Classification, Anatomy, and Dynamics of Joints

Vocabulary flashcards covering functional and structural joint classifications, synovial joint anatomy, lever biomechanics, angular and special movements, major body joints, and joint health.

Arthrology

The study of joints.

Fibrous joint

A structural class of joint where bones are held together by dense connective tissue.

Cartilaginous joint

A structural class of joint where bones are joined by cartilage.

Synovial joint

A structural class of joint where bones are joined by ligaments with a fluid-filled joint cavity separating bone surfaces.

Synarthroses

Immobile functional class of joints, which can be fibrous or cartilaginous.

Amphiarthroses

Slightly mobile functional class of joints, which can be fibrous or cartilaginous.

Diarthroses

Freely mobile functional class of joints, comprising all synovial joints.

Gomphoses

Peg-in-a-socket fibrous articulations of teeth with sockets of the mandible and maxillae, held in place by periodontal membranes and functioning as synarthroses.

Sutures

Immobile fibrous synarthroses found between some skull bones that feature very short fibers and interlocking, irregular edges.

Synostoses

Ossified sutures in older adults.

Syndesmoses

Fibrous joints bound by a broad ligamentous sheet called an interosseous membrane, found between long bones and functioning as amphiarthroses.

Synchondroses

Immobile cartilaginous joints (synarthroses) where bones are joined by hyaline cartilage, such as epiphyseal plates and costochondral joints.

Symphyses

Cartilaginous joints containing pads of fibrocartilage between articulating bones that resist compression, act as shock absorbers, and allow slight mobility (amphiarthroses).

Synovial membrane

The inner layer of the articular capsule composed primarily of areolar connective tissue that covers internal joint surfaces not covered by cartilage and helps produce synovial fluid.

Articular cartilage

Avascular hyaline cartilage lacking a perichondrium located on bone surfaces at synovial joints to reduce friction, absorb compression, and cushion bone ends.

Synovial fluid

A viscous, oily substance in the joint cavity secreted by the synovial membrane that lubricates articular cartilage, nourishes chondrocytes, and acts as a shock absorber.

Extrinsic ligaments

Ligaments that are physically separate from the joint capsule.

Intrinsic ligaments

Thickenings of the articular capsule itself, including ligaments located outside and within the joint capsule.

Bursae

Fibrous, saclike structures lined internally by synovial membrane and containing synovial fluid, designed to alleviate friction where bones, ligaments, muscles, skin, or tendons rub together.

Tendon sheaths

Elongated bursae wrapped around tendons where friction is excessive, commonly found in the wrist and ankle.

Fat pads

Structures that act as protective packing material in the joint periphery and fill spaces when joint shape changes.

Uniaxial joint

A synovial joint in which bone moves in just one plane or axis.

Biaxial joint

A synovial joint in which bone moves in two planes or axes.

Multiaxial joint

A synovial joint in which bone moves in multiple planes or axes.

Plane joint

The simplest and least mobile uniaxial synovial joint, featuring flat articular surfaces that allow limited side-to-side gliding movement.

Hinge joint

A uniaxial synovial joint where a convex surface fits within a concave depression, operating like a door hinge.

Pivot joint

A uniaxial synovial joint in which a bone with a rounded surface fits into a ligament ring to permit rotation on a longitudinal axis.

Condylar joint

A biaxial synovial joint featuring an oval, convex surface articulating with a concave surface.

Saddle joint

A biaxial synovial joint featuring convex and concave surfaces that resemble a saddle shape.

Ball-and-socket joint

A multiaxial synovial joint where a spherical head fits into a cuplike socket, permitting movement in three planes as the most freely mobile joint type.

Biomechanics

The application of mechanical principles to biology.

Effort arm

The part of a lever from the fulcrum to the point of effort.

Resistance arm

The part of a lever from the fulcrum to the point of resistance.

First-class lever

A lever system where the fulcrum is positioned between the effort and resistance, such as in the atlanto-occipital joint of the neck.

