Joints Vertebrate Anatomy Ch. 8

Joints = Articulation Where 2 or more bones meet Function Mobility Protection (sutures in the skull) Weakest parts of the skeleton But, structure of joints does resist various forces to some degree

Classification Structural and Functional Classifications Fibrous - immovable Cartilaginous – slightly moveable Synovial – freely moveable

Fibrous Joints Sutures Bones connected by fibrous sheet – ligament Example: ligament connecting tibia to fibula; radius to ulna Tooth Peg in socket

Cartilaginous Joints Epiphyseal plates Ribs and sternum Symphases Growing parts at the ends of long bones temporary Ribs and sternum Costal cartilage connects Flexibility to allow for expansion and compression of rib cage Symphases Example: pubic symphasis Flexibility and strength

Synovial Joints Articulating bones are separated by a fluid cavity Allows for freedom of movement All joints of limbs are synovial joints

Features of Synovial Joints Articular cartilage Glassy and smooth Cover opposing bone surfaces Absorb compression; prevent crushing

Features of Synovial Joint Joint Cavity Filled with fluid Synovial fluid characteristics Slippery Occupies all free spaces Reduces friction

Features of Synovial Joint Articular Capsule Encloses the joint cavity Composed of membranes

Features of Synovial Joint Reinforcing ligaments Connect bone to bone The more ligaments, the stronger the joint Stretching of the ligaments results in a weaker joint A ligament can only be stretched about 6% of its length before it snaps. Muscle tone is the most important factor in stabilizing joints

Knee Ligaments

Features of Synovial Joint Fatty pads Meniscus Disc of fibrocartilage Separates articular surfaces of bones; improves fit between articulating bone ends Example – knee

Bursae and Tendon Structures and the Synovial Joint Tendons and bursae are not strictly considered parts of synovial joints, but are closely associated with them Tendon Cartilaginous Attaches muscle to bone Tendon sheath wraps around the tendon and protects from friction Bursae Bags of fluid lying between tendons and joints Act like ball bearings Reduce friction as tendon passes over joint

Movements of Synovial Joints Gliding Between carpals, tarsals and vertebrae Angular Flex Extend Abduct adduct Rotation

Types of Synovial Joints Gliding Between carpals/tarsals Hinge elbow Pivot Atlas/axis Ball and socket Hip Saddle Thumb Condyloid Knuckles

Gliding joint

Hinge joint

Condyloid joint

Saddle joint

Ball and Socket joint

Pivot joint

Injuries

Injuries Sprain Ligaments are stretched or torn Sprains heal slowly (cartilagenous tissue poorly vascularized) Completely ruptured ligaments must be repaired surgically Inflammation in the joint can turn ligament to “mush” Some cannot be repaired – use of tendons to replace ligaments – staple onto bone

Injuries Cartilage injury Damaged cartilage can be removed by arthroscopic surgery – meniscus damage is commonly treated with this method

Injuries Dislocation Bones are forced out of normal positions at a joint Repeats of this injury are common due to stretching of ligaments in the initial injury

Injuries Inflammation and Degenerative conditions Arthritis – may be degenerative (osteoarthritis – wear and tear) or inflammatory (rheumatoid arthritis – auto immune disorder)

Injuries Bursitis and Tendonitis - inflammation

Bone Spurs Result when body tries to repair itself by building extra bone Forms in response to pressure; rubbing, etc. over a prolonged period Also forms due to aging Cartilage at joints breaks down Bone rubs against bone Osteoarthritis can lead to bone spurs

Other joint problems Craniosynostosis Sutures in an infant close too early Can cause problems with brain and skull growth Can be corrected with surgery Link