Joints: Anatomy and Physiology Chapter 8

Binghamton University BIOL 251

Artho- or arthr-

Joint

Joints (articulations)

the site where two bones meet that may or may not allow for movement

General functions of joints

Mobility and stability

Mobility

allow movement of various body parts

can be a small or large amount

bones don’t attach during movement

Stability

hold the skeleton together

General classification of joints

Structural and functional

Structural classification

Type of tissue that connects bones at articulating surface

Joint cavity may or may not be present

Types of structural joints

Fibrous, cartilaginous, and synovial

Functional classification

amount of movement allowed by the joint

Types of movement of functional classification of joints

Synarthroses, amphiarthroses, and diarthroses

Synarthroses

no movement

Amphiarthroses

limited movement

wiggle

Diarthroses

free movement

most moveable

not all have the same mobility

Fibrous joints

joints composed of collagen fibers of connective tissue

no joint cavity present

mostly synarthroses, few amphiarthroses

Specific types of fibrous joints

Sutures, syndesmoses, gomphoses

Sutures

Seams composed of bundles of extremely strong and short collagen fibers found on the skull that protect the brain

permits very little movement

Syndesmoses

Bones are connected to one another only by ligaments

Ligaments

band of fibrous tissue that join bone to bone

movement allowed by the joint depends on the length of ligament bands

amphiarthroses

What is the relationship between length and movement allowed of ligaments?

Ligaments between the radius and ulna are pretty long which allows for supination and pronation

Ligaments between tibia and fibula are short so they cannot supinate and protonate like the hand can

Gomphoses

only type of joint that does not join bone to another bone

joins tooth to alveolar socket in jawbone

fibers of this joint are very short, providing very limited movement

Periodontal ligament

joins the bone of the mandible/maxilla to the tooth

Cartilaginous joints

bones joined by cartilage

no joint cavity

synarthroses and amphiarthroses

Specific types of cartilaginous joints

Synchondroses and symphyses

Synchondroses

bones united with a plate of hyaline cartilage

most synarthroses

Symphyses

fibrocartilage joins bone

mostly amphiarthroses

What is the benefit of fibrocartilage at symphyses?

Toughest and strongest cartilage

Found in places bearing a lot of body weight so it prevents bones of joints being damaged

examples: pubic symphysis and fibrocartilage between vertebrae

Synovial joints

possesses a joint cavity

diarthroses

most joints fall under this classification (almost all located in appendicular skeleton)

Why are most synovial joints located in the appendicular skeleton?

More mobility is needed for limbs

Six structures found in all synovial joints

Articular cartilage, joint cavity, articular capsule, synovial fluid, reinforcing ligaments, and innervation and vascularization

Articular cartilage

Hyaline cartilage covering bone ends

Joint cavity

small space between articulating bones

Articular capsule

Two-layered capsule that encloses the joint cavity

Contains fibrous later and synovial membrane

Fibrous layer

Outer layer of articular capsule that is continuous with periosteum of bones

What is the function of the fibrous layer?

Holds articular capsule in place and physically holds bones together

Synovial membrane

Inner layer of articular capsule that lines joint cavity

Where is the synovial membrane NOT found?

Over articular cartilage or inside fibrous or cartilaginous joints

What is the function of the synovial membrane?

Sheet of tissue that produces synovial fluid, secreted into joint cavity

located laterally and medially, off to the sides

Synovial fluid

Slippery fluid occupying space in joint capsule and articular cartilages

What is the function of synovial fluid?

Allows mobility so bones slide past each other

What is the state of synovial fluid when the joint is not active?

Fluid is viscous and is drawn up and stored in articular cartilage

What is the state of synovial fluid when is joint is active?

Fluid thins and becomes watery, is located in synovial cavity

Prevents friction and excessive rubbing

What does “double-jointed” actually indicated?

Really long ligaments

Reinforcing ligaments

Bandlike ligaments that join articulating bones

Relatively thick, extend from one bone to another

What is the function of reinforcing ligaments?

Prevents bones from pulling apart

Innervation to synovial joints

joints supplied with sensory nerve fibers

Why is innervation to the joints important?

Raw materials come from blood supply that are needed to make synovial fluid

vascularization of synovial joints

rich blood supply to joints

Structures that may or may not be associated with synovial joints

Bursae, tendon sheath

Bursae

flattened sacs that contain a small amount of synovial fluid

Where are you most likely to find bursae and why?

Where structures are packed closely, like the should joint, because they reduce friction between adjacent structures

Tendon sheath

elongated bursa that wraps completely around a tendon subjected to frequent friction

Where is the body do you typically see tendon sheaths and why?

Wrists and ankles because tendons allow fingers to move by preventing friction for a particular tendon

Factors influencing joint stability

articular surfaces, ligaments, and muscle tone

How do ligaments impact joint stabilty?

