Tmj Flashcards
•transverse ridge of dense bone
• strongly convex in the sagittal plane
•tilted down at an angle of approximately 25° to the occlusal plane
•the anterior limit of the articular/mandibular /glenoid fossa
• forms most of the articular surface of the mandibular fossa.
•Extends out laterally to the zygomatic arch as the articular tubercle
• provides a surface over which the mandibular condyle glides during mandibular movements
Anterior tubercle/eminence
•is a thin-walled, smooth, concave depression in the temporal bone
• is most easily inspected when the mandible is removed.
••the zygomatic arch extends laterally in front of the fossa and a distinct ridge, the articular eminence, lies anterior to the fossa.
•formed entirely by the squamous portion of the temporal bone
•as the zygomatic process of the temporal bone passes posteriorly, it widens to form the articular tubercle of the mandibular fossa anteriorty.
•lined by articular tissue that extends anteriorly beyond the articular summit onto the preglenoid plane
Articular (glenoid/Mandibular) fossa
thin and often translucent when held to the light (confirmation that it is not a major load-bearing
area of the joint).
Roof of the fossa
formed by the tympanic plate, which also forms the anterior wall of the external acoustic meatus.
Posterior wall
Structural features of synovial joints
1Articular cartilage
2. Joint (articular) capsule
3. Articular (synovial)cavity
4. Presence of accessory / additional structures within the area enclosed by the capsule
• serves as a lubricant between the bony articular surfaces
•also aids metabolite transport to cells in the articular cartilages
•synthesized by the synovial membrane that lines the joint capsule.
Synovial fluid
the articulating surfaces of the skeletal elements
(bones) is covered by a layer of cartilage
(usually hyaline)
Articular cartilage
consisting of.
outer fibrous membrane inner synovial membrane
Joint (articular) capsule
> interlacing bundles of parallel fibers of collagen type I that completely encloses each synovial joint (except where it is interrupted by synovial protrusions
• is attached continuously round the ends of the articulating bones.
Fibrous capsule
•perforated by vessels and nerves
• may contain apertures through which synovial membrane protrudes as bursae.
•lined by a synovial membrane that also covers all non-articular surfaces (bones, tendons and ligaments) that lie partly or wholly within the fibrous capsule.
Fibrous capsule
Lines the
• fibrous joint capsule
•exposed osscous surfaces
• intracapsular ligaments, bursae and tendon sheaths
Synovial membrane
• does not cover intra-articular discs or menisci
•stops at the margins of articular cartilages in a transitional zone that occupies the peripheral few millimetres of cartilage.
•secretes and absorbs a fluid that lubricates the movement between the articulating surfaces.
Synovial membrane
•Pink, smooth, shiny
•Displays a few small synovial villi that increase in size and number with age.
•Synovial villi are more numerous near articular margins and on the surfaces of folds and fringes, and become prominent in some pathological states.
Internal Synovial surface
• Folds and fringes of membrane may also project into a joint cavity; some are sufficiently constant to be named, c.g. the alar folds and ligamentum mucosum of the knee.
• Accumulations of adipose tissue (articular fat pads) occur within the synovial membrane in many joints.
Internal synovial surface
Two layers sinovial membrane
•Intimal layer (highly cellular ) resting on a fibrous
• subintimal layer (vascular) (subsynovial tissue).
•These pads, and also synovial folds and fringes
• are deformable cushions that occupy potential spaces and irregularities in joints that are not wholly filled by synovial fluid.
• they accommodate to the changing shape and volume of the irregularities during movement, a function they share with intra-articular discs and menisci.
Internal synovial surface
•they also increase the area of synovial membrane, and may help to spread synovial fluid over the articular surfaces.
Internal synovial surface
Closed sacs of synovial membrane that occur outside joints
Synovial Bursae
Tendon Sheaths
Synovial bursae
•reduce the friction of one structure moving over the
other
•often intervene between structures, such as
tendons and bone tendons and joints skin and bone
•Connective tissue sac that surround a muscle tendon at places where the tendon crosses a joint.
•contains a lubricating fluld that allows for smooth
motions of the tendon during muscle contraction and joint movements.
Reduce friction
Tendon sheaths
• dense fibrous connective tissue with some chondrification in areas of maximum loading
•oval in shape transversely
Articular disc
• with a thick margin, which forms the:
•peripheral anulus
• central depression on its lower surface
»the central part of the disc itself is avascular and not innervated.
Articular disc
Central depression in its lower surface:
- accommodates the articular surface of the mandibular condyle.
- developed as a mechanical response to pressure from the condyle as it rotates inside the anulus
Articular disc
•attaches around its periphery to the inner aspect of the fibrous membrane of the joint capsule.
