The vertebral disc consists of 10 to 20 concentrate circumferential layers of highly fibrous type I and type II collagen. The nucleus pulposus is made up of glucoaminoglycans, which retains large amounts of water. The nucleus material can be thought of as the consistency of fresh lobster. It is not a jelly donut, as it is commonly described.

How the disc changes

In most cases, after approximately age 35 the nucleus of the disc begins to lose its integrity in holding moisture and supplying the appropriate pH balance to the interior of this closed structure. In addition, small fissures may begin radiating from the inner layers outward. The nuclear material creeps into these fissures, causing disc bulges. Under axial pressure-- as in squeezing a balloon on the top and bottom--the sides of the disc push outward. This can also happen in young, healthy discs when sufficient force is applied either over a long period or in an abrupt manner. The disc is not a shock absorber but designed for movement only. The outer layer of the annulus is innervated with pain receptors that react to stretching.

Where the pain comes from

The area around the disc is quite limited and some bulges may press on nerve roots, causing the classic pain and numbness down the back of the leg to the foot. These symptoms can be also associated with trauma to the outer layers of the disc, which result in inflammation. This inflammatory process also irritates the nerve, causing similar problems. This is a radicular complaint. Lastly, pain is also transmitted through muscle and tendons. It is called sclerotogenous pain pattern.

Pain at night

Pain at night due to back problems are relative to less muscle activity; sitting having dinner, watching television, lying in bed. The transition of the muscles attenuating the forces to relying on the ligaments as the joints compress, and the ligaments deform. The disc undergoes the same process but the nucleus material is less stiff and will creep along the lines of least resistance; mostly it follows gravity, thereby increasing the bulge and stretching the annulus with pain as a consequence.

Postures

Postures in sitting, standing and lying are more critical with this condition. If the pain is more frequent into one side or the other, the idea is to not let your body sag to that side. In addition, when sitting it is important not to slump. The poor habits accentuate the problems that have developed by mere degenerative change or traumatic event.

Why the hip

Depending on the structures impacted by this process, the pain may be referred through the ligaments and or nerves associated with the hip.

Source:

The Biomechanics of back pain; Adams, Bogdul, Burton, Dolan; Churchill Livingstone, 2002

Biomechanics of musculoskeletal injury; Whiting, Zernicke; Human Kinetics, 1998