Biomechanical Response of Four Roussouly's Sagittal Alignment Lumbar to Degeneration of Different Parts of Intervertebral Disc: Finite Element Model Analysis

Background

Spinal degeneration with age is commonly accompanied by excessive kyphosis and low-back pain, however, little is known about the connection between lumbar sagittal morphology and its degenerative biomechanics. This study investigates the biomechanical response of four Roussouly's sagittal alignment lumbar to degeneration of various parts of the intervertebral disc (IVD) based on threedimensional finite element (FE) models.

Methods

Using Roussouly's type parametric FE models, material properties of the degenerate nucleus populous (NP), annulus fibrosis matrix (AFM), and collagen fibers were assumed to be half of the intact IVD. A follower preload and vertical force were applied to simulate physical standing posture.

Results

the reduced strength of the NP and AFM led to the increase of lumbar anteflexion, while the fiber mechanical properties have little effect on it. When facing IVD degeneration, Type 1 lumbar showed increased intradiscal pressures (IDPs) and fiber stress at the L1-2 and L4-S1 segments. Type 2 lumbar exhibited the highest lumbar anteflexion and pelvic rearward rotation, as well as increased IDPs among the models. Type 3 lumbar had the best biomechanical stability. Type 4 lumbar showed the higher AFM stress but the lower IDPs among the four types.

Conclusions

IVD degeneration generated sagittal imbalance by increasing lumbar anteflexion movement (i.e., loss lordosis) and pelvic rearback rotation. The biomechanical response of the four Roussouly's lumbar types differed in intervertebral rotation and stress distribution.