Thoracic Spine ‘Mostability’
The term ‘mostability’ is not one that you will find in any dictionary, at the moment. Gary Gray coined the phrase meaning a hybrid to define mobility and stability or mobile stability. Basically this means the ability of the body to move with control. There is a strong correlation between these two factors when we look at movement at a local and global level.
When someone’s stability decreases their movement tends to shut down e.g. reaching both arms overhead in bilateral stance compared to single leg stance. Mostability is easily seen in the shoulder, we see someone who has full passive range in the shoulder but loss of active range. The shoulder has the motion but not the stability to control it, in this situation the body will choose to decrease range as uncontrolled motion is a threat to the system.
This is relatively easy to see in the shoulder but not as easy in the thoracic spine. We generally tend to assess this area in sitting as this decreases the influence of the lower quadrant and isolates (ish!) the thoracic spine, but this tells us little about its ability to control movement.
I’m well aware that terms such as ‘stability’ are very vague and interpreted very differently. In this context I am not saying that anything is unstable, in the majority of cases the body is inherently stable so if someone has an ‘unstable spine’ they require surgery!
We the know the thoracic spine is inherently stable at a joint level, but do we look at the bodies ability to control motion at the thoracic spine? Generally not.
Now at this point you may be asking, so what?
Well if we look at human function, a large percentage of the time is spent with our weight unevenly spread or on one leg e.g. gait. So, with this in mind we can see that it maybe relevant to assess the thoracic spine ‘mostability’ with our weight unevenly distributed or on one foot?
So we could look at our basic single plane assessment but increasing the demand with single stance and a toe touch on the other leg for example.
As with any joint in the body we need to look at the Tx motion in all 3 planes and in combination. This is known as coupling or ‘trupling’ ( another Gray-ism). When we move we rarely move in one single plane and due to the osteokinematics of joint motion that rarely happens at this level. So as we rotate to one side we will either laterally flex to the same (type 2) or opposite (type 1) side. These would be coupled movements. Trupling occurs with these motions as we will tend to use the sagittal plane motions of flexion with type 2 motion and extension with type 1 motions.
So what do I do to assess the mostability?
One example would be to stand on you right foot with your left toe touching, reach the right arm overhead to the left and use the left arm to reach round to the right. These motions will assess both the thoracic ability to move and control type 1 motion and also the ability of the right leg to balance and control the motion from the top-down.
What is the relevance of this assessment?
The stance position mimics that of the right foot forwards in gait with the regards to the pelvis and lower limbs. Using the arm as drivers we create the type 1 motions that will occur during the gait cycle, and assess the mostability of the system.
This is just one example of how to assess the thoracic spine’s mostability, we could fix one hand in the frontal plane and driver motion in the transverse plane or vice versa. Using this thought process we can see that there is huge variety to how we assess this key area.
But which is the best way to assess your client?
That depends on the person in front of you, their goals and functional requirements.
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