Fracture patterns of the adolescent porcine spine: an experimental loading study in bending-compression.

STUDY DESIGN

To expose functional spinal units from adolescent porcine to mechanical flexion-compression and extension-compression to failure. The biomechanical, radiologic, magnetic resonance imaging, and histologic characteristics are described.

OBJECTIVES

The aim of the present study was to investigate the fracture pattern of functional spinal units from adolescent porcine lumbar spines in in vitro compression loading and bending.

SUMMARY OF BACKGROUND DATA

In several studies, it has been shown that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. A high frequency of abnormalities affecting the spine has been found among athletes participating in sports with high demands on the back. The etiology of these abnormalities is still a controversial issue.

METHODS

Sixteen functional spinal units obtained from eight adolescent male pigs were used. Eight functional spinal units were exposed to flexion-compression and eight functional spinal units to extension-compression loading to failure. They were examined with plain radiography and magnetic resonance imaging before and after the loading. The functional spinal units were finally examined macroscopically and histologically.

RESULTS

Fractures/separations were seen in the growth zone anteriorly and more frequently, posteriorly in functional spinal units exposed to flexion-compression. In the extension-compression group, such injuries occurred only anteriorly. Only large fractures could be seen on plain radiographs and on magnetic resonance imaging. Macroscopically, a fracture/separation could be seen in 15 cases and histologically in all 16 cases. The median angle at failure for the flexion group was 17 degrees (range, 12-19) and for the extension group 17 degrees (range, 13-19 degrees). The median ultimate compression load in the flexion-compression group was 1894 N (range, 1607-3138 N) and in the extension-compression group 1801 N (range, 1158-2368 N).

CONCLUSIONS

The weakest part of the growing porcine lumbar spine, when compressed into flexion- or extension-compression, was the growth zone. The injury was more extensive in extension loading than during flexion loading. Growth zone injuries of the adolescent spine may go undetected on plain radiographs and magnetic resonance imaging.