The more ligaments, the stronger the joint

But can make it weaker if it is the only thing influencing stability

Muscle tone

tendons attach muscle to bone and often wrap around/over joints, muscle always pulls on tendons

Movements allowed by synovial joints

nonaxial, uniaxial, biaxial, multiaxial

Nonaxial movement

no axis around which movement can take place

bones that articulate have flat surfaces

Movement allowed: gliding

Joint shape: plane joint

ex: short bones like carpals and tarsals

Uniaxial movement

Allows for movement of joint around a single axis

Movement allowed: flexion/extension OR rotation

Joint shapes:

Hinge joint

ex: elbows and knees

Pivot joint

ex: 2 major joints in between, radius and ulna

Biaxial movement

Allows for movement of a joint around two axes

Movement allowed: flexion/extension AND adduction/abduction

Joint shapes:

Condylar joint

ex: knuckles on 4 fingers

Saddle joint

ex: base of thumb

Multiaxial movement

Allows for movement of a joint around multiple axes

Movement allowed: flexion/extension, abduction/adduction, AND rotation

Joint shape: Ball-and-socket joint

ex: coxal joint and shoulder joint

Specific examples of synovial joints

Temporomandibular joint, glenohumeral joint, elbow joint, coxal joint, knee joint, femoropatellar joint, tibiofemoral joint

Temporomandibular joint (TMJ)

where the mandible articulates to the temporal bone

Joint shape: modified hinge joint

articular disc divides synovial cavity into superior and inferior

Superior: allows lateral excursion

Inferior: allows elevation/depression

Glenohumeral joint

Should joint - where the humerus articulates with the scapula

Most freely moving joint (multiaxial) in the body which makes it inherently less stable

What provides stability to the glenohumeral joint?

Reinforcing ligaments (the coracohumeral ligament and glenohumeral ligament), rotator cuff, and glenoid labrum

Glenohumeral ligaments

A person can have 0 to 3 of this ligament, which makes the joint more stable the more of it you have

Rotator cuff

4 muscles (and their tendons) encircle the glenohumeral joint to hold it in place

Usually tears by circumduction

More stable than glenoid labrum

Glenoid labrum

Rim of fibrocartilage around glenoid fossa which provides some stability to the glenohumeral joint by helping bones fit together (but it is prone to tearing)

Elbow joint

Where the humerus articulates with the ulna and radius

Hinge joint

What provides stability to the elbow joint?

1. Close fit of trochlea (on humerus) and trochlear notch (on ulna)

2. Muscle and tendon on arm muscles wrap around elbow to provide further stability

3. Ulnar collateral ligament (medial) and radial collateral ligament (lateral) prevent lateral movement

Coxal joint

Where head of the femur articulates with the os coxa

What provides stability to the coxal joint?

Articular surfaces and strong ligaments, the acetabulum has a acetabular labrum to further deepen the socket

Ligaments of articular capsule

Iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament

Ligamentum teres

ligament of the head of the femur that anchors it to the os coxa

Knee joint

Single joint cavity shared by separate joints

Most complex joint

Femoropatellar joint (1)

between patella and femur, allows patella to slide past femur during movement

Tibiofemoral joint (2)

between femur and tibia, 1 is medial and 1 is lateral

What are the stabilizing structures of the knee joint?

Menisci, intracapsular/cruciate ligaments (ACL and PCL)

Menisci

thin layer of fibrous cartilage at outer margins of tibiofemoral joints

forms ridges along outer margins of joint

What can cause damage to the menisci?

Prone to damage with sudden and extreme movements, plus being on the outer margins makes it prone to damage/tearing off easily

Intracapsular ligaments (cruciate ligaments)

Secure articulating bones, prevent displacement, and hyperextension of knee

Anterior cruciate ligament (ACL)

attaches to the anterior portion of the tibia to prevent forward sliding of the tibia and backward sliding of femur

much smaller and more prone to breaking than PCL

Posterior cruciate ligament (PCL)

attaches to posterior portion of the tibia to prevent backward sliding of the tibia and forward sliding of the femur

Arthritis

most widespread crippling disease in North America than can be acute or chronic

Acute forms of arthritis

Bacterial, inflammatory, can easily be treated with antibiotics

Chronic forms of arthritis

inflammatory/degenerative (loss of joint tissue with time), long-lasting

Osteoarthritis

Most common form of chronic arthritis that progresses slowly and is irreversible

Bones spurs can form and bone ends deform, which restricts movement at joint

What increases the likelihood of developing osteoarthritis?

Genetics, how much and how a joint was used

What causes osteoarthritis?

More articular cartilage being destroyed than is replaced

Bone spurs

Abnormal pieces of bone at a joint caused by exposed bone rubbing together

Rheumatoid arthritis (RA)

autoimmune chronic inflammatory disorder that is a bilateral condition

Joints of fingers, wrist, ankles, and feet are most likely to be affected

Individuals with condition have flare-ups followed by periods of remission

Bilateral

If one side of the body is affected, that same part on the other side of the body will be affected as well

Progression of RA

1. Synovial membrane becomes inflamed

2. Lymphocytes and macrophages flood area to destroy cause of inflammation (macrophages also destroy some of synovial membrane)

3. Synovial fluid accumulates and a pannus forms

4. Ankylosis can occur due to cartilage destruction

Pannus

thickening of synovial membrane that breaks down cartilage tissue over time

What happens when ankylosis occurs?

Bones fuse together where cartilage/joints use to be so no movement can occur (since there are no joints there)

Becomes a big mass of bone that physically fuse together