Second-class lever

A lever system where resistance is positioned between the fulcrum and effort, such as when standing on tiptoe.

Third-class lever

The most common lever system in the body, where effort is applied between the resistance and fulcrum, such as at the elbow joint.

Gliding

A simple movement where two opposing surfaces slide back-and-forth or side-to-side, typically along plane joints.

Flexion

Movement in an anterior-posterior plane that decreases the angle between bones, bringing them closer together.

Extension

Movement in an anterior-posterior plane that increases the angle between articulating bones.

Hyperextension

Movement where a joint is extended more than $180^\times$ degrees (e.g., glancing up at the ceiling while standing).

Lateral flexion

Movement of the body trunk laterally in a coronal plane, occurring between vertebrae in the cervical and lumbar regions.

Abduction

Lateral movement of a body part away from the midline of the body.

Adduction

Medial movement of a body part toward the midline of the body.

Circumduction

Movement where the proximal end of an appendage remains relatively stationary while the distal end makes a circular motion, tracing an imaginary cone shape.

Pronation

Medial rotation of the forearm so that the palm of the hand faces posteriorly.

Supination

Lateral rotation of the forearm so that the palm of the hand faces anteriorly.

Depression

Inferior movement of a body part, such as opening the mouth by moving the mandible.

Elevation

Superior movement of a body part, such as closing the mouth by moving the mandible.

Dorsiflexion

Movement limited to the talocrural joint where the dorsum of the foot is bent superiorly toward the leg.

Plantar flexion

Movement limited to the talocrural joint where the dorsum of the foot is pointed inferiorly.

Inversion

Movement occurring only at intertarsal joints where the sole of the foot turns medially.

Eversion

Movement occurring only at intertarsal joints where the sole of the foot turns laterally.

Protraction

Anterior movement of a body part from anatomic position, such as jutting the jaw anteriorly at the temporomandibular joint.

Retraction

Posterior movement of a body part from anatomic position, such as pulling the jaw posteriorly at the temporomandibular joint.

Opposition

Movement of the thumb toward the tips of fingers at the carpometacarpal joint enabling the thumb to grasp objects.

Temporomandibular joint (TMJ)

The only mobile joint between bones in the skull, where the head of the mandible articulates with the temporal bone.

Glenohumeral joint

A ball-and-socket joint formed by the head of the humerus and glenoid cavity of the scapula that permits the greatest range of motion of any joint in the body.

Rotator cuff muscles

A group of muscles (Subscapularis, Supraspinatus, Infraspinatus, Teres minor) whose tendons encircle the glenohumeral joint and provide most of its stability by holding the humerus head in the glenoid cavity.

Anular ligament

A ligament surrounding the neck of the radius that binds the head of the radius to the ulna.

Acetabular labrum

A fibrocartilaginous ring that deepens the acetabulum socket of the hip joint.

Retinacular fibers

Ligamentous fibers of the hip joint's articular capsule that reflect around the femur neck and convey retinacular arteries to supply most blood to the head and neck of the femur.

Ligament of the head of femur

A small intracapsular ligament extending from the acetabulum to the fovea of the head of the femur that provides no strength but contains an artery supplying the femur head.

Anterior cruciate ligament (ACL)

An intracapsular knee ligament extending from the posterior femur to the anterior tibia that prevents hyperextension and anterior displacement of the tibia.

Posterior cruciate ligament (PCL)

An intracapsular knee ligament extending from the anteroinferior femur to the posterior tibia that prevents hyperflexion and posterior displacement of the tibia.

Deltoid ligament

A ligament binding the tibia to the foot on the medial side of the talocrural joint that prevents overeversion.

Lateral ligament

A ligament binding the fibula to the foot on the lateral side of the talocrural joint that prevents overinversion and is prone to sprains and tears.

Osteoarthritis

A primary problem of the aging joint due to wear and tear involving damage to articular cartilage.