Joint Mechanics

Today’s Agenda

• What is a Joint?

• Different Types of Joints

• Range of Movement in Joints

• Structure and Function of Joints

• Characteristics of Synovial Joints

• Types of Synovial Joints

• Joint Movement

What is a Joint?

• Joints are points of contact (also known as articulations) between 2 connected bones

• They are part of the musculoskeletal system

Different Types of Joints

• Joints are classified according to their structure and function

• There are 3 types of joints:

1. Fibrous

2. Cartilaginous

3. Synovial

Range of Movement in Joints

• There are 3 main types of functional classifications for range of movement in joints:

1. synarthrosis – an immovable joint

2. amphiarthrosis – a slightly movable

joint

3. diathrosis – a freely movable joint

Fibrous Joints

• Bound tightly together by connective tissue and allow no movement

• An example of a fibrous joint are sutures which are joints between the interlocking bones of the skull

• Sutures become immobile after birth (synarthrosis)

Fibrous Joints

Cartilaginous Joints

• Cartilaginous joints are also known as fibrocartilaginous joints

• The body of one bone connects to the body of another by cartilage

• Slight movement is possible (amphiarthrosis)• An example of this is the intervertebral discs –

they have a hard outer disc with a soft core which allows some movement while protecting the body against severe jolts such as landing on one’s feet. The bones that connect your ribs to your sternum are another example of this.

Cartilaginous Joints

Synovial Joints

• The most common joint in the body• It allows the most range of movement• The bony surface of the joint is separated by a

lubricating fluid (the synovia) and by cartilage• This type of joint is also joined by ligaments,

tough bands of elastic tissue that enclose then ends of the articulating bones and form the capsule containing the synovial membrane

• They play a major role in human movement and the most common places for synovial joints are at the knee, ankle and shoulder

Synovial Joints

Recap – Structure and Function of Joints

Structure Function

Fibrous --------------------- Synarthrosis

Cartilaginous -------------- Amphirarthrosis

Synovial -------------------- Diathrosis

Characteristics of Synovial Joints

• Synovial joints permit movement between 2 or more bones. They can be distinguished by the following characteristics:

- articulating cartilage

- the joint capsule

- the joint cavity

- the bursae (pl.) (bursa – sing.)

- intrinsic ligaments

- extrinsic ligaments

Characteristics of Synovial Joints

• Articulating cartilage is located at the ends of the bones that come into contact with one another. An example is this hyaline cartilage

• The joint capsule is a fibrous structure that consists of the synovial membrane and fibrous capsule. They synovial membrane allows certain nutrients to pass through while the fibrous capsule keeps the synovial fluid from leaking.

• The joint cavity is located between the two bony articulating surfaces. It is filled with synovial fluid which acts as a lubricant for the joint. It is essential to reducing friction and providing nutrients for the articulating cartilage.

Characteristics of Synovial Joints

• The bursae are small, flattened fluid sacs found at friction points between tendons, ligaments and bones.

• Intrinsic ligaments are thick bands of fibrous connective tissue that help thicken and reinforce the joint capsule.

• Extrinsic ligaments are separate from the joint capsule. They help reinforce the joint by attaching the bones together.

Types of Synovial Joints

• Synovial Joints are distinguished by the types of movement the joint permits.

• There are 6 types of synovial joints: 1. Gliding (Plane or Arthrodial) 2. Hinge (Ginglymus) 3. Pivot (or Trochoid) 4. Ellipsoid 5. Saddle 6. Ball and Socket (Spheroidal)

Gliding Joints

• This joint is also known as a plane or arthrodial joint

• It allows movement in 1 plane (flexion, extension)

• This type of joint connects to flat or slightly curved bone surfaces.

• An example of this joint is the foot between the tarsals or hand between the carpals

Hinge Joints

• Hinge joints are also known as ginglymus joints

• They have a convex portion on one side of the bone fitting into a concave portion of another.

• It allows movement in 1 plane (flexion, extension)

• An example of this joint are the bones of the fingers (phalanges)

Pivot Joints

• This joint is also known as a trochoid joint

• It allows rotation in one plane – a rounded point of one bone fits into a grove of another

• The atlantoaxial joint between the first 2 vertebrae in the neck, which allows the rotation of the head when saying no is an example of this.

Ellipsoid Joints

• This joint s also known as a condyloid joint

• This joint allows movement in 2 planes (flexion, extension; abduction, adduction; circumduction)

• The wrist is a good example of this

Saddle Joints

• This joint allows for movement in 2 planes (flexion, extension; abduction, adduction) but does not allow for rotation.

• An example of this joint is found at the carpo-metacarpal articulation of the thumb

Ball and Socket Joint

• This joint is also known as a spherodial joint.

• With this joint, the “ball” at 1 bone fits into the “socket” of another.

• It allows for movement around 3 axes (flexion, extension; abduction, adduction; rotation; circumduction)

• Examples of these joints are hips and shoulders

Joint Movement

• Uni-axial – joints that allow movement on 1 plane

• Bi-axial – joints that allow movement on 2 planes

• Tri-axial – joints that allow movement on 3 planes

Recap – Type of Joint and Movement Plane

Joint Plane

Gliding ---------------------------- uni-axial

Hinge ------------------------------ uni-axial

Pivot ------------------------------- uni-axial

Ellipsoid --------------------------- bi-axial

Saddle ----------------------------- bi-axial

Ball and Socket ------------------ tri-axial

Homework

• Study for quiz on Thursday

• Workbook in chapter 4 fill out definitions up to ball and socket joint, fill out socket joint diagram

• For Thursday’s class, quiz on muscular system, if there is time Ms. Leo will explain Joint assignment