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It has been observed that the modern day worker assumes a flexed, slouched posture over 50% of their working day.1
When we were younger this was probably no big deal. However, we now know that as we age, sitting in a position of flexion or slouching for a prolonged period of time can cause pain. Robin McKenzie, a physical therapist from New Zealand described this as postural pain syndrome.2
Postural pain syndrome is thought to be due to poor seated or standing posture, which stresses soft tissue structures at their end range of movement without any actual pathology. This poor posture position, if held over time, tends to decrease the blood supply to the area and overloads the supporting soft tissue structures thus causing pain.
The hallmark of postural syndrome is that once the poor posture is corrected, and the end range stress is removed, the pain resolves.
McKenzie3 gives the example of stressing one’s finger by pushing it into an “over extended” position toward the wrist and holding it. As this position is held, pain begins to develop and tends to worsen with time. Once the position is released, the pain subsides. In many cases the treatment is just as simple as that, once again enforcing what our mothers always told us, to “sit up straight.”
There is additional evidence in the literature to support the fact that poor seated posture has ill effects on the musculoskeletal system. For the case of discussion here, we will define poor posture as forward head with rounded shoulders, flexed thoracic and lumbar spine, with the pelvis posteriorly tilted; also called slouched.
Recently-published studies have confirmed that slouched sitting causes the spinal musculature to diminish its activity and place increasing stress on the posterior ligamentous structures of the spine, resulting in increased length or “creep”.4
Bogduk5 defines creep as a constant force that, if left applied for a prolonged period to collagen tissue, will result in further movement or length of the ligamentous tissue. This creep phenomenon — when combined with diminished muscular activity — is thought to result in an imperceptible increase of unprotected movement of the lumbar spine and placing it at greater risk of injury.
He went on to say that sustaining a flexed posture also reduces the resistance of the spinal ligaments. This reduction in resistance makes the spinal support structures weaker and thus increases the chance of injury.
By holding a flexed posture for only five minutes, reduction to resistance is up to 42% and holding this flexed posture for an hour reduces the spine’s ligamentous resistance by up to 67%.
In recently-published animal studies, it was noted that the amount of time necessary to cause the creep phenomenon to occur was as little as 20 minutes duration. Recovery from the creep phenomenon took more than 24 hours and the tissues measured did not ever return to their original resting length.
It has been theorized that the combination of diminished muscle activity combined with ligamentous creep may, in fact, lead to musculoskeletal cumulative trauma disorders over time as the amount of soft tissue damage exceeds the rate of repair and recovery.
These findings may explain why so many individuals with poor seated posture, over time, may experience ongoing or chronic low back pain over time, with no apparent pathological condition identified with radiographic and other special studies.4
McKenzie theorized years ago that the behavior of the lumbar discs mimics that of a cake of soap between your palms wherein squeezing the palms backwards the soap moves forwa and squeezing the fingers together the soap moves toward the wrist.
This being the case, we can see that compressing the anterior aspect of the disc during forward flexion of the spine will cause the nucleus to migrate posteriorly and stretches the posterior annulus.6, 7, 8, 9
In Manual Therapy, Volume 5, Edmonston et al noted with flexion, the vertebral canal is lengthened and this places tension on the spinal cord and peripheral nervous tissues. Flexion causes an increase in intradiscal pressure up to 80%. Conversely, extension of the spine compresses the posterior aspect of the disc moving the nucleus anteriorly. 4,6,7,8,9
The intradiscal pressure is decreased up to 35% with extension (sitting up straight and arching one’s back). Snook et al found that controlling lumbar spine flexion in the early morning was an effective form of self-care with potential for reducing non-specific low back pain.6
Anatomically, we know that the posterolateral aspect of the disc is the weakest point of the structure with less radius, not as firmly attached to the vertebral end-plate and it is not covered by the posterior longitudinal ligament.10,11
If the “creep” phenomenon evidenced above holds true, and recovery takes up to 24 hours irrespective of the load, healthcare workers may be at significantly higher risk of injury strictly due to their poor postures.
Hickey and Hukins noted in Spine, Volume 5 that if the flexed position is maintained, the stress of holding this position will fatigue the posterior annulus and overcome its strength and if overstretching exceeds four percent, irreversible damage will result. As medical professionals, sitting and standing in this relatively poor position for extended periods of time may lead to the debilitating spinal disorders. When back pain sufferers are evaluated, measurement of their back strength has been found to be diminished. 12,13,14
The question of whether the weakness is a result of the back pain, or the back pain is a result of the weakness remains to be answered. Perhaps fatigue also plays a role. Research has shed some light on potential answers but much work remains.
In the meantime, being mindful of one’s seated posture and “sitting up straight” as we were always told is a great step in the direction of prevention. Also, let’s consider finding a “good chair” for the clinic.
References
1. Marklin R., et al. Working Postures of Dentists and Dental Hygienists. Submitted for publication in the J Calif Dent Assoc, 2004.
2. McKenzie R, Kubey C. Seven Steps to a Pain-Free Life: How to Rapidly Relieve Back and Neck Pain. Plume/Penguin Publishing, New York, 2001.
3. McKenzie R, May S. The Lumbar Spine: Mechanical Diagnosis and Therapy, 2nd edition Spinal Publications, 2003.
4. Solomonow, M. et al. Spine. 2003; 28(12): 1235-1248.
5. Bogduk N, Twoomey L. Clinical Anatomy of the Lumbar Spine. Churchill Livingstone, New York, 1987.
6. Snook, SH., et al. The Reduction of Chronic Non-specific Low Back Pain through Control of Early Morning Lumbar Flexion. Spine. 1998; 23:2601-2607.
7. Shah, JS, Hampson, W. and Jayson M. The Distribution of Surface Strain in the Cadaveric Lumbar Spine. J Bone and Joint Surg. 1978; 60B, p. 246-251, 1978.
8. Sheppard J., Rand C., Knight G., Wetheral. Patterns of Internal Disc Dynamic, Cadaver Motion Studies. Orthopedic Transcripts 14. 321, 1990.
9 Sheppard J. J Bone Joint Surg. 1995; 77B. Supplement 2:161.
10. Adams MA. Biomechanics of the Lumbar Motion Segment. In Grieve’s Modern Manual Therapy. (2nd Ed). Eds. Boyling JD, Palastnaga N. Churchill Livingstone, Edinburgh, 1994.
11. Edwards WT, Ordway MS. Spine. 20001; 26:1753-1759.
12. Sini, M. Medx Clinical Data, Kerlin-Jobe/HealthSouth Clinic, Los Angeles, California.
13. Shirado, O. et al. J Spinal Disorders, 1992; 5:175-182.
14. Leggett, S., et al. Spine Volume 24. 1999;889-898.
