A porcine early-onset scoliosis model created using a posterior mini-invasive method: a pilot study.

STUDY DESIGN

An animal study.

OBJECTIVE

To create a reliable porcine scoliosis model representative of early-onset scoliosis (EOS) without violation of the vertebral elements along the curve.

SUMMARY OF THE BACKGROUND DATA

To develop new nonfusion techniques for the treatment of EOS, a reliable large animal model with remarkable growth potential is required. However, a long tethering period which consumed the majority of the rapid growth phase or violation of the vertebral elements was thought to be essential in most of the previous models. Therefore, these models may be suboptimal for mimics of human EOS which was usually idiopathic type without vertebral anomalies.

MATERIALS AND METHODS

This study included 12 female Yorkshire pigs (aged, 5-6 wk; weight, 5-7 kg) in which scoliosis was created by posterior asymmetric tethering from T5 to L3. At the index surgery, 3 separate incisions were preformed, and ipsilateral rib tethering from the 10th to the 13th rib was performed while maintaining the vertebral elements along the maximal curve in a pristine state. Progressive deformity was documented with monthly radiographs. Frontal and sagittal profiles were assessed using the Cobb method. After an 8-week tethering period, the whole instrumentations were removed, and the pigs were observed for an additional 8-week period with serial radiographs to document the progression of the deformity.

RESULTS

Of the 12 pigs enrolled in this study, 2 encountered substantial complications (1 developed a postoperative infection, and the other experienced prolonged postoperative weakness). Of the 10 available for analysis, all pigs developed rapidly progressive, structurally 3-dimensional, idiopathic-type curves with convex to the right in the lower thoracic spine. The mean coronal Cobb angle was 29 degrees immediately postoperatively and progressed to 65 degrees after the 8-week tethering period. Eight weeks after removal of the tether, the scoliosis continued to progress and averaged 68 degrees (range, 58-78 degrees). On the sagittal plane, a mean lordosis of 32 degrees at the thoracic spine and a thoracolumbar kyphosis of 63 degrees were observed at study completion.

CONCLUSIONS

A 3-dimensional rapidly progressive scoliosis model, that is closely approximate to human EOS, can be successfully created in pigs by unilaterally tethering the thoracolumbar spine and the ribcage. This model provides an equivalent EOS-like deformity and leaves adequate skeletal growth potential for biomechanical research as well as validation of fusionless scoliosis correction systems.