There are a couple of malformations of the sacrum and base of the spine that influence the free functioning spine. These two congenital disorders go by the name of lumbarisation (lumbarization) and sacralisation (sacralization).
In the 'modern' human skeleton the sacrum is a solid bony mass of 5 fused vertebrae at the back of the pelvis on which the upright spine sits. However, in earlier evolutionary forms of the human skeleton, the segments of the sacrum were not fused. They were free to move like a tail and participate as an extension of the spine in normal activity.
L6 in lumbarisation is not 'an extra vertebra'. Rather it is one more mobile lumbar segment and one fewer fused segment of the sacrum
The two congenital anomalies of the block-like sacrum are known as lumbarisation and sacralisation. Lumbarisation is where the uppermost segment of the sacrum is not fused. Rather it is free to move and participates, along with the neighbouring lumbar vertebrae in spinal activity. The first sacral segment is said to be lumbarised.
With lumbarisation, anatomists and clinicians have taken to referring to this additional mobile lumbar segment as an 'extra' vertebra, which has led to confusion in the minds of the patients. There is no extra vertebra jammed into the length of the spine, but simply one extra mobile vertebra and one less fixed one.
A sacralised lumbar segment (also referred to as 'one less vertebra') can be semi-fused one one side only or both sides
The other congenital anomaly is where the bottom lumbar segment (L5) is fused to the sacrum below, or to the ilium at the side (the large ear-shaped bones of the pelvis). Sacralisation with the sacrum can be termed central sacralisation, whereas to the sides it can be either uni- or bi-lateral transverse sacralisation. Being fused or semi-fused the L5 segment has more in common with its sacral neighbours than its lumbar ones, so it is said to be sacralised.
Just to confuse matters, the vertebra in question is often not fused all the way across. It may be fused on one side but not the other. Its participation with spinal movement on one side only makes for very wonky movement and the other working lumbar links above have to cope with that. Where strain sets in there will be pain.
With sacralisation there may be fusion of the transverse process to the pelvic bone (ilium) on one or both sides, or there may be a false joint or pseudarthrosis. This makes for wonky spinal movement
It has always been assumed that congenital sacralisation and lumbarisation are clinically unimportant, but I don't agree. Generally speaking, I believe both anomalies of the sacrum and base of spine cause trouble, usually because of the incomplete nature of each. With lumbarisation, it is rare for this additional joint to be completely free and, with sacralisation, it is rare for it to be totally fused. The pure extreme of both is rarely found, rather a no man’s land in between.
There is a certain safety to be had in a joint being completely fused, which helps explain the orthopaedic surgeon’s penchant for fusing problem joints. The rationale had always been – drastic as it sounds - if a joint hurt to move then join it up to neighbouring bones to stop it moving.
That surgical fusion inevitably led to other problems later on in nearby healthy joints, which were sometimes as unwelcome as the original complaint, is another matter; the case for fusion can be clearly seen. However, if the fusion was not quite solid, everybody was left in a quandary. Indeed, surgical fusions which do not quite ‘take’ are the bane of the back surgeon’s life.
You can see where the whiter area of 'bony rub' of the pseudarthrosis on the right (looks on the left to you here) has caused the bone to become sclerotic or more dense
I find exactly the converse is true of spines that demonstrate lumbarisation of the first sacral segment. Although the extra joint between the first and second sacral segment is said to be free, in truth it is usually not free enough. Again the spine is caught in no man’s land, attempting to incorporate this additional joint in its everyday function. Invariably, the ring-in joint is not up to the task - and this is more likely to be the case with advancing years.
With not being quite mobile enough, a lumbarised first sacral segment is more vulnerable to trauma. As we get older and all our joints aren't as loose an errant everyday movement can tweak it, because the effort is too much for it to cope with. And, like the joint that is meant to be fused, it also gets hurt. This phenomenon explains the latter day diagnosis of a congenital anomaly that has been there all one's life, but only recently started to cause grief.
The Treatment Options for Sacralisation and Lumbarisation
My solution is to get both types of congenital anomalies moving again– the semi-fused and the semi-free. Attempting to get movement into a radiologically fixed joint always strikes my fellow medical practitioners as bizarre (if not mad), but treatment is usually short-term and highly rewarding for the patient. All the usual appeasing, self-mobilisation and strengthen exercises described in exercises for back pain can be put into action here.
With sacralisation and lumbarisation there is a vast variety in the shape of the different pieces of anomalous bone and also where that bone is making a pseudarthrosis (false joint). With unilateral transverse sacralisation for example, instead of the transverse process being a fine lateral sprig it can be a huge bony mass, rather like an elephant's ear, that articulates with both the ilium and the top of the sacrum.
Conservative treatment of the above type of anomaly involves manual mobilisation of the false joint with the hands to make it move better. Treatment also involves muscle strengthening the segmental union between all the lumbar vertebrae, not unlike the techniques used to shore up an unstable vertebra and developmental instability as a result of surgical fusion.
With anomalies of the sacrum and lower spine, there is a seemingly endless variety of different shapes and types of bony mass . . . . and bony unions at various false joints (pseudarthroses)
Sacralisation of the fifth lumbar segment also has another far-reaching effect, one not associated with joint mobility. This relates to the altered centre of gravity of the base of the spine. With the L5 fused to the sacrum, the seat of spinal movement is raised. L4, the new base of spinal movement, lacks the secure shoring afforded L5 and this can lead to problems.
Normally, L5 sitting on the sacrum means the spine originates deep within the pelvis where it is firmly anchored by a three-dimensional array of very strong ligaments. The dense strands of the stellate (star-shaped) ligament fan out either side in robust semi-circles from the fifth lumbar vertebra to various parts of the the inner pelvic bones, lashing the spine securely to the sacral table.
The most mobile segment in the spine in terms of forward bending is the second vertebra up from the bottom, L4. Its inherent mobility means the usual problem with a sacralised L5 is that L4 is too flimsy to cope and the L4-5 joint becomes over-used. Usually, by the middle to late decades, it starts to suffer excessive strain and eventually becomes painful.
The extensive ilio-umbar ligament firmly secures the base of the spine to the sacrum and inner pelvic bowl
For these reasons, treatment for lumbar sacralisation must always involve strengthening exercises of the muscles both front and back of the spine. The spinal intrinsic muscles (multifidus) must be re-educated to bolster the bending strength of L4 as the raised seat of spinal movement and you can see here about spinal strengthening and the Roman Chair. At the same time, stronger abdominal muscles help create a stronger retaining wall at the front. You can read all about the best abs exercises for bad backs here.
You also might like to understand how it could be that a congenital spine disorder (such as lumbarisation and sacralisation) can suddenly become painful in later life, when it's been there all along, since birth.
Read Spine Disorders to get the gen.
You may also like to watch what you can do yourself, whatever the pathology, and whatever the pictures say, to make your spine more plastic, and compliant, and biddable. Not like some painfully rigid pretzel about to snap!
(videos not downloadable on iPad and iPhone - see The Back App for downloading to these devices)
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