Comparison of Laminoplasty on Lordotic, Straight and Kyphotic Cervical Alignments Suggest Poor Outcomes for Kyphotic Cervical Alignment: Finite Element Analysis

Background: Cervical laminoplasty is a useful for treatment of cervical myelopathy. However, this procedure has limitations for kyphotic cervical alignments. We used the finite element (FE) analysis and investigated the biomechanical changes in an intact and laminoplasty models with lordosis, straight, and kyphosis cervical alignments. Methods: A three-dimensional FE model of the cervical spine (C2-C7) with ligaments was created from computed tomography. The model was modified with the following cobb angles and the C3-C6 laminoplasty was conducted; a) laminoplasty-lordotic model (LM-L; C2-C7 angle: -10°), b) laminoplasty-straight model (LM-S; C2-C7 angle: 0°), and c) laminoplasty-kyphotic model (LM-K; C2-C7 angle: 10°). A pure moment with a compressive follower load of 100N to represent the weight of the head/cranium and cervical muscle stabilization was applied to these models. The range of motion (ROM), annular stress, nucleus stress and facet forces were analyzed. Results: ROM of LM-K increased when compared to the other models except for flexion. The LM-K had the highest mobility with 49% increase in ROM observed under extension, compared to the intact model. In all motion except for flexion, LM-L models’ ROM decreased by more than 10%, and LM-S and LM-K models’ ROM increased by more than 10% at C2-C7 compared to the intact model. The annular stresses and nucleus stresses in LM-K were higher compared to the other models. The maximum increase in annular stresses was about 194% in LM-K compared to the intact model, observed at the C3-C4 segment. The facet contact forces were lowest in the LM-K, compared to the other models. Conclusions: Patients with a cervical kyphosis alignment are at a disadvantage of increased kyphosis compared to cases with lordosis or straight alignment and should be treated with caution.