The transverse processes of the atlas are the largest in the cervical spine, projecting further laterally than at any other cervical level. Each contains a transverse foramen through which the vertebral artery passes. The anterior and posterior tubercles of the transverse process provide attachment for several muscles and the anterior atlantoaxial ligament.
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| Ossification | The transverse process of C1 is part of the lateral mass ossification centre, completing fusion by age 3-6. The transverse foramen is formed by the junction of the anterior and posterior intertransverse bars. |
The atlas transverse process tip is the most lateral palpable point in the suboccipital region, identifiable between the mastoid process and the posterior mandibular angle. It is the target for C1 nerve root injection and atlantoaxial joint injection performed via lateral or posterior approach. The transverse process may fracture in high-energy cervical trauma. The vertebral artery is immediately adjacent and at risk during C1 lateral mass screw placement.
Find the tip of the mastoid process behind the ear lobe and the angle of the mandible below the ear. In the gap between them, just below and in front of the mastoid tip, press gently inward to feel a firm bony knob; this is the transverse process of C1. It is normally tender, so use light pressure.
A rare fracture from lateral bending or direct trauma that can injure the vertebral artery as it passes through the transverse foramen of the atlas.
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