Table 2.

Changes in three variables of lumbar intervertebral disc geometry morphology12, 22, 24, 28, 42

Variables of lumbar disc morphology	Normal	Mild	Moderate	Severe
Height loss
Anterior disc height loss (mm)	0	2.42 (20%)	4.84 (40%)	7.26 (60%)
Posterior disc height loss (mm)	0	1.55 (20%)	3.50 (40%)	5.25 (60%)
Anterior osteophytes
Osteophytes of L4 low vertebral (mm)	0	3.01 (10%)	6.02 (20%)	9.03 (30%)
Osteophytes of L5 upper vertebral (mm)	0	2.96 (10%)	5.92 (20%)	8.88 (30%)
The changes of intervertebral disc area
Nucleus pulposus area (mm2)	613	463	333	223
Annulus ground area (mm2)	762	912	1042	1152

Height loss: Compared with a normal intervertebral disc, disc height in mild, moderate, and severe degeneration decreased by 20%, 40%, and 60%, respectively. The percentage of anterior disc height loss and posterior disc height loss are the same. For example, the 20% of anterior disc height loss of normal intervertebral disc is 2.42 mm

Anterior osteophytes: Osteophytes in the L₄ lower vertebra were classified as 10% (mild degeneration), 20% (moderate degeneration), or 30% (severe degeneration) of the normal sagittal diameter of an L₄ vertebra. Classification of osteophytes of the L₅ upper vertebra was the same as described above. For example, 10% of the normal sagittal diameter of an L₄ vertebra is 3.01 mm.