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Lumbar Sacral Biomechanics

The Lumbar Sacral Junction Effect

Saul Yudelowitz Bsc (Hons)

As a musculoskeletal specialist I have been treating patients with lower back pain for almost a decade. It is imperative to realise that optimising the body for the tasks that the patient wants to achieve is vital for the success of any treatment program. Over the last decade our world has changed tremendously with respect to the typical requirements that patients need. We sit on our travels to work, we sit at work, we sit on our travels back home and then we sit again when we are at home. This is coupled with bouts of exercise by some people, anything from regular to random. So how the spine adapts to these new requirements could be argued as a significant cause of lower back and neck pain. From a biomechanical perspective the lumbar sacral junction (L/S junction) is the foundation of the entire spinal mechanics and most adaptations are based on this foundation. We know that when the spine is hyper flexed for long periods, especially when loaded as when lifting an object the discs will over time begin to degenerate. This degeneration could lead to many different problems like

Reduced disc height leading to approximation of the facet joints.

Annular tears, disc bulges, disc prolapsed, leading to a change in the chemistry of the disc thereby affecting disc function.

There are many more knock on effects that disc degeneration has on the biomechanics of the spine however there is an important contribution from the L/S junction. If the L/S junction is flexed during most functions like sitting and exercising the L5/S1 disc is placed in a compromised position predisposing it to degeneration. Due to the shape of the L5/S1 discs it is another reason that this is clinically the most common disc to degenerate however there are other reasons for this like its position at the base of the spine thereby taking more weight.

We also know from a biomechanical perspective that if there is an area that is flexed in the spine there will be an area that is extended. Clinically patients that present with an area of the spine that is hyper extended typically have pain from the facet joints that have been approximated.

Since it is very common to find patients sitting with a flexed L/S junction it should become more common to see patients presenting with lower lumbar disc degeneration and middle/upper lumbar and lower thoracic spine degenerative joint disease. This is probably due to the compensation that the spine makes to maintain us upright. The cervical spine also has a difficult time compromising from a flexed L/S junction. When the entire lumbar spine is flexed the cervical spine will hyper extend creating faced approximation, patients typically present with anything from hypertonic muscles to neurological symptoms in the upper extremities.

For long term success of treatment, the L/S junction needs to be in its neutrally extended position when sitting, this will allow for a smooth neutral extension of the lumbar spine as well as a neutral thoracic kyphosis and neutral cervical extension. This will allow the scapula to sit on the ribcage in a neutral position thereby reducing neck pain.

Should you have any questions or would like to know how to get the L/S junction into neutral extension when sitting please feel free to contact us.

The information contained in this Newsletter was prepared from medical and scientific sources which are referenced and are believed to be accurate and reliable. The information herein should not be used to treat or to prevent any medical condition unless it is used with the full knowledge, compliance and agreement of your personal physician or other licensed health care professional. Readers are strongly advised to seek the advice of their personal health care professional(s) before proceeding with any changes in any health care program.


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