Chapter 9 A&P

Sternoclavicular joint

A saddle joint formed by the manubrium and the sternal end of the clavicle, partitioned into two parts by a fibrocartilaginous articular disc.

Acromioclavicular joint

A plane joint between the acromion and the lateral end of the clavicle; a dislocation here is referred to as a shoulder separation.

Glenohumeral (shoulder) joint

A ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula; it permits the greatest range of motion but is the most unstable joint in the body.

Glenoid labrum

A fibrocartilaginous ring that encircles the socket of the glenohumeral joint to deepen the cavity.

Rotator cuff muscles

A group of muscles (subscapularis, supraspinatus, infraspinatus, and teres minor) that provide most of the stability for the glenohumeral joint.

Humeroulnar joint

One of the two articulations of the elbow hinge joint, occurring between the trochlear notch of the ulna and the trochlea of the humerus.

Humeroradial joint

An articulation within the elbow where the capitulum of the humerus meets the head of the radius.

Annular ligament

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

Subluxation of the head of the radius

An incomplete dislocation where the head of the radius is pulled out of the annular ligament, occurring almost exclusively in children under $5$ years of age.

Acetabular labrum

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

Retinacular fibers

Ligamentous fibers of the hip articular capsule that reflect around the femur neck and contains arteries supplying most of the blood to the head and neck of the femur.

Ligament of head of femur (ligamentum teres)

A small intracapsular ligament from the acetabulum to the fovea of the femoral head; it typically contains a small artery but does not contribute to joint stability.

Subcapital fractures

Fractures that occur within the hip articular capsule, usually in older individuals with osteoporosis, and may result in avascular necrosis.

Tibiofemoral joint

One of two articulations in the knee joint, located between the condyles of the femur and the condyles of the tibia.

Patellar ligament

A structure that extends from the patella to the tibial tuberosity.

Medial and Lateral Meniscus

C-shaped fibrocartilage pads on the tibial condyles that provide cushioning and change shape to conform to articulating surfaces.

Anterior cruciate ligament (ACL)

An intracapsular knee ligament that prevents hyperextension and anterior displacement of the tibia.

Posterior cruciate ligament (PCL)

An intracapsular knee ligament that prevents hyperflexion and posterior displacement of the tibia.

Unhappy triad

A severe knee injury involving simultaneous damage to the tibial collateral ligament, medial meniscus, and ACL.

Talocrural joint

A highly modified hinge joint (ankle joint) that permits dorsiflexion and plantar flexion.

Deltoid ligament

A strong ligament binding the tibia to the foot on the medial side that prevents overeversion.

Pott fracture

A fracture resulting from overeversion of the foot where the medial malleolus is avulsed and the fibula is fractured.

Ankylosis

The fusion of bone ends following the ossification of scar tissue, often seen in advanced cases of rheumatoid arthritis.

Gouty arthritis

A type of inflammatory arthritis typically seen in middle-aged or older males caused by increased levels of uric acid.

Gliding

A movement where two opposing surfaces slide back-and-forth or side-to-side with only limited movement possible in any direction, typically occurring along plane joints like those between carpals or tarsals.

Angular motion

A type of motion that increases or decreases the angle between two bones, including movements such as flexion, extension, abduction, and adduction.

Flexion

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

Extension

Movement in an anterior-posterior plane that increases the angle between articulating bones, representing the opposite of flexion.

Hyperextension

The extension of a joint beyond its normal range of motion.

Lateral flexion

Movement of the trunk of the body laterally in the coronal plane, specifically 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

A sequence of movements where the proximal end of an appendage remains relatively stationary while the distal end makes a circular motion, creating an imaginary cone shape.

Rotation

A motion where a bone pivots on its own longitudinal axis.

Pronation

Medial rotation of the forearm so the palm of the hand is directed posterior.

Supination

Lateral rotation of the forearm so the palm of the hand is directed anterior.

Depression

The inferior movement of a body part, such as moving the mandible while opening the mouth.

Elevation

The superior movement of a body part, such as moving the mandible while closing the mouth.

