[Design and animal study of a posterior instrumentation system with sliding ring pedicle screws without arthrodesis in the immature spine].

Objective: To evaluate a sliding ring pedicle screw system without arthrodesis for the treatment of scoliosis in the immature spine.

Methods: Twelve goats of 3 months old were randomized into three groups: limited anchoring group, multi anchoring group, and blank contrast group. Growth of the spine and sliding of the instruments were assessed through conventional radiography and three dimensional CT reconstruction scan. Vertebral columns were resected 3 months after operation and pathological sections were observed.

Results: Three-dimensional CT scan and pathological analysis indicated no difference in structural development of the instrumented segments of the spine in the two operated groups as compared with the same segments of the spine in the control group. According to gross anatomic evaluation and radiographic measurement, the increase in height from L5 to T10 averaged 43.0 mm in limited anchoring group, 43.5 mm in multi anchoring group and 40.9 mm in blank contrast group. Total sliding in the instrumentation system was 41.2 mm in limited anchoring group and 39.4 mm in multi anchoring group, respectively. There were no statistically significant difference in the longitudinal growth of the spine among the three groups.

Conclusions: The sliding ring pedicle screw system can glide smoothly to accommodate the growth of the immature spine in an in vivo animal model.