[Anatomy research of cervical laminoplasty with preservation of the posterior ligament complex.]

Objective: To evaluate the feasibility of cervical laminoplasty with preservation of the posterior ligament complex for enlarging the spinal canal. Methods: Six up-to-standard human corpse specimens were divided into two groups by simple randomization (start from C4 group, S4; start from C5 group, S5; 3 corpses in each group). Decompression operation of C3-C6 level was performed in a predetermined sequence by using the new procedure with preservation of the posterior ligament complex.The basic depth of spinal canal was measured with a depth gauge at fixed point after the right bone groove of single level was completed.The operation of the contralateral bone groove was continued, and then the spinal canal was measured again when the spinous process was pulled backward by using a tissue forceps until the ligament complex was just tight.Retreat value (RV) of vertebral lamina was obtained by calculating the difference between the two measurements.The earlier measured levels needed to be remeasured when the operation area increased by one level. Two independent sample and one-sample t test were used to analyze the measurement results. Results: RV of vertebral lamina was small after finishing the first level of the decompression operation [S4: (0.87±0.72) mm; S5: (1.83±0.29) mm], and the value reached its maximum after the completion of C3-C6 level.The overall average RVmaxs from C3 to C6 level were (2.37±0.52) mm, (4.27±0.78) mm, (3.73±0.93) mm and (2.16±0.77) mm, respectively.The overall average retreat rates (RR) were 17%±7%, 32%±9%, 29%±10% and 16%±6%, respectively. The overall average RVmax of C4 and C5 level reached or exceeded the decompression threshold value of 4 mm (t=0.839, -0.703, both P>0.05). The average RVmax of C4/C5 level was similar in the two groups (t=-1.204, 1.189, both P>0.05); however, the difference of average RVmax between C3 and C6 level was significant (t=-4.429, 4.196, both P<0.05). Conclusions: Cervical laminoplasty with preservation of the posterior ligament complex can enlarge the sagittal diameter of spinal canal and relieve the compression of spinal cord.In addition, RV of each level increases as the number of the operation level increases, and the ability of vertebral lamina to retreat is quite different from C3 to C6 level.The decompression effect in the middle of the operation area is better than that on the cranial and tail side.