Abstract: BACKGROUND: In the follow-up of patients after cervical microendoscopic laminoplasty, we observed that most of the herniated cervical discs decreased spontaneously. The resorption of herniated nucleus pulposus phenomenon has attracted our attention.  
OBJECTIVE:  To measure and compare the volume changes of patients with herniated cervical discs after cervical microendoscopic laminoplasty and conservative treatment using picture archiving and communication systems software three-dimensional volume method, and to discuss the characteristics and clinical significance of the resorption of herniated nucleus pulposus phenomenon.
METHODS:  A retrospective analysis of 68 patients with degenerative cervical spondylosis from January 2014 to June 2018 in the Department of Orthopedics, the First Affiliated Hospital of Zheng University (all had surgical indications) was conducted. Thirty-five people received cervical microendoscopic laminoplasty surgery, and 33 people insisted on conservative treatment for fear of surgery. The volume changes of herniated cervical discs patients in the two groups were measured and analyzed by picture archiving and communication systems software and three-dimensional volume method. The measurement results were evaluated with indexes such as the absorption ratio and absorption rate of the herniated cervical intervertebral disc, the re-protrusion ratio and the re-protrusion rate. The maximum error rate of 5% measured by picture archiving and communication systems software was taken as the reference standard of measurement error of cervical disc herniation. The Odom score was used to evaluate the clinical efficacy of conservative treatment and surgical treatment.  
RESULTS AND CONCLUSION: (1) The follow-up time in the cervical microendoscopic laminoplasty group was 7-76 months. There were 122 herniated cervical discs in 35 patients, 91 of them were absorbed by herniated intervertebral disc, and the absorption ratio was 74.6%(91/122) and the absorption rate was 5%-100%. Statistical analysis showed that there was no significant difference in the absorptive ratio between disc herniation, central type and lateral type, inclusive type and ruptured type (P > 0.05). There were 17 cases of disc re-protrusion, and the re-protrusion ratio was 13.9% and the re-protrusion rate was 5.0%-48.0%. In the cervical microendoscopic laminoplasty group, resorption of herniated nucleus pulposus could be seen as early as 7 days after operation and 76 months at the latest. (2) In the conservative treatment group, the follow-up time was 2-60 months. There were 105 herniated cervical discs in 33 patients. No resorption of herniated intervertebral disc was observed. Another 57 intervertebral discs were re-herniated, and the ratio of re-protrusion was 54.3% and the rate of re-protrusion was 5.0%-80.3%. (3) In the final follow-up, the excellent and good rate of clinical efficacy was 83% in the cervical microendoscopic laminoplasty group and 36% in the conservative treatment group (P < 0.01). (4) There were statistically significant differences in the absorption ratio and re-protrusion ratio between the cervical microendoscopic laminoplasty group and the conservative treatment group (P < 0.01). (5) It is indicated that there are extensive resorption of herniated nucleus pulposus phenomena after cervical microendoscopic laminoplasty, and the occurrence time is early and the duration is long. There is no significant difference in the absorption ratio of different segments. The confirmation of this phenomenon provides a new basis for the selection of anterior and posterior cervical spine surgery strategies and combined anterior and posterior surgery.

Key words: degenerative cervical spondylosis, minimally invasive, laminoplasty, conservative treatment, resorption of herniated nucleus pulposus, three-dimensional volume measurement