The words hypermobile and hypomobile can be used in a few different ways to describe the SI joint, or any joint in the body.
Let’s start by talking about what these words actually mean.
Hypomobility refers to a joint that’s moving less than a healthy joint would. (The prefix hypo- means “less”).
Hypermobility refers to a joint that’s moving more than a healthy joint would. (The prefix hyper- means “more”).
I have experienced both hypo- and hypermobility in my SI joints. And while it’s important to know exactly why your SI joints are causing pain (are they moving too much or too little?) these issues can best be thought of as two sides of the same coin.
When an SI joint locks up, it means that the hip bone has moved out of alignment relative to the sacrum and gotten wedged in a non-optimal location. Technically, that’s a case of hypomobility— if the hip bone is stuck, it’s no longer moving as much as it’s supposed to.
But, to take a step back for moment… how did things get this way? How did the hip bone move so far out of its normal range of motion that it is now wedged abnormally against another bone?
Hypermobility is what allowed that to happen in the first place– the ligaments that were supposed to hold the hip bone in place weren’t doing their job.
Two sides of the same coin
So, you can see how in cases of ligament instability like mine, the terms hypo- and hypermobility can simply refer to the same problem at different moments in time. Both terms simply refer to how much the hip bone is moving in relation to the sacrum.
According to my PT mentors, it’s pretty common to find that when one SI joint is hypomobile (stuck), the other is hypermobile. It’s the body’s attempt to compensate– when motion is restricted on one side of the body, the body will find a way to increase motion on the other side.
I use the word hypermobile in another way on this blog as well.
So, what I just explained to you above is how hypo- and hypermobile can be used to explain the amount of motion in a given joint.
However, the word hypermobile can also be used to describe a genetic condition where your body doesn’t make connective tissue properly.
I personally was born with joints that are hypermobile– that is to say, my ligaments naturally move more than they were intended to do. This has left me vulnerable to all kinds of injuries and problems, because when you have hypermobile joints, it ends up putting extra stress on the ligaments that hold the joint together.
I don’t want to go into too much detail and totally lose you in this post, but if you want to read more about this type of joint hypermobility, you can check out this post:
I also describe a few additional factors in what makes a joint more or less stable in:
That’s all for now! Hope this was helpful!