Joints 2

Stability of synovial joints

Three factors determine stability of joints to prevent dislocations:
1. Shape of articular surfaces (minor role)
▪ Shallow surfaces less stable than ball-and-socket
2. Ligament number and location (limited role)
▪ The more ligaments, the stronger the joint
3. Muscle tone (most important)
▪ Keeps tendons taut as they cross joints
▪ Extremely important in reinforcing shoulder and knee joints and arches of the foot

Nonaxial movement

gliding movements only

uniaxial movement

movement in one plane

biaxial movement

movement in two planes

multiaxial movement

movement in or around all three planes

Gliding movement

– One flat bone surface glides or slips over another similar surface
– Examples
▪ Intercarpal joints
▪ Intertarsal joints
▪ Between articular processes of vertebrae

Angular movements

– Increase or decrease angle between two bones
– Movement along sagittal plane
– Angular movements include:
▪ Flexion: decreases the angle of the joint
▪ Extension: increases the angle of the joint
– Hyperextension: movement beyond the
anatomical position

– Abduction: movement along frontal plane, away from
the midline
– Adduction: movement along frontal plane, toward the
midline
– Circumduction
▪ Involves flexion, abduction, extension, and
adduction of limb
▪ Limb describes cone in space

Rotation

turning of bone around its own long axis, toward midline or away from it
– Medial: rotation toward midline
– Lateral: rotation away from midline
– Examples
▪ Rotation between C1 and C2 vertebrae
▪ Rotation of humerus and femur

Special movements

– Supination and pronation: rotation of radius and ulna
▪ Supination: palms face anteriorly
– Radius and ulna are parallel
▪ Pronation: palms face posteriorly
– Radius rotates over ulna

– Opposition: movement of thumb
▪ Example: touching thumb to tips of other fingers on same hand
or any grasping movement

– Dorsiflexion and plantar flexion of foot
▪ Dorsiflexion: bending foot toward shin
▪ Plantar flexion: pointing toes

– Elevation and depression of mandible
▪ Elevation: lifting body part superiorly
– Example: shrugging shoulders
▪ Depression: lowering body part
– Example: opening jaw

– Protraction and retraction: movement in lateral plane
▪ Protraction: mandible juts out
▪ Retraction: mandible is pulled toward neck

Types of synovial joints

There are six different types of synovial joints
– Categories are based on shape of articular surface, as well as movement joint is capable of
▪ Plane
▪ Hinge
▪ Pivot
▪ Condylar, or ellipsoid
▪ Saddle
▪ Ball-and-socket

Plane joint

has flat articular surface that allows nonaxial movement (gliding)

Hinge joints

one surface is shaped like a cylinder the other is shaped like a trough. This allows for uniaxial movements such as flexion and extension

Pivot joints

a bone and ligament surround an axil (ie round bone). Allows uniaxial
movement around a vertical axis (a rotation)

Condylar joints 

have oval articular surfaces that allow biaxial movement (both medial/laterall and anterior/posterior axis's). Ex Metacarpal/Phelangial and wrist.

Saddle joints

Articular surfaces are concave or convex (one of each). They allow biaxial movement in both a medial/lateral and anterior/posterior planes (ex carpometacarpal joint of the thumb

Ball and Socket joint

one bone has a spherical head and the other has a cup shaped “socket’. This allows multiaxial movement. Examples include the shoulder and hip joints

Tempromandibular joints

is a modified hinge joint
• Mandibular condyle articulates with temporal bone
– Posterior temporal bone forms mandibular fossa, while anterior portion
forms articular tubercle

• Articular capsule thickens into strong Lateral ligament

• Two types of movement
– Hinge: depression and elevation of mandible
– Gliding: side-to-side (lateral excursion) grinding of teeth
• Most easily dislocated joint in the body

Shoulder joint

glenohumeral, is the most freely moving joint in body
• Stability is sacrificed for freedom of movement

• Ball-and-socket joint
– Large, hemispherical head of humerus fits in small, shallow glenoid cavity of scapula
▪ Like a golf ball on a tee

• Articular capsule enclosing cavity is also thin and loose
– Contributes to freedom of movement

• Glenoid labrum: fibrocartilaginous rim around glenoid cavity
– Helps to add depth to shallow cavity
– Cavity still only holds one-third of head of humerus

Reinforcing ligaments
– Primarily on anterior aspect
– Coracohumeral ligament
▪ Helps support weight of upper limb
– Three glenohumeral ligaments
▪ Strengthen anterior capsule, but are weak support

• Reinforcing muscle tendons contribute most to joint stability
– Tendon of long head of biceps brachii muscle is “superstabilizer”
▪ Travels through intertubercular sulcus
▪ Secures humerus to glenoid cavity

– Four rotator cuff tendons encircle the shoulder joint
▪ Subscapularis
▪ Supraspinatus
▪ Infraspinatus (behind)
▪ Teres minor

Elbow joints

humerus articulates with radius and ulna
• Hinge joint formed primarily from trochlear notch of ulna articulating with trochlea of humerus
– Allows for flexion and extension only

• Anular ligament surrounds head of radius
• Two capsular ligaments restrict side- to-side movement
– Ulnar collateral ligament
– Radial collateral ligament

Hip joint

(coxal)

a ball-and-socket joint
• Large, spherical head of the femur articulates with deep cup-shaped
acetabulum

• Good range of motion, but limited by the deep socket
– Acetabular labrum: rim of fibrocartilage that enhances depth of
socket (hip dislocations are rare)

• Reinforcing ligaments include:
– Iliofemoral ligament
– Pubofemoral ligament
– Ischiofemoral ligament
– Ligament of head of femur (ligamentum teres)
▪ Slack during most hip movements, so not important in stabilizing
▪ Does contain artery that supplies head of femur
• Greatest stability comes from deep ball-and-socket joint

Knee joint

the largest, most complex joint of body
• Consists of three joints surrounded by single cavity
1. Femoropatellar joint
▪ Plane joint
▪ Allows gliding motion during knee flexion

2. Lateral joint and Medial joint
▪ Lateral and medial joints together are called tibiofemoral joint
▪ Joint between femoral condyles and lateral and medial menisci of tibia
▪ Hinge joint that allows flexion, extension, and some rotation when knee partly flexed

• Joint capsule is thin and absent anteriorly
• Anteriorly, quadriceps tendon gives rise to three broad ligaments that run from patella to tibia
– Medial and lateral patellar retinacula that flank the patellar ligament
▪ Doctors tap patellar ligament to test knee-jerk reflex
• At least 12 bursae associated with knee joint

• Capsular, extracapsular, or intracapsular ligaments act to stabilize knee joint

• Capsular and extracapsular ligaments help prevent hyperextension of knee
– Fibular and tibial collateral ligaments: prevent rotation when knee is extended
– Oblique popliteal ligament: stabilizes posterior knee joint
– Arcuate popliteal ligament: reinforces joint capsule posteriorly

• Intracapsular ligaments reside within capsule, but outside synovial cavity

• Help to prevent anterior-posterior displacement
– Anterior cruciate ligament (ACL)
▪ Attaches to anterior tibia
▪ Prevents forward sliding of tibia and stops hyperextension of knee
– Posterior cruciate ligament
▪ Attaches to posterior tibia
▪ Prevents backward sliding of tibia and forward sliding of femur