Summary Cervical facet joints injections and epidural injections are the two most common interventions in managing chronic cervical pain. The C2-C3 joint and the third occipital nerve are very dangerous targets to be injected due to the proximity of the vertebral artery in the last portion V3 from the transverse process of C2 to the foramen magno.
This study demonstrates that the distance between the facet C2-C3 and vertebral artery increases of 90% by a 45 degrees head rotation. The position over mentioned seems to be more protective during the Third Occipital Nerve block and during the C2-C3 facet blockage because the vertebral and segmental arteries are shifted medially far and behind the articular pillar on coronal plane. The augmented distance is confirmed either by TC and ultrasound scan.
Riassunto Le iniezioni delle faccette articolari cervicali e le iniezioni epidurali sono i due interventi più comuni nella gestione del dolore cervicale cronico. L’articolazione zigoapofisaria C2-C3 e il terzo nervo occipitale sono “target” molto pericolosi da iniettare a causa della vicinanza dell'arteria vertebrale nell’ultimo tratto V3 dal processo trasverso di C2 al forame magno.
Questo studio dimostra che la distanza tra la faccetta C2-C3 e l'arteria vertebrale aumenta del 90 per cento con una rotazione controlaterale del capo di 45 gradi. La posizione sopra menzionata sembra essere più protettiva durante il blocco del terzo nervo occipitale e durante il blocco della faccetta C2-C3 perché le arterie vertebrali e segmentali sono spostate medialmente e dietro il pilastro articolare sul piano coronale. La distanza aumentata è confermata dalla TC e dall'ecografia.
Key wordsUltrasound, Vertebral artery, third occipital nerve, cervical facet, head position, cervical pain, cervicogenic headache
Parole chiave Ultrasuoni, Arteria vertebrale, terzo nervo occipitale, faccette cervicali, posizione del capo, cefalea cervicogenica
Cervical facet joints injections and epidural injections are the two most common interventions in managing chronic cervical pain.1-3
Most of the adverse events of these procedures are described only in some case reports, while intravascular injections due to wrong needle placement are widely described.4
C2-C3 is the most dangerous level to be treated because of the proximity of the vertebral artery and spinal segmental artery, which from the transverse process of C2 to the occipital bone are shifted laterally or medially by head rotation.
The Third Occipital Nerve (TON) lies over the facet C2-C3, so the blockage of the TON has the same risks.5
In a prospective study where 43.000 facet joint blocks were performed, the intravascular penetration as an adverse event occurred in 20 percent of fluoroscopically directed cervical facet joints injections.6In a randomized comparison between ultrasound and fluoroscopy guided third occipital nerve block an intravascular injection were noted in 10 percent of patients of the fluoroscopy group.7Nevertheless, there is paucity of literature on adverse effect of ultrasound guided cervical facet joint nerve blocks.
The aim of this study is to show that the head rotation can move the vertebral artery far from the facet C2-C3 and so the intravascular penetration can be avoided.
We have identified 50 patients, 25 males and 25 females, who were been previously selected for a diagnostic angio-TC
The sample was homogeneous by age and all e patients have been studied by the same sonographer and controlled by angio TC.
Distance from the lateral end of C2-C3 facet to the center of vertebral artery just above C2 transverse process have been measured in head neutral position and in head rotated 45 degrees contralateral. Head positions were controlled by TC.
We conducted motion analysis. First, each vertebra was semi automatically extracted using intensity threshold techniques. Second, segmented images of the vertebrae in the neutral position were superimposed over images of 45° position using voxel-based registration, then the spatial migration of each vertebra was expressed by a matrix. Third, segmental motions at occiput (Oc)–C1, C1–2 and C2-C3 were calculated by converting the matrix obtained by the registration into a matrix representing relative motion with respect to the inferior adjacent vertebra. The results were expressed with the sequence of pitch (X), yaw (Y), roll (Z), and translations, using a previously defined coordinate system. The rotation angle was calculated as the sum of the right (–RY) and left (+RY) rotation angles. The results have been analyzed by T-test
The mean distance from the lateral end of C2-C3 facet to the center of vertebral artery in the female group was 0.967 cm in head neutral position and 1,445 cm in head rotated 45 degrees position(p=0,026401).
The mean distance from the lateral end of C2-C3 facet to the center of vertebral artery in the male group was 0.883 cm in head neutral position and 1,546 cm in head rotated 45 degrees position(p=0,009067).
The mean distance from the lateral end of C2-C3 facet to the center of vertebral artery in all the sample, regardless of the gender, was 0,852 cm in head neutral position and 1,55 cm in head rotated 45 degrees position (p=0,000346) (Figure 1).
The ultrasound scanning confirms the augmented distance between vertebral artery and facet joints obtained simply by head rotation (Figure 2)(Charts of Figure 2).
It is difficult to estimate the real number of adverse events linked to cervical spine injections, but they are sometimes very catastrophic, and the risks cannot be negligible. During the treatment over discussed, the real danger is represented by the spinal segmental artery, that arises from the deep or ascending cerebral artery and supports the posterior spinal artery. The injection of particulate steroids in these vessels can have disastrous consequences, and for this reason, is strongly recommended the use of non-particulate steroid, especially dexamethasone.8Animal studies demonstrated that in some steroids preparations , carrier may have directly toxic effects on CNS, resulting in injury.9
In 2007 anonymous surveys were sent to all U.S. physician members of the American Pain Society. 287 respondents were asked about awareness of complications, year of occurrence, practice setting and specialty of the treating physician, use of fluoroscopy/contrast/local anesthetic/corticosteroid, doses administered, and CT/MRI/autopsy findings: 78 complications were reported, including 16 vertebrobasilar brain infarcts, 12 cervical spinal cord infarcts, and 2 combined brain/spinal cord infarcts. Brain infarcts invariably involved the cerebellum, brainstem, or posterior cerebral artery territory. Thirteen cases resulted in a fatal outcome.10
This study demonstrates that the distance between the facet C2-C3 and vertebral artery increases of 90% by a 45 degrees head rotation, and, by the way, also the distance from the segmental arteries .
The ultrasound guided C2-C3 facet injection is usually performed on coronal plane,11 and often is not so easy to put all the needles into the ultrasound beam. This is a potentially cause for an intravascular injection due to the vertebral arterial complex proximity.
The 45 degrees controlateral head rotation moves far from the needle target the vertebral artery, and shifts the segmental artery just behind the articular pillar, reducing the risk of intravascular injection. The relationship between the intertrasverse tract of the vertebral artery and ipsilateral lower facets joints is not influenced by head rotation.
Differences between the male and female group are not statistically relevant.
The position with 45 degrees controlateral head rotation seems to be more protective during the third occipital nerve block and during the C2-C3 facet blockage because the vertebral and segmental arteries are shifted medially far and behind the articular pillar on coronal plane. The augmented distance is confirmed either by TC and ultrasound scan.
This data allows a safer approach to these targets also by an ultrasound guided technic.
Conflict of interest
The authors certify the study was conducted without conflicts of interest.