Figure 4

Principle of the interspinous gap change test. During flexion of the lumbar spine, the spinous process of the upper vertebra is translated superiorly and anteriorly in relation to the spinous process of the lower vertebra. “a” distance between the upper and lower spinous processes in supero-inferior direction in a flexion state; “b” distance between the upper and lower spinous processes in antero-posterior direction in a flexion state (A). During extension of the lumbar spine, the spinous process of the upper vertebra is translated inferiorly and posteriorly in relation to the spinous process of the lower vertebra. “a*” distance between the upper and lower spinous processes in supero-inferior direction in an extension state; “b*” distance between the upper and lower spinous processes in antero-posterior direction in an extension state (B).