Study Design. To evaluate the effect of change in screw dimensions and
hole augmentation in pedicle screw revisions, the insertional torque
was determined, and results were compared with those in control specim
ens in an in vitro study using cadaveric thoracolumbar spines. Objecti
ves. To determine the best method of salvage for failed pedicle screws
, by evaluating the insertional torque after placing a larger diameter
or longer screw into a stripped hole. Use of a shim and use of larger
and longer screws were also investigated. Finally, the effect on inse
rtional torque of simply removing and replacing a pedicle screw in its
original hole was investigated. Summary of Background Data. The effec
ts of using bigger or longer screws and shims to salvage failed pedicl
es have been studied. The interaction between how much larger, how muc
h longer, and inserting with or without shims, has not been well studi
ed. Optimizing reinsertional torque through the use of bigger screws r
isks exceeding the pedicle capacity. Using longer screws risks violati
on of the anterior vertebral body, thereby placing the great vessels a
nd viscera at risk. By knowing the relative contribution of increase i
n length and diameter, the surgeon can optimize the risk-benefit ratio
. Methods. Eight cadaveric spines from T10 to S1 were harvested. The s
pecimens underwent radiographic screening and bone densitometry. A mod
ified Latin square randomization was designed to evaluate the screw di
ameters and lengths. Each pedicle was its own control. A 35- x 6.5-mm
screw was used as a control. Test screws were placed after pedicle scr
ew hole failure was achieved and documented by stripping. For the test
screws, the diameters were increased by 1 mm and 2 mm, the lengths we
re increased by 5 mm and 10 mm. Shims were added randomly. The peak in
sertional torque was measured for each control screw and test screw pl
acement. In addition, during each screw placement, the screw was remov
ed and replaced to determine the effect. Results. Insertional torque,
after the pedicle screw is removed and replaced in the same hole, was
decreased by 34% (P < 0.000005). Increasing the diameter of the salvag
e screw by 2 mm caused the insertional torque to be increased by 8.4%
of the original. Increasing the length of the screw did not improve th
e salvage screw insertional torque. There was an interaction effect fo
r the l-mm increase in diameter and the increase in length. At this di
ameter, increasing the length had a significant effect (P = 0.009) on
the salvage torque. Using a shim created no improvement in salvage ins
ertional torque (P = 0.77). There was a poor linear correlation betwee
n torque and bone mineral density (r = 0.18) in these osteoporotic spe
cimens. Conclusions. Removing and replacing a pedicle screw in its ori
ginal hole substantially decreases its mechanical fixation. For pedicl
e salvage, increasing the diameter causes the greatest restoration of
strength. Shims had no effect in pedicle salvage in osteoporotic speci
mens.