The most common causes of a missed C-spine abnormality are failure to adequately visualise the injured region and inadequate understanding of the C1/C2 anatomy. Therefore errors commonly relate to:

▪ C1/C2 fractures or subluxations.

▪ Low C-spine fractures ¹^–⁴, frequently involving the C7 vertebra.

The standard radiographs

Three-view trauma series.

Abbreviations

AP, anterior-posterior projection;

C-spine, cervical spine;

C1, Atlas vertebra;

C2, Axis vertebra;

CT, computed tomography;

ED, Emergency Room/Department;

Peg, odontoid peg;

T1, first thoracic vertebra.

Normal anatomy

Lateral view

The Coffee Bean Shadow.

The anterior arch of C1 is a shadow that is always visible on a lateral radiograph. It looks like a reversed capital D. We call this shadow the “Coffee Bean” shadow because we think it resembles a coffee bean. Use it as your anatomical starting point when assessing the C1–C2 anatomy.

AP Peg view

Long AP view

Analysis: the checklists

Injuries are most often missed because of poor radiographic technique and/or inaccurate film interpretation ¹^,²^,⁴^–⁶. Most errors are avoidable⁵. Missed C-spine abnormalities occur most commonly at the top or at the bottom of the C-spine¹^,².

□ Whatever the level of violence, C-spine injuries frequently occur at the C1–C2 level ¹^,³^,⁴^,⁶.

□ The most common fracture in elderly patients following a fall is a high cervical injury ¹^,³.

□ Between 9% and 26% of patients with one fracture or dislocation of the spine will have further fractures demonstrable radiographically at other levels ⁵.

□ If you have detected one injury you must still complete the checklists, in order to find any additional abnormalities.

Priority 1: Lateral view checklist

Identify the odontoid peg and assess its position and anatomical relationship to the C1 vertebra. Overlapping structures (eg mastoid, ear lobes, C1 vertebra) can make this difficult. Questions 1–5 will help you to overcome this.

Ask yourself ten important questions:

1. Is the radiograph technically adequate? Ensure that the C1–C2 articulation and the superior surface of the T1 vertebra are clearly seen.

2. Have I identified the anterior arch of the C1 vertebra (the “coffee bean”)?

3. Is the anterior cortex of the odontoid peg (the Peg) closely apposed to the “coffee bean”?

4. Is the line of the anterior cortex of the Peg continuous with the anterior cortex of the body of C2? Any displacement implies a Peg fracture or fracture of C2 body.

5. Is the line of the posterior cortex of the Peg continuous with the posterior cortex of the body of C2? Any displacement or break indicates a Peg fracture.

6. Is Harris’ ring ⁷ normal? A break in either the anterior or posterior margin of the ring indicates the high probability of a fracture of the Peg/body of C2 (p. 176).

7. Are the posterior arches of C1 and C2 intact?

8. Are the other vertebrae (C3–C7) intact (p. 192)?

9. Are the three main contour lines/arcs normal (p. 178)?

10. Are the pre-vertebral soft tissues normal (p. 179)?

Questions 2 and 3.

Recognising the anterior arch of C1 is key to detecting the abnormalities that may involve the C2 vertebra.

The arch looks like a small coffee bean, and is always easy to identify on the lateral view.

The gap between the Peg and the coffee bean should not exceed 3 mm in adults or 5 mm in children ¹.

This is a normal lateral view.

Questions 4 and 5.

Check that the anterior cortex of the Peg is continuous with the anterior cortex of the body of C2.

Also check that the posterior cortex of the Peg is continuous with the posterior cortex of the body of C2. Any displacement or break in either of these lines indicates a Peg fracture.

Question 6. Harris’ Ring ⁷. Many lateral views will show a white ring projected over the base of the Peg and over part of the body of C2 (see above). This ring may appear slightly incomplete at its inferior and/or superior aspects—that is a normal appearance. However, if either the anterior or posterior margin of the ring appears disrupted then a fracture through the base of the Peg or the body of C2 is very possible and a C2 fracture will need to be excluded (p. 188).

Question 7. Check that the posterior arches of C1 and C2 are intact.

Question 8.

Check that the vertebral bodies (C3–C7) are intact.

The vertebral bodies below C2 have a fairly uniform square or rectangular shape.

The anterior and posterior heights should be approximately the same. The front to back widths of all of the vertebrae are approximately similar.

Question 9. You can trace the three main contour lines (arcs) as follows:

Line 1: along the anterior margins of the vertebral bodies (anterior line).

Line 2: along the posterior margins of the vertebral bodies (posterior line).

Line 3: along the bases of the spinous processes (spinolaminar line).

Each line should be a smooth unbroken curve or arc. No kink. No step. Trace these lines along the full length of the cervical spine. Line 1 extends from the top of the anterior cortex of the Peg to the anterior margin of the body of T1 vertebra.

Potential Pitfall: Line 3 will sometimes show a slight step at the C2 level, particularly in children ⁸.

Apply this rule: this step should not be more than 2 mm posterior to the smooth arc as it is traced upwards between C3 and C1 vertebrae.

Question 10. Are the pre-vertebral soft tissue shadows normal? The soft tissue shadow ⁷^,⁹^–¹¹ anterior to the vertebral bodies has a characteristic configuration and width. Any bulge or local increase in width indicates haemorrhage and connotes an important injury.

NB: The absence of a bulge does not exclude a ligamentous or bone injury. Indeed, even with a major injury, a soft tissue bulge due to a haematoma is fairly rare.

Maximum normal width of the prevertebral soft tissues

Level	Width	Approximate % of a vertebral body (AP) width
C1–C4	7 mm	30%
C5–C7	22 mm	100%

Priority 2: AP Peg view checklist

The anatomical arrangement of the C1–C2 articulation allows extensive neck rotation whilst providing maximum stability. This stability depends on the integrity of the ligaments, particularly the C2 transverse ligament. Various other ligaments enable C1 vertebra to be held in the optimal position above the body of C2 vertebra. Any deviation from this alignment indicates either ligamentous disruption or a broken vertebra.

Ask yourself three important questions:

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Tags: Accident and Emergency Radiology A Survival Guide

Jan 5, 2016 | Posted by admin in EMERGENCY RADIOLOGY | Comments Off