lower back pain and instability


Spinal instability is a complex problem and many factors contribute to it.  It can be the result of an injury, degenerative aging, or genetics.  Many factors play into spinal instability, not just "weakness of the trunk."  

What is spinal stability? Spinal stability refers to the control and support between segments of the spine.  When there is a problem in the stabilizing mechanisms of the spine to provide support of the segments, spinal instability may be the result.  

Clinical Findings:

Recurrent lower back pain with onset of minor perturbations, symptoms exacerbated by minor provocations; aberrant movement during active motions, feeling of catching in the back at mid points between end ranges, feeling of instability. Not everyone who has chronic or acute lower back pain has spinal instability.

Lets review anatomy and talk about the muscles that contribute to the spinal stability

If you are currently in PT for lumbar instability and have been diagnosed with this condition, it is important that you understand the general roles of the muscles at contribute to stabilization of the spine.

1. Lumbar multifidus- helps control the neutral position of the spine, and controls lordosis; tensions fascia called the thoracolumbar fascia, proprioception and control of shear forces.

In studies, people with chronic lower back pain show atrophy of the lumbar multifidus.  The multifidus shows greater fatigue rate compared to the paraspinals.  Dysfunction is associated with decreased activation, increased fatigue, and change in the muscle composition.  

2. Transversus abdominus- arises  from the TL fascia between the top of the pelvis (iliac crest) and 12th rib.  

Active during trunk movements, helps to provide stability and rigidity, and should be able to contract prior to movement of the limbs; Considered a global muscle

In lower back pain, the TrAb switches roles and studies show that this muscle loses its ability to control spinal stiffness, and becomes inhibited (which makes it difficulty to contract with volitional control in isolation)

3. Internal Oblique

Provides stabilization to the sacroiliac joints and couples the production of trunk flexion, rotation, and sidebending

4.  External Oblique:

Has roles with trunk flexion, trunk rotation, and sidebending, and assists in expiration

5.  Rectus abdominus

Rectus abdominus  has the main role of Trunk Flexion. Generally when people talk of six pack abs, this is the layer they are referring to.

6. Diaphragm: contributes to intra-abdominal pressure and works with the TrAb to increase tension in TL fascia; Increases spinal stiffness to forces and contributes to stability in the upper lumbar spine

7.  Pelvic Floor: Controls intra-abominal pressure and movement at the sacrum and coccyx.

Contributes to intra-abdominal pressure and stiffness of the SI joints

There is increasing evidence that diaphragm and pelvic floor muscles contribute to postural response of the trunk muscles 

8. Psoas Major- hip flexor attaches to the transversus process of the upper lumbar spine; often feels tight in people with lower back pain

9. Quadratus Lumborum:

Sidebands the trunk, stabilizes lower rib cage and controls spinal buckling

10. Hip extensors and abductors:

Weight bearing control of the pelvis

May become overactive with LBP along with the erector spinae muscle group.

Try to review pictures online to make yourself familiar with the anatomy.

Next blog we will discuss ways to retrain these muscles, starting with the deepest layer of the TrAb and Multifidus for neuromuscular re-education.  

Source: MT-ST MAPS Stabilization. 2018,