Skull Osteology Notes

Osteology of the Skull

Organization of the Skull

  • Divisions of the Cranium
    • Cranial Fossa and Bone contributions
  • Regional Anatomy of Disarticulated Skull (NC)
  • Clinical Correlations: Depressed and Signature Fractures
  • Regional Anatomy of the Face
  • Examples of Facial Fractures

Learning Objectives

  • Describe the macroscopic organization, growth, and function of the articulated skull (cranium and face).
  • Describe and identify the major arthrology of the bones of the skull: specifically, fontanelles, sutures, and TMJ joint.
  • Apply anatomical knowledge to interpret clinical indications of skull fractures.

Macroscopic Bone

  • Compact (cortical) bone
  • Spongy/Cancellous (Trabecular) bone
  • Osteoblasts: Bone-forming cells
  • Osteoclasts: Bone-resorbing cells
  • Osteocytes: Mechanical sensors

Function of Bone

  • Support, protection, supplies.
  • 'Levers' for movement.
  • Produces red blood cells (RBCs).
  • Stores minerals, such as calcium.

Terminology

Elevations or Projections
  • External bone surfaces are rarely smooth or featureless.
  • Articular Surfaces: form joints and determine possible movement.
  • Points of Attachment: For muscles, joint capsules, and ligaments.
  • Routes for Nerves/Vasculature
  • Openings or spaces
Attachments
  • Protuberance: Roughened bony area where muscles attach; example: external occipital protuberance.
  • Process: Marked bony prominence, often elongated; sometimes used as an articulating surface; example: mastoid process.
Articulating
  • Condyle: Large, smooth, rounded articular oval process; example: mandibular condyle.
  • Facet: Small articular surface, often flattened; example: Superior articular facet of vertebra.
Openings
  • Foramen: Circular opening in a bone usually for blood vessels and/or nerves; example: foramen magnum.
  • Notch: Deep depression/gutter or U or V-shaped cut into bone surface; example: superior orbital notch.
  • Meatus: Opening/start/end of a canal or tube-like passageway; example: external acoustic meatus.
  • Canal: Passageway through a bone; example: optic canal.
  • Fissure: Narrow elongated (slit-like) opening through a bone usually for blood vessels and/or nerves; example: Superior orbital fissure of skull.
  • Sinus: Large cavity within a cranial bone; example: frontal sinus.

Skull Structure

  • Protection for the brain and receptors.
  • Muscle attachments.
  • Skull = Cranium + Facial Skeleton
    • Neurocranium
    • Basicranium
    • Paranasal Sinuses
    • Mandible
  • 22 Separate Bones (excluding ossicles of ear)
Neurocranium
  • Superior domed part, which covers cranial cavity and brain
    • Paired Temporal, Parietal and unpaired frontal, occipital and sphenoid bones
Basicranium
  • Floor of cranial cavity
    • Temporal, sphenoid and occipital bones
Viscerocranium
  • Facial skeleton
    • 14 bones support teeth
    • Form nasal and orbital cavity
    • Paired nasal, palatine, lacrimal, zygomatic, maxillary bones; inferior nasal conchae and unpaired vomer.

Head/Brain Growth

  • 90% adult size à 1 Year Old
  • 95% adult size à 6 Years Old
  • Complete size à 7 Years Old
Fontanelles
  • Anterior Fontanelle à 24 Months (Scheuer& Black, 2000)
  • Posterior Fontanelle à 3 Months (Scheuer& Black, 2000)

Sutures

  • Metopic Suture (L+R Frontal bones)
    • Stage I: Open
    • Stage II: Fusing
    • Stage III: Fused
    • Stage IV: Obliterated

Functional + Structural Classification of a Suture?

  • Immovable fibrous joint (Dense Fibrous CT) that form the boundaries between the bones
    • Allows moulding of the head during parturition
    • Allows the cranium to grow and expand during childhood

Clinical Correlation: Depressed Fracture

  • Clinical Presentation: Shallow trench noted on the skull's surface, periosteum and dura are intact.
  • Clinical Stem: After forceps delivery, a shallow dent is noticed in a 1-day-old infant’s head. MSCT investigation is requested, with VRR shown.
    • Location of the fracture?
  • Pathology:
    • Birth Trauma – results from pressure caused by the mother’s pelvic bones against the soft skull
    • Forceps during delivery

Anatomy of the Facial Skeleton

  • 2 cavities: nasal and orbital cavity
  • 14 bones in total
  • paired nasal, palatine, lacrimal, zygomatic, maxillary bones; inferior nasal conchae and unpaired vomer.

Paranasal Sinuses

  • Para = ‘near or alongside to’
  • Nasal = referring to the nose or nasal cavity
  • Sinus = space or cavity
    • Frontal sinuses (2 or more)
    • Maxillary sinuses (2)
    • Sphenoid sinuses (2)
    • Ethmoid Air Cells

Clinical Correlation: Frontal Bone Fracture

  • Clinical Stem: 16-year-old female suffers a head butt from an opposition player at football. A clinical depression in her forehead is noted and AP/Lateral VRR Provided.
    • What SINUS is likely to be affected?

Clinical Correlation: Neurocranial Fractures

  • Spade trauma to parietal/occipital bones.
  • Gunshot trauma to the temporal bone.
  • Fracture-a-la-Signature:
    • Forensic medicine derivation à shape/size may give info on the type of weapon used.
    • Typically non-accidental injury

Clinical Correlation: Zygomaticomaxillary Complex Fracture

  • Clinical Stem: 18 Year old male victim of an assault to the facial skeleton. The assailant delivered a ‘hook’ punch to the side of the victims face. The patient has difficulty communicating and opening his jaw. Further, he lacks sensory sensation to the orbital and zygomatic regions.
  • Pathology:
    • Epidemiology à 40% of midface fractures
    • TRIPOD à fracture of the: lateral orbital margin, zygomatic arch, inferior orbital rim, maxillary sinus