The iliolumbar ligament is an often overlooked bit of soft tissue. This ligament connects your hip bone (the ilium) to the lumbar spine, which is why it is called the iliolumbar ligament.
First, a quick review of what a ligament is. Ligaments are located at joints and they are responsible for making sure the joint is stable. For example, when you kick your leg out your shin bone stops and does not continue past the knee joint because of the ligaments in your knee. Ligaments are there to maintain stability at joints by limiting movement to a certain angle. Another example, this one involving a common injury, is the ankle. The most common ankle sprain is when someone “rolls” their ankle and the ligaments at the outside of the foot are injured. The rolling over the foot stretches the ligament enough to tear it, and that is the sprain.
Ligaments are all over the body, at all your joints. The iliolumbar ligament is tasked with maintaining stability at the lumbosacral spinal and pelvic joints. Just like other ligament injuries, the problem occurs when the joint moves beyond it's normal range of motion for some reason. This need not be a sudden movement but can also be caused by postural issues. For example, people who sit cross-legged with one ankle on the opposite knee are actually causing stretching of the lateral ligaments of the crossed knee. Over time this may cause and cause instability of that knee. When an individual sets down for much of the day they are stretching the muscles and ligaments of the lower back, and over the long term this will weaken and stretch these muscles and ligaments. Slouching in a seat puts a lot of pressure on the lumbar spine and can really stretch that lowest spinal joint where it meets the hip and tailbone. If this posture is a regular occurrence, then over time this may cause instability and tearing of the ligament. Even if the posture alone does not cause the injury, the instability created by the poor posture stretching the ligament will make an offense more likely whenever this person uses their back.
An injured ligament can feel like burning pain becoming sharper with movement. An iliolumbar igament injury will probably cause enough localized inflammation to irritate the scaatic nerve, which would then mimic a disc injury to the low back. It is difficult to differentiate these conditions without orthopedic testing at a chiropractor or orthopedists of office, or advanced imaging like MRI.
It is always best to consult a medical professional who specializes in lower back pain if you are experiencing any pain such as this type.