Atlantoaxial Joint

Classification

Type: Synovial pivot (median atlantoaxial — the dens and anterior arch of C1) plus two lateral synovial plane joints (lateral atlantoaxial — C1 lateral masses on C2 superior facets)
Degrees of freedom: Primarily 1 (axial rotation); small amounts of flexion/extension and lateral flexion
Region: Upper cervical spine (craniocervical junction, along with the anatomy/joints/atlantooccipital joint)

Articular Surfaces

Median atlantoaxial joint: The anterior arch of C1 (posterior facet) articulates with the anterior surface of the dens (odontoid process) of C2. The transverse ligament forms the posterior boundary, holding the dens against the anterior arch. This is a true pivot joint — C1 rotates around the dens.
Lateral atlantoaxial joints (×2): The inferior articular facets of C1 (flat to slightly convex) articulate with the superior articular facets of C2 (flat to slightly convex). Both surfaces are slightly convex, which creates inherent instability but allows the significant rotation that defines this joint.

Movements and ROM

Movement	Normal ROM	Plane	Muscles Producing
Rotation	40–45° (each side)	Transverse	anatomy/muscles/obliquus-capitis-inferior (primary C1-C2 rotator), anatomy/muscles/rectus-capitis-posterior-major, anatomy/muscles/splenius-capitis, anatomy/muscles/sternocleidomastoid
Flexion	5–10°	Sagittal	Same muscles as C0-C1 flexion; motion limited by the tectorial membrane
Extension	10°	Sagittal	Suboccipital extensors
Lateral flexion	5°	Frontal	Limited by the alar ligaments

The "no" joint. C1-C2 provides approximately 50% of total cervical rotation. When you shake your head "no," half the movement occurs here. Loss of C1-C2 rotation produces compensatory over-rotation at the lower cervical segments, which may lead to facet joint irritation and accelerated degeneration at C3-C4 and C4-C5.

Capsular Pattern

Rotation is most limited The capsular pattern at C1-C2 primarily restricts rotation. This is the defining movement at this joint and the first to be lost in capsular pathology.

Resting Position

Neutral (midway between flexion and extension)

Close-Packed Position

Full extension
Maximum dens engagement, ligaments taut

End-Feels

Movement	Normal End-Feel	Type
Rotation	Capsular (firm)	Alar ligaments (contralateral), joint capsules, and muscular tension
Flexion	Capsular (firm)	Tectorial membrane, posterior capsule
Extension	Bony / capsular	Posterior arch of C1 contacts C2 lamina

Ligaments

Transverse Ligament of the Atlas

Attachments: Lateral mass of C1 (one side) → lateral mass of C1 (opposite side), crossing behind the dens
Function: The most critical ligament in the body for preventing catastrophic injury. It holds the dens against the anterior arch of C1, preventing posterior displacement of the dens into the spinal cord. The atlantodental interval (ADI) — the space between the anterior arch and the dens — is normally ≤3 mm in adults and ≤5 mm in children. An ADI >3 mm indicates transverse ligament insufficiency.
Injury mechanism: Forceful flexion (the dens is driven posteriorly by the flexed atlas). RA — pannus formation erodes the transverse ligament attachment points on the C1 lateral masses. Down syndrome — ligamentous laxity predisposes to transverse ligament insufficiency. Odontoid fracture removes the bony anchor the ligament holds.
Assessment test: Sharp-Purser test (with extreme caution, only when instability is suspected): in sitting, with the head slightly flexed, apply a posterior pressure on the forehead while stabilizing C2 spinous process. A positive test is anterior-to-posterior sliding of C1 on C2 (felt as a "clunk") — indicates transverse ligament insufficiency. Refer immediately. Many clinicians consider this test too dangerous to perform routinely.
Condition link: Atlantoaxial instability, RA-associated cervical instability

Alar Ligaments

Attachments: Lateral aspect of the dens → medial occipital condyles and lateral masses of C1
Function: Check ligaments for rotation and lateral flexion. They prevent excessive rotation to the contralateral side and limit lateral flexion. Disruption causes excessive rotation and may allow the dens to compress the spinal cord during rotation.
Assessment test: During passive rotation, palpate the C2 spinous process. Normally, C2 begins to rotate with C1 after approximately 20–30° of rotation (the alar ligaments couple C2 motion to C1 rotation). If C2 does not rotate with C1 (excessive uncoupled rotation), suspect alar ligament disruption.

