[General Spine] The myth of lumbar instability: the importance of abnormal loading as a cause of low back pain

[Hooch]

http://www.springerlink.com.ezproxy....4n14l4p12072t/


I read the full paper and found it very interesting, exposed me to some ideas I hadn't come across. In brief they've noticed in other degraded joints that regardless of whatever the neural process of pain generation is reestablishing a normal load bearing joint will relieve pain. They contend that 'spot loading' of different parts of the vertebrae due to degeneration produces pain.

Abstract

Spinal fusion became what has been termed the “gold standard” for the treatment of mechanical low back pain, yet there was no scientific basis for this. Operations of fusion for low back pain were initially done at the beginning of the last century for back pain thought to be related to congenital abnormalities or for past spinal infection. The recognition of the disc as a cause of sciatica, commonly associated with back pain, and the recognition that a degenerate disc led to abnormal movement suggested the concept that this abnormal movement was the cause of pain, and this abnormal movement came to be called “instability”. Much biomechanical expertise confirmed the fact that degenerate discs led to abnormal movement, there were many hypothesis as to why this caused pain. However clinical results of fusion for back pain were unpredictable. The failure of pedicle screws and cage fusion to improve the clinical results of fusion despite near 100% fusion success, and the introduction of “flexible stabilization” and artificial discs, which demonstrated that despite the often unpredictable movement permitted by of these devices, clinical success was similar to fusion, directed attention to the other role of the disc, that of load transfer, which these devices also affected. Abnormal load transfer was already known to be critical in other joints in the body and had led to the use of osteotomy to realign joints. The relevance of load transfer to the future design of spinal implants used in the treatment of low back pain is discussed, and some finite element studies are reported demonstrating the likely effect of abnormal loading beneath an incompletely incorporated plate of an artificial disc, perhaps explaining in part the somewhat disappointing clinical results to date of the implantation of artificial discs.

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The artificial disc does not create a pattern of normal movement, and
is not designed to do so. It does not necessarily require the
removal of the posterior innervated annulus, often regarded
as a source of back pain, which continues to be moved and
stressed after operation. The one mechanical effect it has is
to alter load transmission, whilst allowing movement.

The interface between the implant and the underlying
vertebrae is critical. It is through this interface that load
must be transmitted. Bony integration must not only stop
movement, but it must be sufficiently extensive that the
area of bone transmitting load is adequate. Our experience
with cages demonstrated that a small area of bony integration
sufficient to stop movement, but insufficient to
transfer load over a wide footprint was associated with
continued pain.

With the artificial disc with a larger foot print transfer of
load is through plates resting on the vertebrae—a universal
feature of currently used disc replacements. This load
transfer may be abnormal if the bone–plate interface is a
mixture of fibrous tissue and bone, producing an irregular
pattern of load transfer. This clearly could be one of the
reasons that disc replacement is so far not a better procedure
than fusion in prospective randomized trials
comparing the two techniques"

[trkdoc714]

Hooch,

I tried to follow the link to read the article in it's entirety but it led to the C Q University student login.

The portion you posted was interesting to say the least. It's always good to read other thought lines with a broader scope of issues to consider when repairing the spine.

Bob

[Justin]

Hooch,

I tried to follow the link to read the article in it's entirety but it led to the C Q University student login.

The portion you posted was interesting to say the least. It's always good to read other thought lines with a broader scope of issues to consider when repairing the spine.

Bob

It was published in the European Spine Journal in 2008. Here's a link to the PubMed entry: The myth of lumbar instability: the importance of ... [Eur Spine J. 2008] - PubMed result

[helmut]

It would be interesting to see what Spinal Kinetics found out during the development of the M6. I am sure that they included all the mechanics of the spine in their research.
I was told that the criteria of placing a artificial disc correctly is similar to the lid on a toilet, it just has to be large enough to be equally supported by the stronger periphery of the vertebrae. The center of the bone is much weaker than the periphery.
Mechanically speaking it is of course of huge importance that the device is placed in the perfect spot, thats why a experienced surgeon can make a big difference.

As soon as a disc is "flat" because of a bulge or tear etc. it would seem logical that the spine is mechanically affected in a lot of different ways and a artificial disc has to compensate for all of those.

As far as I am concerned I am pretty happy not to have a fusion in my back but instead a ADR. Mechanically speaking fusion appears to me somewhat hopeless to ever truly distribute weight as it was when the spine was healthy. Fusion is good in some cases more or less as a last option I think.

[Hooch]

Whoops, I can't seem to edit the post either.

The other thing they were alluding to with fusion was they found a fusion cage device, doe to higher density\less flexibility or whatever, will transmit load through the vertebrae in preference to the bony fusion. So this creates a spot load at the point of contact of the cage.

It's interesting as it provides some insights I hadn't heard into 'failed back surgery syndrome', technically correct operations but with the patient still in pain. This is undoubtedly a physical, and not a psychological, phenomenon.