10. Principles of articulation Flashcards
What is an articulation?
An articulation or joint or arthrosis is a point of contact between:
neighbouring bones
bone and cartilage
bone and teeth
Joint classification
Different types of joints classified by:
- structure - function - movement
Example of ‘shoulder’ articulation:
glenohumeral
sternoclavicular
acromioclavicular
Joint classification
Structural classification
Functional classification
Structural classification
Presence or absence of a synovial cavity and the type of connective tissue.
Described as either fibrous, cartilaginous, or synovial
Functional classification
Based on the degree of movement permitted:
Synarthrosis (immovable)
Amphiarthrosis (partially moveable)
Diarthrosis (freely moveable)
Fibrous joints
No synovial cavity
Held together by a fibrous connective tissue
Permits little or no movement (synarthrosis/amphiarthrosis)
Three types of fibrous joint:
- Suture
- Syndesmosis
- Interosseous membrane
Suture
Fibrous joint
Unite skull bones
Thin layer of dense connective tissue
Irregular
Interlocking edges provide strength, permit no movement (synarthrosis)
Ossification of a suture forms a synostosis
e.g. left & right sides of frontal bone fuse ~6 years of age
syndesmosis
fibrous joint
More connective tissue than seen in a suture
Crosses a greater distance than a suture
Connective tissue typically arranged into bundles (ligament)
Typically permit slight movement (amphiarthrosis)
examples of syndesmosis
anterior tibiofibular ligament (fibula to tibia)
gomphosis (dentoalveolar)
interosseous membranes
Sheet of dense connective tissue
Binds adjacent long bones
Amphiarthrosis
Two main examples between the radius and ulna in forearm, and tibia and fibia in the leg
Cartilaginous joints
No synovial cavity
Held together by a fibrocartilage or hyaline cartilage
Permits little or no movement (synarthrosis/amphiarthrosis)
Two types of cartilaginous joint:
1. Synchrondosis
2. Symphysis
Synchrondosis
Cartilaginous joint
The connective tissue is hyaline cartilage
Synarthrosis
Example: epiphyseal plate (growth plate)
At skeletal maturity the epiphysis, metaphysis and epiphyseal plate fuse forming a synostosis
Symphysis
Connective tissue is fibrocartilage
Adjacent bones lined with hyaline cartilage, but with a broad disc of fibrocartilage connects the bones
Amphiarthrosis
All symphysis occur in the midline of the body:
Junction of the manubrium and sternum
Intervertebral discs
Pubic symphysis
Synovial joints
Synovial (joint) cavity between articulating bones
Freely moveable - diarthrosis
Layer of hyaline cartilage called articular cartilage
Articular cartilage
a synovial joint structure
Covers the bones at synovial joints
Avascular
Composed of collagen and proteoglycan
Orientation of collagen structure imparts resistance to compression & an extremely low resistance surface
Articular capsule - a synovial joint structure
Encapsulates a synovial joint
Composed of two layers:
1. outre fibrous membrane connecting to periosteum
2. Inner layer termed synovial membrane
Outer fibrous membrane of articular capsule
Outer fibrous membrane connects to periosteum
- Flexibility permits movement
- Fibres arranged into bundles – high tensile strength
Synovial membrane
Inner layer of articular capsule
- areolar connective tissue rich in elastic fibres
- occasionally contains structural articular fat pads
Synovial fluid - synovial joint structure
Secreted by synovial membrane
Rich in hyaluronic acid, secreted by fibroblast-like cells, and interstitial fluid from blood plasma
Lubricates articular surface – reducing friction
Provides some shock-absorbing properties
Supplies nutrition to, and removes waste products from the avascular articular cartilage
Phagocytes remove microbes and debris
Accessory ligaments of synovial joints
Intracapsular ligaments within the joint capsule
- Excluded from synovial fluid by folds in synovial membrane - e.g. anterior and posterior cruciate ligaments of the knee
Extracapsular ligaments outside the joint capsule
- e.g. fibular and tibial collateral ligaments of the knee
Accessory articular discs
