Unilateral laminoplasty with lateral mass screw fixation for less invasive decompression of the cervical spine: a biomechanical investigation

PURPOSE: To compare the stabilization behavior of additional unilateral mass screw fixation with current standard procedures in patients with cervical spondylotic myelopathy (CSM) in a biomechanical study.

METHODS: Ten human C2-C7 cervical specimens were tested under various segment conditions: native (NAT), laminoplasty (LP), laminoplasty with unilateral (LPU) or bilateral (LPB) stabilization, laminectomy with bilateral stabilization (LCB), and laminectomy. The instrumented level was from C3 to C6. For each segment condition, in vitro flexibility tests were performed using a spinal simulator and an applied load of ±2.5 Nm. The three-dimensional kinematics of the entire cervical segment in three main loading directions [flexion-extension (FE), lateral bending (LB), and axial rotation (AR)] was measured with an ultrasonic motion analysis system. Analysis of variance followed by a post hoc test was used to determine differences under the specific segment conditions to assess the parameters range of motion (ROM) and neutral zone (NZ).

RESULTS: For FE, the total ROM of laminoplasty (-6.3 % difference to NAT) and laminectomy (+6.4 %) remained at the level of native (p > 0.56), whereas the instrumentations LPU (-37.1 %), LPB (-44 %), and LCB (-43.2 %) lead to significant reductions (p < 0.01) without significant differences in LPU to LPB and LCB (p > 0.38). The same results were found with LB. For AR, the stabilization of all instrumentations was less pronounced, but had the same tendency seen for FE and AR. The results for the NZ showed equivalent values as that for ROM.

CONCLUSION: The degree of stabilization was as expected for LC and LCB; namely, no stabilization for LC and maximal stabilization for LCB. LPU exhibited almost the same degree of stabilization as LCB. LPU could be a new treatment option for less invasive decompression for multilevel CSM.