Distractional failure forces comparison of different anchor sites for the pediatric growing rod technique

To analyze the distraction load-to-failure force supported by pedicle, lamina or rib linked to different constructs in pediatric cadaveric thoracic spine.

Eighteen pediatric cadaveric thoracic spines with rib cages were randomly assigned into three testing groups: A (lamina and pedicle), B (rib and pedicle), and C (rib and lamina). Each specimen was sectioned into six units from T1-T2 to T11-T12. A longitudinal load-to-failure test simulating growing rod distraction force was performed with an ElectroForce(®)3500 machine, and yield forces were statistically analyzed.

The results showed that pedicle and lamina anchors could provide a similar capacity against distraction force in group A (P > 0.05), which was almost double that of ribs in groups B and C (P < 0.05). The data showed that T5 and T7 pedicles and laminas seem to provide the lowest distractional force. Furthermore, break pedicle insertion provides 75.6 % of distractional force as compared to the same segments with intact pedicle insertion.

Our results suggest the lamina as a proximal thoracic anchor site for pediatric spinal deformity. The pedicle and lamina of T5 and T7 vertebrae seemed to provide a lower distractional force than other thoracic segments in our test.