Abstract: BACKGROUND: Volume of disc herniation is an important measurement index for quantitative evaluation of disc herniation degree. Previously, the volume of cervical disc herniation that was completely absorbed after cervical microendoscopic laminoplasty was found unable to be confirmed by volume quantitative measurement. The reason was related to the fact that some tissues posterior to the vertebral body that could not be absorbed were included during measurement.  
OBJECTIVE: To compare and analyze the effect of inclusion and removal of the posterior vertebral structure on the volume measurement of herniated lumbar intervertebral discs, and to preliminarily observe the early changes of the volume of herniated intervertebral discs after lumbar microendoscopic laminoplasty.
METHODS:  Totally 98 patients with lumbar disc herniation (191 intervertebral discs) in First Affiliated Hospital of Zhengzhou University were enrolled. Lumbar spine MRI images of patients before and 1 week after lumbar microendoscopic laminoplasty were collected. The volumes were measured using PACS software. There were two measurement methods: one group included the posterior vertebral structure and the other group removed the posterior vertebral structure. The reduction rate, reduction ratio, unchanged ratio, enlargement ratio, and enlargement rate of the herniated lumbar intervertebral discs before and after the operation under the two measurement methods, and the absorption ratio and absorption rate of the herniated lumbar intervertebral disc under two measurement methods at 1 week after operation were compared.  
RESULTS AND CONCLUSION: (1) In the inclusion group, 123 disc herniations with reduced volume after lumbar microendoscopic laminoplasty (reduction ratio of 64.4%, maximum reduction rate of 34.17%); 45 disc herniations were unchanged in volume, ratio of 23.6%; 23 disc herniations showed increase in volume, increase ratio of 12%, and maximum increase rate of 59.9%. In the exclusion group, 143 disc herniations were reduced in volume after lumbar microendoscopic laminoplasty (reduction ratio of 74.9%, maximum reduction rate of 51.47%), 28 disc herniations were shown unchanged in volume, constant ratio of 14.7%, and 20 disc herniations increased in volume, increase ratio of 10.5%, maximum increase rate of 60.26%. (2) The absorption ratio and absorption rate of herniated lumbar intervertebral disc were lower in the inclusion group than that in the exclusion group (P < 0.01). (3) It is concluded that the measurement method of disc herniation volume by exclusion of posterior vertebral structure is closer to the actual state with a high accuracy. Lumbar microendoscopic laminoplasty can induce the herniated lumbar disc to spontaneously absorb in the early stage postoperatively.

Key words: lumbar microendoscopic laminoplasty, herniated lumbar intervertebral disc, natural absorption, herniated lumbar disc volume, posterior vertebral structure, MRI