Cruciform Ligament

Attachments: The transverse ligament plus superior and inferior longitudinal bands extending from the transverse ligament to the occipital bone (superiorly) and the body of C2 (inferiorly)
Function: Reinforces the transverse ligament. The cruciform complex as a whole anchors the dens and prevents posterior displacement.

Apical Ligament

Attachments: Tip of the dens → anterior margin of the foramen magnum (basion)
Function: Minor stabilizer; considered a vestigial structure. Resists vertical translation of the dens.

Mobilization Techniques

Hands-on instruction is required. The descriptions below provide clinical reference detail for understanding and supervised practice. They are not a substitute for instructor-led technique training. Correct hand placement, force dosage, and tissue response interpretation require hands-on coaching and feedback.

Safety Considerations at C1-C2

Mobilization of C1-C2 carries the highest risk of any spinal mobilization. The vertebral arteries loop around the lateral masses of C1 before entering the skull — sustained or forceful rotation can compress or stretch these arteries. The spinal cord is immediately posterior to the dens — any posterior displacement of the dens threatens cord compression. Mandatory pre-treatment screening:

VBI screening (sustained extension, rotation, combined positions — monitor for dizziness, nystagmus, visual changes, nausea)
Upper motor neuron screening (Babinski, clonus, Hoffman's, hyperreflexia — any positive sign is an absolute contraindication)
Assessment of atlantoaxial stability (ADI, Sharp-Purser if indicated)
History: RA, Down syndrome, recent trauma, anticoagulant use

General Contraindications

Absolute: All contraindications listed for anatomy/joints/atlantooccipital mobilization apply, plus: positive Sharp-Purser test, ADI >3 mm, odontoid fracture, os odontoideum, RA with cervical involvement (until cleared by imaging), positive upper motor neuron signs
Relative: Elderly patients (vertebral arteries are more rigid and vulnerable), anticoagulant therapy, significant cervical DDD

C1-C2 Rotational Mobilization

Purpose: Restores rotation at C1-C2 — the most commonly restricted movement at this joint. Used for unilateral rotation restriction producing cervicogenic headache or reduced cervical rotation ROM. Patient position:

Supine on the treatment table
Head cradled by the clinician's hands, at or slightly beyond the table edge
Cervical spine in neutral flexion/extension — slight flexion (chin tuck) locks the lower cervical spine and isolates C1-C2 rotation

Hand placement:

Stabilizing hand: Cradles the occiput, supporting the weight of the head. The web space may contact the occiput posteriorly.
Mobilizing hand: The index finger contacts the lateral mass of C1 (palpable between the mastoid process and the angle of the mandible — the widest transverse process in the cervical spine). The contact is gentle but specific.

Technique execution:

With the head in slight flexion (to lock lower cervical segments), gently rotate the head toward the restricted side
Grade I–II: Small oscillatory rotational movements within the pain-free range. For acute cervicogenic headache or when pain prevents end-range assessment.
Grade III: Oscillations at end-range rotation, into the capsular resistance. The alar ligament and contralateral joint capsule provide the barrier.
The total oscillation amplitude is very small. C1-C2 mobilization uses the least force and smallest amplitudes of any spinal mobilization.
Duration: 15–30 seconds per set, 2–3 sets
Reassess active rotation between sets

Indications:

Unilateral rotation restriction at C1-C2 (tested by rotating the head with the cervical spine flexed to lock lower segments)
Cervicogenic headache with ipsilateral C1-C2 rotation restriction
Post-whiplash rotation limitation isolated to the upper cervical spine

Technique notes:

The key to isolating C1-C2: Flex the cervical spine slightly (chin tuck). This locks the lower cervical facets (close-packed position of the lower cervical spine is extension) and forces rotation to occur at C1-C2.
Common error: Rotating through the entire cervical spine rather than isolating C1-C2. If lower segments are moving, the cervical spine is not sufficiently flexed.
Common error: Excessive force — C1-C2 requires very little force; the joint is highly mobile by design.
Reassessment: Re-test active cervical rotation (total ROM). An increase of 5–10° per session with reduced headache intensity confirms C1-C2 involvement.
Integration: Perform after suboccipital and obliquus capitis inferior release.

C1-C2 Lateral Glide

Purpose: Restores lateral translatory motion at C1-C2. Useful when rotation restriction is accompanied by reduced lateral glide (the two are coupled at C1-C2). Patient position:

Supine, head cradled