Lower Back Lumbar Segmental Instability

Someone with a lower spine that frequently moves through a larger-than-normal range of movement is more susceptible to low back pain. This tendency of moving beyond its normal range is known as lumbar segmental instability.

The normal range of the movement is defined as the neutral zone. A person with lumbar instability tends to move beyond the normal range of movement into the extreme end ranges.

What keeps the spine stable?

In order to understand what causes lumbar segmental instability, we first need to understand what keeps it stable in the first place. The human body holds the spine stable or steady through the help of three basic structures – the passive, active and neural structures.

1. Passive structures in the lumbar spine are the vertebrae, the discs, then joints and ligaments. These are structures that do not move.
2. Active structures are the global and local muscles. These contract or relax depending on the direction of the force required.
3. And finally the neural structures; nerves that control and direct the muscles. This control is also known as motor control.

A stable lumbar spine segment coordinates global and local muscles using the motor control system to supply compressive forces along the spinal passive structures for stability. This coordination helps maintain the spine's normal curvature at a segmental level as we move about.

Active Structures

The global muscles include:

• Rectus abdominis,
• External oblique
• The thoracic part of lumbar illiocostalis (an erectae spinae muscle). ·

These three muscle groups are large torque producing muscles that provide general trunk stability and allow movement to occur.

The local muscles attach directly to the lumbar vertebrae. They are:

• Lumbar multifidus,
• Psoas major,
• Quadratus lumborum,
• Lumbar parts of lumbar illiocostalis and longissimus (more erectae spinae muscles),
• Transverse abdominus,
• The diaphragm and
• Posterior fibres of internal oblique.
• Interspinalis/ Intertransversii

These muscles control the segmental stability that is lacking in this condition.

The two lowest spinal segments, L4 and L5 vertebrae, are the most susceptible to segmental instability. This could be due to pathological/ degenerative changes to the passive structures that sometimes show up on x-rays. Instability can also occur if there is a loss of motor control and muscle strength/stamina within the neutral zone.

What does it feel like?

A person with lumbar segmental instability typically has a patient-history something along these lines.

1. Back pain may have started after a direct injury to the area, or it may have just developed gradually.
2. The pain tends to be recurrent and has more debilitating effects as time goes on.
3. That person will try to do as little as possible in an episode of pain. According to a survey (O’Sullivan 1997), people most commonly describe the pain sensation as · catching, · locking, · giving way or · feeling of instability.

Classically, the most painful postures are sitting or standing for long periods of time, or being in bent over postures.

The most painful movements are

• bending forwards,
• moving unexpectedly quickly,
• standing up straight after being bent over, lifting or sneezing.

So basically….

The lumbar spine moves in an uncontrolled manner, causing pain. Because the big muscles and little muscles don’t work together properly and the body is unable to control each segment as the body moves.

How do I get rid of it!?

A physiotherapist will need to perform an assessment to find out what type of segmental instability is present (and the type of control that is lacking due to which structure – passive, active or neural). Based on the findings, an intervention will be planned.

In cases where the passive structures have degenerated, it is often possible to train the active and neural structures to compensate for the lower level of stability provided by the passive structures.

With this sort of condition, the exercises that are required are more ‘brain’ exercises than ‘muscle’ exercises. A new way of moving has to be re-learnt, and it requires a lot of concentration.