SI joint dysfunction tends to begin with an injury to the ligaments that are meant to hold the joint in place. This can happen through blunt force, like falling on your butt, or through repetitive motions and sports that subject the ligaments to more force than they are able to handle over time.
In general, I think these factors can be grouped into two main categories:
Acute Onset– symptoms that arise quickly and abruptly in response to one specific event, such as an injury.
The SI joint is made to absorb a lot of force and disperse it throughout the body (both transmitting force up from the legs and down from the trunk). However, it’s possible to experience an event or perform an action that will create too much force for the joint to bear.
One pretty common way to injure the SI joint is in a fall. When you fall and your pelvis hits the ground, it can send more force through the SI joint ligaments than they’re meant to handle, and they can become sprained (similar to how can sprain the ligaments in any other joint, such as the ankle). This is how Kerry (a reader who agreed to share her story with you) first injured her SI joints– she slipped on an icy sidewalk.
You can sprain the SI joint ligaments through anything that creates a very forceful impact on the pelvis. I know another woman who injured her SI joint by holding her foot down on the brake when her car was rear ended. The force of that accident ended up sending more force through her right SI joint than the ligaments could handle, and they were sprained.
Chronic Onset– symptoms that built up over time.
A major factor here has to do with muscle weakness or imbalance.
Muscle imbalance refers to the concept muscles might be pulling unequally on a joint. It’s not necessarily that one is super weak or one is super strong; it just means that their functions aren’t balanced when they are supposed to be.
For example, one potential cause of SI joint dysfunction can be tight hamstring muscles (the muscles in the back of the thigh). These muscles attach to the hip bones, so when they are chronically tight, they’re chronically pulling on the hip bones (and, therefore, on the SI joint).
How does this happen? It’s not like the hamstrings developed a freakish level of strength overnight. Instead, it might be that the person has developed dysfunctional movement patterns which have caused other muscles in their body to become weak. The hamstrings might be overworked because they’re trying to compensate for these other weak muscles. So a good strengthening program would restore balance here.
Another chronic cause of SI joint dysfunction that I’ve heard is having a wallet in your back pocket and then sitting on it all day at work. (I suppose this is more relevant to men, wardrobe-wise). Sitting like that, day in and day out, can create uneven stress on the SI joints, which are meant to distribute body weight equally. (Credit to Madden PT for pointing this out!).
A combination of both:
I, personally, had both acute and chronic factors that led to my SI joint problems. The chronic factor is that I had been suffering from a knee injury for weeks. I had been unable to exercise, so my muscles were weak. And when I did walk, I was limping, which means I was putting stress on my muscles and joints unevenly.
However, I also had an acute factor, in the form of blunt force hitting one of my SI joints. I was actually at the hospital to get an x-ray for my knee. I was having trouble walking, so I went to sit down in one of the hospital wheelchairs. I thought I was about to sit on a soft seat cushion, so I dropped down, exhausted, only to find that the cushion was not so much a cushion so much as a piece of fabric stretched over a metal bar.
The back of my right hip (aka my right butt cheek) slammed down super hard on the metal bar.
Looking back, I believe that the impact of my butt hitting that bar was what caused the initial sprain of my ligaments, although it took a while for the symptoms to fully manifest.
Without this precipitating incident, I might never have developed SI joint dysfunction. However, I also believe that the chronic factors of being weak, out of shape, and using my muscles uneasily, also made things a lot worse.
It’s possible I might not have really noticed my initial ligament sprain that much, or that it wouldn’t have gotten so bad, so quickly, if I hadn’t also been dealing with this knee injury at the exact same time.