Who gets it?
There are two types of causes for an SIJ sprain. Traumatic and atraumatic; meaning that it either came from a traumatic onset or something less obvious or something which may have taken a long time to occur.
Traumatic causes include falls, hip fractures, and repeated heavy lifting.
Atraumatic causes include Osteoarthritis, infection, pregnancy, scoliosis, leg length discrepancy and previous spinal surgery.
Population-wise, young adults exposed to traumatic onset via sport and females who are pregnant are more likely to experience an SIJ sprain along with older adults who experience degenerative changes.
The SIJ also known as the Sacroiliac joints are the two points in the lower spine where the hip bones connect with the spine. The joint itself is the connection of the sacrum (just above the tailbone) and the ilium (the big hip bone). This joint is quite stable and secure, responsible for helping absorb shock and evenly dispersing weight from the upper body into the legs. The joint is a synovial joint meaning that it has fluid within it to allow for smooth movement between the cartilage and is surrounded by tissue to secure all that is within it. It also means that there is a risk of injury.
As mentioned before, the SIJ is mainly responsible for transferring weight from the upper body towards the lower body. It also absorbs shock to help us mobilize ourselves (walk) and other movements such as bending at the hip and picking things up. The amount of movement at the joints is quite limited however, this is to maintain that security and stability which is its main role. Men can obtain around 1.2 degrees of movement on average, and women approximately 2.8 degrees. More movement at this joint can increase the probability of obtaining a sprain.
What is a sprain?
A sprain is a term used to describe a joint that has undergone some form of trauma causing damage to the supporting ligaments. This is different to a strain as only muscles and active structures can be strained. The term sprain is commonly used with ligaments in the ankle and knee, however, it applies to joints which have to stabilize and surrounding ligaments too.