To determine the grade of spondylolisthesis, or slippage, the disc is divided in quarters. The grade is equal to the number of quarters of slippage. If there is no slippage, the grade is zero. If the slippage is equal to one quarter of the total width of the disc, the slippage is grade one. If the slippage is three quarters of the width of a disc, it is a grade three spondylolisthesis. If the slippage is more than four quarters (the whole disc space) then it is called a grade 5. In a grade 5 spondylolisthesis, the spine is completely dislocated.

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