Dr Loren Fishman, a back-pain and rehabilitative medicine specialist who has long incorporated yoga into patient care and studies Iyengar Yoga, published an article in the New York Times on 5/8/13 called Advice on Practicing Yoga in Middle age.
Responding to questions about practicing yoga with herniated disc Dr. Fishman made the following statements:
– A herniated disc responds to extension, and may be worsened by flexion
– DGR, with bulging discs, is inhibited from back bends by a yoga-phobic physician. But back bends will very likely help.
– And about 5 percent of the time, the treatments reverse: extension helps stenosis, flexion is good for herniated discs.
– Unfortunately, Cate in NY, who also has sciatica and a herniated disk, cannot do either forward or backward bends. But she can do sideways poses like vasisthasana (side plank), which we have shown with M.R.I.s to reduce stenosis and herniated discs.
So I looked in my anatomy books to understand this more specifically:
Intervertebral Discs and Vertebrae: IV discs join the vertebra together. The fluid, gelatinous inner part of the disc is the nucleus pulposus, and is confined by a fibrous ring called the anulus fibrosus. The discs account for 20-25% of the length of the spinal column and at birth the central core of the disc is 88% water. In middle and older age there is a decrease in vertebral bone density, which causes the superior and inferior surface (top and bottom) of the vertebrae to become increasingly concave. Due to this concavity, the IV disc bodies actually increase in size; women 10% and men 2% (front to back) and in thickness about 10% in both genders. Interestingly, this bone loss and thinning of the vertebral mass are believed to account for the majority of age related height loss. The IV discs become circumferentially broader when the spine is compressed and thinner when stretched (as in hanging or suspended).
Herniation: As we age (20-70), the disc dehydrates and the inner and outer part merge together, forcing the outer ring to take more weight with compressive forces. Flexion of the vertebral column creates pressure anteriorly and over stretches the posterior spine squeezing the nucleus pulposus backwards (posterolateral) towards the thin and overstretched anulus fibrosus. Herniation occurs when the nucleus pulposus pushes in to the anulus fibrosus, which in turn pushes on the nerve roots. Posterolateral herniations are the most common and typically the cause of nerve pain due to the proximity of the nerve root. Approximately 95% of posterolateral lumbar herniations are at the L4-L5 or L5-S1 vertebral level.
Sciatica: Is often caused by a herniated L4 disc which compresses the L5 or S1 sciatic nerve root. Chronic sciatica causes pain, which can shoot down the posterior leg, and acute sciatica can be the result of localized nerve inflammation. Other causes include a tight piriformis muscle and spinal stenosis. Hip flexion with knee extension can exacerbate or relieve sciatica. Stretching the piriformis/rotator muscles can relieve sciatic as well.
Spinal Stenosis: The canal (foramina) of the spinal cord can narrow with age and compress the nerve roots as they leave the spine. Lumbar Stenosis is most common in the L4 vertebrae. If there is herniation of L4 along with stenosis it further compromises the already limited vertebral canal.
Moore and Dalley (2006) Clinically Oriented Anatomy, 5th edition, Lippincott Williams & Wilkins, Baltimore, MD.
Lasater, Judith (2009). Yogabody: Anatomy, Kinesiology, and Asana. Rodmell Press, Berkeley, CA.