Dorsiflexion

A movement limited to the talocrural (ankle) joint where the superior surface of the foot moves toward the leg.

Plantar flexion

A movement at the talocrural joint where the dorsum of the foot is pointed inferiorly, such as a ballet dancer standing on tiptoes.

Eversion

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

Inversion

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

Protraction

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

Retraction

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

Opposition

Movement of the thumb toward the tips of the fingers at the carpometacarpal joint, enabling the grasping of objects.

Biomechanics

The practice of applying mechanical principles to biology.

Lever

An elongated, rigid object that rotates around a fixed point called a fulcrum.

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 where the fulcrum is between the effort and the resistance, such as the atlanto-occipital joint of the neck.

Second-Class Lever

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

Third-Class Lever

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

Temporomandibular Joint (TMJ)

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

Articular disc

A thick pad of avascular dense regular connective tissue in the TMJ that divides the synovial cavity into two chambers.

Sphenomandibular ligament

A ligament of the TMJ that extends anteriorly and inferiorly from the sphenoid to the mandible.

Temporomandibular ligament

A ligament that extends inferiorly and posteriorly from the articular tubercle to the mandible.

Joints (articulations)

Places of union between bones, bones and cartilage, or bones and teeth.

Arthrology

The study of joints.

Fibrous joint

A structural class where bones are held together by dense connective tissue and lack a joint cavity.

Cartilaginous joint

A structural class where bones are joined by cartilage and lack a joint cavity.

Synovial joint

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

Synarthroses

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

Amphiarthroses

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

Diarthroses

A functional class of freely mobile joints; this includes all synovial joints.

Gomphoses

A 'peg in a socket' fibrous joint where teeth are held in place by fibrous periodontal ligaments in the mandible or maxillae.

Sutures

Fibrous joints found between some skull bones that have interlocking, irregular edges and function as synarthroses.

Syndesmoses

Fibrous joints bound by an interosseous membrane (broad ligamentous sheet) that function as amphiarthroses.

Synchondroses

Cartilaginous joints where bones are joined by hyaline cartilage and function as immobile synarthroses.

Symphyses

Cartilaginous joints featuring pads of fibrocartilage that act as shock absorbers and allow slight mobility (amphiarthroses).

Costochondritis

Inflammation of the costochondral joints causing localized chest pain, which may be mistaken for a myocardial infarction.

Articular cartilage

Avascular hyaline cartilage on bone surfaces at synovial joints that reduces friction, absorbs compression, and lacks a perichondrium.

Articular capsule (joint capsule)

A double-layered sleeve in synovial joints consisting of an outer fibrous layer and an inner synovial membrane.

Synovial membrane

The inner layer of the articular capsule composed of areolar connective tissue that helps produce synovial fluid.

Synovial fluid

A viscous, oily substance that lubricates articular cartilage, nourishes chondrocytes, and acts as a shock absorber.

Extrinsic ligaments

Ligaments that are physically separate from the articular capsule of a synovial joint.

Intrinsic ligaments

Ligaments that represent a thickening of the articular capsule itself.

Bursae

Fibrous, saclike structures containing synovial fluid and lined by synovial membrane that alleviate friction.

Tendon sheaths

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

Fat pads

Accessory structures in synovial joints that act as protective packing material and fill spaces when joint shape changes.

Uniaxial joint

A synovial joint classification where the bone moves in just one plane or axis.

Biaxial joint

A synovial joint classification where the bone moves in two planes or axes.

Multiaxial (triaxial) joint

A synovial joint classification where the bone moves in multiple planes or axes.

Plane joint

The simplest and least mobile synovial articulation, featuring flat surfaces and uniaxial side-to-side gliding movement.

Hinge joint

A uniaxial synovial joint with a convex surface fitting into a concave depression.

Pivot joint

A uniaxial synovial joint where a bone with a rounded surface fits into a ligament ring, allowing 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 with convex and concave surfaces resembling a saddle shape.

Ball-and-socket joint

The most freely mobile multiaxial synovial joint, featuring a spherical head of one bone fitting into a cuplike socket.