Test your knowledge: articular tropism

Question:

Some authorities believe that articular tropism is a predisposing factor for instability or future malfunction of symmetrical function of left-right articular motion. It can lead to pain and dysfunction. Others believe it has no clinical significance. 

Can you recognize the tropism in the following 3 human bones? And what is your opinion of this tropism in relation to articular function?

Answer:

Articular tropism is asymmetrical orientation of joints so that one vertebral level the plan of one apophyseal joint is more inclined in frontal or sagittal plane than the plane of the contralateral joint. It is most common at the lowest two lumbar levels (picture of the inferior L5-S1 joints) and it is reported to occur in one quarter of the human spines. Tropism can cause imbalanced movement between facets and probably leads to altered spinal mechanics of the segment. Premature degenerative changes often occur at vertebral levels where tropism is present. 

- In the picture of the cervical vertebra you can recognize the tropism of the vertebral foramen of the vertebral artery of the cervical spine. In the foramen on the right there is a complete ossification so there has been an alternative route for the vertebral artery in this case. 
- In the picture of the sacrum you can see a different inclination of the facet joints. The one on the left has no concave curve, which is seen in normal anatomy at this place. 
- The picture of the thoracic vertebra has a facet joint, which lies in a transverse plane which is very uncommon and a weird orientation for coupled motion in this region. The facet joint at the left is more normal oriented as seen in thoracic vertebra.