Corresponding author: John E. Lonstein, M.D., Twin Cities
Spine Center, Piper Building, Suite 600, 913 East 26th Street, Minneapolis,
Minnesota 55404-4515, E-mail address: jelonstein@tcspine.com
To The Editor:
I read with interest the paper entitled "Complications Associated
with Pedicle Screws" (81-A: 1519-1528, Nov. 1999), by Lonstein et
al. This is a very timely, well written article, and I was most
interested in the rate of complications directly related to pedicle-screw
placement and in the problems associated with the insertion of pedicle
screws, which, they mention, had not previously been reported in
the literature. I am particularly curious as to how many of the
pedicle screws that required intraoperative replacement had caused
any damage either to the nerve roots or to other adjacent soft-tissue
structures.
The relevance of this question lies in the fact that, following
an operative procedure, many of us tend to look only at the last
radiograph in which all of the pedicle screws should be in perfect
position. However, not infrequently, as Lonstein et al. point out,
the pedicle screws may be initially misplaced and then replaced
in a better position intraoperatively. Meanwhile, damage may have
been done, by the original misplaced screws, to neural or other
structures.
I think there is merit in the technique described by Myles et
al.1, wherein two pin devices
with beads in their mid-portion are used to accurately identify
the site of placement of the pedicle screw. One of the advantages
of this system is that if these pins are misplaced, they are so
small and blunt-tipped that it is highly unlikely they would cause any
significant damage to neural structures.
Philip G. Perkins, M.D., F.R.C.S.(C)
Perkins Medical Practice
144 North Sixth Street
Reading, Pennsylvania 19601-3525
E-mail address: pperkins@permed.com
J. E. Lonstein, F. Denis, J. H. Perra, M. R. Pinto, M.
D. Smith, and R. B. Winter reply:
We thank Dr. Perkins for his comments and question. As he notes,
we reported that sixty-five screws cut out of the pedicle during
insertion, of which thirty-six were safely reinserted, twenty-seven
could not be safely reinserted, and two lateral screws were left
in place. None of these screws was associated with any nerve-root,
visceral, or soft-tissue injury. In addition, there were four dural
tears; three occurred during sounding of the pedicle and one, during
tapping. Dural repair was possible in two cases, and there were
no neurological injuries, no postoperative spinal-fluid collections,
and no wound problems.
We used intraoperative pedicle markers commonly in the earlier
part of the series, until we gained experience in pedicle-screw
insertion. This is a useful technique, but we have experienced a
potential problem on a few occasions since the time of the reported
series. If the initial sounding of the pedicle is not wholly in
the pedicle but medial in the pedicle, the marker film will show
the pin to be in the pedicle. With screw insertion and a medial
tract, it is possible for the screw to remain medial, to penetrate
the medial cortex, and to irritate the adjacent nerve root. Immediate
postoperative radiographs may be of questionable value for accurate
screw placement, necessitating the use of thin-cut computed tomography
scans for diagnosis of this problem.
John E. Lonstein, M.D.
Francis Denis, M.D.
Joseph H. Perra, M.D.
Manuel R. Pinto, M.D.
Michael D. Smith, M.D.
Robert B. Winter, M.D.
Corresponding author: John E. Lonstein, M.D.
Twin Cities Spine Center
Piper Building, Suite 600
913 East 26th Street
Minneapolis, Minnesota 55404-4515
E-mail address: jelonstein@tcspine.com