Cervical Spine - Odontoid Peg

Radiographic Positioning

Adult

Other related pages of interest Applied Radiography Radiographic Anatomy Radiographic Protocols

Name of projection	Cervical Spine - Odontoid (Peg)
Area Covered	Cervical vertebra C1 - Lateral masses, transverse processes Cervical vertebra C2 - Odontoid process, body of C2 Zygopophyseal joints
Pathology shown	Pathologies of C1 and C2, including Jefferson fractures and odontoid fractures
Radiographic Anatomy	Cervical Spine Radiographic Anatomy
IR Size & Orientation	18 x 24 cm Portrait
Film / Screen Combination	Regular (CR and DR as recommended by manufacturer)
Bucky / Grid	Moving or Stationary Grid
Filter	No
Exposure	65 kVp 16 mAs
FFD / SID	100 cm
Central Ray	Directed to the centre of the open mouth Parallel/along the line of the occlusal plane of the top teeth and the base of skull (the angle may be cephalad, caudal or perpendicular depending on the patient presentation)
Collimation	Centre: The centre of the open mouth Shutter A: Open to include the acanthion superiorly Shutter B: Open to include the corners of the open mouth laterally
Markers	Lateral Marker orientation AP
Shielding	Gonadal (check your department's policy guidelines)
Respiration	Suspended
Positioning	In general, Ensure the removal of artefacts that may superimpose the anatomy of interest, such as dentures or tongue jewellery Only request the patient move into position if the possibility of spinal injury has been ruled out Take care to ensure no rotation of either the head, neck or torso. If the patient is erect, Using the upright bucky, position the patient in an AP position. (This allows the patient to rest their back against the bucky, and may help to minimise patient movement) Position the midsagittal plane so that it is perpendicular to the IR Position the interpupillary line so that it is parallel to the IR (in an erect patient, this will also be parallel to the floor) Have the patient open their mouth as wide as possible Raise or lower the chin so that the occlusal plane of the upper teeth and the base of the skull are in line and are perpendicular to the IR/bucky The central ray will then be perpendicular to the IR/bucky If the patient is supine, Often this may be the case due to trauma, in which case do not move the patient, work around them Position the IR so that it is either in the table bucky, or is on the barouche posterior to the upper cervical spine Angle the central ray along the line of the occlusal plane of the upper teeth and the base of skull
Critique PACEMAN	Positioning No rotation is evidenced by The atlantodontal spaces should be equal (see notes below) Correct alignment of the central ray with the occlusal plane and the base of skull is evidenced by The superimposition of the mandible/teeth over the base of the skull (see notes below) The entire odontoid process is seen with without superimposition of other anatomy or artefacts Area Covered Cervical vertebra C1 - Lateral masses, transverse processes Cervical vertebra C2 - Odontoid process, body of C2 Zygopophyseal joints Collimation Centre: Odontoid process Shutter A: Open to include the tip of the odontoid process superioly and the spinous process of C2 inferiorly Shutter B: Open to include the atlantoaxial joints and C1 transverse processes laterally Exposure Bony trabecular patterns and cortical outlines are sharply defined
Special Notes	Determining direction of rotation Rotation in the midsagittal plane may show the atlantodontal spaces asymmetrical. This may mimic pathology such as a fracture of the C1 ring (Jefferson's fracture) so care should be taken with patient positioning and central ray angle. Example: If the left atlantodontal space is wider, then the head may be turned facing toward the right side. Superimposition of the mandible/teeth over the base of skull The upper teeth should superimpose the base of skull. They should not superimpose the odontoid process (dens). If the upper teeth are not superimposed over the base of skull, first determine which structure is the base of skull and which are the teeth. Often the outline of the individual teeth can be seen. If the teeth are more inferior/lower, then raise the chin half the distance of the difference seen on the image. If the teeth are more superior/higher than the base of skull margin, then lower the chin half the distance of the difference seen on the image see The AP Odontoid Peg Projection and Odontoid-lateral mass Asymmetry