•attached to the bilaminar zone (posterior attachment), posteriorly
Articular disc
divides the articular (synovial cavity into two parts:
- Superior (discotemporal/ upper) space/cavity-
- Inferior (discomandibular / lower) space/cavity-
Superior (discotemporal/upper) space/cavity/compartment
allows the head of the mandible to translocate forward (protrusion) onto the articular tubercle and backward (retraction) into the mandibular fossa.
• contains approximately 1.2 ml of synovial fluid
allows mainly the rotation (hinge)-like depression and elevation of the mandible.
•contains approximately 0.9 ml of synovial fluid
• Inferior (discomandibular / lower) space/cavity/ compartment:
allows greater depression of the mandible by preventing backward movement of the angle of the mandible into structures in the neck.
Forward or protrusive
Parts of the articular disc
a. Anterior band
b. Intermediate zone (thinner)
c. Posterior band
thickest part of the articular disc
its upper surface is concavo-convex where it fits against
the :
a convex articular tubercle/eminence
b. concavity of the articular fossa
Posterior band
•the articular disc is attached posteriorly to a richly vascularized and innervated region, known as the
Bilaminar zone
has 2 laminae as posterior attachments of the articular disc
highly vascular and innervated region
located between the
posterior band of the TMJ disc posterior portion of the TMJ cansule.
Bilaminar Zone (retrodiscal zone/ posterior attachmenu
normal function is to provide attachment
(the other parts of the disc function to provide intra-
articular support)
Bilaminar zone
•composed of fibroelastic tissue
•attached to the squamotympanic fissure
•medial portion -with a condensation of elastic fibers visible as the posterior oblique protuberance on arthroscopy
Upper(superior) lamina
Composed of fibrous non elastic tissue
attached to the posterior aspect of the condyle
of the mandible
Lower inferior lamina
Main purpose of collagen in tissue
Resist tensile forces
Varies in the individual regions, reflecting the direction of the tensile forces imparted to the disc
The orientation of the collagen
Forms a ring like structure with a three dimensional framework of collagen fibrils
Collagen
similar to that found in the superficial layers of the head of the condyle and the articular fossa, predominates in the disc.
Type 1 collagen
Their concentration varies with the area of the disc, being highest in the superficial layer of the intermediate zone
• Principal glycosaminoglycans (GAGs) in the intercelular matrix
Chondroid sulphate
Dermatan sulphate
are very hydrophilic and, as such, play an important role in the resistance and distribution of compressive load applied to the temporomandibular joint.
GAGS
principal articulating surfaces of the TM joint:
PArticular Eminence and preslenoid plane of the squamous temporal bone
•Anterior and Superior surfaces of the Mandibular
Condyle
•Both covered with fibrocertilage
4 layers of the fibrocartilage covering the condyle
Superficial layer
• consists of densely packed fibers of type I collagen that is arranged mostly parallel to the articular surface and aligned in an anteroposterior direction (this can be seen as striation on arthroscopy).
• this covers a thin cellular layer, the proliferative zone that is continuous with the cambial layer of the periosteum beyond the margins of the joint.
• The third layer, of bypertrophic cartilage, is rich in intercellular matrix; it contains chondrocytes scattered throughout its depth, and randomly orientated fibers of collagen type lI.
•The fourth layer, immediately above the subchondrar bone, is the zone of calcification.
•Although the number of chondrocytes within the hypertrophic zone decreases with age, undifferentiated mesenchymal cells have been identified in postmortem specimens of all ages. This indicates that a capacity for proliferation and repair persists in condylar cartilage, and may be the reason why condylar remodelling occurs throughout life
Ligaments associated with TM Joint
• Temporomandibular (Lateral)
•Sphenomandibular
• Stylomandibular
ligament closest to the joint
just lateral to the capsule
runs diagonally backward from the margin of the articular tubercle to the neck of the mandible.
Temporomandibular (lateral) ligament
A broad ligament
Preinforcing the joint capsule laterally
Temporomandibular (lateral) ligament
Flat thin band
Medial to the temporomandibular joint
• runs from the spine of the sphenoid bone at the bas the skull to the lingula of the mandibular forame the medial side of the ramus of the mandible.
Sphenomandibular Ligament
• descends from the spine of the sphenoid and widens as it reaches the lingula of the mandibular foramen
P has an average width at its insertion into the mandible of about 12 mm.
Sphenomandibular Ligament
• the vessels and nerves to mylohyoid pierce the ligament adjacent to the lingula.
•the medial ptery goid is inferolateral.
• the sphenomandibular ligament is separated from the pharynx by fat and a pharyngeal vein.
Sphenomandibular Ligament
thickened band of deep cervical fascia
•stretches from the apex and adjacent anterior aspect of the styloid process to the angle and posterior border of the mandible.
Stylomandibular ligament
