The Mighty Quadratus: Part 1

Today we explore the Quadratus lumborum and its functional anatomy.

It is useful to think of the QL as having two 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. 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 posterir. Approximately half of the fascicles of this second division act on the twelfth rib; the rest act on the lumbar spine.

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, 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) type II motion is normal, and now the QL becomes prime mover. Due to the angle of attachment here, it can create shear and potentially contribute to injury.

Whew!! Stay tuned for the QL and gait tomorrow!

Yup, if you are reading this, you are a gait geek too!!

Shawn and Ivo