What are the causes of moderate facet joint hypertrophy?

Aging and. Aging will lead to degeneration of the facet joints as can injury or trauma which can accelerate this process as can smoking which degenerates the discs which alters the mechanics of the spine segments creating more stresses on the facet joints leading to degeneration. Underlying rheumatologic conditions will affect these joints too.
Facet Arthropathy. Facet arthropathy/arthritis and ligamentous hypertrophy suggests the covering over the facet joint and spinal canal is thickening. These are joints in the spine where the bones articulate and can develop bone spurs and cause the clicking with pain typically with extension. Usually a life of heavy lifting type jobs or extension based exercise/lifestyle can lead to this issue. Some is normal life.