Effects of Laminae Expansion on Cervical Stability and Spinal Nerve Tension after open-door Laminoplasty
Date Issued
2012
Date
2012
Author(s)
Tu, Chun-Ming
Abstract
Objective: To investigate the effect of lamina open angle on the cervical stability and nerve root tension during expansion open-door laminoplasty (EOLP).
Introduction: Multilevel cervical radiculomyelopathy is often treated with cervical laminectomy and fusion (CLF) or EOLP. For the CLF surgery, spinous process, laminae and surrounding ligaments of surgery level are removed to decrease compressive stress on spinal cord. However, the rigid fixation constrains movement of cervical spine, and the compensational range of motion (ROM) at adjacent level often leads to early disc degeneration. For the EOLP surgery, most of posterior elements of surgery levels are reserved. The procedures of EOLP begins with the opening of lamina at nerve compression side and creating a hinge groove at the contralateral side. The lamina were then flipped to release the pressure on spinal cord. There is no standard for the lamina open angle yet. Larger lamina open angle can better decompress the spinal cord and prevent myeloradiculopathy recurrence. However, the larger open angle may also increase the risk of C5 palsy. Posterior intersegmental ligaments above the surgery level, e.g., the supraspinous ligaments, interspinous ligaments and ligamentum flavum, are dissected for the easier operation of laminae expansion, especially for wider laminae expansion. However, the effect of ligament preservation on spinal stability remains unclear. The propose of this study is to find the suitable lamina open angle that can sufficiently decompresses spinal cord without causing C5 palsy and the effect of ligament preservation on cervical spine stability after EOLP and CLF surgeries.
Material and Methods:
(a) Threshold of C5 nerve-root overstretching. A displacement-controlled tensile test was performed at a speed of 5 mm/min to find the toe region of C5 nerve roots. Toe region is defined as the initial segment of force-deformation curve, where the deformation does not linearly increase with the applied force due to the laxity nature of biological tissue.
(b) Safety margin of lamina open degree. Eight C5 vertebrae with preservation of spinal cord and nerve roots were dissected from 6-month-old pigs, and applied with 50% cervical stenosis simulation by inserting the silicon blocks into spinal canal. The cross-sectional area of spinal cord and nerve root deformation during lamina opening were measured pre and post the artificial stenosis. The suitable lamina open degree was estimated by overlapping the open angles which the decompression of spinal cord is more than 30% and threshold of nerve-root overstretching found from the results of protocol (a).
(c) Evaluation of cervical stability after EOLP and CLF. Eight multilevel cervical spines (C3-C7) were dissected from 6-month old pigs. Intact specimens were applied with 2 Nm pure moment in flexion, extension, and lateral bending. Thereafter, the C4-C6 of specimens were sequentially applied with EOLP of 30-degree laminae opening with C3-4 ligaments preserved, EOLP of 30-degree laminae opening with C3-4 ligament removal, and EOLP of 45-degree laminae opening with C3-4 ligament removal and CLF. Stability tests were performed after every surgery simulations. In EOLP surgery, 30-degree laminae opening was defined as the lower limit of lamina open angle defined in Protocol (b), and the 45 degree opening was defined as upper limit for clinical practice. Light-reflection markers were inserted in each vertebra for motion tracking. The total ROM and intersegmental ROM of cervical spine were measured.
Results. (a) The mean threshold of C5 nerve-root deformation was 2.01 mm. (b) The lamina open angle corresponding to the threshold of C5 nerve root deformation was 31 degree, and the lamina open angle that reaches 30% recovery of cross-sectional area of spinal cord was 27 degree. Hence, in protocol (c), the lamina open angle was 30° for narrow-opening EOLP, and 45° for wide-opening EOLP. (c) Total ROM. Among the four directions of motions, only the ROM of flexion was significantly affected by EOLP. The ROM of flexion slightly decreased after 30-degree EOLP. The removal of C3-4 posterior ligaments significantly increased ROM. The increase of laminae open angle further increased the ROM in flexion. All directions of ROMs decreased post CLF. Intersegmental ROM. After EOLPs, motions of C3-4 and C4-5 significantly altered during flexion and extension. Motions of other segments were similar to the intact level after each kinds of EOLP. During flexion, motions of C3-4 and C4-5 slightly decreased after 30-degree EOLP, significantly exceeded the intact level after excision of C3-4 intersegmental ligaments, and then remained the same after the increase of lamina open angle. Trend for intersegmental motion changing of all EOLP was similar to that in flexion. After CLF, the intersegmental ROMs of implanted segment (C4-5 & C5-6) were significantly lower than the intact level during flexion, extension and left/right lateral bending. Intersegmental ROMs of adjacent cranial segment (C3-4) and adjacent caudal segment (C6-7) significantly increased during flexion, but decreased during extension and lateral bending compared to the one in intact level.
Conclusion: In this study, 30 degree lamina open angle was suggested be the range of EOLP that sufficiently decompress spinal cord and maintain cervical stability without violating C5 nerve root and compensation of adjacent intersegmental motions.
Subjects
Laminoplasty
Lamina open angle
Cervical stability
C5 palsy
Type
thesis
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