Summary Statement. Novel radiopaque UHMWPE sublaminar cables may be a promising alternative to gliding pedicle screws or titanium sublaminar cables within a growth-guidance system for the surgical treatment of early onset scoliosis. Introduction. Growth-guidance or self-lengthening rod systems are an alternative to subcutaneous growing rods and the vertical expandable prosthetic titanium rib for the treatment of early onset scoliosis. Their main perceived advantage over growing rods is the marked decrease in subsequent operative procedures. The Shilla growth-guidance system and a modern Luque trolley are examples of such systems; both depend on gliding pedicle screws and/or sliding titanium sublaminar wires. However, the unknown consequences of metal-on-metal wear debris are reason for concern especially in young patients. In this study, instrumentation stability, residual growth in the operated segment after surgery and biocompatibility of the novel radiopaque UHMWPE cables as an alternative to gliding pedicles screws or titanium sublaminar wires were assessed in an immature sheep model. Materials and methods. Twelve immature sheep were treated with segmental sublaminar spinal instrumentation: dual CoCr rods were held in place by pedicle screws at the most caudal instrumented level (L5) and novel radiopaque UHMWPE (Bi. 2. O. 3. additive) woven cables were placed at 5 thoracolumbar levels. Lateral radiographs were taken at 4-week intervals to evaluate growth of the instrumented segment. Four age-matched, unoperated animals served as radiographic control. After 24 weeks follow-up, the animals were sacrificed and the spines were harvested for histological evaluation and CT analysis. Results. No neurological deficits and no complications occurred during the initial postoperative period. One animal died during follow-up due to unknown cause. At sacrifice, none of the cables had loosened and the instrumentation remained stable. Substantial growth occurred in the instrumented segment (L5-T13) in the intervention group. No significant difference in growth of the operated segment was found between the intervention and control groups. Histological analysis showed fibrous encapsulation of the novel radiopaque UHMWPE sublaminar cable in the epidural space, with no evidence of chronic inflammation. Discussion. Novel radiopaque UHMWPE cables may be a promising alternative to gliding pedicle screws or titanium sublaminar cables within a growth-guidance system. UHMWPE cables may improve growth results due to the smooth surface properties of the UHMWPE cable and address concerns regarding the consequences of metal-on-metal wear debris

INTRODUCTION. Growth-guidance constructs are an alternative to growing rods for the surgical treatment of early onset scoliosis (EOS). In growth-guidance systems, free-sliding anchors preserve longitudinal spinal growth, thereby eliminating the need for surgical lengthening procedures. Non-segmental constructs containing ultra-high molecular weight polyethylene (UHMWPE) sublaminar wires have been proposed as an improvement to the traditional Luque trolley. In such a construct, UHMWPE sublaminar wires, secured by means of a knot, serve as sliding anchors at the proximal and distal ends of a construct, while pedicle screws at the apex prevent rod migration and enable curve derotation. Ideally, a construct with the optimal UHMWPE sublaminar wire density, offering the best balance between providing adequate spinal fixation and minimizing surgical exposure, is designed preoperatively for each individual patient. In a previous study, we developed a parametric finite element (FE) model that potentially enables preoperative patient-specific planning of this type of spinal surgery. The objective of this study is to investigate if this model can capture the decrease in range of motion (ROM) after spinal fixation as measured in an experimental study. MATERIALS AND METHODS. In a previous in vitro study, the ROM of an 8-segment porcine spine was measured before and after instrumentation, using different instrumentation constructs with a sequentally decreasing number of wire fixation points. In the current study, the parametric FE model of the thoracolumbar spine was first validated relative to ROM values reported in the literature. The rods, screws, and sublaminar wires were implemented, and the model was subsequently used to replicate the in vitro tests. The experimental and simulated ROM”s for the different instrumentation conditions were compared. RESULTS. Good agreement between in vitro biomechanical tests and FE simulations was observed in terms of the decrease in ROM for the complete construct with wires at each level. The stepwise increase in total ROM with decreasing number of wires at the construct ends was less prominent in silico in comparison to in vitro. CONCLUSION. Important first steps in the implementation and validation of a growth-guidance construct for EOS patients in a patient-specific FE model of the spine have been made in this study. The parametric nature of the FE model allows for rapid personalization. Although further improvements to the model will be necessary to better distinguish between different spinal instrumentation constructs, we conclude that the model can well capture essential aspects of spinal motion and the overall effect of instrumentation