B. Jeanneret et al., POSTERIOR STABILIZATION IN L5-S1 ISTHMIC SPONDYLOLISTHESIS WITH PARALAMINAR SCREW FIXATION - ANATOMICAL AND CLINICAL-RESULTS, Journal of spinal disorders, 9(3), 1996, pp. 223-233
Combined anterior and posterior fusion with posterior instrumentation
may be indicated in the treatment of select cases of L5-S1 spondylolis
thesis. The instrumentation, however, is expensive and usually bulky,
occasionally requiring removal. In an effort to avoid these problems,
an L5-S1 paralaminar screw technique was developed for posterior stabi
lization after an L5-S1 anterior interbody fusion. The technique invol
ves the placement of cortical screws from the base of the articular pr
ocess of S1 to the pedicle of L5. This study evaluates the anatomic ap
plications and clinical results of this technique. The relationship be
tween the screw and L5 nerve root was examined using five cadaveric sp
ecimens with olisthesis of 0, 25, 50, and 75%. This work demonstrates
that the screws can only be inserted safely if an L5-S1 olisthesis of
at least 25% is present. If <25%, the screws will either impinge on or
directly injure the L5 nerve root. In the clinical study, the outcome
s of 20 patients who had an isthmic spondylolisthesis of 25-81% and we
re treated with partial reduction, L5-S1 anterior interbody fusion, an
d L5-S1 posterior paralaminar screw fixation were reviewed. Nineteen p
atients had adequate posterior stabilization to completely heal an L5-
S1 anterior interbody fusion without loss of the correction. In one pa
tient, a pseudarthrosis occurred secondary to poor surgical technique
of both anterior and posterior fusions. This patient required an addit
ional L4-S1 posterior fusion 9 months later and had a good clinical ou
tcome. No other complications due to screw placement occurred We concl
ude that this procedure can be used safely and reliably for the poster
ior stabilization of L5-S1 after stable anterior L5-S1 interbody fusio
n in residual slips of at least 25%. Prerequisites are proper patient
compliance and low weight. Compared with other posterior instrumentati
on systems, this screw fixation is inexpensive and does not require im
plant removal. The disadvantages of the method are the degree of diffi
culty of the procedure and the limited clinical application to cases o
f L5-S1 spondylolisthesis with corrected residual slips of 25 to 50-60
%. The procedure is technically demanding and should be limited to tho
se surgeons who are comfortable with the method.