Flexion Bias and Your Back Pain

With some back conditions, specific positions can change the symptoms. These positions are known as biases and they include flexion and extension.

These biases are also called direction preferences. If your back feels better and/or your symptoms abate when you bend forward, for example, it's likely that the injury or condition you experience has a flexion bias.

A bias occurs due to the movement of tissue in the joint. With certain position changes, the relationship of space, muscles, tendons, ligaments, cartilage, and bones changes slightly within and around a joint, worsening or relieving painful pressure and compression. And defects in tissues—such as bone spurs or out-of-place structures—will move slightly with position changes as well.

How Does Flexion Affect Back Pain?

Spinal stenosis, which is a condition that narrows the space in the intervertebral foramen, generally has a flexion bias. Many people who have pain due to spinal stenosis find that bending their spine forward (aka spinal flexion) makes it feel better. 

The reason is that bending forward makes more space in the intervertebral foramen. This, in turn, allows the nerve that passes through the foramen to do so without being touched or pressured by nearby (and quite often misshapen due to arthritis) bone.

Other conditions that usually have a flexion bias include spondylosis and spondylolisthesis. For injuries and conditions with a flexion bias, symptoms tend to increase when your back is extended (arched).

Extension Bias

The opposite of flexion bias is extension bias. As you can probably guess, an extension bias occurs when the movement of arching your back makes your symptoms feel better. 

Examples of conditions that tend to have extension biases are herniated and bulging disc. People who have either of these conditions often find that when they bend forward (into spinal flexion) their symptoms worsen, and when they arch their back, it feels better.

Directional Preferences Help Classify Your Low Back Pain

Flexion and extension bias is part of a non-pathoanatomical system of classification. It's used for mechanical low back pain caused by disc problems, facet joint pain or dysfunction, sacroiliac joint dysfunction, and spinal instability due to a problem in the pars (an area at the back of a vertebra where processes emanate and become part of the facet joints.). 

The non-pathoanatomical system takes its cue (for evaluation and treatment choices) from the symptoms you report and what your therapist observes in your movements. This system is used in the McKenzie method and other physical therapy treatment methods.

The pathoanatomical approach to classifying low back pain is based on identifying structural changes and their effects through a physical examination, which includes a neurological examination. Defects in movement, sensation, and reflexes are used to help identify the cause of back pain. And diagnostic tests can visualize structural changes, such as a herniated disc or a compressed nerve.

These two diagnostic systems are used together to help your medical team understand how structural changes in your back are affecting your pain and movements. And all of this is used to help design the best treatment plan for your back pain.