Low Back Pain Part I: Anatomy

Spine and Pelvis

What is our low back? What are we referring to when we say our low back hurts? Let’s first take a look at the bones that make up our low back - the vertebrae in our spine and our pelvis. We have 24 vertebrae in our spine connecting our skull to our pelvis which allow us to freely flex, extend, and rotate our body to enable movement. Our lumbar spine consists of five vertebrae starting just below our rib cage extending to our sacrum where they complete the spinal column. The pelvis consists of our sacrum (the base of our spine), our coccyx (tailbone, which sits right below our sacrum), and the ilia, pubis, and ischium which form the wings of our pelvis and the joint for which our femur attaches. The sacrum and coccyx start out as separate pieces when we are born but fuse together as we age.

The parts of the pelvis that are related to the low back are our sacrum and ilia, AKA the wings of our pelvis. The sacrum is sandwiched between our two ilia and form our right and left sacroiliac (SI) joints which are prime suspects in causing low back pain. The SI joints are robust joints that are fortified with multiple ligaments and tendon attachments to some of the strongest muscles in our body. These joints are important for dispersing the forces of gravity that run through our body as we move and bend while stabilizing the transition of our upper body to our lower body. Without the the diffusion of these forces, the impacts of gravity would continue to different joints along the anatomical chain such as the ankles, knees, and neck causing pain and instability. Due to their role in stabilization, there is not a ton of motion in our SI joints, but there is still movement present. Our SI joints can become stuck or hypermobile due to the rotation of the sacrum or ilia and cause back problems. Here is a list of the major muscles and ligaments that have attachments to our pelvis that can influence the movement and stability of our SI joints.

  • Sacroiliac ligament
  • Iliolumbar ligament
  • Sacrospinous ligament
  • Sacrotuberous ligament
  • Gluteus muscles (maximus, medius, minimus)
  • Piriformis
  • Tensor fascia lata (TFL – forms IT band)
  • Quadriceps (vastus medialis, vastus lateralis, vastus intermedius, rectus femoris)
  • Hamstrings (semitendinosus, semimembranosus, biceps femoris)
  • Sartorius
  • Gracilis (groin muscle)
  • Adductors (groin muscles - longus, brevis, magnus)
  • Pectineus
  • Latissimus dorsi
  • Quadratus lumborum (QL)
  • Abdominal muscles (rectus abdominus, external oblique, internal oblique)
  • Psoas

As as we can see, low back pain can become quite complicated to properly diagnose. What may be a piriformis issue for one person could be a QL problem for another, even though they both have similar SI joint dysfunction. Chiropractors spend countless visits adjusting the pelvis in an attempt to introduce motion so it will move back into place. Eventually this may work, but we need to address the muscles that are pulling the bones out of position in the first place to truly make progress with back pain. We don't want your back pain to feel better only when you see your doctor, results should last well beyond your appointment.