Does Removing the Spinal Tether in a Porcine Scoliosis Model Result in Persistent Deformity?: A Pilot Study

Abstract

Background Using a tethering technique, a porcine model of scoliosis has been created. Ideally, tether release before placement and evaluation of corrective therapies would lead to persistent scoliosis. Questions/purposes Does release of the spinal tether result in persistent deformity? Methods Using a unilateral spinal tether and ipsilateral rib cage tethering, scoliosis was initiated on seven pigs. The spinal tether was released after progression to a Cobb angle of 50°. Biweekly radiographs were taken for 18 weeks after tether release to evaluate longitudinal changes in coronal and sagittal Cobb angles. Postmortem fine-cut CT scans were used to evaluate vertebral and disc wedging and axial rotation; results were compared to a previously published data set of 11 animals euthanized before release of the tether (control group). Results Radiographic analysis demonstrated two responses to tether release: a persistent deformity group and an autocorrective group. Differences between these two groups included number of days with the tether in place before reaching a Cobb angle of 50°and degree of deformity immediately after scoliosis induction. CT analysis of the tether release versus tether intact groups demonstrated progression in vertebral body wedging without differences in apical rotation. Conclusions With the appropriate inducing parameters, release of the spinal tether does not systematically result in deformity correction. Tether release resulted in a reduction in Cobb angle in the first several weeks followed by steady curve progression. Deformity progression was confirmed using detailed CT morphometric analysis. Clinical Relevance The tether release model will be used to evaluate corrective nonfusion technologies in future investigations.

Utility of an allograft tendon for scoliosis correction via the costo‐transverse foreman

“…With regard to the establishment of scoliosis and natural progression, our results agreed with the previous studies . However, the rib fusion mass of the concave side resulted in a rigid spinal deformity similar to that encountered in congenital scoliosis; this fact compromised the tether correction in the scoliotic plane.…”

“…In the subsequent treatment study, 8 weeks after an initial surgery to induce scoliosis, all the pigs developed identical spinal deformity on three planes . In the treatment surgery for this group, all the spinal and rib tethers were removed and the animals randomized into either treatment or no treatment groups.…”

“…In the treatment surgery for this group, all the spinal and rib tethers were removed and the animals randomized into either treatment or no treatment groups. Interestingly, intra‐operatively during the second surgery, significant rib fusion and heterotopic bone formation were observed at the site of the previous concave rib tethering, which extended from T8 to T12 levels . The vertebral segments within this range (T8–T12) were extremely rigid with little flexibility on testing, even after removal of the polyethylene tether.…”

“…Wedging changes at T7, T13, L1, and apex were measured via the three dimensional CT reconstruction. Wedging changes were defined by the Cobb angle between the superior and inferior endplates, which were measured on the most middle slice in coronal plane . The wedging angle was negative if the vertebra wedged toward the convex side, namely when the height of right side was lower than that of the left side.…”

Porcine model of early onset scoliosis based on animal growth created with posterior mini-invasive spinal offset tethering A preliminary report

“…The first results reported the difficulty to obtain a reverse process in the concavity [28][29][30][31]. The precocity, the length of time the tether is in place and the vertebral dysplasia are surely involved in the deformity persistence.…”