Open Door Laminoplasty (ODL) with titanium mini-plate stabilization is a posterior decompression surgical procedure currently used to treat patients with severe cervical stenosis. Various ODL techniques exist currently that involve the resection of the posterior ligaments partially or totally. In techniques where the posterior ligaments are removed completely, the spinous processes are also removed. The biomechanical effect of resection of posterior ligaments and removal of spinous processes in ODL has not been evaluated previously. Moreover, no previous biomechanical study used ODL with titanium mini-plate stabilization in a cadaveric model. The purpose of this study was to compare different ODL techniques with progressive ligament resection and laminectomy biomechanically using a multi-level cadaveric model and investigate the effect of resection of posterior ligaments on the stability of the cervical spine.
In the current study, nine cervicothoracic specimens were tested in flexion-extension (FE), lateral bending (LB) and axial rotation (AR) using a custom built flexibility spine testing machine. In each test direction, a pure moment of ±1.5 Nm was applied continuously at a rate of 2 °/s for three cycles. The specimens were tested sequentially in the following order; 1) Intact, 2) ODL with ligament preservation, 3) ODL with resection of terminal ligaments, 4) ODL with total ligament resection and 5) total laminectomy. Flexibility parameters like range of motion (ROM) and neutral zone (NZ) were obtained for the last loading cycle and normalized against the respective intact values. Repeated measures ANOVA at α=0.05 was used to determine differences between surgical cases. Post-hoc Tukey tests were carried out on significant groups to determine the differences.
There was no significant difference in overall FE ROM within the different laminoplasty groups. Laminectomy caused instability to the spine by increasing the overall C2-T1 FE ROM by 20% (p<0.0001). The kyhosis of the spine was increased after resection of terminal ligaments (p=0.03). Surgery caused an increase in overall AR ROM. Further analysis of the intersegmental and surgical levels showed an increase in AR ROM at the terminal C2-C3 (p=0.01) and C7-T1 (p=0.01) levels. An increase in overall AR NZ was seen after surgery. The ROM and NZ were not affected due to surgery in LB.
The current study showed that ROM and NZ of human cadaveric cervicothoracic spinal segments were not affected by resection of posterior ligaments after laminoplasty. There was however a general trend observed in FE where the laminoplasty reduced the overall ROM after which the ROM increased with increased ligament resection.