[A novel self-growing rod technique for early onset scoliosis: an experimental study based on a porcine scoliosis model].

OBJECTIVE: To evaluate the efficacy of a growth-guidance growing rod in an established porcine scoliosis model via the Cobb angle correction and the continued spinal growth.

METHODS: Immature pigs (age: 6 weeks old, weight: 6-8 kg) were instrumented and tethered using a three separate incisions fashion.After considerable scoliosis was induced, the pigs were randomly assigned to an experiment group (EG) and a sham group (SG). In EG, the growing rod was implanted and the pigs were euthanized 8 weeks postoperatively; while in SG, the whole instrumentations were only removed and the pigs were followed up over a 8-week period.Dorsoventral (DV) X-ray radiographs were taken prior to and immediately after the growing rod implanting surgery, and at 4-week intervals to assess the Cobb angle orrection and instrumentation positioning.The continued spinal growth and the rod sliding were also assessed from the radiographs.

RESULTS: Of the 16 pigs, one pig encountered infection during the inducement of the experimental scoliosis and thus was excluded from analysis.Of the remaining 15 pigs, all animals developed progressive, structural scoliosis.The 15 pigs were randomized into EG(n=10) and SG(n=5). Two pigs in EG encountered infection and were also excluded from analysis.Of the remaining 8 pigs in EG, no neurologic complications, implant failure or infection were observed.In EG, the Cobb angle of the scoliosis before the growing rod implanted was (52.1 ±14.1)° and it decreased to (25.4±15.2)° postoperatively.After 8 weeks, the Cobb angle was (20.2±11.4)°.In SG, the Cobb angle of the scoliosis after 8-week tethering period was (55.2±15.7)° and it decreased to (53.6±15.8)° after removal of the tethering.The curvature remained stable (51.2°) during the subsequent 8 weeks.During the 8-16th week, the spinal height increased 14.2 cm and radiographic analysis of the growing rod sliding revealed an average distraction of 39.8 mm in EG; while in SG, the increased spinal height was 14.9 cm.The difference of the increased spinal height between EG and SG was not significant (P=0.821).

CONCLUSION: The novel growing rod system can provide substantial correction of deformity, and additionally, allow for continually spinal growth without significant growing disturbance.