Abstract: BACKGROUND: Recent literature reported that patients with cervical herniated disc after cervical microendoscopic laminoplasty had extensive natural resorption of herniated nucleus pulposus, but there was still no unified measurement method for cervical herniated disc.  
OBJECTIVE: The methods by two-dimensional distance and three-dimensional volume were used to respectively measure and observe the resorption of herniated nucleus pulposus phenomenon after cervical microendoscopic laminoplasty, so as to evaluate and select a more accurate and reliable method. 
METHODS: Retrospective analysis was performed in 20 patients who underwent cervical microendoscopic laminoplasty in the Department of Orthopedics, First Affiliated Hospital of Zhengzhou University from June 2013 to November 2019, including 11 males and 9 females, aged 31 to 63 years old (averagely 51 years old), with a course of 1 to 11 months (averagely 4 months). Two-dimensional distance method and three-dimensional volume method were used to measure the degree of cervical herniated disc, and the absorption ratio, absorptivity, absorbancy, re-herniation ratio and re-herniation rate were used to evaluate the measurement results. 
RESULTS AND CONCLUSION: (1) The patients were followed up for 6 to 34 months, with 67 cervical herniated discs in 20 cases. In the two-dimensional distance group, resorption of cervical herniated discs after surgery occurred in 56 patients. In the three-dimensional volume group, resorption of cervical herniated discs after surgery occurred in 61 patients. The absorption ratios of the two were 84% and 91%, respectively, and the difference was not significant (P > 0.05). The absorptivities of the two groups respectively were 12.30%-71.24% and 7.71%-87.80% in the two-dimensional distance group and three-dimensional volume group, respectively. (2) In the two-dimensional distance group and the three-dimensional volume group, the small absorption ratio, the medium absorption ratio and the large absorption ratio respectively were 49% (33/67), 34% (23/67), 0 (0/67) and 36% (24/67), 49% (33/67) and 6% (4/67),  and the differences in absorbancy between the two groups were statistically significant (P < 0.05). (3) The average absorptivity of the two-dimensional distance group and the three-dimensional volume group was 31% and 42% respectively. However, there was significant difference in the absorptivity between the two-dimensional distance group and the three-dimensional volume group (P < 0.05). (4) In the two-dimensional distance group and the three-dimensional volume group, the re-protrusion ratios respectively were 1.49% (1/67) and 0. The re-herniation rate was 12.18% in the two-dimensional distance group. (5) The excellent and good rate of cervical microendoscopic laminoplasty patients was 85% (17/20). No aggravation or death occurred. (6) It is indicated that the three-dimensional volume method is more accurate and more suitable for quantitative observation of cervical herniated disc volume than the two-dimensional distance method, which can provide reliable basis for the diagnosis and treatment of cervical spondylotic myelopathy.

Key words: cervical microendoscopic laminoplasty, endoscope, cervical disc, minimally invasive, two-dimensional distance, three-dimensional volume, disc herniation