Fibrocartilage pads lie between articular cartilage of some synovial joints e.g.meniscus of the knee
Called meniscii or articular discs
Help maintain joint stability
Direct the flow of synovial fluid
Meniscal tears (common in athletes)
Nerve and blood supply to synovial joints
Nerve endings same as those that supply associated muscles
Distributed to the articular capsule and associated ligaments
Pain and proprioception
Many components of the synovial joint are avascular
Rely on numerous branching of arteries and veins to supply associated tissue
Bursae and tendon sheaths
Moving parts of joints can cause friction
Bursae are fluid filled sacs lined with synovial like membrane
Bursae cushion movement between body parts
Tendon sheaths are similar to bursae
Specialised membranes that wrap around tendons
Especially where many tendons come together and/or pass through a synovial joint capsule
Types of synovial joints - movement
Planar Hinge Pivot Condyloid Saddle Ball & Socket
Types of synovial joints - planar
Surfaces flat or slightly curved
Permit back and forth, and side to side movements
Examples include:
- intercarpal joints (between carpal bones at the wrist)
- intertarsal joints (between tarsal bones at the ankle)
Types of synovial joints - hinge
Concave surface of one bone fits the convex surface of another Permits motion in a single axis (flexion and extension) Examples include: - knee joints - elbow joints
Types of synovial joints - pivot
Rounded or pointed surface of one bone
pivots inside a ring formed by the other bone and a ligament
Permits rotation in it’s longitudinal axis (monoaxial)
Examples include:
- radioulnar joints
- atlanto-axial joint
Types of synovial joints - condyloid
Convex oval projection of one bone fit into
the oval depression of the other.
Permits movement around two axis (biaxial; flexion and extension, and abduction and adduction)
Examples include:
- wrist joint
- metacarpophalangeal joints
Types of synovial joints - saddle
One bone fits into the saddle shaped bone it opposes
Modified condyloid joint
Permits movement around two axis (biaxial; flexion and extension, abduction and adduction, (sometimes limited rotation))
Examples include:
- d1 carpometacarpal joint
Types of synovial joints - ball and socket
Ball-like surface of one bone fits into the
cup-like depression of the other
Triaxial movement around three planes (triaxial; flexion and extension, abduction and adduction, and rotation)
Examples include:
- shoulder joint
- hip joint
joint systems example
Interactions between humerus, scapula, clavicle, and sternum, allow wide ranging movement. The component joints include:
acromioclavicular
sternoclavicular
glenohumeral
Glenohumeral (shoulder) joint
Synovial ball and socket joint
Joint between the proximal humerus and the scapula (glenoid fossa)
Due to the shallowness of the glenoid cavity, it is the most mobile joint in the body
Glenoid labrum; a narrow rim of fibrocartilage – deepens glenoid Stabilised by three ligaments: - glenohumeral - coracohumeral - transverse humeral Four associated bursae
glenohumeral joint - rotator cuff muscles
Most strength from rotator cuff muscles: supraspinatus infraspinatus teres minor subscapularis
Join the scapula with the humerus
Encircle the joint and fuse with joint capsule
Acromioclavicular joint
Technically a synovial gliding joint (planar) but it acts like a pivot
Joint between the acromion (part of the scapula) and the clavicle
Stabilised by three ligaments:
-acromioclavicular
-coracoacromial
-coracolclavicular (conoid and trapezoid)
Allows the movement of the scapula, permitting greater arm rotation (above the head)
Sternoclavicular joint
Synovial saddle joint
Medial clavicle fits into a hollow formed by the superlateral surface of the manubrium and the medial costal cartilage of the first rib.
Fibrocartilagenous articular disc divides the joint into two synovial cavities
Reinforced by interclavicular, anterior, and posterior sternoclavicular ligaments
Although a saddle joint – is capable of triaxial movement – all movement is passive
What is the most mobile joint in the body?
Glenohumeral joint
because of the shallowness of the glenoid cavity
