The obsolete C-Spine X-Rays - Part 1

In this day and age, most hospitals and certainly all the trauma centres prefer to CT Cervical-spine rather than performing a series of Cervical Spine X rays. Few centres have gone a step beyond, where they perform a head to pelvis (PAN-CT) scan PRIOR to resuscitation, which is then followed by simultaneous Clinical and CT based ABCD assessment.

That said, I believe that C-Spine X rays still hold a place in the developing world where cost becomes a significant issue during management of trauma victims. Emergency Physicians often get caught up in financial discussions with patients and their families, therefore we need to choosy while ordering blood investigations and imaging studies. And also, C-Spine X-Rays is a good way to start evaluating low risk injuries. In this three part series, I intend to provide a framework and stepwise interpretation of C-Spine X-Rays. 

Trauma C Spine views:

1. AP
2. Lateral
3. Open Mouth (Peg View)

• Swimmer's view: It is named after the swimming stroke referred to as freestyle. This view can be requested in addition to standard 3 trauma views to demonstrate the upper thoracic  and the seventh cervical vertebrae.

The most common reasons for missed injuries is inadequate films (which fail to show C7-T1 junction) and poor understanding of C1-C2 anatomy.

Anatomy Review

Key Points: It is critical to understand C1-C2 anatomy. C1 vertebra lacks a body. C1 instead has a ring which incorporates the odontoid process (odontoid process = dens = peg) of C2 vertebra. Often, these three different names for odontoid process cause a bit of confusion. I am going to refer to it as "peg" for the rest of this post. 

Look at the images below to visualise C1-C2 anatomy. Peg (labelled as odontoid process of C2 in the image below) sits between the Anterior Arch of Atlas (C1 vertebra is also called as Atlas) and transverse ligament. 

Peg is labelled as Dens the all the above 3 (Ant,Post and Lateral) images

See how peg (also known as odontoid/dens) fits into the ring of C1 vertebra seen from the lateral view

Lateral View (STEPS)

1. Assess adequacy of the film (Is C7-T1 junction seen? - Avoid interpreting inadequate films. Patients with inadequate films need a CT scan. Swimmer's view can be used as an adjunct to improve visualisation due to poor body habitus. At the outset, choose a CT over X-rays in difficult body habitus and elderly. 

Inadequate film (C7-T1 not visualised)

Adequate (C7-T1 junction seen)

                                       

Swimmer's view

2. Identify the Anterior Arch of Atlas (AAA) and measure the distance between AAA and Peg (< 3mm in Adults and < 5mm in Kids) - Increased space between these two structures suggests transverse ligament injury.

Pre-dental space on X Tay

3. Identify Peg: Anterior cortex of peg should be continuous with the body of C2 (Remember, Peg itself is a part of C2) and the posterior cortex of the peg should be in continuation with the posterior cortex of body of C2. Any break in the anterior or posterior cortex indicates a Peg fracture.

Image of Left - Not the that the anterior cortex of peg continuous with the body of C2 and the posterior cortex of the peg is in continuation with the posterior cortex of body of C2. Image on Right- Obvious step in the continuity of C1-2 indicating peg #. This finding may not be very prominent. 

4. Identify Harris Ring - A white incomplete ring seen at the base of peg which is occasionally incomplete at inferior and superior aspects (This is NORMAL). If the anterior or posterior margin of the ring looks disrupted, suspect a fracture thru the base of peg or C2 body.

Harris Ring, Marked with black Arrow heads. Look at all the above images now and try to localise the harris ring.

5. Look at the THREE Lines, heights of all the vertebra and pre vertebral soft tissues: 

• Each line should run smoothly without any steps. 
• The anterior and posterior heights of vertebra should be approximately same
• Any swelling on the soft tissues shadows anterior to the vertebra indicates haemorrhage. However, the absence of swelling cannot exclude an injury. So be worried if you increase in the width of pre-vertebral soft tissues but don't be reassured completely if it looks normal. Remember these numbers (3x7=21)

Pre-dental space - < 3mm in adults
Pre-vertebral Soft tissues width at C1-4 - < 7mm

Pre-vertebral Soft tissues width at C5-7 - < 21mm

Images taken from:

• http://www.shutterstock.com/pic-415445710/stock-photo-cervical-spine-structure-vertebral-bones-cervical-bones-anatomy-of-human-bone-system-human.html
• http://www.aafp.org/afp/1999/0115/p331.html
• https://www.med-ed.virginia.edu/courses/rad/cspine/interpretation1.html
• https://www.ceessentials.net/article20.html
• http://accessemergencymedicine.mhmedical.com/searchResults.aspx?q=jefferson+fracture&f_SemanticFilterTopics=jefferson+fracture&fl_SiteID=52&fl_TopLevelContentDisplayName=Images&adv=True
• http://clinicalgate.com/cervical-spine-5/
• https://www.studyblue.com/notes/note/n/radiology-c-spine-neck/deck/8336200