T5 :El concepte d'articulació

• Articulation concept
• Articulations relate two or more bones to each other in the contact area
• They allow the movement of these bones with each other
• Union between two rigid pieces that allows some movement between them
• Zone of union between two or more bones that allows movement

Types of joints

• Fibrous joints: bones are united by resistant and fibrous tissue, allowing little to no movement, for example: sacrum joints, skull joints, some ankle and pelvic joints
• Cartilaginous joints: formed between bone and cartilage; they perform movements without the need for synovium, for example: those existing between the ribs, sternum, and intervertebral discs of the vertebral column
• Symphysis: surfaces united by fibrocartilaginous tissue
• Synchondrosis: surfaces are joined by hyaline cartilage
• Synovial joints: the synovial articulations are wrapped by a sliding cover called "synovia", and they allow a wide range of movements
• Synarthrosis and amphiarthrosis are joints in which there is little or no movement
• Diarthrosis: it has a greater amplitude or complexity of movement than other types of joints, an example: a hip joint
• Synarthrosis are maintained united by bone growth, or by resistant fibrous cartilage, they are rigid, without mobility (skull bones) or with very limited mobility (distal union between cubit and radius)
• Amphiarthrosis are maintained united by elastic cartilage and present little mobility
• True amphiarthrosis: it includes the articulations of the vertebral bodies (sacro-coccygeal and sacro-vertebral)
• Diarthroanfiartrosis: Subtype of articulation between diarthrosis and amphiarthrosis, this may present an articular cavity within the interosseous ligament (pubis, sacroiliac, and upper sternal).
• Elements that are part of a diarthrotic articulation are: the surface of the articular cartilage, the membrane, synovial fluid, menisci, ligaments, and articular capsule

Diarthrosis Classification (according to the type of movement)

• Arthroid: gliding movement; examples are the acromioclavicular joint
• Trochoid: rotational movement; an example is the radiocubital superior joint
• Trochlea: flexion and extension movements; an example is the humero-cubital joint
• Saddle joint: also called reciprocal fit, abduction-adduction, flexion-extension; an example is the trapeziometacarpal joint
• Condyle: abduction-adduction, flexion-extension; an example is the humero-radial joint
• Enarthrosis: segments in the sphere, abduction-adduction, flexion-extension, internal-external rotation, circumduction; an example is the scapulo-humeral joint

Articular Vascularization

• The epiphysial, metaphyseal, and periosteal arteries form a perarticular plexus that provides irrigation to the joint
• The synovial membrane is highly vascularized

Joint Innervation

• The articular capsule and ligaments are innervated with sensitive and motor nerves
• This allows for reflexive regulation and posture control (proprioception).

Articular elements

• The articular capsule is composed of an external fibrous layer and an internal synovial membrane
• The fibrous layer is made of dense irregular connective tissue (periosteum)
• The synovial membrane has a subintima and intima and is made up of lax connective tissue with elastic fibers
• The synovial fluid (secreted by the synovial membrane) is viscous and has an alkaline pH; it contains hyaluronic acid, lubricin, and plasma
• It lubricates the joint
• It provides nutrients and oxygen to the chondrocytes (cartilage cells) of the articular cartilage
• It contains macrophages

Tendons

• Tendons are made up of oriented dense connective tissue (type I collagen), they are not contractile
• They can be classified according to the disposition:
• Without a synovial sheath: located in zones with low friction
• With a synovial sheath: located in zones with increased friction
• Their function is to connect the muscle to the bone, and to transmit the force of muscular contraction to produce movement
• Tendons can also connect the muscles of soft structures such as the eyeball

Ligaments

• They are made up of fibrous connective tissue (similar to tendons)
• The tissue is structured in a group of small, linear, and undulating entities (fascicles)
• They are made of a band-like structure made of resistant fibers that connect the tissues that attach to the bones in the joints
• Their function is to unite and stabilize anatomical structures between bones and cartilage that form part of the joints
• Ligaments connect adjacent bones

Histological structure of joints

• Fibrous capsule outer fibrous layer + inner synovial membrane
• Outer fibrous layer Dense irregular connective tissue (periosteum)
• Synovial membrane, subintima and intima (inner) → Lax Connective tissue with elastic fibers
• Synovial fluid, (secreted by the synovial membrane), viscous and alkaline pH, hyaluronic acid, lubricin glycoprotein, and plasma
• Lubricates the joint
• Provides nutrients and oxygen to the chondrocytes of the articular cartilage
• Presence of macrophages

Histogenesis

• Comes from the mesenchyme
• This mesenchyme will transform into Tx. Fibrous or cartilage (bone Tx.) by the 5th-6th week of a development
• The process will generate joint formation, in different types