TMJ results in TMJ syndrome.

Condition is associated with pain in jaw, neck and shoulders along with ringing in ear (tinnitis).

Jaw can easily be dislocated -- mandibular condyle slides to far laterally or forward,

past normal location on articular tubercle.

Humeroscapular or Shoulder Joint

Multiaxial, Ball-and-Socket Joint. Most mobile joint of body.

Head of humerus articulates in shallow glenoid fossa of scapula (although depth is increased by glenoid labrum, a fibrocartilagenous band around the glenoid fossa).

Allows flexion, extension, (rotation), adduction, abduction and circumduction.

High mobility due to:

1.Shallowness of glenoid cavity

2.Loose or "redundant" ligaments.

Stability due to:

1.Rotator cuff muscles (a.k.a. "SITS muscles" ) or musculotendinous cuff muscles.

Baseball pitchers often have "rotator cuff injuries"-- this is when SITS muscles and/or their tendons are damaged.

Elbow Joint

2 uniaxial joints:

1.Olecranal joint formed between ulna and humerus, allowing flexion and extension.

Trochlea of humerus articulates with trochlear notch of ulna.

2.Radioulnar joint formed between radius and ulna, allowing supination and pronation.

Head of radius pivots in radial notch of ulna and capitulum.

One joint capsule houses both joints.

Medial and lateral collateral ligaments reinforce joint.

lateral epicondylitis = "tennis elbow"

medial epicondylitis = "golfer’s elbow"

Coxal or Hip Joint

Multiaxial, ball-and-socket joint.

Head of femur articulates in acetabulum formed by pelvic bones.

Compared with shoulder joint:

Greater strength and less mobility.

Like glenoid fossa, acetabulum is ringed by fibrocartilagenous lip or labrum.

Three major ligaments surround the outside of the joint and form the capsule. Ligaments arise from 3 bones of pelvis and attach to greater trochanter and neck of femur (thus, they are called iliofemoral, ischiofemoral and pubofemoral ligaments).

The teres ligament is present within the joint and attaches the head of femur to acetabulum.

Strength of ligaments of hip is so great that little muscular strength is needed to maintain standing position. But, walking with an upright posture means that hip joint must bear considerable loads during one's lifetime. Osteoarthritis of the hip is common.

Tibiofemoral or Knee Joint

Largest and most complicated joint of the body. It is a modified hinge joint.

It is a composite joint

1.medial femoral and medial tibial condyles articulate.

2.lateral femoral and lateral tibial condyles articulate.

3.patella and patellar surface of femur.

Functions of Patella: protection and leverage.

Basic motions are flexion and extension. Some rotation possible.

Main flexors are hamstring muscles, main extensor is quadriceps femoris.

Rotation is allowed by articulation of round surface of femoral condyles with therelatively flat surface

of tibial condyles. Medial articulation is wider than lateral articulation -- results in feeling that knee "locks into position."

Main ligaments:

1.Collaterals (tibial and fibular)--sides of knee.

2.Cruciates (anterior and posterior)--cross within joint. Named for their attachment sites on tibia.

3.Patellar ligament

The anterior cruciate becomes more taut with extension, prevents hyperextension and forward sliding.

The posterior cruciate becomes more taut with flexion to prevent backward dislocation and hyperflexion.

ACL reconstruction

Meniscus (menisci, pl). Crescent shaped fibrocartilagenous plates within knee joint. Lateral and Medial

Functions:

Cushion between ends of bones that meet in joint.

Fill space of non-matching surfaces

Medial Meniscus is often injured, esp. in football--it is attached to medial collateral ligament.

When knee is twisted, the ligament can tear the meniscus.

"The 3 Cs of knee injuries"

1.Cartilage

2.Cruciates

3.Co-laterals

Bursa in knee joints--around patella.

"Water on the knee" is really frictional, or pre-patellar bursitis

Talocrural or Ankle Joint

Two hinge joints involving three bones.

Distal End of tibia and medial malleolus articulate with talus.

Distal End of fibula and lateral malleolus articulate with talus.

Stability of joint is from malleoli and ligaments. (Deltoid ligament on tibial side; collateral ligament on fibular side).

Movements: dorsiflexion and plantar flexion.

Tendons (Achilles & extensor muscle) limit extent of movement.

(Inversion and Eversion entail ankle plus intertarsal joint movement)

Intervertebral Articulations

The joints between vertebrae and intervertebral discs are considered cartilaginous, semi-moveable joints (amphiarthroses). There are synovial, gliding joints between the articular processes of adjacent vertebrae. Some movement is allowed between vertebrae and the vertebral column is stabilized by numerous ligaments and muscles.

As a whole, the spinal column can flex, extend and rotate.

Intervertebral discs: "hockey puck" shaped discs made up of a tough outer coat of fibrocartilage, the annulus fibrosus and a spongy internal nucleus pulposus. The nucleus pulposus is a remnant of the notochord, essentially the original "spine" of the embryo. The discs permit small movements and give resiliency to the vertebral column by acting as shock absorbers. A ruptured disc is when the nucleus pulposus breeches the annulus fibrosus.

Arthritis & Related Disorders

Rheumatism: any painful state of the supporting structures of the body.

Arthritis: a form of rheumatism in which is characterized by joint inflammation.

Arthritis Foundation web site

HealthCentral Topic Center on Arthritis

Rheumatoid arthritis

*Autoimmune attack on cartilage and joint linings.

*Synovium thickens. Pannus formation. Joints may fuse.

*Smaller joints affected. More women than men are affected.

*Genetic factors and some environmental agent suspected. A relatively modern disease (little evidence of it prior to 1700's)

*Treatment: anti-inflammatory agents, non-steroidal anti-inflammitory drugs (NSAID)

like aspirin and ibuprofen, steroids (short term).

Genetic Differences in Immune System gene is related to severity of R.A.

Lyme disease

Bacteria triggers immune reaction which is similar to rheumatoid arthritis. Carried by ticks (esp. deer ticks).

Children with Lyme disease are often misdiagnosed as having juvenile rheumatoid arthritis.

Osteoarthritis

*Degenerative joint disease.

*Aging, wear-and-tear, irritation.

*Larger joints affected.

Gouty Arthritis

*           Uric acid salts (sodium urate) accumulate in joints.

*           Damages cartilage. Pain.

*           Middle-aged men affected the most.

*           Genetic and diet related. Some environmental factors.

Ankylosing Spondylitis

*Inflammitory disease which intervertebral joints and sacroiliac.

*Can lead to ankylosis (loss of movement at joint) and kyphosis.

*Occurs more in young men.

*Genetic links but no known cause.

Ankylosing spondylitis resource page

Other Conditions Related to Joints

Dislocation: displacement of bone from joint; tearing of ligaments, tendons, and capsule.

Subluxation: partial dislocation.

Sprain: forcible wrenching/twisting of joint with partial rupture.

(Note: Strain: overstretching of muscle.)