A basic science study that used a porcine cervical spine model to produce disc prolapse subsequently exposed to an extension protocol.
This study investigated whether extension or combined extension and side flexion could move the displaced portion of nucleus from the annulus towards the nucleus.
SUMMARY OF BACKGROUND DATA:
Previous research has established that repeated flexion can create disc prolapse, the question here is whether repeated extension can reverse the process.
The C3/4 segments of 18 porcine cervical spines were dissected and potted in cups. Specimens were preloaded, then axially compressed (1472 N), and repeatedly rotated in either pure flexion or combined flexion and side flexion at a rate of 0.5 degrees /s. Specimens that prolapsed were axially compressed and repeatedly and rotated into extension.
Based on a blinded radiologist’s review of the radiograph images, all 18 specimens contained healthy discs before testing, but after testing 2 of the 18 specimens had endplate fractures, whereas 11 of the 18 specimens had prolapsed. Prolapsed nucleus was reduced in 5 of the 11 prolapsed specimens after the reversal testing, whereas the remaining 6 did not change. Subclassification analysis revealed that the prolapsed discs that centralized had significantly less disc height loss (P < 0.01). Neither the classification of the herniation (circumferential or radial) nor the angle of lordosis of the specimens was linked to the behavior of the specimens.
This study showed that with repeated flexion, in porcine cervical spines, disc prolapse was initiated and that the displaced portion of nucleus can be directed back towards the center of the disc in response to particular active and passive movements/positions.
This study is interesting as it backs up a central tenant of Robin McKenzie’s popular treatment for low back pain. The study reinforced that repeated spine flexion (forward bending) causes the nucleus of a spine disc to work rearward causing disc protrusions (bulges), and as discussed in my last blog, eventually extrusions (ruptured or herniated disc) where the gel-like nucleus of the disc squirts from the disc, generally resulting in severe pain and often numbness and tingling in the legs.
In this study they (in agreement with McKenzie’s theory) found that repeated extension (backward bending) could sometimes reverse the process, helping to move the disc back to the center. I’ve met one of the primary researchers in this paper (Stuart McGill) and asked him if he started recommending repeated back extension to his exercise program in light of this study. He said he still didn’t, because the repeated extension would eventually result in arthritis in the facet joints of the spine. Rather, he thought laying prone (on one’s stomach) with the head raised either on two fists or up on elbows (at most) and staying in that position for as long as 15 minutes would likely have the same positive effect without stressing the facet joints of the spine. Since then, I have added this exercise/stretch to my physical therapy treatment programs of a number of my patients with low back pain. If it provides relief of symptoms I keep it, if it causes any irritation I discard it.
McGill also cautioned that extension in this study only worked in 45% of the spines with prolapsed discs while 55% did not. Also, it seemed to work in spines with only moderate disc height loss, and not in those with severe disc height loss secondary to disc prolapse. The cut off was about 60%, in which those discs that had at least 60% disc height maintained benefited from extension, while those with disc height of less than 60% (average of ~45%) did not.
What’s interesting is that while Robin McKenzie’s basic hypothesis has been largely justified by research, his diagnostic methods and treatment programs have not. In addition to other factors I discuss in my prior blogs, this is likely because repeated extension still works less than 50% of the time in those with disc protrusion as found in this paper. Like McGill cautioned, the extension forces in McKenzie’s more aggressive extension stretches may still be too great, potentially leading to additional spine problems. I still think McKenzie’s books are worth reading for physical therapists, as I think my own treatment programs benefited a lot after I started reading books about treatment methods I didn’t necessarily agree with. McKenzie was clearly ahead of his time, coming up with his hypotheses and programs well before the majority of this research existed.
As always, if you have any further questions or need for clarifications, please don’t hesitate to ask. Being aware that some of my blog ideas are contentious and occasionally a bit out of the field of my expertise, I encourage my readers to come forth with any questions/comments that are of interest or concern. Your comments are valued and welcomed.
Chad Reilly is a licensed physical therapist, located in North Phoenix, practicing science based medicine with treatment protocols unique and effective enough to proudly serve patients from Phoenix, Scottsdale, Mesa, Chandler, Tempe, Peoria, and Glendale.