Sciatica is a fairly common cause of back pain. It is characterized by sharp nerve pain that shoots down the buttocks and into the leg, usually on one side of the body. It is important to note that another common cause of lower back pain, sacroiliac (SI) joint dysfunction, can cause a very similar pain pattern. Sciatica is more well-known than SI joint dysfunction, so the chance of receiving a proper back pain diagnosis for SI problems is lower.
Sciatica is caused by a compression or irritation of the sciatic nerve, which runs from the lumbar spine down to the foot on each side of the body. The condition has a number of potential causes, including lumbar disc herniation and piriformis syndrome. The pain generally starts in the lower back and can travel as far down as the foot.
The SI joints are located at the back of the pelvic girdle where the hip bones (ilia) meet the base of the spine (sacrum). A number of situations can cause an SI joint to be either too mobile or not mobile enough. Impact from a fall, for example, can wrench the joint out of its normal limited range of motion. Hormonal changes during pregnancy cause ligaments to loosen, potentially causing the SI joints to become hypermobile. Poor body mechanics, such as gait problems due to flat feet or leg length discrepancy, can cause excess stress on an SI joint. Any biomechanical dysfunction affecting the alignment of and forces on the pelvis can irritate one or both SI joints. The symptoms of this condition are very similar to sciatica: a sharp pain that shoots through the buttocks and down the leg.
A few common discrepancies between symptoms may help to differentiate the two conditions. SI joint pain often doesn’t travel lower than the knee, though it can; sciatica symptoms often occur below knee level. If the SI joint is hypermobile, it can tug on the dense web of ligaments and muscles that support it. Pain from this can be expected to manifest mainly in the hips and lower back, and may radiate to the groin. SI pain is usually triggered by standing on the leg on the side of the affected joint.
On top of the similarity of symptoms, distinguishing between these two conditions is further complicated by the fact that SI joint dysfunction and sciatica may co-exist. When an SI joint is irritated, either by hyper- or hypomobility, it becomes inflamed. The sciatic nerve, which runs near the joint on its journey down to the leg, can become irritated by this inflammation.
Solidifying a proper diagnosis is best done with professional help. Doctors generally order imaging tests like MRIs when sciatica is suspected; they look for disc protrusion or bone spur interference as causes. If these are lacking, it’s a good idea to seek out a physical therapist or any other health professional trained in gait and general movement analysis. These experts can analyze how you move to decipher any abnormalities at the pelvic level. Another way to test the SI joints is to have an injection; a numbing agent is injected into the joint and will resolve pain if the joint is its source.
It’s important to find the true cause of your pain because treatments for these two conditions are different (unless SI joint dysfunction is causing sciatica). Chiropractic care may be used for either, but the target joints are different. Exercise therapy is also used for both conditions, but the exercises prescribed differ. Whether the SI joint is hyper- or hypomobile also needs to be determined, since hypermobility requires stabilization and hypomobility requires mobilization.
Being aware of common misdiagnoses puts you in a position to find your real back pain cause. There is significant overlap of symptoms between sciatica and SI joint dysfunction; be aware that these two conditions are often distinct phenomena that require different treatments.