Effect of dual screws across the vertebral neurocentral synchondrosis on spinal canal development in an immature spine: a porcine model.

BACKGROUND Questions remain as to the effect of pedicle screws on spinal canal development in young children. The purpose of this study was to determine the effects of unilateral placement of dual screws across the neurocentral synchondrosis on spinal canal development as assessed with histological analysis and measurement of the canal dimensions in an immature pig model. METHOD Twenty-seven one-month-old pigs were assigned to two groups on the basis of the surgical approach used to place unilateral double screws that did or did not cross the neurocentral synchondrosis. In one group, sixteen pigs underwent a posterior approach from T7 to T14 and were divided into four subgroups: no screws (without screw fixation), short screws (dual pedicle screws that did not cross the neurocentral synchondrosis), long screws (dual pedicle screws that crossed the neurocentral synchondrosis), and screw removal (long dual pedicle screws that were removed at six weeks postoperatively). In the other group, eleven pigs underwent an anterior approach, with double vertebral body screws placed via thoracotomy. These animals were divided into two subgroups: short screws (dual vertebral body screws that did not cross the neurocentral synchondrosis) and long screws (dual vertebral screws that crossed the neurocentral synchondrosis). All animals were killed at seventeen weeks. The total area, width, and depth of the spinal canal were measured on axial computed tomography (CT) images. Quantitative histological analysis was performed to measure the rate of neurocentral synchondrosis closure. RESULTS Use of unilateral double pedicle screws across the neurocentral synchondrosis through a posterior approach resulted in 97% neurocentral synchondrosis closure with a 20% decrease in the canal area and a 15% decrease in the canal depth. Use of unilateral double vertebral body screws across the neurocentral synchondrosis through an anterior approach resulted in 71% neurocentral synchondrosis closure with a 15% decrease in the canal area and an 8% decrease in the canal width. CONCLUSIONS Unilateral double pedicle screws crossing the neurocentral synchondrosis adversely affected spinal canal growth in immature pigs. CLINICAL RELEVANCE Pedicle screws should be used with caution in very young children, and a delay in surgical treatment until they are older should be considered.