Procedures · Head, Spine and Pelvis

Cervical Spine Positioning Series

Compare the four routine cervical spine projections: open mouth, AP axial, oblique, and lateral.

Cervical spine · Mouth closed

Left

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The routine cervical spine series

The projections this region is examined with. Set them up yourself in Practice positioning.

AP open-mouth (C1 and C2)

Anteroposterior projection through the open mouth · central ray 90° to the image receptor

Demonstrates: The odontoid process (dens) and body of C2, the lateral masses and transverse processes of C1, and the atlantoaxial joints — through the open mouth. The C1-C2 zygapophyseal joints appear ONLY on this projection, just as the other cervical zygapophyseal joints appear only on the lateral. Correct flexion is proved by the lower margin of the upper incisors superimposing the base of the skull, with neither the teeth nor the skull base over the dens; no rotation is proved by the mandibular angles and mastoid tips lying equidistant from the vertebrae.
Part position: Supine or erect, with the arms at the side and the midsagittal plane aligned to the central ray and the midline of the table. Adjust the head so that, with the mouth open, a line from the lower margin of the upper incisors to the mastoid tips lies 90° to the image receptor. Have the patient open the mouth wide as the LAST step, moving only the lower jaw, with the tongue kept in the floor of the mouth so its shadow stays off C1 and C2.
Central ray: 90° to the image receptor, centered to the midsagittal plane through the center of the open mouth. When the head cannot be adjusted, the central ray is angled instead, keeping it parallel to the line from the lower margin of the upper incisors to the mastoid tips.
Why it is positioned this way: On a plain AP the combined shadow of the skull base and the mandible buries the first two cervical vertebrae — on this skeleton the dens reads about three-quarters hidden with the mouth closed. Opening the mouth swings the lower jaw off the beam path and clears a window onto C1 and C2; nothing about the tube changes. The flexion rule is a balance with a failure mode on each side: too much flexion drops the teeth over the dens, too much extension drops the base of the skull over it.

Also covered by this projection

When the upper dens still hidesIf correct positioning cannot demonstrate the upper half of the dens, it is taken through the foramen magnum instead: the Fuchs method, an AP with the chin elevated until the tip of the mandible and the base of the skull line up with the beam, or the Judd method, its PA mirror. Neither is used on a trauma patient.

Rotation imitates injuryThe atlantoaxial joints are normally symmetric, so the spaces either side of the dens must match. Rotating the head makes them asymmetric and can imitate a fracture or subluxation — which is why the mandibular angles and mastoid tips are checked for equal distance to the receptor before the exposure.

Trauma changes the orderFor a trauma patient the collar stays on and nothing is moved until a physician has cleared the horizontal-beam lateral image or a CT of the cervical spine. The open mouth waits its turn.

AP axial cervical spine

Anteroposterior axial projection · central ray 15° to 20° cephalad

Demonstrates: The C3 to T2 vertebral bodies, their intervertebral disk spaces, and the space between the pedicles. No rotation is proved by the spinous processes and sternoclavicular joints lying equidistant from the lateral borders of the column. C1 and C2 are NOT expected here — the mandible and the base of the skull should superimpose them, which is why the open-mouth projection exists.
Part position: Supine or erect, with the arms at the side. Align the midsagittal plane to the central ray and to the midline of the table. Adjust the head so a line from the lower margin of the upper incisors to the mastoid tips lies 90° to the image receptor, which brings the line from the tip of the mandible to the base of the skull parallel to the angled central ray. Check that neither the head nor the thorax is rotated.
Central ray: Angled 15° cephalad with the patient supine, or 20° cephalad erect, centered to the midsagittal plane at the level of the upper margin of the thyroid cartilage, to pass through C4.
Why it is positioned this way: The lower anterior margins of the last four or five cervical bodies are lipped, so the bodies overlap slightly and a straight beam closes their disk spaces. The cephalad angle sends the beam parallel to the plane of the disks and opens them — measured on this skeleton, the cervical disk planes ask for about 13°, right beside the prescribed range. More lordosis needs more angle, which is why the erect patient gets 20° and a kyphotic patient more still.

Also covered by this projection

Where C4 isThe centring level is palpated, not guessed: the upper margin of the thyroid cartilage lies at C4, roughly midway between the mandibular angle and the jugular notch. The lateral and both obliques center to the same level.

Do not swallowRespiration is suspended and the patient is asked not to swallow during the exposure — the larynx and hyoid travel with a swallow, and the motion blurs the very soft-tissue margins the projection is judged on.

