Joints are classified by function and structure
They are further classified by structure (what type of tissue holds them together - fibrous or cartilaginous)
Synarthroses
Can be fibrous or cartilaginous, or can describe fused bones
Fibrous (held together by fibrous connective tissue)
Diarthroses
Freely movable joints
Held together by a joint (articular) capsule
All diarthroses are synovial joints
Examples are hip, shoulder, elbow, knee, fingers, toes, vertebral facet joints, many others
Structure of synovial joints
Articular cartilage
Bony surfaces of articulating bones are covered by articular (hyaline) cartilage
Surface of cartilage is slick and smooth, reduces friction
Synovial fluid is lies in between, lubricates, distributes nutrients, and absorbs shock
Articular capsule
Consists of two layers
Fibrous outer layer of joint capsule, may contain ligaments
Ligaments connect bone to bone
Differs from tendons which connect muscle to bone
Aerolar inner synovial membrane, synovial membrane secretes synovial fluid
Synovial fluid
Thick viscous fluid secreted by the synovial membrane, a specialize interestital fluid
3 major functions
Lubrication
When joints are compressed, synovial fluid is squeezed out of the articular cartilage (which is like a sponge)
Nutrient distribution
Nourishes the joint and removes waste products
Shock absorbtion
Reduces force traveling through the joint
Accessory structures
Cartilages and fat pads
Structures which lie in between to articulating surfaces
Include menisci of the knee and TMJ
Menisci is a pad of fibrocartilage found in synovial joints, they accomodate for irregular shaped bones to more comfortably fit together
Ligaments
Connect bone to bone, support, strengthen and reinforce synovial joints
Can be found inside or outside of the joint capsule
Ligament prevent synovial joints from moving too far
If overstretched, can be some tearing which is referred to as a sprain
Mention prolotherapy
Occasionaly can rupture in which case the two ends of the ligament are no longer together
Sometimes requires surgery, sometimes muscles can compensate and stabilize the joint
Lateral ankle ligament ruptures - peronelas can compensate and stabilize the joint
Muscle tearing is referred to as a strain
Bursae
Small, fluid filled pockets of connective tissue, contain synovial fluid
Form where tendons, ligaments and other soft tissue structures might run agains other tissues, especially bones - reduces friction
Tendon sheaths are tubular bursae that surround tendons where they cross bony surfaces