The Cervical vertebrae
If one were to attempt design the cervical spine as a project for a PHD in an engineering school, we would be faced with a remarkable challenge. How do we create a structure that is strong enough to support the head yet flexible enough to allow us to watch our backs in a dark alley? This is further complicated by the requirement that the structure contains and protects the spinal cord and the exiting nerve roots, which are extraordinarily delicate.
Nature has provided a remarkable structural compromise. The weight of the head is born primarily by the vertebral bodies and lateral masses. The intervening discs behave as deformable cushions that permit motion. The shape of the articular processes, the flexibility of the joint capsules and supporting muscles, tendons and ligaments along with the deformability of the intervertebral disc, determine the limits of motion.
It is useful to separate the cervical spine into two functional zones, A) the cranio-cervical junction which we will arbitrarily define as extending from the superior end plate of C3 to the inner rim of the foramen magnum and B) the remainder of the cervical spine.
The spine has three functions. What are they?
Function 1) The lumbar and thoracic spine function to keep the body erect. The cervical spine must hold the head erect so that the eyes face forward.
Function 2) Protect the spinal cord and nerve roots.
Function 3) Allow mobility
Every time we look at an imaging study, it is our role as radiologist, to determine how well the spine accomplishes each of these tasks. It important for the trainees in radiology to get in the habit of specifically forming an opinion about each of these 3 functions. The details of the report of the imaging study should depend on the recognition of any functional failure of the spine.
What other information other than spinal function should we analyze when looking at films?
We get important information as to the health of the patient’s bone. We must evaluate the relative mineral content as well as structural integrity.
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Slide 10) As previously mentioned, when evaluating any imaging study of the cervical spine, one must determine how well the neck is succeeding in holding up the head. The normal cervical spine has a gentle lordotic curve. This curve is very variable in normal people and depends on the position and angle of the head. A straight cervical spine is not necessarily abnormal. Reversal of the curvature or a focal deformity of the curvature is abnormal.
The cervical vertebral bodies are cylinders having a dense cortical border and a more compressible inner matrix. The heights of the intervertebral disc spaces either remain the same or increase as one descends down the cervical spine. A normal disc may never be narrower than its next highest mate.
Function 1 Holds up the head (2)
Slide 11) The spine should be straight in the frontal plane. The head being held erect with the eyes projecting forward. The spinous process although very variable in shape, should project in the midline. Lateral bending of the neck is limited by the height of the disc spaces and the uncinate processes. It would be totally impossible, however, if it were not for simultaneous rotation of the zygapophiseal joints. In order to bend or tilt the head to the side, the superior articular processes on the outside of the curvature slide upward upon its lower mate and the superior articular process on the inside of the curve, slide downward on its mate.
Slide 12) Here is a radiograph to evaluate. Is the curvature of the spine normal or abnormal? Click below to check your answer.
Slide 13) Remember that the curvature of the neck is dictated by the position of the patient’s body and head. One can straighten or flex the neck at will.
Slide 14) Try this film.
Slide 15) Angulations of the spine and reversal of the normal lordosis is not normal. No one can voluntarily bend the neck in such a way that the normal gentle curve is broken and reversed.
Slide 16) The spinal cord is enclosed within a water sack surrounded by two separate insulating cushions. All of the above lie within a bony canal. It is obvious that if our engineering project were to optimize the spine to protect the spinal cord the bony ring would be complete and non-flexible. However the real spinal canal is made of a chain of vertebra connected by soft tissue. The spinal cord within the bony ring is well protected and is rarely injured except with bony catastrophe. The spinal cord segments between the bony rings are much more liable to be injured even without catastrophic bony injury. The width of the spinal canal is most often estimated from lateral radiographs. It is usually possible to measure the AP diameter from the posterior edge of the vertebral body to the inter-laminar line.
What are the 2 other protective cushions?
Function 2 Protect the neural structures
Slide 17) The epidural veins act as a second fluid cushion. The epidural fat, which acts as the third cushion, can be considered as if it was the Styrofoam within the bony box of the spinal canal. Neural compression is very unlikely when the nerve roots are surrounded by epidural fat.
Function 3
Slide 18) The integrity of the bony neural ring is best evaluated by cross sectional imaging in the axial plane. The cross sectional area of the spinal canal is determined by, among other things, the shape of the vertebral body. Flat or convex posterior vertebral bodies tend to have larger canals than vertebrae which are convex towards the canal.
The cryomicrotome section and the adjacent drawing document the relationship of the neural structures to the bony ring. There is very little epidural fat in the cervical spinal canal.
