Arthrology

Chapter 9

Arthrology Is…

Study of joints Joints are defined as places where

the rigid elements of the skeleton meet.

HOWEVER, joints can be between the “soft” parts of the skeleton.

Classification of Joints

2 Methods of Classification Functional Classification *focuses on the amount of movement allowed. Structural Classification *focuses on the material that binds the joint together.

ARTHROLOGY

Types of Joints 1. SYNOSTOSIS - called a synarthrosis or

syndesmosis - is a bone to bone union - begins as a joint where there is a

fibrous membrane between the two bones. They are sometimes called FIBROUS JOINTS or LIGAMENTOUS UNIONS.

- These are NON-MOVEABLE - Fontanelles are examples

2. AMPHIARTHROSIS (cartilagenous joints)

- moveable and immoveable - cartilage between two bones - these joints allow some

movement while still providing protection.

3. DIARTHROSIS (synovial joints) - allow for free movement - have three characteristics: 1. synovial membrane - a serous membrane that

produces synovial fluid which reduces friction and absorbs shock.

2. articular cartilage 3. capsule -dense connective tissue

covering the joint

Summary of Joint Classes

Structural Class Characteristics Types Mobility

Fibrous Bones united by collagen fibers

1. Suture2. Syndesmosis3. gomphosis

1. Immobile (synarthrosis)

2. Slightly moveable (amphiarthrosis)

3. Immobile

Cartilaginous Bone ends united by cartilage

1. Synchondrosis (hyaline)

2. Symphysis (fibrocartliage)

1. Immobile2. Slightly moveable

Synovial Bone ends covered with articular cartilage and enclosed within a capsule lined with a synovial membrane

1. Plane2. Hinge3. Pivot4. Condyloid5. Saddle6. Ball and socket

Freely moveable (diarthrosis) which depends on joint design

The synovial fluid helps reduce friction, disipate heat, and absorb shock.

The articular cartilage acts similarly to “teflon”, which helps reduce friction and pressure.

The joint capsule covers and protects the synovial membrane.

There are several ligaments that help hold the portions of the joint together.

Intracapuslar Ligament – hold the bones together. Not found in every joint.

Extracapsular Ligament – called the collateral ligament. It is a single band that is actually a thickening of the joint capsule.

The synovial membrane is 3-dimensional, like a knee support enclosing the entire joint. It is NOT found between the bones. It produces the synovial fluid.

BURSAE are found between the muscle and tendons and the bone/joint. These are fluid filled sacs that reduce friction. In some cases they are extensions of the synovial sac. When they become tubular, they can envelope the tendons and become a SYNOVIAL SHEATH. When these bursa become dry, friction and inflammation result, causing BURSITIS.

We can increase the surface area of a joint by having a MENISCUS. The knee has this sort of anatomy.

This type of cartilage can be torn by torque. Meniscal cartilage cannot heal itself.

How Do Muscles Act on Bones?

Flexion vs. ExtensionDorsiflexion vs. PlantarflexionAbduction vs. AdductionCircumductionRotationPronation vs. SupinationProtraction vs. RetractionElevation vs. DepressionInversion vs. Eversion

Types of Joints (Articulations)

1. Ball and Socket Joint - allow for the most freedom of movement - triaxial movement – flexion, extension,

abduction, adduction, circumflexion, and rotation

2. Hinge Joint - uniaxial – allows movement in only one

direction. Back and Forth - allows only flexion and extension in one

plane (sagittal) - many times the articular surfaces will have a

distinct shape (ie: spool shaped trochlear surface of the humerus)

3. Pivot Joint - allows rotation (uniaxial) - rounded, pointed, or conical surface on one

bone that fits into a ring of bone on another.4. Saddle Joint - biaxial - allows flexion, extension, abduction,

adduction, and circumduction. - surfaces are inverted relative to each other.

5. Condyloid Joint - biaxial - one bone is concave (hollowed

out depression) and the other is convex (rounded or elliptical).

- allows flexion, extension, abduction, and adduction.

- NO ROTATION

6. Sliding or Gliding Joint - biaxial - side to side, back and forth - two flat surfaces that slide over each other - NO ANGULAR MOTION7. Tongue and Groove (Mortise and Tenon) - uniaxial - one side is a slot, the other side is an

extension that fits into the slot. - NO SIDE TO SIDE MOVEMENT - Allows flexion and extension

Introduction to Myology and Movement

Human motion and walking is due to a system of levers that are made from bones and muscles.

A lever has a fulcrum, or pivot point; a force, or energy that has to be applied; and a resistance, or opposition to movement.

