facet-joint-biomechanics

A study 1 conducted by several researchers in the Department of Orthopedic Surgery in Rush University Medical Center in Chicago USA looked closely on the biomechanics of the lumbar facet joint, and its effects on the overall spine mechanical behavior.

Why Conduct Such a Study?

Facet joints, also known as zygapophyseal, are complicated biomechanical structures in the spine. It has a complex 3D anatomy, in addition to variable mechanical functions when there are different spinal movements and effects on the overall spine mechanical behavior.

The facet joint’s 3D morphology is linked to its biomechanical function. The failure of the facet joint’s biomechanical function can lead to osteoarthritic changes in it. It can also implicate other spinal disorders. This includes degenerative spondylolisthesis.

The review article summarized the anatomy of the lumbar facet joint relevant to its biomechanical function. It also examined the biomechanical behaviors of the lumbar facet joint when put under different loading conditions.

What Was the Methodology?

Facet joints and intervertebral disks are part of the entity called the spinal motion segment. It’s also called the three-joint complex.

Sometimes, it’s also referred to as the articular triad. As they function together, the structures in the spinal motion segments give physiological spinal motion. It protects the spine through preventing activities that can cause injury.

The loss of intervertebral disk height is associated with disk degeneration. This affects the mechanical behavior of facet joints.

Sufficient understanding and proper knowledge of the anatomical geometry of the facet joint surface and capsular structures is essential for understanding the biomechanical function of the lumbar facet joint.

What Were the Results?

Interaction Between the Intervertebral Disc and the Facet Joint

Intervertebral disks and facet joints are part of the spinal motion segment. As they function together, the structures in the spinal motion segments provide physiological spinal motion. It protects the spine through preventing activities that can cause injury.

Mechanisms of Axial Compressive Load Transmission Through the Facet Joint

There are complex mechanisms by which facet joints transfer the axial compressive load because the lumbar facet joints from a synovial joint with low friction and nearly vertical articulating surfaces.

There are 3 possible mechanisms:

  • Through the articular joint surfaces.
  • Through capsular ligaments.
  • Through direct connection in between the tips of the articular processes and the lamina (the pars interarticularis).

Axial compressive load transmission via direct contact in between the tips of articular processes and the neural arch is essential, especially when the lumbar spine is extended.

Facet Biomechanical Functions at Different Spinal Positions

Facet joints accomplish different biomechanical functions when faced with different spinal positions. This section reviewed the biomechanical behaviors in:

Extension

Contact between the tips of the inferior articular process and the pars interarticularis can occur in lumbar extension. Especially if the intervertebral disk loses its height. The results of finite element analysis simulations suggest that hyperextended activities can cause impaction of the inferior process.

Forward Flexion

In a lumbar forward flexion, the inferior articular processes move superiorly in allusion to the superior articular process of the lower level.

Facet joints have an essential part in keeping lumbar stability in forward flexion. Apart from the restriction of normal physiologic flexion, the one that is being forced over the superior process is the inferior articular process. Afterwards, the compressive loads borne by the facets amplify again compared to those supported in the neutral position.

This phenomenon, however, is considered as a possibility that can cause degenerative spondylolisthesis.

Axial Rotation

The facet joint’s articular surfaces press together on one side, and then often open up on the other. This is what happens in a lumbar axial rotation.

We have the results of trabecular orientation and photoelastic experiments. And it suggests that the superior articular processes undergo bending stress within an axial rotation through compression in the tension and in the lateral direction.

Lateral Bending

There’s limited information present in publications on the facet joint’s biomechanical behavior under lateral bending. Here, the inferior articular process glides in the superior direction. It does so in reference to the superior articular process of the inferior vertebra. It’s on the convex side of the spinal curve, and on the opposite direction on the concave side.

What Was the Conclusion?

The lumbar facet joint has a complex 3D geometry. It has small components inside of the small joint. They are all directly linked to facet joint’s biomechanical functions and the motion segment in different spinal positions.

But if we oversimplify the facet joint as a flat joint, it may keep us from properly understanding the functions of the facet joint.

Axial load transmission and forward translation in motion segments can’t be wholly comprehended if one does not consider the special relationship among the lumbar spine’s posterior elements. Medical imaging modalities make room for 3D modeling plus the spinal model’s reslicing in the clinic.

But extracting valid information can’t be done if we do not understand the facet joint’s 3D geometry and its function.

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