Lumbar Spine Age Changes

Standard descriptions of the lumbar spine refer to the healthy, young, adult spine. There is also variation to what is "normal" for the lumbar spine. With aging you see fairly uniform changes in the lumbar spine, and so normality changes with advancing age. Many changes in the lumbar spine are not associated with symptoms and are therefore not pathological, but rather part of the normal ageing process.

Biochemical Changes

The changes in collagen, proteoglycans, and elastic fibres have major biomechanical effects on the disc. With age they become drier, and with an increase in collagen and reduction of elastin, they become more fibrous and less resilient. The increased collagen and collagen-proteoglycan binding leads the disc to become stiffer (more resistant to deformation), and the decreased water-binding capacity means they are less able to recover from creep deformation. This can lead to a change in mobility.

Area of Change	Biochemical Changes
Metabolism	In childhood, the disc adapts to anaerobic metabolism after the regression in infancy of the meagre blood supply to the disc.
Proteoglycans	synthesis, size, and the concentration in the nucleus pulposis (NP) decreases with age. Proteoglycans account for 65% of the dry weight in early adult life, decreasing to 30% by age 60. There is a reduction in large proteoglycan aggregates by adolescence The concentration of chondroitin sulphate falls, with keratan sulphate remaining constant. This means a rise in the keratan sulphate/chondroitin sulphate ratio.
Collagen	Collagen content increases, with an increase in collagen-proteoglycan binding, in both the anulus fibrosis (AF) and NP. Fibril diameter in the NP increases, so that the type II collagen of the NP resembles the type I collagen of the AF. Reciprocally, the average fibril diameter in the AF decreases. Overall, there is less distinction between the collagen of the NP and the AF Increase in the amount of type I collagen in the outermost laminae of the posterior quadrant of the AF, and a decrease in the type II collagen. This suggests some changes are not age related but related to internal stresses related to location.
Elastic fibres	Reduction in the AP from 13% at age 26 to 8% at age 62.
Non-collagenous proteins	Increase in concentration, with the appearance of distinctive non-collagenous proteins. Their function is unknown.
Water content	Decrease in water content with age from 88% at birth, to 65-72% by age 75. Most of the dehydration occurs during childhood and adolescence, with a final reduction of AP water content by 6% from early adulthood to old age Factors leading to reduced water content: loss of proteoglycans, change in KS/CS ratio, increased collagen and collagen-proteoglycan binding leaving fewer polar groups of the PGs to bind water

Structural Changes

Header text	Header text
Viable cells	Viable cells decrease in the NP. Proportion of cells that exhibit necrosis rises from 2% in infancy, to 50% in young adults, to 80% in old age. Lipofuscin granules accumulate
NP and AF distinction	There is less distinction between the NP and AF as the disc becomes more fibrous. They coalesce, and the NP becomes encroached by the AF.
NP changes	The NP becomes more solid, dry, and granular after middle age. There is less ability to exert fluid pressure with a drier more fibrous NP, with it being less able ot transmit weight directly, and less able to exert radial pressure on the AF. There is therefore a greater vertical load borne by the AF.
Collagen lamellae	Collagen lamellae of the AF increases in thickness, and becomes more fibrillated, and cracks and cavities may develop. These can enlarge and become clefts and fissures. There is an increase in incomplete lamellae These changes can occur due to repeated minor insults with an overloaded AF during trunk movements over the course of activities of daily living.
Tensile strength	Reduction in the tensile strength of the AF, but no simple relationship between age and tensile properties.
Intervertebral disc height	Intervertebral disc height increases with age. There is an increase in AP diameter by 10% in females, and 2% in males, and a 10% increase in height of most discs. The upper and lower surfaces of the discs increase in convexity. Disc height maintenance with age is "normal." Any loss of trunk stature is due to decreases in vertebral body height. Disc narrowing is due to a process other than ageing.

Vertebral Endplate Changes

Header text	Header text
Newborn	The vertebral endplate is part of the growth plate of the vertebral body The articular region of the endplate is formed by fibrocartilage The vertebral body side of the endplate is formed by columns of proliferating cells that extend into the ossifying vertebral body
Age 10-15	The articular region of the endplate becomes thicker The growth zone decreases in thickness Proliferating cells become fewer
Age 17-20	Vertebral growth slows vertebral endplate is gradually sealed off from the vertebral body by development of the subchondral bone plate After age 20, only the articular region of the original growth plate persists
Age 20-65	The endplate becomes thinner Cell death in the superficial cartilage layers In the subchondral bone of the endplate, vascular channels are gradually occluded leading to a decrease in permeability of the endplate to nutrients for the disc Vertebral endplate strength decreases, but this depends on the underlying vertebral body so they should be considered together

References

Bogduk, Nikolai. Clinical and radiological anatomy of the lumbar spine. Edinburgh: Elsevier/Churchill Livingstone, 2012.