Abstract
INTRODUCTION
Surgical correction of spinal deformities in the growing child can be applied with or without fusion. Sublaminar wiring, first described by Luque, allows continuation of growth of the non-fused spine after correction of the deformity. Neurological complications and wire breakage are the main clinical problems during the introduction and removal of currently used sublaminar wires. In this pilot study a posterior hybrid construction with the use of a medical-grade UHMWPE (Dyneema Purity®) sublaminar wire was assessed in an ovine model. We hypothesized that such a hybrid construction can safely replace current titanium laminar wires, while providing sufficient stability of the non-fused spinal column with preservation of growth.
MATERIALS AND METHODS
This study included 6 Tesselaar sheep, age 7±2months. Two pedicle screws (Legacy system, Medtronic) were placed at lumbar level. Four consecutive laminae were attached to two titanium bars (4.5 mm) using 3 mm diameter UHMWPE (Dyneema Purity®) on the left side and 5 mm diameter on the right side. The sublaminar wires were fixed with a double loop sliding knot and tightened with a tensioning device. As a control, in one animal titanium sublaminar wires (Atlas cable, Medtronic) were applied. After sacrifice the spine of the animals was harvested. Radiographs were taken and CT scans were performed. The vertebrae were dissected and placed in formaldehyde for macroscopic and histological evaluation.
RESULTS
The animals were sacrificed after a (minimal) postoperative period of 15 weeks. One animal developed a wire fistula and one animal died the first postoperative day due to complications of the anesthesia. None of the 3 or 5 mm knots loosened and no neurological complications occurred. An average of 8.7 mm growth was seen over the segment operated on. Computed tomography confirmed the preserved stability. Even though no decortication was performed, variable bone bridges with fused levels were seen on CT. Macroscopic and histological analysis showed no inflammation at lamina and dura levels containing Dyneema Purity®, with the exception of the case with the fistula where it was observed locally.
DISCUSSION
This pilot animal model study shows that the UHMWPE laminar wire made by Dyneema Purity® has good handling and tensioning properties and can provide sufficient stability in fusionless spinal instrumentation while allowing substantial growth. The examined model showed to be a feasible spinal study model, without occurrence of neurological problems. Reactive periostal bone formation with fusion levels led to some restrictions in this model. In the future it will be necessary to test the described construction in a large animal scoliosis model.
