Roman engineers perfected the arch – can your sacroiliac joints take the stress?

It all comes down to the principles of engineering.

When you’re standing up, gravity is pulling the weight of your torso straight down.

Fortunately, you have two legs and two feet to support you.

Unfortunately, they’re off to each side.  Neither of them is directly under your center of weight.

Roman engineers designed arches to hold up a structure using supports on each side. How does your body pull off this design feat?

In your body, the central vertical force of gravity is transmitted through the sacroiliac joints on either side.  They link the sacrum to the hip bones.

Then, as the song goes, the hip bone’s connected to the thigh bone, and so forth and so on down to your feet.

Sacroiliac Joint

What can go wrong with this brilliant system?

Shear stress.

The body has been designed to cope with lots of physical stresses. For example, the force of compression – in the lumbar spine, for instance – squashes the vertebrae together, squeezing the disc in between.

Shear stress, on the other hand, is a force that tries to make one bone side-slip relative to its neighbor.  In the sacroiliac joint it’s easy to visualize the effect. Your body weight is trying to force the sacrum downward between the two hip bones. (The ilium – plural ilii – of the picture above).

The situation is challenging enough when you’re standing on both feet. When you’re walking, each step involves shifting to one-sided weight-bearing. That focuses all the shear stress on one sacroiliac joint at a time.

How the Body Adapts to Shear Stress of the Sacroiliac Joint

First, the well-organized body minimizes shear stress by engaging core support – contracting the oblique and transverse abdominal muscles to limit the amount of side-to-side weight shift with each step. This reduces the stress on the sacroiliac joints.

Second – contracting your hip rotators (i.e. the piriformis muscle) cinches together the sacroiliac joint as you shift your weight onto it. This stabilizes the sacroiliac joint so it can better accommodate shear stress.

Third – the tough ligaments spanning the sacroiliac joint itself are the body’s last line of defense against shear stress.  Unfortunately, when your first two coping mechanisms aren’t working robustly, too much stress is placed on the sacroiliac ligaments. The result is pain or injury. Over the years, as your ligaments lose their resilience and deteriorate with age, your margin of safety becomes smaller and sacroiliac pain becomes more likely.

Preventing Sacroiliac and Piriformis Pain

1. the plank pose strengthens your core muscles and trains your brain to engage them effectively
2. balancing exercises on one leg develop supportive strength of the piriformis
3. when standing, avoid sagging onto one leg
4. when carrying, hold the weight on alternate sides
5. stretching the piriformis will help keep it in top shape

Your Doctor of Chiropractic Can Help Protect You from Sacroiliac and Piriformis Pain

Your doctor of chiropractic is uniquely qualified to

1. Make sure you’re using good principles of movement organization when you stand, walk, or carry
2. Recommend and review core support exercises with you
3. Analyze and correct alignment problems in the feet, knees, hip, or spinal joints that could lead to pelvic imbalance and increased sacroiliac stress
4. Fashion customized foot orthotics to balance forces affecting the sacroiliac joint
5. Manually release trigger points in the piriformis muscle
6. Analyze and correct an altered or restricted pattern of glide in the sacroiliac joint

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