Pain Caused By Low Back Ligaments

By Ben Benjamin, PhD
March 22, 2010

Pain Caused By Low Back Ligaments

By Ben Benjamin, PhD
March 22, 2010

Q: An injured sacrotuberous ligament can cause pain down the back of the leg. True or false?

A: True. This is its referred pain pattern. The sacrotuberous ligament is a thin, fan-shaped structure that runs obliquely downward from the posterior-superior and posterior-inferior iliac lines and the lateral margins of the sacrum and coccyx, inserting on the ischial tuberosity of the pelvis (the bone you sit on). (Figure 1)

Each structure in the low back has a specific referred pain pattern associated with it (Figure 2). For example, the sacroiliac ligaments generally refer pain straight across the lowest portion of the back. The ilio-lumbar ligament refers pain on one side of the low back across the top of the ilium, the lateral hip, and the groin area. The sacrotuberous ligament has a distinctive pattern. It refers pain down the central portion of the back thigh, and if more severe, down the central portion of the calf into the heel. This injury is frequently confused with a hamstring injury when the pain is felt only in the lower buttock and down the back of the thigh.

There are a few easy steps to check whether this type of pain is originating in the hamstring or in the sacrotuberous ligament. First, have the person bend forward with the knees straight. Note the pattern of pain. Pain down the back of the thigh can be caused by either structure, but only the sacrotuberous ligament refers pain into the calf.

Now, have the client lie down and hold the knee at a 90° angle. Ask them to pull the heel toward the buttock as hard as they can while you resist with equal force (Figure 3). If this test is painful in the hamstring region, you know there is a hamstring injury, because resisted tests place stress on muscles and tendons, not on ligaments.

If you suspect an injury to the sacrotuberous ligament, a final step in assessment is direct palpation. Injury to this structure usually occurs at the lateral margins of the sacrum, rather than the attachment to the ischial tuberosity. You can access the ligament with the client lying prone, but it is more easily accessible with a client in a side-lying position with the knees drawn up.