K. Sairyo et al., NEUROCENTRAL SYNCHONDROSIS FRACTURE IN IMMATURE SPINES ASSOCIATED WITH PEDICLE SCREW TYPE FIXATION DEVICES, Journal of spinal disorders, 11(2), 1998, pp. 142-145
The purpose of this study is to clarify the weak point in immature lum
bar vertebrae associated with pedicle screw instrumentation, Ten immat
ure thoracic and lumbar vertebrae were collected from calf spines, Aft
er installation of 6- and 7-mm-diameter pedicle screws into the pedicl
es of each specimen, pullout force was applied to the screw using the
uniaxial MTS system until failure. Tightening torque during installati
on was measured. From the load-displacement curve, failure load was ca
lculated and failure site was confirmed by radiographs. Inner pedicle
diameters were measured after the pullout test, and percent fills of t
he pedicle screw were calculated. Mean tightening torque was 1.4 or 2.
1 (Nm), mean failure load was 852.5 or 1.015.0 (N), and mean percent f
ill was 81.4 or 93.5% for 6- or 7-mm screws, respectively. Tightening
torque and percent fill in 7-mm screws were significantly (p < 0.01) g
reater than that in 6-mm screws; however, failure load showed no signi
ficant difference (p = 0.10) between the two screw groups. Failure by
screw pullout occurred at the screw-bone interface or through the neur
ocentral synchondrosis (NS). NS fractures were observed in 20% of 6-mm
screws, 60% of 7-mm screws, and 40% overall, whereas interface failur
es occurred in 80% of 6-mm screws, 40% of 7-mm screws, and 60% overall
. In NS fracture group, tightening torque (p < 0.05) and percent fill
(p < 0.01) were significantly greater than in the interface failure gr
oup. The results led us to conclude that the mechanism of the NS fract
ure is unclear. However, NS fracture could be one of the conceivable c
omplications associated with pedicle screw fixation in the immature sp
ine.