The pathogenesis of slippage and deformity in the pediatric lumbar spine: a radiographic and histologic study using a new rat in vivo model.

STUDY

DESIGN

Rat lumbar spines with posterior destabilizing surgery were evaluated radiographically and histologically.

OBJECTIVES

To create an appropriate rat model showing the vertebral slippage and deformities frequently observed in pediatric patients with spondylolysis, and to clarify their pathogenesis.

SUMMARY OF BACKGROUND DATA: There are controversial hypotheses regarding the pathogenesis of slippage and deformities of the pediatric spine with pars defects. Furthermore, there is no appropriate animal model mimicking those conditions.

METHODS

After posterior destabilizing surgery, the lumbar spines of young (4-week-old) and adult (26-week-old) rats were radiographically examined at weekly intervals during 3 weeks, and histologically 3 weeks after the surgery.

RESULTS

Slippage occurred in the young rats, but not in the adult rats. In the young rats, 7.2% slippage was observed 1 week after the surgery, whereas the slippage in the adult rats was 0%. The difference in percentage of slippage between the two groups was significant (P < 0.05). Lumbar deformity also was seen in the young rats, but not in the adult rats. The lumbar index of L6, as an indicator of L6 rounding, was 91.7% immediately after surgery. It had decreased to 87.7, 84.6, and 74%, respectively, 1, 2, and 3 weeks after surgery. Histologic examination showed growth plate injury in the young group and pronounced disc degeneration in the adult group.

CONCLUSIONS

The young rat with posterior destabilizing surgery was an appropriate animal model, mimicking the slippage and deformities radiographically seen in pediatric patients with spondylolysis. The histologic examination indicated that vertebral growth plate impairment was the basic lesion causing such slippage and deformities in pediatric spines.