AXIAL SKELETON: CRANIOVERREBRAL JOINTS Flashcards
What is included in the craniovertebral joint?
- Atlanto-occipital joint
- Atlanto-axial joint (lateral and median)
*Atlanto-axial joint allows for rotation of the head
What is the Atlanto-occipital joint?
- Between the lateral masses of C1 (atlas) and the occipital
condyles - Type of condyloid joint (Flexion: main movement; Extension; Limited lateral flexion and rotation)
- Cranium and C1 are connected by the AAO and PAO
- Help prevent excessive movement of the atlanto-occipital joints
What is the Lateral atlanto-axial joints?
- Between the lateral masses of C1 and the superior articular facets of C2
- Type of Plane Joint (gliding movement)
What is the Median atlanto-axial joint?
- Between the dens of C2 and the anterior arch and transverse
ligament of the atlas - Type of Pivot Joint (trochoid or uniaxial)
- Contains Transverse ligament of atlas (TLA): Very important
What is the Transverse Ligament of Atlas (TLA)?
- Keeps the odontoid process against the anterior arch of the atlas
- Extents between the tubercles of the medial aspects of the lateral masses of C1 vertebrae
*Odontoid process is more radiodense in an x-ray due to the overlapping of the C1 and C2 (den connects with C1)
What causes the rupture or injury of the Transverse ligament of the atlas (TLA)?
- Trauma from vertical force (diving accident; fall from horse)
- Connective tissue disease, which softens the transverse ligament of C1
- Congenital anomalies from Down Syndrome causes lax or agenesis of the transverse ligament
What occurs during the rupture of the transverse ligament of atlas?
- The dens is set free, resulting in atlanto-axial subluxation or incomplete dislocation
- When complete dislocation occurs, the
dens may be driven into the upper cervical region of the spinal
cord, causing quadriplegia - Complete dislocation can cause the dens to be driven into the medulla of the brainstem, causing death
What ligaments strengthen the Median atlanto-axial joint?
- Ligaments connecting the C2, especially the odontoid process, and the occipital bone
- Cruciate ligament
- Apical ligament of the dens
- Alar ligaments
- Tectorial membrane
What is the Cruciate ligament?
- Strengthens the median atlanto-axial joint
- Consist of the Transverse ligament of the atlas and two bands:
a. Superior longitudinal band (Passes to occipital bone)
b. Inferior longitudinal band (Passes to body of C2 vertebrae)
What is the Apical ligament of the Dens (AL)?
- Arises from the tip(apex) of the odontoid process to the anterior margin of the foramen magnum
- Strengthens the median atlanto-axial joint
What is the Alar ligament?
- Short cords extending from the sides of the dens of the axis to the lateral margins of the foramen magnum
- Prevents excessive rotation at the atlanto-axial joint
- Strengthens the median atlanto-axial joint
What is the Tectorial membrane?
- Upper section of the posterior longitudinal ligament
- Passes posteriorly over the median atlanto-axial joint and its ligaments
- Runs from the
body of C2 to the internal surface of the occipital bone (foramen magnum) and covers the alar ligaments and transverse ligaments of the atlas
*attaches to the clivus (internal surface of the basilar portion of the occipital bone)
What occurs in a fracture on the C2 vertebrae?
- Common fracture (40-50%)
- Affects the dens of the axis
- Affects the vertebral body of the axis
What occurs in a fracture on the dens of C2?
- Most common
- May result from a lateral blow to the head
- May result from a complication of a disease (osteoporosis or osteopenia)
- Occurs mostly at the base of the den
- Delay or lack of healing due to the transverse ligament of C1 entering the fracture site causing instability of the joint
- Leads to avascular necrosis because of lack of blood supply to the separated fragments
What occurs in a fracture of the C2 vertebral body?
- Occurs below the level of the base of the dens
- Healing process is usually normal because the blood supply to the fragments is not affected and the transverse ligament of C1 does not interfere with the fragments