Slide 19) The term “neural foramen” is a misnomer. Foramen implies an opening like a door. Actually the nerves exit through a canal with an entrance zone, a mid zone and an exit zone. The roots lie in a groove within the transverse process posterior to, and in contact with, the vertebral arteries.
Lateral x-ray
Slide 20) Let us now review that which is seen on lateral radiographs of the cervical spine.
A properly positioned lateral radiograph will project the central ray of the beam though the middle of the neck. The vertebral endplates will therefore parallel one another. The anterior corners of the bodies are usually asymmetric. The inferior corners tend to point downward. The superior corners are either straight or slightly beveled. This beveling is due to variations in ossification of the anterior ring apophyses.
Lateral x-ray 2
Slide 21) The cortical margins of the vertebral bodies form a gentile lordotic curve. There should be no angles or steps.
The anterior faces of the laminae appear as crescents of cortical bone which, when connected, form the interlaminar line. The interlaminar line should parallel the course of the curve of the posterior vertebral bodies.
Slide 22) There are many published criteria for evaluating the size of the spinal canal. I would suggest however, a very simple way of evaluating the size of the canal which I have called the Pinky test. For all but the shortest people, the pinky should fit within the spinal canal. Very short people should use the 4th finger.
Slide 23) Does this patient have a small spinal canal or not?
Slide 24) This patient fails the pinky test. The canal is congenitally small and made smaller by bony osteophytes. Did you notice the ossification of the posterior longitudinal ligament?
Lateral x-ray 3
Slide 25) The articular pillars project over the spinal canal on the lateral radiograph. The articulating surfaces of each pair of joints are usually superimposed one upon the other. One does, however get a sense of their integrity. The facets should be smooth and regular with a well-defined cortical bony margin. The joints are superiorly angled approximately 30 degrees.
Slide 26) The transverse processes through which traverse the vertebral arteries can be seen superimposed upon the vertebral bodies. Note the trough-like appearance. The exiting nerves lie upon these troughs.
Oblique Radiograph
Slide 27) The complete radiographic analysis of the cervical spine includes two oblique views. On these images one can see the length of the neural foramina, the articular processes, and the uncovertebral joints. The neural foramen is a keyhole shaped structure.
Slide 28) Another view showing the channel which is called the neural foramen. The uncinate process and unco-vertebral joint in indicated by the blue arrows.
Oblique radiograph close up
Slide 29) The exiting nerve lies upon the transverse process in the inferior portion of the foramen. The superior, lateral border of the foramen is primarily soft tissue, being made up of the zygapophiseal joint capsule. Bony spurs arising from a degenerative joint, project downward on the nerve from the posterolateral capsule. Uncinate spurs project directly into the exiting nerve.
Slide 30) Here is a typical oblique cervical radiograph. Does this patient have foraminal stenosis?
Slide 31) There is no substitute for flawless technique.
Frontal Radiograph
Slide 32) The frontal radiograph is often neglected as an important diagnostic tool. The spinous processes project through the vertebral bodies and should align in the midline. There is considerable variation in their size and shape but the distance between each of them is quite consistent. The cervico-thoracic junction is well seen and the upper ribs and pulmonary apices are optimally seen.
Frontal Radiograph
Slide 33) The central ray of the x-ray beam is usually parallel to the vertebral end plates of the lower vertebrae. Consequently they are well seen. The central ray of the beam is never normally parallel to the zygapophiseal joints consequently the joint surfaces are not visualized.
The uncovertebral joints are easily discernable in this view.
Frontal Radiograph
Slide 34) The neural arches can be seen projecting through the vertebral bodies. One can actually follow the entire arch out to the transverse process.
Pillar Views
Slide 35) In order to optimally visualize the lateral masses it is necessary to angle the central ray parallel to the plane of the joints. This is accomplished by having the patient lie supine with the chin slightly elevated if possible. The patient then turns the head to the side and the x-ray beam is angled caudally. This projection is ideal for the evaluation of fractures and arthritis.
Pancost
Slide 36) Can you determine the exact cause of this patient’s neck pain?
Pancost tumor
Slide 37) It is never possible to determine if a degenerated disc is causing neck pain because so many normal people have degenerative disease with no pain. Abnormal curvature may be due to pain but is not the cause of pain. The lateral view does not help us here at all. On the frontal radiograph we can identify a soft tissue mass at the pulmonary apex. Remember that the pulmonary apices are best seen on lordotic chest views and AP views of the neck.
OPLL
Slide 38) Describe at least 4 abnormalities on this film. Then determine if you can if the spine has failed or not. If it has, which function has failed?
