Nerve Supply of the Scalp and Nerve Blocks for Hair Transplant

Part 1 - Anatomy of Scalp Innervation

The 7 Scalp Nerves (by region)

Regional Breakdown

Anterior Scalp (V1 territory)

• Supraorbital nerve - exits via the supraorbital notch/foramen (located along the midpupillary line at the orbital rim). Divides into a superficial branch (forehead skin through frontalis) and a deep branch (scalp to lambdoid suture, ~2-3 cm lateral to midline).
• Supratrochlear nerve - exits via the supratrochlear notch, ~1 fingerbreadth medial to the supraorbital nerve. Supplies the medial forehead and anterior scalp near midline.

Temporal Scalp (V2 + V3 territory)

• Zygomaticotemporal nerve (V2) - pierces the temporalis fascia to supply the anterior temporal hairline. It ramifies as it exits, so both subcutaneous and subfascial injections are needed for a reliable block.
• Auriculotemporal nerve (V3) - runs with the superficial temporal artery, just anterior to the tragus. Supplies the large posterior temporal area and most of the hairline above the ear.

Posterior Scalp (Cervical plexus)

• Greater occipital nerve (C2 dorsal ramus) - the workhorse of posterior scalp anesthesia. Becomes superficial at the inferior border of obliquus capitis inferior, runs medial to the occipital artery, and ascends to the vertex.
• Lesser occipital nerve (C2 ventral ramus) - runs along the posterior border of the sternocleidomastoid, supplies the scalp behind the ear.
• Great auricular nerve (C2/C3 ventral rami) - largest ascending branch of the cervical plexus, supplies the mastoid area, posterior auricle, and adjacent scalp.

All these nerves travel in the subcutaneous layer, above the epicranial aponeurosis (galea aponeurotica). This is the critical anatomical point - injections must reach the subcutaneous plane.

Part 2 - Nerve Blocks for Hair Transplant

Equipment

• 25-gauge needle, 5-10 mL syringes
• Local anesthetic: lidocaine 1-2% with epinephrine 1:100,000 to 1:200,000 (epinephrine reduces bleeding and prolongs duration)
• Alternatively: bupivacaine 0.25-0.5% for longer procedures; ropivacaine 0.3-0.5% is also used
• Total volume needed: approximately 20-30 mL for a complete ring block

The Ring Block Concept

Nerve-by-Nerve Block Technique

1. Supraorbital Nerve Block

• Landmark: Palpate the supraorbital notch/foramen at the orbital rim, in the midpupillary line (~2.5 cm from midline)
• Technique: Insert a 25-gauge needle just above the eyebrow at the orbital rim. Inject 2-3 mL of LA subcutaneously.
• Coverage: Forehead and anterior scalp to the vertex

2. Supratrochlear Nerve Block

• Landmark: ~1 fingerbreadth (1 cm) medial to the supraorbital notch, above the medial eyebrow
• Technique: From the same insertion point used for the supraorbital block, redirect the needle medially through the same skin puncture. Inject 2-3 mL subcutaneously. This is essentially a medial extension of the supraorbital block.
• Coverage: Medial forehead, nasal root area of the scalp

These two blocks together anesthetize the entire anterior scalp from hairline to vertex.

3. Zygomaticotemporal Nerve Block

• Landmark: Lateral edge of the supraorbital margin, extending down toward the zygomatic arch
• Technique: Because the nerve pierces the temporalis fascia, inject 3-5 mL both subcutaneously AND deep to the temporalis fascia (bifascial injection). Begin at the lateral orbital margin and extend toward the zygomatic arch.
• Coverage: Anterior temporal hairline region

4. Auriculotemporal Nerve Block

• Landmark: 1-1.5 cm anterior to the superior border of the tragus, at the level of the root of the zygoma, where the superficial temporal artery is palpable
• Technique: Palpate and avoid the superficial temporal artery. Inject 2-3 mL subcutaneously anterior to the tragus. Aspirate before injecting.
• Coverage: Temporal scalp, temporoparietal area above the ear
• Caution: Close proximity to the superficial temporal artery - mandatory aspiration before injection

5. Greater Occipital Nerve Block

• Landmark: The nuchal line (imaginary line from external occipital protuberance to mastoid process). The greater occipital nerve lies just medial to the occipital artery, approximately 2.5-3 cm lateral to the external occipital protuberance (or halfway between the EOP and the mastoid process)
• Technique: Palpate the occipital artery as your primary landmark. Insert a 23-25 gauge needle and inject 3-5 mL subcutaneously after careful aspiration (the occipital artery runs alongside the nerve)
• Coverage: Entire posterior scalp up to the vertex

6. Lesser Occipital Nerve Block

• Landmark: 2.5-3.5 cm lateral and 1-2 cm caudal to the greater occipital nerve injection point, along the posterior border of the mastoid process
• Technique: Fan-like injection of 2-3 mL subcutaneously in this area
• Coverage: Scalp lateral to the ear, posterior to the auricle

7. Great Auricular Nerve Block (if needed)

• Landmark: Along the posterior border of the sternocleidomastoid muscle, at the level of the mastoid tip
• Technique: Subcutaneous infiltration of 2-3 mL
• Coverage: Mastoid area and inferior posterior auricle - this nerve rarely encroaches on the main hair transplant field and is sometimes omitted

Summary of Injection Points

ANTERIOR:   Supratrochlear [medial] ← → Supraorbital [lateral]
                         ↓ (both above eyebrow)

TEMPORAL:   Zygomaticotemporal (at lateral orbital rim)
            Auriculotemporal (1 cm anterior to tragus)

POSTERIOR:  Greater occipital (3 cm lateral to EOP, medial to occipital artery)
            Lesser occipital (2.5-3 cm further lateral from GON point)
            Great auricular (along posterior SCM)

Practical Tips for Hair Transplant

Contraindications to Scalp Block

• Known allergy to local anesthetics (absolute)
• Absent bone flap (craniectomy defect) - risk of intrathecal spread, especially at occipital injection site (absolute)
• Active local site infection (relative)
• Bleeding disorder/anticoagulation (relative)

Why Nerve Blocks Beat Pure Local Infiltration for Hair Transplant