Muscles vs. Ligaments

By Ben Benjamin, PhD
May 29, 2009

Muscles vs. Ligaments

By Ben Benjamin, PhD
May 29, 2009

Q: How do you determine whether back pain is being caused by a muscle injury or a ligament injury?

A: The best way to differentiate back pain caused by muscle injury from pain caused by a ligament injury is by noting which type of assessment test causes pain. With a muscle injury, resisted tests cause pain; with a ligament injury, passive tests cause pain. In a resisted test, the client actively engages their muscles, attempting to perform a movement, and the therapist provides resistance so no motion occurs. This type of action (often referred to as an isometric contraction) puts muscles and their tendons under stress. In a passive test, the client does not perform any muscular exertion, but instead stays passive, like a rag doll. This tests structures that do not initiate movement, such as ligaments, bursas and joints.

To illustrate the difference between the two types of tests, I'll give an example of each. First is a test for injury to the erector spinae muscles of the low back - a resisted test. To assess these structures, you have the client lie prone on the table and then place your hand on their upper back. As the client tries to extend the low back by lifting the upper back against your hand, you apply an equal and opposite force so no movement occurs. (Figure 1) When the erector spinae muscles in the low back are injured, this test causes pain in the low back.

In contrast, to test the iliolumbar ligament, the ligament that attaches the L5 transverse process to the ilium, you have the client stand passively and simply allow their body to bend to the side. (Figure 2) This movement stretches the iliolumbar ligament, so when that ligament is strained, the test causes pain in the low back.