The anatomy of functional leg length discrepancy

If your length length discrepancy is functional, it means that it’s not a structural issue—it’s a result of how you’re using your body. Functional leg length discrepancy may also be diagnosed as lateral pelvic tilt or pelvic torsion.

At the root of functional leg length discrepancy is chronic tightness in the quadratus lumborum, internal and external obliques, and iliopsoas. These are all strong core muscles that laterally tilt the pelvis and provide essential core stability in full-body movements. Since we use them so much, it’s very easy for them to become chronically tight as a result of overuse and imbalanced movement patterns.

When you have functional leg length discrepancy, other back muscles that laterally flex the spine (bend the spine to one side) will likely be tight as well, including the longissimus, iliocostalis, and latissimus dorsi. If your lateral flexion progresses to more than 11 degrees, it may be diagnosed as scoliosis.

Our entire body is connected like a pulley system. When one part moves out of alignment, the rest of our body will adjust to balance us out. So, if you’re hiking one hip up, you’re likely compensating for this misalignment by shifting other parts of your body out of alignment as well.

For example: If you’re hiking your right hip up, you may be shifting your weight to your left side, and the left side of your rib cage might be pulled down toward your left hip. So, the muscles on the left side of your waist and lower back and in your left hip will be tight too—just in a different pattern than on your right side. They’ll be pulling your rib cage downward instead of hiking your hip up.

Another way we compensate for lateral pelvic tilt is by rotating our body in various ways. It’s very common to have some rotation of the hips, pelvis, and spine along with functional leg length discrepancy.

Here’s an example: If you’re using your right and left sides differently, and standing with more weight on one side than the other, you can easily develop lateral (outward) rotation on one side and compensating medial (inward) rotation on the other. You might inwardly rotate the hip that you tend to lean on, and outwardly rotate the hip that you’re hiking up. Your gluteal muscles will likely become tight on both sides as a result of this rotation, because different parts of our gluteal muscles rotate our hips both inward and outward.

In this pattern, your internal rotators and adductors (the muscles on the inside of your thighs that pull your legs together) will become tight on the side that you’re leaning on and rotating inward. These muscles attach to the bottom of the pelvis, so they can pull your pelvis downward on that side, exacerbating your overall pattern.

If your lower hip is inwardly rotated, your tensor fascia latae on that side will become tight, creating tension in your iliotibial band. This tension, along with increased body weight being put on this side, can easily lead to knee problems.

Pelvic torsion also commonly occurs with functional leg length discrepancy. This describes the misaligment of the pelvis when one side is tilted forward and the other is tilted backward.

The pelvis can also be rotated on the transverse plane (imagine a Lazy Susan). So, one hip might be pulled forward while the other is pulled backward.

This twisting will continue up our spine; our obliques, multifidi, and rotatores will become tight, rotating our vertebrae and leading to adjustments in our upper body. We may pull one shoulder backward and the other forward, pull one shoulder downward and the other upward, and turn or tilt our head to one side.

Full-body patterns of posture like what I’m describing begin in the core of our body; this is where our strongest muscles are located and where we initiate movement. Movement of our arms and legs are extensions of the movements that begin in our core. So, while we might experience misalignment, pain, or other symptoms in various areas of our body, it’s extremely important to address the root cause of our problems by releasing chronic tension and imbalances in our core muscles. (I’ll talk about how to do that in the last section of this post).