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Measure Joint re-positioning with MOTI

Updated: May 19, 2021

The guys from the R&D team are back from the lab with new data where they used MOTI to measure joint re-positioning. But what is joint re-positioning, what can it tell us and what can we use it for?

To answer this, we quickly need to revise how our body is designed with regards to sensing where it is in space. We have written a bit about it previously (see here). In short, in our body we have sensors built into our joints, ligaments and muscles that help us plan and coordinate our movements. For joint re-positioning, it means that we are able to start in a particular position with e.g. our neck, move out of that position and then find back to the starting point with pretty good accuracy (we are talking a few degrees here ;-)). This is possible because of the millions of receptors we have in and around our joints that continually send information to our brain. The brain then processes the information, assesses, re-calculates and then creates an output that matches the task required of the system. Pretty smart, right?

Ok fair enough, but why is it important to measure this?

In injury, the information from the receptors in and around our joints is disturbed and, in some cases, lost for good. A good example is when we have an injury to the ligaments around the knee or in the neck when we sustain a painful whiplash injury to the neck. In whiplash in fact (which often occurs in e.g. car accidents), it has been shown that patients have a worse re-positioning sense than those who have neck pain without a previous history of trauma. Moreover, it has been shown that those who have neck pain without a history of trauma (so no whiplash), have a worse joint positioning sense than those with no pain at all. What do we make of that? What this may tell us is that pain per se affects our ability to plan and execute accurate movement. Moreover, an injury to ligaments and muscle seems to further affect our performance.

This knowledge is important and has helped researchers and clinicians to better understand the underlying cause of symptoms and thereby guide the choice of treatment. But…assessing joint re-positioning is difficult with the naked eye (reads = impossible) because as mentioned above, the margins can be small. Significant, but small and can therefore be difficult to capture in a clinical setting without help from advanced equipment, designed for such purposes.

Can MOTI be used for this?

Finally, we got to the point of this blog. MOTI has a function to measure joint re-positioning off-set, recently, we conducted a small study where we investigated whether/if/how MOTI performed when assessing joint re-positioning sense. What we did was we included 14 healthy people from a university population and asked them to participate in an experimental session where the joint repositioning sense around the wrist was investigated. In the session we attached MOTI to the dorsum of the hand (see figure 1). The wrist was then passively moved out to a reference point measured with MOTI into flexion or extension. Upon return to the starting point, the participant was asked to move the wrist out to the same position as before, with the eyes closed.

Figure 1 Experimental setup during the joint re-positioning task

Interestingly (but perhaps to no surprise), the participants were not spot-on in finding the same position again. What was perhaps more interesting was that their ability to find the same position into extension was poorer than finding the same position in flexion (see figure 2). For this can be many reasons. The most plausible one is perhaps that as we use the flexors of our forearms more during everyday life than the extensors (e.g. when writing this blog), we get more proprioceptive training and therefore become better at positioning our fingers the right place on the keyboard.

Figure 2 Joint re-positioning in Extension (blue bar) and Flexion (red bar)

Future steps – MOTI and joint re-positioning

This small study showed that MOTI can be of use in measuring joint re-positioning. Needless to say, more studies investigating the diagnostic accuracy of MOTI for such purposes are needed. As you might guess, these are on the way so stay tuned.



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