A&P - 9.4 Synovial Joints (anatomy and accessory structures)

synovial joint - general characteristics

• articulating bones are separated by a fluid-filled cavity

• joints of limbs

• all are diarthrotic

• most common type of joint in the body

• presence of a joint cavity

anatomy of a synovial joint

• joint cavity

• joint capsule

  • articular capsule

  • synovial membrane

• synovial fluid

• articular cartilage

joint cavity

space enclosed by the articular capsule of a synovial joint that is filled with synovial fluid and contains the articulating surfaces of the adjacent bones

• the fluid-filled space within the joint capsule

joint capsule

layers of connective tissues that enclose the synovial cavity

• fibrous connective tissue structure that surrounds and encloses a joint

layers of the joint capsule

• articular capsule

• synovial membrane

articular capsule

connective tissue structure that encloses the joint cavity of a synovial joint

• thick outer layer continuous with the periosteum around the articulating bones

• adds strength and helps to stabilize the joint

synovial membrane

thin layer that lines the inner surface of the joint cavity at a synovial joint

• inner soft tissue whose network of capillaries leak plasma from the bloodstream to produce the synovial fluid

synovial fluid

thick, lubricating fluid that fills the interior of a synovial joint

functions of synovial fluid

• lubrication

• nutrient distribution

• shock absorption

function of synovial fluid - lubrication:

when part of an articular cartilage is compresses during movement, some of the synovial fluid is squeezed out of the cartilage and into the space between the opposing surfaces

• in turn, this thin layer of fluid markedly reduces friction between moving surfaces (weeping lubrication)

function of synovial fluid - nutrient distribution:

synovial fluid in joint must circulate continuously to provide nutrients and waste disposal for the chondrocytes of the articular cartilage

• circulates whenever the joint moves, and the repeated compression and expansion of the articular cartilage pumps synovial fluid into and out of the cartilage matrix

function of synovial fluid - shock absorption:

when a joint is subjected to compression, the synovial fluid provides a cushion against the shock

• example:

  • when you jog your knees are severely compressed and the synovial fluid distributes that force evenly across the articular surfaces and outward to the joint capsule

articular cartilage

thin layer of hyaline cartilage that covers the articulating surfaces of bones at a synovial joint

• provides a slick, smooth surface to the bones which reduces friction during movement

exercise and articular cartilage

• exercise warms synovial fluid

  • becomes less viscous, more easily absorbed by cartilage

• cartilage then swells and provides a more effective cushion

  • warm-up period before vigorous exercise helps protect cartilage from undue wear and tear

  • this is why you warm up before exercising and cool down after exercising

• repetitive compression of nonvascular cartilage during exercise squeezes fluid and metabolic waster out of the cartilage

• when weight removed, cartilage absorbs synovial fluid like a sponge taking in oxygen and nutrients to the chondrocytes

• without exercise, cartilage deteriorates more rapidly from inadequate nutrition and waste removal!!

accessory structures of synovial joint

in complex synovial joints, such as the knee, a variety of additional accessory structures provide support and stability

list of accessory structures of a synovial joint

• ligaments:

  • extrinsic

  • intrinsic

  • intracapsular

• tendon

• tendon sheath

• articular disc (meniscus)

• fat pad

• bursa

accessory structure of a synovial joint - ligaments:

strong band of dense connective tissue spanning between bones

• support, strengthen, and reinforce synovial joints

• allow for normal movement of a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movement

types of ligaments in a synovial joint

classified based on their relationship to the fibrous articular cartilage

• extrinsic ligament

• extracapsular ligament

• intrinsic ligament

• intracapsular ligament

extrinsic ligament

ligament located outside of the articular capsule of a synovial joint

extracapsular ligament

outside the joint capsule

• patellar ligament

• MCL & LCL

intrinsic ligament

ligament that is fused to or incorporated into the wall of the articular capsule of a synovial joint

intracapsular ligament

ligament that is located within the articular capsule of a synovial joint

• ACL & PCL

accessory structure of a synovial joint - tendon:

dense connective tissue structure that anchors a muscle to bone

accessory structure of a synovial joint - tendon sheath:

connective tissue sac that surrounds a tendon at places where the tendon crosses a joint

• similar in structure to a bursa, but smaller

• contains a lubricating fluid to prevent friction and allow smooth movements of the tendon

accessory structure of a synovial joint - articular disc (meniscus)

a pad of fibrous cartilage situated between opposing bones within a synovial joint

• may subdivide a synovial cavity, channel the flow of synovial fluid, or allow for variations in the shapes of the articular surface

articular disc

fibrocartilage structure found between the bones of some synovial joints

• provides padding or smooths movements between the bones

• strongly united the bones together

accessory structure of a synovial joint - fat pad:

localized masses of adipose tissue covered by a layer of synovial membrane

• commonly superficial to the joint capsule

• protect articular cartilages and act as packing material for the joint

• serve as a cushion between the bones

• when the bones move, the fat pads fill in the spaces created as the joint cavity changes shape

accessory structure of a synovial joint - bursa:

fluid filled lubricating sac that forms in connective tissue

• contains synovia fluid and is lined by a synovial membrane

• found between moving structures such as skin, muscles, tendons/ligaments usually found near joints

• act to reduce friction

common types of bursae

classified by their location

• subcutaneous bursa

• submuscular bursa

• subtendinous bursa

subcutaneous bursa

bursa that prevents friction between skin and underlying bone

• examples:

  • prepatellar bursa - located over the kneecap

  • olecranon bursa - at the tip of the elbow

submuscular bursa

bursa that prevents friction between bone and a muscle or between adjacent muscles during movement 

• examples:

  • trochanteric bursa - found at the lateral hip, between the greater trochanter of the femur and the overlying gluteus maximus muscle

subtendinous bursa

bursa that prevents friction between bone and a muscle tendon

• examples:

  • suprapatellar bursa - protects the tendon of the large anterior thigh muscle from the distal femur just above the knee

  • subacromial bursa - protects the tendon of shoulder muscle as it passes under the acromion of the scapula