Dieser Beitrag ist auch verfügbar auf:
English 
Deutsch (German)
Rotational movements should be avoided in advanced spinal degeneration and after spinal surgery. Why is that?
In this article, I would like to explain to you what generally changes in the spine due to aging. You will quickly notice that the possibilities are manifold and that very individual consequences have to be drawn in each individual case.
At the spine, aging means above all that the intervertebral discs lose water. This results in a loss of pressure and body height. The anterior column loses height what results in kyphosis. This process of kyphosis is exacerbated by the loss of height due to concomitant osteoporosis +/- fractures.
At the same time, the loss of water in the intervertebral discs leads to segmental instability, which must be compensated for by the body. This can happen in two ways: So-called spondylophytes grow on the front and sides of the vertebrae. These bone attachments are painless and stabilizing.
Without stabilization via the spondylophytes, much of the load is transferred via the facet joints, which are not primarily suited for this type of load transfer. The overloading of the joints is simultaneously accompanied by painful destruction of the articular cartilage and significant growth of the joints – facet arthrosis.
Both processes – spondylophytes and facet arthrosis – lead to increasing stiffening of the spine.
Vulnerability
Now, as the spine gets stiffer and stiffer, you don’t immediately think that’s going to make it more vulnerable. But that is exactly the case: a rigid rod breaks, a flexible rope does not. However, the stiffening does not proceed uniformely. Thus, there are areas in the aging spine where peak loads can be discharged. The following areas are at risk:
- Areas of already higher grade instability such as degenerative spondylolisthesis.
- Transition of the rigid thoracic spine (thoracic spine) into the somewhat more mobile lumbar spine (lumbar spine)
- freshly operated segments without screws, e.g. after decompression or disc surgery from behind. Due to decompression, the vertebral arches are weakened and can fracture more easily. Because these fractures are not gaping and are only a few millimeters in size, they usually cannot be diagnosed by x-ray, CT or MRI. However, due to their proximity to nerves, they can cause pronounced pain.
- Boundary areas to stiffening operations
Why, of all things, is the spine susceptible to twisting?
In principle, it can be assumed that force transmission to vulnerable segments is increased in any direction of spinal motion (forward/backward/side-to-side tilt and rotation). However, the moment of force is distributed more homogeneously over the anatomy during tilting than during rotation. Significant shear forces occur at the vertebral arches, especially after decompression. These can then discharge in the form of a fracture. In addition, a person cannot maximize forward, backward or sideway tilt at will under his own power, otherwise he would lose his balance.
The situation is quite different for rotations. The pelvis is fixed and we are used to acting freely in the shoulder girdle, both sitting and standing. Torsion of the trunk is thus an integral part of daily life. As long as the increasing restriction of this degree of freedom is accepted in the course of life, there is no danger either. Various sports activities and physiotherapeutic exercises are aimed at improving the mobility of the healthy or only slightly degenerated spine through rotations. This should be avoided as much as possible in the operated spine for the reasons mentioned above.
More interesting details of the spine – biomechanics
The thoracic spine is less mobile than previously thought
If it was previously assumed that an extraordinarily good rotational mobility existed here due to the roof tile-like arrangement of the thoracic facet joints, this assumption must be relativized.
The essential stabilizer against rotational forces is the rib cage and here in particular the connection to the sternum. If the whole construct is put under load (as it happens physiologically), the amplitude of motion is reduced considerably (see figure opposite, dark bars).
Coupled movements
Flexion in the lumbar spine lowers rotational resistance, allowing 14% more rotation in maximum flexion and 24% less rotation in maximum extension.1Drake JD, Callaghan JP. Do flexion/extension postures affect the in vivo passive lumbar spine response to applied axial twist moments? Clin Biomech (Bristol, Avon). 2008 Jun;23(5):510-9. doi: 10.1016/j.clinbiomech.2007.12.005. Epub 2008 Jan 29. PMID: 18234402. For the thoracic spine, an opposite effect of kyphosis can be assumed, since here there is a compression of the stabilizing thoracic thoracic spine unit. Indicative of such an effect are the above results with and without load.