OPLL
Slide 39) This patient has Diffuse Idiopathic Skeletal Hyperostosis with crests of bone projecting from the vertebral edges. The C5/6 disc is degenerated. The spinal canal is congenitally small. The spine has failed, however, because of a large plaque of ossification of the posterior longitudinal ligament causing myelopathy.
Slide 40) Another quiz case. Has the spine failed here, if it has, in what way?
Slide 41) This is quite an abnormal radiograph. There is severe degenerative disc disease at C 5/6, and disc space narrowing at C3/4. There is abnormal curvature of the spine. The spine has failed in its supportive function because of a metastatic lesion of the C 3 vertebra.
Flexion –Extension.
Slide 42) It is occasionally important to evaluate the limits of motion of the cervical spine. This may be done with lateral radiographs in maximum flexion and extension. As the head moves into the flexed position, the superior articular processes glide upward and forward. The discs deform to allow the motion. The anterior margins of the discs narrow and the posterior portion of the discs widen. This is normal. Each vertebra moves slightly forward upon its next lower mate. The distance between the spinous processes will widen but the widening should remain proportionate between the motion segments.
Flexion extension
Slide 43) In extension the reverse occurs. The spinous processes come closer together. The superior articular processes glide downward. The anterior portion of the disc widens and the posterior portion of the disc narrows. The C5/6 tends to open and close slightly more than the other levels perhaps because it is usually the most mobile segment.
Video fluoroscopy
Slide 44) It is possible to use standard Video fluoroscopy to evaluate neck motion. Cervical motion is quite complex. We will focus now on the lower spine. Click on the word motion to view the video clip. Windows media player will run. It is possible to enlarge the screen by clicking in the appropriate box on the player bar. I suggest you replay the video several times while listening to the discussion. On each run, focus your attention on a single anatomical feature and watch how that structure moves.
The most important thing to observe is the sequence of vertebral motion. Motion begins at the craniovertebral junction and descends in an orderly fashion throughout the cervical spine. There should never be asynchrony of motion. The segments should never move before their next higher mate. Premature motion is an important sign of segmental instability and ligamentous laxity or injury.
Note first how the head rocks forward on C1. C1 flexes on C2 followed by each sequential vertebra. Concentrate only on the anterior edges of the vertebral bodies. Repeat the process looking at the posterior bony edges of the vertebra and then the interlaminar line. Note how the spinous processes diverge in flexion and appose in extension.
Slide 45) How has the spine failed here?
Slide 46) This patient has Swan neck deformity caused by wide posterior laminectomy. C3 is fused to C4 and the C4-C5 disc has become hypermobile. The spine has failed all three of it functions. The spinal cord is no longer protected by a bony ring. The spine is unable to move normally because of the fusion and the hypermobile segment, and the head is held up abnormally.
Cervical dynamics MRI
Slide 47) It is possible to perform MRI in flexion or extension. Several different techniques have been devised to show what the discs and joints look like in different phases of motion. This series was performed throughout the dynamic range from flexion to extension. Note how the normal discs change shape when flexed and extended. The anterior annulus bulges in flexion and the posterior annulus bulges in extension.
Slide 48) This patient complained of bilateral leg weakness and bowel and bladder problems. A diagnosis of spondylitic myelopathy was made and a wide posterior decompression was performed. How successful do you think the surgery was?
Slide 49) This surgery failed. The patient was having increasing signs of spinal cord compression especially in the upper extremities. Can you determine to most likely cause?
Slide 50) Two abnormalities are documented on the extension MR image. The bulging disc at C3-4 has increases in size. The most important finding, however, is that the contracted muscles of the posterior neck are pressing the spinal cord forward against the discs, osteophytes and the back of the vertebral bodies. It is important to note that the area of maximal cord compression is not at the C3/4 level where the disc is bulging but behind the C 5 vertebra. It is critical not to become a disc fixated radiologist.
Slide 51) Part 2
Slide 52) We begin our tour through the cervical spine with axial views of atlas and axis. C1 is a specialized vertebra that attaches the skull to the mobile spine. The superior articular processes are concave crescents, which articulate with the convex occipital condyles. There is never any rotation or lateral bending possible between the skull and C1. The skull does flex and extend on C1.
Slide 53) The anterior arch of C1 prevents the head from falling backwards in extension.. The powerful transverse ligament, which holds the dens in place, attaches from two small tubercles on the inner surface of the C1 ring.
Slide 54) Sagittal reformatted CT of the occipital condyles and the superior articular processes of C1 show the distinctive concave shape of the C1 facet and the convex surface of the occipital condyle. It is obvious why flexion is possible in a joint of this shape while rotation is not.