What is the tube angle for a PA oblique C spine?

It certainly helps to label the right side from the left when performing studies of the spine or any extremity. We tend to forget that not everyone puts an ID marker in the left-hand corner of the file, or that doctors always take posterior obliques of the cervical spine. When films are sent out of our office for any reason, it is very helpful to have right/left labels on the film. I know every one of us would agree, but not everyone does it. In my own private study, questioning my colleagues and clients, almost a third of us (maybe more) do not take the time to label films. This might actually be an interesting study for ChiroPoll, but I do not want to know the actual numbers. I think the results might not reflect well on our profession.

I'm here to remind you to label your patients' films right and left. Here are the general rules. In the AP projection, it is obvious that only right or left needs to be labeled. In the lateral projection of the axial skeleton, the sides are not generally labeled because it is too difficult to see the difference. The side that is closest to the film is the side that has the least distortion, but that is difficult to see when the structures are small. With larger structures such as the knee, for example, the condyle closest to the film is the smallest.

Again, however, lateral views of the spine are not labeled as to which side is closest to the film. The lateral view of an extremity should of course be labeled the same as the AP.
There are two ways to perform oblique positions in a cervical or lumbar series: anterior to posterior and posterior to anterior. It doesn't matter which way you choose to perform the view as long as you are consistent and label them to identify which foramina or facet is closest to the film.

The side (right or left) closest to the film is always marked. Oblique positions are determined by the right or left side of the patient and the anterior or posterior surface being closest to the film. Therefore, a RPO position means an oblique view, with the right posterior body surfaces in contact with or closest to the film, table or bucky. Likewise, a LAO position is an oblique view, with the left anterior body surfaces in contact with or closest to the film, table or bucky.

With anterior obliques, the patient faces the bucky and the body is rotated 45 degrees away from the film. The head is then positioned parallel with the plane of the bucky, with the chin tilted upward slightly. Patients tend to want to tilt their heads away from the bucky. Don't allow that to happen. When the patient tilts the head away, it's difficult to determine if the foramina are narrowed due to pathology or positioning.

With posterior oblique views, the patient faces the tube and the body is rotated 45 degrees away from the film. The head is then positioned parallel to the bucky and the chin is tilted slightly upward.

For both cervical anterior and posterior oblique views, the tube should be tilted 15 degrees: caudad for anterior obliques and caphald for posterior obliques. The central ray should be at the C4 level. To identify anterior from posterior oblique views, if you are only using "R" and "L" markers, the marker should be placed in front of the spine for anterior obliques and behind the spine for posterior obliques. If you are using "RPO" or "RAO" markers, it doesn't matter.

Remember, the oblique views of the cervical spine demonstrate the intervertebral foramina, uncovertebral joints, apophyseal joints and pedicles. The rules by which foramina are demonstrated are: posterior obliques demonstrate the contralateral foramina, i.e., RPO demonstrates the left foramina; the anterior obliques demonstrate the homolateral structures, and RAO shows the right foramina.

Right and left posterior oblique views of the lumbar spine are performed with the body rotated approximately 30-35 degrees toward the side being examined. (The side that is closest to the bucky is the side examined.) The central ray is positioned approximately two inches above the iliac crest (L3) and two inches medial to the ASIS of the side that is away from the film. Exposure should be made upon expiration.

Anterior oblique views are performed with the body rotated 30-45 degrees away from the bucky. The central ray is positioned two inches above the iliac crest, and the spine centered to the midline of the bucky. In this case, the side farthest from the film is the side that is visualized. For example, in a right anterior oblique view, the left apophyseal joints are visualized. In the right posterior oblique view, the right apophyseal joints are visualized.

If we don't label our oblique views, there is no way of knowing which side we are demonstrating on the film.

Reference

Buehler M, Pugh J, Sandman T. Physics and Technology in Routine Radiography. National College of Chiropractic, 1979.

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- Technique:
    - routine oblique views require rotating the patient's head and body;     - may be obtained in AP or PA projections:     - erect position is more comfortable;     - entire position is rotated 45 deg to one side to avoid rotational differences among different vertebral segments;

    - central beam directed to C4 vertebra with 15-20 deg cephalic tilt;

- Trauma Oblique:     - this view shows the pedicles and articualr processes well;     - oblique views often are superior to any other view, including MRI or CT scans, for visualizing articular process frx & subluxations;     - in difficult question of facet subluxation, flexed oblique views also can be obtained;     - uncinate processes, pedicles, laminae, & inferior & superior articular facets are well seen using this technique;

    - C7-T1 relationship, which is frequently obscured on lateral film, may be seen on the oblique and obviate need for a swimmer's view;

- Technique Trauma Oblique:     - trauma oblique series can be obtained without moving the head but by angling the tube 30-40 deg from the horizontal;     - trauma oblique is obtained w/ x-ray beam 45 deg off vertical, patient supine, & ungridded cassette horizontal & located           towards opposite side of the patient;     - this view shows pedicles & articular process well, although appearance of spine is slightly spread out;     - major benefit of oblique view is that patient can remain supine;     - no rotation of the torso or head is required;

    - furthermore, oblique views often are superior to any other technique, including CT or MRI scans, for visualizing articular process 

    - in difficult questions of facet subluxations, flexed oblique views also can be obtained

Introduction

Oblique views in radiography tend to be problematic. The common questions are

• Which way do I oblique the patient?
• How much do I oblique?
• What is the anatomy demonstrated?
• AP or PA?
• How do you label the images?
• Where do I centre the beam?
• What FFD should I use?
• How much do I angle the beam?
• What exposure technique should be employed?
  

