Low Back Pain Treated With Repeated Extension

Mar 15, 2017

Corrective Exercise, Orthopedics, Back Pain Relief

Background

If you’ve had low back pain before or work with people who have low back pain, you’ve probably heard about the Mckenzie method and repeated extension. Do you know the story of how Robin McKenzie first stumbled on this idea?

He was working with a patient who was suffering from chronic low back pain with radicular symptoms down the leg. Robin was running late in the clinic and told the patient to go lay face down on the treatment table and that he would be back in a few minutes. What Robin didn’t know, was that the treatment table had been left up at an inclined angle. When he returned to the room, he found his patient lying face down with his head on the elevated portion of the table and his back arched back at a steep angle. Initially, Robin was worried to find his patient in this position because that much extension was thought to really compromise the spine. The patient had been lying there like that for about five minutes and Robin was nervous that he would be in much more pain because of that. However, when he addressed the patient, the patient told him that all the pain in his leg had subsided. From then on, Robin experimented with lumbar extension as a treatment intervention and eventually developed his own method of treatment that has been widely accepted across multiple disciplines.

If you want to hear the story from Robin McKenzie himself, skip to minute 8:38 on this video.

There is no doubt that repeated extension can be an effective treatment intervention for low back pain, especially with disc pathology. However, the mechanisms behind it are controversial and not fully understood. I am not at all questioning the effectiveness of repeated extension, but simply offering some insight on its proposed mechanisms.

Let’s Review Disc Biomechanics

To understand the mechanisms of repeated extension for disc pathology, you must first have a basic understanding of the mechanics of the disc. In many physical therapy programs, the “jelly doughnut” analogy is used to describe disc mechanics. This analogy may hold true for a healthy disc, but does not explain the disc mechanics of a pathological disc.

The lumbar disc has three main jobs. It serves to bind together the vertebral bodies, permit movement of spinal segments, and transmit loads. The actual anatomy of the disc is complex and will not be described in full. Briefly, it consists of a fibrous outer layer called the annulus, and a viscous fluid inner layer called the nucleus. In the lumbar spine, the nucleus sits in the posterior 1/3 of the disc. How does the disc respond to movement?

Forward Bending in a Healthy Disc

• The anterior annulus is compressed and will bulge anteriorly
• The posterior annulus is drawn taut
• The nucleus will translate slightly posterior

Backward Bending in a Healthy Disc:

• The anterior annulus is drawn taut
• The posterior annulus is compressed and will thus bulge posteriorly
• The nucleus will translate very slightly anterior

The image below shows a spinal segment of a person facing to the right.

Now, it is important to realize that the mechanics described above do not hold true for a pathological disc. When the back portion of the annulus has torn and the disc material has bulged posteriorly, the mechanics are different. The intradiscal pressure has been altered and the viscous fluid of the nucleus will now follow the path of least resistance. Thus, forward bending will compress the anterior disc creating a higher pressure anteriorly, causing the disc to bulge further posteriorly. This can increase the disc bulge. What about backward bending?

When McKenzie first theorized how this all works, he suggested that backward bending would push the bulging disc material forward, thus reducing the bulge. This would only hold true if the disc was healthy. Since annulus has torn and the disc has bulged posteriorly, backward bending will actually cause the nucleus to move further posteriorly down the pressure gradient.

The image below depicts what likely happens in a pathological disc with backward bending.

Forward Bending in an Unhealthy Disc:

• May dislodge disc material posteriorly
• Risk of increasing the tear due to build up of tensile force on posterior annulus
• Increases load on disc

Backward Bending in an Unhealthy Disc:

• The anterior disc will still be drawn taut
• Nucleus will move down the pressure gradient posteriorly

Doesn’t this all mean that repeated extension would be a bad thing to do with a pathological disc? Not necessarily.

The theory originally proposed that backward bending can push back the nuclear material into the disc has never been proven. However, repeated backward bending is a common treatment for disc pathology. Here’s why:

How Repeated Extension May Help Low Back Pain

There are many theories out there about why repeated extension works. The following outline of proposed mechanisms is adapted from Dr. Stanley Paris.

1. Gait control theory and Central Desensitization: The firing of large fiber proprioceptors can block the transmission of nociception (pain). This then allows the hypersensitive central nervous system to accept movement. Repetitive motion can help the nervous system to become desensitized to movement.
2. Reduces Fear of Movement: Help relieve the fear of movement and perceived threat of movement. This helps promote functional recovery.
3. Mobilizes Facet Joints: Backward bending actually loads the facet joints and stretches the capsule. Pain-free end-range loading of joints can again help desensitize the nervous system through chemical, and neurophysiological effects. Mechanical stretching of the capsule can stimulate mechanoreceptors and help with muscle inhibition.
4. Elevates the Water Content of the Disc: Repetitive motion has been shown on T2 weight MRI to increase the water content of the disc. This can lessen the irritability of the disc to  peripheral nociceptors (pain fibers).
5. Promotes Nutrition and Circulation: Movement in general can help bring nutrients into the area and enhance local circulation necessary for healing.
6. Reducing Neural Tension: Backward bending causes slackening of the cauda equina.

How To Use These Exercises

Can Repeated Extension Cause Harm?

Yes, of course it can. Backward bending with a pathological disc has the potential to further extrude an already extruded prolapse. It could potentially compromise nerve roots by narrowing the intervertebral foramen. However, if implemented at the correct time, repeated extension exercise can reduce pain and improve overall mobility and function. The best time to initiate backward bending is immediately after disc injury. Maintaining a lordosis (extended lumbar spine) after immediate injury can help allow the outer annulus of the disc to heal.

I do not advocate for anyone to just try repeated extension exercises without a proper examination by a medical professional. It can be contraindicated with certain conditions such as post-laminectomy patients or persons with spondylolysis and spondylolisthesis.

For more information on this topic, I encourage you to read this book. It is meant for patients with back pain and provides tools for the patient to treat themselves. It is also a great read for clinicians.

Thanks for reading! If you have comments or questions regarding this post, please feel free to contact me.

References

1. Fennell AJ, Jones AP, Huskins DWL. Migration of the Nucleus Pulposis within the Intervertebral Disc during Flexion and Extension of the Spine. Spine. 1996; 23: 2753 — 2757
2. Spohr C, Paris SV, Graham Smith A. Disco Myelogram – A Clinical Biomechanical Study of Disc Behavior. IFOMPT Proceedings, 5th International Conference, Vail Colorado, 1992, 28-
3. Paul F. Beattie, PT, PhD, OCS, FAPTA, Cathy F Arnot, DPT, OCS, Jonathan W. Donley, DPT, ATC, Harmony Noda, DPT, Lane Bailey, DPTThe Immediate Reduction in Low Back Pain Intensity Following Lumbar Joint Mobilization and Prone Press-ups Is Associated With Increased Diffusion of Water in the L5-S1 Intervertebral Disc. Journal of Orthopaedic & Sports Physical Therapy 2010 40:5, 256-264
4. Disc images shown above are from Foundations of Clinical Orthopedics Seminar Manual written by Stanley Paris and Peter Loubert for University of St. Augustine for Health Sciences.