Creation of a Porcine Kyphotic Model

Abstract

Study design: Large animal study.

Objective: Create a thoracic hyperkyphotic deformity in an immature porcine spine, so that future researchers may use this model to validate spinal instrumentation and other therapies used in the treatment of hyperkyphosis.

Summary of background data: Although several scoliotic animal models have been developed, there have been no reports of a thoracic hyperkyphotic animal model creation in an immature animal. The present study was designed to produce a porcine hyperkyphotic model by the time the pig weighed 25 kg, which corresponds to the approximate weight of a child undergoing surgery for early-onset scoliosis (EOS).

Methods: Successful surgical procedures were performed in 6 consecutive 10-kg (male, 5-week-old) immature Yorkshire pigs. Procedure protocol consisted of 1) a left thoracotomy at T10-T11, 2) screw placement at T9 and T11, 3) partial vertebrectomy at T10, 4) posterior interspinous ligament transection, and 5) placement of wire loop around screws and tightening. Weekly x-ray imaging was performed preoperatively and postoperatively, documenting progressively increasing kyphosis as the pig grew. Necropsy was performed 5-6 weeks after surgery, with CT, slab section, and histologic analysis.

Results: Average T9-T11 kyphosis (measured by sagittal Cobb angle) was 6.1° ± 1.4° (mean ± SD) preoperatively, 30.5° ± 1.0° immediately postoperation, and significantly increased to 50.3° ± 7.2° (p < .0001) over 5-6 weeks in 6 consecutive pigs at time of necropsy.

Conclusions: An animal model of relatively more rigid-appearing thoracic hyperkyphotic deformities in immature pigs has been created. Subsequent studies addressing management of early-onset kyphosis with spinal instrumentation are now possible.

Level of evidence: Level V.

Keywords: Animal model; Early-onset scoliosis; Immature spine; Pig; Thoracic hyperkyphosis.

Figure 1.

Localizing site of thoracotomy prior to incision (1A). Site of thoracotomy (1B).

Figure 2.

Exposure of spine (2A). Control of segmental vessels and mobilization of aorta (2B).

Figure 3.

Placement of screws and partial resection of T10 vertebral body (3A). Wire loop placed around screws and tightened (3B).

Figure 4.

Imaging at completion of procedure. Lines indicate the measurement of the Cobb angle between T9-T11. In this example, the Cobb angle was 31° immediately postop.

Figure 5.

3D reconstruction of computer tomography images (5A) and slab section of deformity at necropsy (5B). Histology of kyphotic deformity (5C). The anterior portion of the T9-T11 growth plates was disturbed by the vertebrectomy and are partially fused (white arrow). The posterior portion of the growth plates remain active after intial surgery (black arrows). Growth plates and intervertebral discs in adjacent segments remain healthy.

Figure 6.

The average sagittal Cobb angle between T9-T11 was 6.1 ± 1.4° preoperatively. An average kyphosis (measured by sagittal Cobb angle) of 30.5 ± 1.0° was generated at the time of surgery and increased to 50.3 ± 7.2° at necropsy. A significant increase in kyphosis was observed throughout the course of the study. *: p<0.05 compared to preop. . #: p<0.05 compared to surgery.

Figure 7.

Comparison of necropsy specimen of porcine thoracic kyphotic deformity (left) with sagittal CT image of congenital thoracic kyphosis in a 9 year old child (right).