INTRODUCTION
Atlantoaxial arthrodesis is inherently a difficult procedure with several surgical
options for attaining fusion. Aside from cable fixation, upper C-spine screw fixation
techniques include posterior transarticular screw fixation, pars screw placement,
pedicle screw placement, and translaminar screw placement [1]. Before screw fixation became a popular technique for arthrodesis, wiring techniques
developed by Gallie, Brooks and Jenkins were most commonly used [1]. Later, Magerl developed an instrumentation technique using transarticular screws
[2], [3]. Various challenges to this technique lead to the gradual evolution of segmental
fixation. Lateral mass screw placement with pedicle screw fixation was probably described
first by Goel et al in 1994, with Harms and Melcher [4] describing clear landmarks and use of polyaxial screws and rods for fixation. A
further variation of posterior upper cervical fixation was developed by Wright out
of concern for possible violation of the vertebral artery at C2 by crossing two intralaminar
screws to achieve fixation [5], [6].
Any upper cervical spine fixation technique is technically demanding, with some risk
of injury to the vertebral artery, carotid artery, spinal cord, and exiting cervical
nerve roots. Posterior C1 lateral mass screw placement can be especially challenging
because of the location of the C2 exiting root relative to the most commonly suggested
starting point located below the C1 laminar ridge on the posterior aspect of the inferior
C1 lateral mass.
This comparison case study presents the impingement of a C2 root in its foraminal
exit zone through C1 lateral mass screw placement.
CASE REPORTS
Case 1
A 69-year-old woman presented with a primary complaint of neck pain and radiculopathy,
existing for the previous 11 months, which radiated from the base of her neck into
her occiput. After failing nonoperative care and temporarily responding favorably
to selective C2 root injections, it was determined that C1-C2 facet had become significantly
degenerated and a posterior fusion was offered to the patient ([Fig 1]).
Fig 1
Computed tomographic images of patient 1 showing adequate foraminal space on the
left and foraminal impingement on the right due to facet arthrosis.
The arrow on the left points to the C2 nerve root , which runs through a patent foramen.
On the right the arrow shows a large posterior osteophyte impinging upon the C2 nerve
root.
Surgical procedure
The surgery was performed with the patient prone in a Mayfield head holder on a Jackson
OSI table. Uneventful posterior midline exposure of the C1 and C2 segments was carried
out. The left and right C2 nerve roots were dissected. The C2 nerve root on the right
side was found to be prominent and substantially thickened, which blocked the retraction
of that nerve root. After identifying the medial border of the posterior arch of the
C1, small holes were drilled to facilitate access to the C1 lateral mass. Two 22 mm
screws were inserted at a 15-degree angle. Two translaminar screws were placed in
the lamina of C2, both on the left and right sides. The screws were then connected
by 3.5 mm rods between C1 and C2, using a torque driver to lock them into place. The
patient remained stable throughout the entire surgery, which was completed without
any obvious complication. Six weeks postoperatively she stated that she was totally
pain free.
Case 2
A 75-year-old woman with a history of rheumatoid arthritis was evaluated because of
dominant neck pain that had been present for 8 months. There was no history of trauma,
or significant episodes of prior neck pain. The pain was localized on the right side
of her neck and radiated cranially. Conservative treatment modalities including activity
modification, physical therapy, and medications did not improve the symptoms. Computed
tomographic (CT) scans showed degenerative changes of the discs at C5-C6, autofusion
at C2-C3, and right facet arthropathy at C1-C2 ([Fig 2]). Before the procedure, she received an injection at the C2-C3 facet to help confirm
if the pain was coming from the joint. After she had received no relief from the injection,
but with confirmed significant relief from a prior C2 root injection, it was decided
that the pain was localized to the degenerated C1-C2 articulation. The patient elected
to proceed with C1-C2 arthrodesis to relieve her pain.
Fig 2
Left and right computed tomographic images of patient 2 showing adequate foraminal
space on the left but not on the right.
Surgical procedure
With the patient prone in a Mayfield head holder on a Jackson table, posterior exposure
of the C1 and C2 segments was carried out and the C2 roots were bilaterally exposed.