A wheel is a lever with the pivot in the center.

3 Types of Human Levers Systems

Class 1: Fulcrum is between the force and load.

load

Force

fulcrum

This type of lever pulls our head into an extended position once flexed.

Class 2: The load is between the force and fulcrum.

The muscles that elevate us to our tip toes – plantarflexion of the foot on the leg.

Class 3 Lever

The load is opposite the fulcrum.

Examples of this type of lever are muscles that move the forearm.

Requirements For Movement

1. An alive muscle2. A stimulus - nerve impulse3. At least 2 bones - diarthrosis - the joint must allow for movement in

plane that the muscle shortens. - the muscle must be able to pull the

load - force must be greater than the

resistance

Muscles that stabilize a limb so it can move is a FIXATOR.

For example, the trapezius stabilizes the clavicle and scapula so we can move the arm but not have the head of the humerus become deflected in any direction.

A muscle that provides most of the force for a particular movement is the PRIME MOVER. For example, the deltoid is the prime flexor of the arm on the shoulder.

Muscle pairs must work together:

AGONIST – assists movementANTAGONIST – resists movement

For example: The triceps surae (gastrocnemius and soleus complex) plantarflexes the foot on the leg. This is the plantarflexory agonist. The muscles that work against the triceps are the dorsiflexory muscles (tibialis anterior and long extensors).

The opposite is also true: The plantarflexors are the antagonists to the dorsiflexors.

SYNOVIAL JOINTS

Occurs at ends of bones Articular cartilage enclosed within an

articular capsule and lined with a synovial membrane.

All freely moveable (diarthrosis) Type of movement depends on the shape

and design of the joint. 6 Types 1. Plane 4. Condyloid 2. Hinge 5. Saddle 3. Pivot 6. Ball and Socket

Part of a Synovial Joint

Joint Cavity – fluid filled potential space. Articulating surfaces: simple joint – 2 articulating surfaces compound joint - >2 articular surfaces Articular Cartilage – hyaline cartilage. Spongy

cushions absorb compression Articular Capsule 2 layers: 1. fibrous capsule – outside, dense irregular

CT that is continuous with the periosteum. 2. synovial membrane – loose CT. Makes

synovial fluid for protection.

Synovial Fluid *viscous fluid resembling raw egg whites. *filtrate of blood *contains glycoproteins Reinforcing Ligaments *bands that hold the joint together. *Extracapsular – outside the capsule *Intracapsular – internal to the capsule Neurovascular Bundle *Nerves and Blood Vessels *Detect pain when joint is disrupted (ie: sprains,

dislocations)

Synovial joints have lubricating devices to allow the bones to move across one another with minimal friction.

Synovial joints are subject to compression. Compression occurs when muscles that hold the bones together contract.

Lubricating fluid is squeezed out of the joint onto the opposing surfaces. When pressure on the joint ceases, the fluid rushes back into the articular cartilage. The fluid is absorbed back into the cartilage ready for the next compressive force. This is called weeping lubrication.

MOVEMENTS OF SYNOVIAL JOINTS

Movement caused by muscular contraction.

3 Types of Movments: 1. Gliding – sliding of flat surfaces

across each other. Found mainly between the carpals and between the tarsals.

2. Angular – increase or decreases the angle between the two bones

3. Rotation – movement of bone around its long axis.

SYNOVIAL JOINTS ARE CLASSIFIED BY SHAPE

The shapes of the articulating surfaces determine the movement allowed at a joint.

Types of synovial joints: 1. plane – flat articular surfaces. Short gliding

movements are allowed. 2. hinge – cylindrical end of one bone fits into

the trough of another bone. Angular movement is in one plane. Uniaxial joint along one plane.

3. pivot – rounded end of one fits into a ring formed by another bone.

4. Condyloid – egg shaped articular surface fits into the oval concavity in another.

5. Saddle Joint – has both convex and concave areas.

6. Ball and Socket – spherical head of one bone fits into a round socket in another.

Disorders of Joints

Injury 1. Sprain - stretching or tearing of a ligament 2. Dislocation - joint alignment is interrupted - Subluxation is a partial or incomplete dislocation of a joint.

Inflammatory Conditions

1. Bursitis - inflammation of a bursa - Bursae are sacs of fluid that

serve to protect boney prominences.2. Tendinitis - inflammation of a tendon sheath

3. Osteoarthritis - most common type of arthritis - degenerative condition of the articular cartilage - Enzymes wear down the cartilage matrix due to “wear and tear”4. Rheumatoid Arthritis - inflammation of the synovium - autoimmune in origin - often results in ankylosis of the joint