This page is dedicated to answering some of these questions

The oblique view of the cervical spine can be important in patients with pain and/or altered sensation in their upper limbs. This can be caused by pressure on the nerves which exit the cervical spine through the intervertebral foramina. The oblique view shows the intervertebral foramina formed by the inferior notch of the pedicle of the vertebrae above and the superior notch of the pedicle of the vertebrae below.

The presence of osteo-arthritis in the unco-vertebral articulations of the lower cervical spine frequently produces pressure on the nerve-roots lying in the intervertebral foramina. This is a common cause of brachialgia in middle age. Oblique radiographs of the cervical spine are necessary if the condition is to be confirmed radiologically. <a class="external" href="http://www.journals.elsevierhealth.com/periodicals/jfrad/article/PIIS0368224256800304/abstract" rel="nofollow" target="_blank">http://www.journals.elsevierhealth.com/periodicals/jfrad/article/PIIS0368224256800304/abstract</a>

Oblique cervical spine views can be performed erect or supine and AP or PA.

The Labelling Convention

Some centres will prefer the side marker to also refer to the intervertebral foramina demonstrated. The cervical spine images on this page all have the side marker on the side of the intervertebral foramen demonstrated. i.e. If an oblique cervical spine image has a left side marker, the left intervertebral foramina are demonstrated (see left) This convention is a simple aid to the radiologist. The convention also has utility for the radiographer in terms of avoiding mislabelling through consistency and clarity of thinking.A further more general convention is to present the image in the anatomical position- AP oblique not PA oblique n.b. labelling has an English spelling with 2 "L"s and an American spelling with one "L"

PA TechniqueThe PA technique tends to be the most confusing because the image is flipped horizontally for viewing

For the left oblique the patient is positioned like this.	Image prior to horizontal flipping (note the positioning is PA oblique and the side marker is PA)	After horizontal flipping of image

Which way do I oblique the patient?

• always do both obliques- left and right (either AP or PA)

How much do I oblique?

• 45 degrees with the patient's head in the lateral position
  

What is the anatomy demonstrated?

• aim to include all of the cervical spine anatomy
  

AP or PA?

• your choice- consider which technique is easier and safer for the patient
  

How do you label the images?

Where do I centre the beam?

• Cone to include all of the cervical spine anatomy and the centre point will look after itself
• Note that the cervical spine is not in the 'centre of the neck' in the lateral projection- it is a posterior neck structure
  

What FFD should I use?

How much do I angle the beam?

• 15 degrees caudal for PA technique and 15 degrees cephalic for AP technique

What exposure technique should be employed?

• 70 - 75 kVp, short exposure time to minimise movement unsharpness
  

What Went Wrong?

The patient is under-rotated (too PAish). Also, the patient's head is not in the lateral position causing the mandible to be superimposed over C1/C2. Note that the intervertebral foramina are partially "closed", particularly at the lower cervical level. The beam collimation is arguably too generous.	This patient is severely over-rotated. Some of the intervertebral foramina are visible but are obscured to varying degrees.

Trauma Obliques of the Cervical Spine

The oblique projection of the cervical spine is either a routine view or a supplementary view in many Emergency Departments. Whilst this is a relatively easy examination in an ambulant non-trauma patient, a special approach is required in a trauma patient who cannot be moved. This page considers two approaches to the problem and a useful positioning aid.

Technique 1

This technique is a non-grid technique in which the X-ray cassette is placed on the table top. The X-ray tube is angled 45 degrees as shown

The image is distorted, but does provide valuable visualisation of the cervical facet joints and intervertebral foramen

Technique 2

This technique is a grid or non-grid technique in which the X-ray cassette is placed under the X-ray table at an angle of 45 degrees. The X-ray tube is also angled 45 degrees as shown

Again, the image does provide valuable visualisation of the cervical facet joints and intervertebral foramen. Note that the superimposition of the mandible over the cervical spine bony anatomy was unavoidable in this case.

The Tostevin Cassette Holder

This cassette holder can be found at the Royal Perth Hospital, Western Australia and was designed by John Tostevin. This must be the ultimate accessory for trauma oblique cervical spine radiography.

Oblique cervical spine radiography is difficult to master at first. With practice you will find that you can cone the X-ray beam more tightly. With confidence you may also find that you can use a 10 x 8 inch (18 x 24cm) cassette rather than a 12 x 10 inch (24 x 30cm) cassette.

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