Then, 30 mm C1 lateral mass screws were placed under image intensifier guidance using
standard technique of identification of local landmarks. Partial laminectomy was performed
at C2 and the spinous process of C2 was identified as the drilling point. Next, 30
mm translaminar screws were placed at C2 directed by blunt probe diagonally across,
between the two layers of the lamina. The construct was locked together with the rod
system and set screws. A torque driver was used to solidly lock the rods and screws
together. The procedure was completed without obvious complications.
Postoperative course
On postoperative day 1, the patient started rehabilitation but was limited because
of a new onset of severe positional headaches occurring on the right side of her head.
She also complained of multiple episodes of nausea and vomiting, which were initially
believed to be caused by the anesthesia. However, she continued to report persistent
headaches on postoperative days 2 and 3. On postoperative day 3, CT scans showed an
encroachment on the nerve root by the surgical screws into the foramen of C1-C2 ([Fig 3]). To correct this problem, on postoperative day 4, the patient underwent a second
operative procedure in which the right C1 screw was removed, and a sublaminar cable
was placed around the C1 arch and fixated with the head of the C2 laminar screw. She
was discharged 4 days later from the hospital and returned home in a cervical collar.
On postoperative day 10, after the second surgery, the patient began rehabilitation
and reported that her pain was under control and the recurring headaches had stopped.
At the 3-month postperative visit, she stated her neck pain had completely resolved.
The patient’s 3-month postoperative CT scan showed early fusion, and stable instrumentation.
She continued to do well at her 6-month and 1-year visits.
Fig 3
Left and right computed tomographic images of patient 2 after screw placement. The
screw on the right fills the foramen.
DISCUSSION
Indications for atlantoaxial fusion include congenital abnormality of the dens, atlantoaxial
rotatory subluxation, fracture of the dens, and rheumatoid arthritis [1]. Patients with congenital abnormality of the dens, atlantoaxial rotatory subluxation,
fracture of the dens, and rheumatoid arthritis all may benefit from C1-C2 arthrodesis
with segmental instrumentation. In general, patients with rheumatoid arthritis seem
to be affected by increased complications because of comorbidities and loss of normal
anatomy caused by destructive changes [7]. Atlantoaxial arthrodesis has evolved from cable and wiring methods to the use of
contemporary rigid segmental screw fixation techniques. These advancements of technique
have allowed for better fusion rates with increasing stabiliza
tion of C1-C2 while maintaining desirable alignment and avoiding postoperative halo-vest
immobilization [2], [3].
Grob et al [2] demonstrated in a case study of 161 patients that the technique developed by Magerl
et al for atlantoaxial fusion through transarticular screw fixation is possible with
relative safety. Case series by Wang et al [8] and Bransford [9] showed safe placement of lateral mass screws to be possible. With these improvements,
segmental screw fixation of the atlantoaxial joint seems to be more widely use [9].
As shown in our case 2, screw impingement in the presence of altered anatomy likely
contributed to the patient’s symptoms. Once the offending screw was removed, her pain
improved dramatically. Based on her rapid symptom resolution we believed that this
was due to C1 lateral mass screw impingement on the C2 nerve root. The subject of
screw impingement on C2 roots has been described as a more theoretical worry with
little or no clinical consequence. In case of controversy, neurolysis or intentional
neurotmesis of the C2 root had been suggested as a method to avoid root irritation,
but we found no clear guidance in the literature on this subject [4].
Given this limited case experience and our review of the literature, we are less clear
about ideal management of patients intended for posterior segmental C1-C2 fixation.
In case of a shallow inferior C1 lateral mass, seen in [Fig 2], alternate fixation such as transarticular screw placement or cable-based arthrodesis
might be preferable. Based on our review of the literature, management of a C2 root
caused by screw impingement seems less than clear.
CONCLUSION
Currently, there seems to be no agreement in the literature as to management of a
C2 root being impinged intraoperatively. Is it acceptable to allow for screw impingement
on the C2 root and can it be watched expectantly or can the C2 root be cut without
undue consequences to the patient? Based on our limited experience, we prefer using
alternative techniques for fixation in such cases and avoid either scenario.
