Today we are going to look at what I feel is one of the most important muscles to evaluate and treat with low back pain patients, as well as those with gait and lower extremity disorders. 

Let's look at some of the functional anatomy of the QL.

It is useful to think of the QL as having three divisions. Though they can’t act independently, it helps when thinking about it from a functional standpoint. The first, or lower division arises from the medial portion of the iliac crest and adjacent iliolumbar ligament, inserting onto the transverse processes of the lumbar vertebrae, running in the coronal plane from lateral to medial and posterior to anterior in the saggital plane. These are often called the "iliolumbar" fibers. The second, or upper division arises from the lumbar transverse processes of the upper 4 lumbar vertebrae at their upper and lower corners and insert into the inferior border of the 12th rib, running in the coronal plane from medial to lateral and in the saggital plane from anterior to posterior. Approximately half of the fascicles of this second division act on the twelfth rib; the rest act on the lumbar spine. These are often called the "lumbocostal" fibers. The last set, or 3rd division runs from the iliac crest laterally to the 12th rib and are called the "iliocostal" fibers

The QL is primarily a coronal plane stabilizer. Acting unilaterally with the lower body fixed and feet on the ground, it laterally bends the lumbar spine. Normally, with lateral bending of the lumbar spine while in a lordotic posture, we see what is called type I coupled motion, or deviation of the spinous process to the side of lateral bending. The QL would oppose (or perhaps more correctly attenuate) this motion,possibly acting eccentrically, having a moment of moving the spinous process to the opposite side of contraction. Perhaps it is when the QL become dysfunctional, pulling the ipsilateral transverse process outward (and thus moving the spinous to the opposite side) that we see aberrant (or Type II) motion in the lumbar spine. It is interesting that when the lumbar spine is flexed (as in sitting or forward bending, or even a loss of the lumbar lordosis) type II motion is normal, and now the QL becomes prime mover. Due to the angle of attachment here, it can create shear in the lumbar spine and potentially contribute to injury.

The Quadratus and Gait

Acting unilaterally without the ipsilateral foot fixed on the ground, it can raise the ilia on the side of contraction (as in a pull up or side bend on a Roman chair). The quadratus lumborum is more active than other muscles during isometric side support postures (like planks) where the body is held horizontally almost parallel to the floor as subjects supported themselves on one elbow on the floor together with both feet.

It is active during single limb support during stance phase of gait on the contralateral side (along with the external oblique on that side) to elevate the ilium. This is coupled with the ipsilateral (stance phase leg) anterior fibers of the gluteus medius and minimus pulling the iliac crest toward the stable femur.

Sahrmann (1) states “the QL is optimally situated to provide control of lateral flexion to the opposite side via its eccentric contraction to provide control of the return from lateral flexion via its concentric contraction. The muscle is also positioned to play a role in the rotation that occurs between the pelvis and spine during walking”. This makes you really think about the interplay of this muscle, and another stance phase stabilizer, the psoas major, which attaches opposite the QL on the anterior aspect of the vertebral body, IN FRONT of the transverse process.

Acting bilaterally, it extends the lumbar spine, deepening the lordosis and acting to limit anterior shear of the vertebral bodies.

It is able to stabilize the 12th rib during forced expiration, thus acting as an accessory muscle of respiration. This fixation is important when we need to superimpose pelvic movements upon it. Furthermore, it increased activation in response to increasing compression in static upright standing postures.

Think of the QL, especially during gait abnormalities or recalcitrant low back pain. The more it is stressed, often the more it is activated. If someone had mild weakness of the stance leg gluteus medius, it may be called into play to pick up some of the slack. Expect to see increased activity paraspinally, with particular attention paid to the 12 rib attachments.

In our flexor dominant society, the QL may play a role in generating unilateral shear forces on the lumbar spine (along with the ipsilateral psoas), especially in individuals with poor ankle rocker or decreased hip extension.