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The Frontal Bone - Complete Guide for DPT Students

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What is the Frontal Bone?

• The forehead (the flat part of your skull above your eyes)
• The roof of both eye sockets (orbits)
• The floor of the front part of the brain cavity (anterior cranial fossa)

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Structure: 3 Parts of the Frontal Bone

1. Squamous Part (Vertical/Forehead Part)

• This is the large, flat, shell-shaped part - what you feel when you touch your forehead.
• It faces forward and slightly upward.
• It has both an outer surface (what you can see/touch) and an inner surface (facing the brain).

2. Orbital Part (Horizontal Part)

• Two flat, thin, horizontal plates that form the roof of the eye sockets.
• These same plates also form part of the floor of the anterior cranial fossa (where the frontal lobes of the brain sit just above them).
• Because they are thin, they can be damaged easily in trauma.

3. Nasal Part

• A small, downward-projecting notch between the two orbital plates.
• Articulates (joins) with the nasal bones and the ethmoid bone below.

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Bony Landmarks (The "Features" You Need to Know)

On the Outer Surface (External):

On the Inner Surface (Endocranial/Internal):

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Articulations (Which Bones Does the Frontal Bone Join?)

Bregma = the point where the coronal suture meets the sagittal suture (a key skull landmark)

Metopic suture = the line where the right and left halves of the frontal bone fused during childhood (usually closes by age 2, but can persist as a visible ridge in some adults - called metopism)

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The Frontal Sinus

• Located inside the frontal bone, just above the root of the nose.
• Lined with mucous membrane.
• Drains into the nasal cavity via the frontonasal duct.
• It is paired but usually asymmetrical in size.
• Not present at birth - starts developing around age 2 and is fully formed by puberty.
• Clinical point: Can become infected (frontal sinusitis) and cause pain over the forehead.

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Muscle Attachments

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Nerve Supply to the Region

Through the Supraorbital Foramen / Notch:

• Supraorbital Nerve (branch of the frontal nerve, from ophthalmic division V1 of trigeminal nerve, CN V)
  • Carries sensation from: forehead skin, upper eyelid, scalp as far back as the vertex
  • Exits the skull through the supraorbital foramen (or notch) at the supraorbital margin

Through the medial orbit:

• Supratrochlear Nerve (also from V1 - frontal nerve)
  • Supplies the medial forehead and upper nose skin
  • Exits about 1 cm lateral to the midline at the supraorbital ridge

Quick Memory Tip:

V1 (Ophthalmic division) supplies the entire forehead region. The two key branches are supraorbital and supratrochlear. Both exit near the superior orbital margin.

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Key Foramina / Openings

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Clinical Relevance (High-Yield for DPT!)

1. Frontal Bone Fractures

• The frontal bone is thick and strong - it takes high-energy trauma (car accidents, heavy blows) to fracture it.
• Because so much force is needed, frontal bone fractures are often associated with:
  • Traumatic brain injury (TBI)
  • Cervical spine injury (always check the neck!)
  • Other facial fractures
  • Ocular injuries (up to 25% of cases)
• A forehead laceration over the frontal sinus area should raise suspicion for an underlying fracture.
• CSF Rhinorrhoea (cerebrospinal fluid dripping from the nose) = fracture involving the posterior table of the frontal sinus - this is an emergency.
• Diagnosis: CT scan of the head/face.

2. Pott's Puffy Tumor

• This is NOT actually a tumor! It is a subperiosteal abscess (pus collection under the periosteum) of the frontal bone.
• Caused by osteomyelitis (bone infection) of the frontal bone, usually from frontal sinusitis spreading into the bone.
• Classic presentation: Soft, "doughy" swelling of the forehead skin - it feels squishy, not hard.
• Most common in adolescents.
• Dangerous because the infection can spread intracranially (to the brain).

3. Epidural Hematoma at the Pterion

• The pterion is the H-shaped junction where the frontal, parietal, sphenoid, and temporal bones all meet - just behind the temple.
• The bone here is very thin.
• The middle meningeal artery runs just inside this area.
• A blow to the temple = thin bone fractures = tears the artery = extradural (epidural) hematoma
• Classic presentation: "lucid interval" (patient is briefly OK after the blow, then rapidly deteriorates)
• Very important for DPT - you may see head injury patients in rehab.

4. Supraorbital Nerve Block

• The supraorbital nerve exits through the supraorbital foramen and can be blocked (injected) for pain relief in:
  • Frontal headaches
  • Scalp surgeries
  • Trigeminal neuralgia management
• As a physiotherapist, you should know that pressure on the supraorbital notch causes forehead pain.

5. Sinusitis

• Frontal sinusitis = infection/inflammation of the frontal sinus.
• Presents with pain and tenderness when pressing over the forehead (especially the medial eyebrow area).
• Can complicate into Pott's puffy tumor or meningitis if untreated.

6. Hyperostosis Interna Frontalis

• Benign bony thickening of the inner table of the frontal bone.
• Almost exclusively in middle-aged and older women.
• Usually asymptomatic - found incidentally on X-ray or CT.

7. Hair-on-End Appearance

• In conditions like thalassemia and sickle cell disease, the diploë (spongy layer) of the frontal bone widens.
• This produces a characteristic "hair-on-end" or "sunburst" appearance on skull X-rays - most severe in the frontal bone.

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Quick Summary Table

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Memory Aids

• "Forehead = Frontal" - it covers everything you see as your forehead
• "SOF carries V1" - Supraorbital Foramen carries the supraorbital nerve (V1 branch)
• "Corrugator = Corrugated iron (wavy) = the frowning wrinkle muscle"
• "Pott's puffy = pus + puffy swelling on forehead, soft and doughy"
• "Pterion = Dangerous Thin Bone = middle meningeal artery underneath"
• "Frontal crest + crista galli = two pegs holding the falx cerebri tent"

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