Basic Structure & Function of Joints (10/9b) [Biomedical] Flashcards
Arthrology
study of the classification, structure, and function of joints
Movement occurs through sequenced rotations around the joints
Joint surfaces transfer and disperse internal and external forces
Classification of Joints by
Movement potential
- Synarthroses
- Diarthroses
Mechanical analogy
-Joint types
Synarthrotic joints
Allow slight to essentially no movement
Stabilized by dense connective tissue with high concentration of collagen
- By flexible fibrocartilage or hyaline cartilage
Fibrous joints, cartilaginous joints
- EX: Symphysis pubis, intervertebral disc, syndesmosis, interosseous tissue
Function is to transfer forces between the bones
Diarthrotic/Synovial joints
Allow moderate to extensive movement
Seven elements of all synovial joints
Seven Elements of All Synovial Joints
Articular cartilage Joint capsule Synovial membrane Synovial fluid Ligaments Blood vessels Sensory nerves
Articular cartilage
Cartilage that covers the articular surface of the bone
“Like a cap of low-friction paint on the end of your bone”
Joint capsule
Connective tissue “envelope” that encloses the joint
2 histologically distinct layers
- Outer fibrous layer = dense connective tissue (has nerves that tell you about stretch)
- Inner layer = synovial membrane
Synovial membrane
~ 3-10 cell layers thick
Specialized cells produce synovial fluid
Like someone saran-wrapped your joint and folded it up a lot
Highly innervated
Synovial fluid
Contains hyaluronan and glycoproteins
Lubricates the joint surfaces
Provides nourishment to articular cartilage
When you move, the fluid gets squeezed out of synovial membrane to lubricate the joint
Ligaments
Connective tissue that attach between bones
Prevent excessive joint movement
Capsular or Extracapsular ligaments
Blood vessels
Penetrate capsule & extend to junction of fibrous and synovial layer
You need blood to heal
Sensory nerves
Innervate external and internal capsular layers
Pain & proprioception
Synovial Membrane - Synovitis
Inflamed capsule, occurs in synovial membrane
Also leads to inflammatory fluid in the synovial fluid → affects viscosity
Ligaments - Capsular ligaments
Thickenings of joint capsule
Broad sheet of fibers
Resist movement in multiple planes
Ligaments - Extracapsular ligaments
Cord like structure
Partially or completely separate from joint capsule
May resist movement in one or two planes
Other Joint Support Elements
Intra-articular discs/menisci Peripheral labrum Fat pads Bursae Synovial plica
Intra-articular Discs or Menisci
Fibrocartilage structures
Increase joint congruency → improves stability
Provide shock absorption
Highly mobile
Peripheral Labrum
Fibrocartilage structure
Extend around the periphery of joint
Deepen joints concavity and support capsular attachment
Highly mobile
Like a rubber washer that seals and supports your joint
Fat Pads
Reinforces capsule & fills in ‘recesses’ in the joint
Often interposed between fibrous layer & synovial membrane
Cushions surfaces to reduce forces
Fills space and is protective shock absorber
Bursae
Extension or outpouching of synovial membrane
Spaces filled with a little synovial fluid
Cushions and prevents friction between moving tissue surfaces
Can palpate when they are inflamed
Related to folds in the capsule
Synovial Plicae
Redundancy or folds in synovial membrane
Redundancy is necessary to prevent undue tension during motions
When inflamed, creates pathological synovial plicae
Becomes a mechanical block
Not all joints have plica (knee has it)
Synovial Joint Types
Hinge Pivot Ellipsoid Ball and Socket Plane Saddle Condyloid
Joint Type - Hinge
Single axis of rotation
Motion occurs perpendicular to axis of rotation (i.e. hinge)
EX: Humeral ulnar joint
Joint Type - Pivot
Single axis of rotation
Rotation occurs parallel to the axis of rotation
EX: Humeral radial joint
Joint Type - Ellipsoid
Two axes of rotation
One side elongated concave surface & other elongated concave surface
Biplanar motion flexion/extension & abduction/adduction
Limits spin motion at joint
EX: wrist
Joint Type - Ball and Socket
3 axes of rotation
Spherical convex surface and cuplike concave surface
Allows 3 degrees of freedom for joint angular motion
EX: hip, shoulder
Joint Type - Plane
Lack a definitive axis of rotation
Sliding and rotation of one surface on the other
EX: fingers
Joint Type - Saddle
2 axes of rotation
Perpendicularly oriented convex and concave surfaces
Allows ample biplanar motion but limits spin motion
EX: thumb
Joint Type - Condyloid
Primarily 2 axes of rotation
Spherical convex ball articulates with relatively flat or non-concave surface
Motions vary based on particular structure
EX: knee
Ovid vs Saddle Joints
OVID
- Paired joint surfaces that are imperfectly spherical
- Shape of most synovial joints in the body
SADDLE
- Convex surface perpendicularly bisects concave surface
- Very few examples of this in the body
*Planar joints are exception to this binary classification
Fixed axis of rotation
all points experience equal rotation
moment arm can be somewhat stable
in joints, axis of rotation is rarely fixed
Instantaneous axis of rotation
the axis changes as the joint changes position
the moment arm and mechanical advantage of muscles changes as you change position
muscles are stronger in certain positions than others
