Novel Radiopaque UHMWPE Sublaminar Wires in a Growth-Guidance System for the Treatment of Early Onset Scoliosis: Feasibility in a Large Animal Study.

Study Design. In vivo analysis in an ovine model.Objective. To evaluate the feasibility of radiopaque UHMWPE sublaminar wires in a growth-guidance spinal system by assessing stability, biocompatibility and growth potential.Summary of Background Data. Several growth-guidance systems have been developed for the treatment of early onset scoliosis (EOS). The use of gliding pedicle screws and metal sublaminar wires during these procedures can cause metal-on-metal debris formation and neurological deficits. Novel radiopaque UHMWPE wires are introduced to safely facilitate longitudinal growth and provide stability in a growth-guidance system for EOS.Methods. Twelve immature sheep received posterior segmental spinal instrumentation; pedicle screws were inserted at L5 and radiopaque UHWMPE (bismuth trioxide) wires were passed sublaminarly at each level between L3 and T11 and fixed to dual cobalt-chromiun rods. Four age-matched, unoperated animals were evaluated to serve as a control group. Radiographs were taken to measure growth of the instrumented segment. After 24 weeks, the animals were sacrificed and the spines were harvested for histological evaluation and high resolution peripheral quantitative computed tomography (HR-pQCT) analysis.Results. No neurological deficits occurred and all instrumentation remained stable. One animal died from an unknown cause. Substantial growth occurred in the instrumented segments (L5-T11) in the intervention group (27± 2 mm), which was not significantly different to the control group, (30 ± 4mm, p = 0.42). HR-pQCT analysis clearly showed safe routing and fixation of the UHMWPE wires and instrumentation. Despite the noted growth, ectopic bone formation with the formation of bony bridges was observed in all animals. Histology revealed no evidence of chronic inflammation or wear debris.Conclusions. This study shows the first results of radiopaque UHMWPE sublaminar wires as part of a growth guidance spinal system. UHMWPE sublaminar wires facilitated near-normal longitudinal spinal growth. All instrumentation remained stable throughout follow-up; no wire breakage or loosening occurred and no adverse local tissue response to these wires was observed.