Bio 201 Module 2 Joints

Ball-and-Socket Joints

• Smooth, hemispherical head fits within a cuplike socket
• Shoulder joint: Head of humerus fits into glenoid cavity of scapula
• Hip joint: Head of femur fits into acetabulum of hip bone
• Only multiaxial joints in the body

Movement of Synovial Joints

• Terms used in kinesiology, physical therapy, etc.
• Many movements are presented in pairs with opposite or contrasting meanings
• Understanding anatomical planes and directional terms is crucial

Zero Position

• Position of a joint when a person is in the standard anatomical position
• Joint movements are described as deviating from or returning to the zero position

Flexion, Extension, and Hyperextension

• Flexion: Movement that decreases a joint angle; common in hinge joints
• Extension: Movement that straightens a joint, generally returning a body part to the zero position
• Hyperextension: Further extension of a joint beyond the zero position
• Flexion and extension occur at nearly all diarthroses, hyperextension is limited to a few

Abduction and Adduction

• Abduction: Movement away from the midline of the body in the frontal plane
• Hyperabduction: Raising arm over back or front of head
• Adduction: Movement towards the midline of the body in the frontal plane
• Hyperadduction: Crossing fingers or ankles

Elevation and Depression

• Elevation: Movement that raises a body part vertically in the frontal plane
• Depression: Movement that lowers a body part in the same plane

Protraction and Retraction

• Protraction: Anterior movement of a body part in the transverse plane
• Retraction: Posterior movement of a body part in the transverse plane

Circumduction

• One end of an appendage remains stationary while the other end makes a circular motion
• Examples: Finger, hand, thigh, foot, trunk, head
• Sequence of flexion, abduction, extension, and adduction movements

Rotation

• Movement in which a bone spins on its longitudinal axis
• Examples: Rotation of trunk, thigh, head or arm
• Medial (internal) rotation: Bone turns inwards
• Lateral (external) rotation: Bone turns outwards

Supination and Pronation

• Supination: Forearm movement that turns the palm to face anteriorly or upwards; radius is parallel to the ulna
• Pronation: Forearm movement that turns the palm to face posteriorly or downwards; radius spins on the capitulum of humerus, crossing the stationary ulna

Movements of Head and Trunk

• Flexion, hyperextension, and lateral flexion of vertebral column

Common Joint Injuries

• Sprain: Ligaments are stretched or torn, heal slowly due to poor vascularization; completely torn ligaments require surgery or replacement
• Cartilage Injuries: Remain torn due to avascularization; arthroscopic surgery may be used to remove damaged tissue; joint stability decreases after removal
• Dislocation (luxation): Bones are forced out of alignment, must be reduced (returned to normal position)

Knee Injuries

• Highly vulnerable to rotational and horizontal stress
• Common injuries: Meniscus and Anterior Cruciate Ligament (ACL)
• Heal slowly due to scanty blood flow
• Arthroscopy: Procedure to view interior of the joint via a thin scope inserted through a small incision; less tissue damage than conventional surgery and quicker recovery

Inflammatory & Degenerative Conditions

• Bursitis: Inflammation of a bursa; usually caused by blow or friction
• Tendonitis: Inflammation of tendon sheaths
• Arthritis: Broad term for pain and inflammation; most common crippling disease in the United States
• Rheumatologists: Physicians who treat arthritis and other joint disorders
• Osteoarthritis
• Rheumatoid Arthritis (RA)
• Gouty Arthritis (Gout)

Osteoarthritis

• Most common form of arthritis, often referred to as 'wear-and-tear arthritis'
• Results from years of joint wear, leading to softening and degeneration of articular cartilage
• Accompanied by crackling sounds called crepitus
• Bone spurs develop on exposed bone tissue causing pain
• Rarely occurs before age 40, affects 85% of people over 70 years old
• Obesity is a risk factor
• Most likely to affect joints of fingers, intervertebral discs, hips, and knees

Rheumatoid Arthritis (RA)

• Autoimmune attack against joint tissues
• Misguided antibodies (rheumatoid factor) attack synovial membrane, leading to enzyme degradation of articular cartilage and joint ossification
• Ankylosis: Joint becomes solidly fused and immobilized
• Remissions occur
• Steroids and aspirin control inflammation

Gouty Arthritis (Gout)

• Hereditary disease, more common in men
• Metabolic disorder resulting in excess uric acid build-up
• Uric acid: Normal waste product excreted in urine; excessive production or slow excretion leads to urate crystals forming in soft tissues and joints
• Great toe is most affected joint