AP oblique (posterior oblique) cervical spine

Right posterior oblique · 45° rotation · central ray 15° to 20° cephalad

Demonstrates: The intervertebral foramina and pedicles of the side FARTHEST from the receptor — a right posterior oblique demonstrates the LEFT foramina, and both sides are always taken for comparison. The foramina of C2 through C7 should be open and uniform, with the pedicles of interest in full profile. On-end pedicles at the midline of the body mean over-rotation; obscured foramina mean under-rotation; and the mandibular rami must not superimpose the vertebrae.
Part position: Erect preferred, seated or standing, or supine when the patient cannot stand. Rotate the whole body and the head together 45° — measured with an angle gauge, not judged by eye. Protract the chin so the mandible clears the vertebrae, and elevate it just enough to keep the acanthiomeatal line level; extending the head further drops the base of the skull over the posterior arch of C1.
Central ray: Angled 15° to 20° cephalad, centered to the midsagittal plane at the level of the upper margin of the thyroid cartilage, to pass through C4.
Why it is positioned this way: The cervical intervertebral foramina open 45° to the midsagittal plane AND point 15° to 20° inferiorly, so this projection needs two angles at once: the 45° body rotation lines the beam up with the foramina side to side, and the cephalad angle lines it up top to bottom. Swept over every combination on this skeleton, the foramina open widest at 40° of rotation with a generous cephalad angle — right beside the prescribed 45° and 15° to 20°.

Also covered by this projection

Anterior obliques insteadTurning the patient the other way — RAO or LAO, facing the receptor — reverses both rules at once: the central ray goes 15° to 20° CAUDAD, and the projection demonstrates the foramina CLOSEST to the receptor, so an RAO shows the right side. Anterior obliques are preferred where practical because they lower the dose to the thyroid.

The rule, region by regionEach spinal region answers the "which side?" question differently, and all three answers are right. Lumbar posterior obliques show the zygapophyseal joints CLOSEST to the receptor (RPO, right). Thoracic AP obliques show the zygapophyseal joints FARTHEST from it (RPO, left). Cervical posterior obliques show the intervertebral foramina — a different structure altogether — FARTHEST from it (RPO, left). Memorising one rule and carrying it across regions is the classic exam trap.

The long SID and the air gapThese projections tolerate 40 to 72 inches (100 to 180 cm) of SID, and the longer distance is recommended. The rotated position holds the spine away from the receptor, and that air gap lets much of the scatter miss the receptor entirely — which is why a grid is optional here.

Lateral cervical spine

Left lateral position, erect · central ray 90° to the image receptor

Demonstrates: All seven cervical vertebral bodies in profile with their intervertebral joint spaces, the articular pillars, the spinous processes, and the zygapophyseal joints of C2 through C7 — which sit at 90° to the midsagittal plane and therefore appear ONLY on this projection. The image must include the C7-T1 junction; a lateral that stops at C6 has not cleared the cervical spine. This is clinically the single most important image of the series.
Part position: Erect in the left lateral position, seated or standing, with the shoulder against the image receptor and the midcoronal plane aligned to the central ray. Elevate the chin and protract it so the mandibular rami clear the vertebrae. As the final step, have the patient relax both shoulders down and forward as far as possible — on full expiration, with 5 to 10 lb (2.3 to 4.5 kg) weights in each hand when needed — because the shoulders are what bury C7.
Central ray: 90° to the image receptor, directed horizontally, centered to C4 at the level of the upper margin of the thyroid cartilage, with the top of the receptor about 1 to 2 inches (2.5 to 5 cm) above the external acoustic meatus.
Why it is positioned this way: The shoulder holds the cervical spine several inches from the receptor, and that object-to-receptor distance would magnify and blur the image at a standard distance — so this projection is taken at 60 to 72 inches (150 to 180 cm) SID, the long distance restoring the sharpness the gap costs. The same gap earns its keep on the way out: scatter leaving the neck diverges across it and misses the receptor, which is why a grid is optional here.

Also covered by this projection

Trauma: the horizontal-beam lateralFor a trauma patient this image comes FIRST, taken supine with a horizontal beam, the collar on, and nothing moved — every other cervical projection waits until a physician has cleared it or a CT. The geometry is the same lateral, acquired without touching the patient.

When C7-T1 will not showThick shoulders can bury the cervicothoracic junction however hard they are depressed. The answer is the cervicothoracic (swimmer’s) lateral: the arm nearest the receptor raised with the forearm on the head, the far arm down and slightly posterior, central ray to T1. It lives in the thoracic series, since it covers C5 to T3.

Flexion and extension lateralsA functional study for anteroposterior mobility — after injury such as whiplash, or to check a fusion — repeats this lateral in full flexion and full extension. Never attempted on a trauma patient until the standard lateral or CT has been cleared by a physician.

Procedures lessonVertebral column