What do chiropractic adjustments do to your anatomy?

Last week I visited a chiropractor for the first time since moving to Vermont. I went to him because, for several years now, I've experienced varying degrees of pain or discomfort at various levels of my vertebral column: lower cervical, mid-thoracic, lower lumbar, all on the left side. I have to say, I'm kind of annoyed by the left side of my body. Sure, it carries its weight most of the time, but it doesn't seem to be happy about it. Tingling in the sole of my left foot when I'm wearing certain boots, iliotibial band syndrome (or something like it) in my left lower limb, left gluteal muscles that don't agree with extended periods of sitting. Nothing that prevents me from running or downhill skiing or any of the activities of daily living, but just enough to make me think, "Maybe I should do something about this."

The most annoying problem area is mid-thoracic. Every few months when I least expect it, I have a back attack: sharp yet hard-to-pinpoint pain in my back and lower neck that makes it hurt to turn my head, sit, stand, or really any activity that requires me to be upright. Mercifully the acute phase typically lasts an hour or less, eventually morphing into a more tolerable burning pain that flares up only if I flex my neck too far or turn my head too far to the left. What triggers the back attack is usually a mystery. Sleeping in a bad position? Leaning over a cadaver table in the anatomy lab? Maybe, but more often than not the attack seems unrelated to anything. Stretching, massaging, and ibuprofen can ease the pain, but mostly it's a matter of waiting for the body to heal itself, a "self-limiting" injury as the clinicians like to say. And the discomfort never disappears completely.

So did the chiropractor make a difference? Yes, at least in the neck and midback (the jury is still out on the lumbar region). I notice an increase in neck mobility, especially in turning to the left. I notice substantially reduced pain when I lower my head as far as it can go. I notice that my left arm isn't bothering me now when I run. And I hasten to add that I'm not a chiropractic True Believer. In fact, I'm automatically skeptical of just about everything that comes out of my chiropractor's mouth. Chiropractic seems to have a foundation that is still primarily anecdotal and philosophical, not scientific. That's not to say that it's all baloney. I know there are studies that support its effectiveness for certain conditions in certain patient populations. Whatever. I don't want to get mired here in the devisive "chiropractic vs. allopathic" debate. What I've started wondering is more specific: What exactly happens to your anatomy (joints, muscles, nerves, etc.) during a chiropractic adjustment (or any similar sort of spinal manipulation)?

It turns out that there are a number of reasonable working models and at least a trickle of supporting data. One place to start is a 2002 review article in the Annals of Internal Medicine. It's by William Meeker, DC, MPH, and Scott Haldeman, DC, PhD, MD, FRCPC. Scott Haldeman, a neurologist in Irvine, California, may very well be the only person on Earth with that combination of letters after his name. According to the authors, there are at least five mechanical, anatomical, and/or neurological things that chiropractic manipulations may do (I'm paraphrasing):

1. Release part of a joint capsule that has become entrapped in facet joints, joints between pairs of vertebrae that have been shown to be very sensitive to pain.
   
2. Reposition part of an intervertebral disc (the rubbery disc between successive vertebrae).
   
3. Loosen fibrous tissue that formed in a previous injury.
4. Inhibit overactive reflexes in muscles of the spine or limbs.
5. Reduce the compression or irritation of nerves.

They also cite studies suggesting that chiropractic adjustments increase the range of joint motion, increase pain tolerance, increase muscle strength, and so on. Lest you get too excited about chiropractic, they also discuss the issue of serious complications from spinal manipulations. Nasty things like vertebral artery dissection and cauda equina syndrome. Such complications are rare but they do happen, and so far there is no way to predict who might have an increased risk.

Probably the most compelling study I've seen so far is one called The Effects of Side-Posture Positioning and Spinal Adjusting on the Lumbar Z Joints (which, coincidentally, was also published in 2002). With funding from the National Center for Complementary and Alternative Medicine, the authors recruited healthy young volunteers to undergo MRI scans before and after a lumbar manipulation on one side. Data analysis (and rather striking images like the one below) show that the adjustments produced increased separation of the facet joints (also called zygapophysial joints or Z joints). Of course, whether that's good or bad is a matter of debate, one that will hopefully be illuminated by more data.

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Two MRI cross-sections of the lumbar spine in the same individual. The bottom of the image is towards the back of the person. R = right; L = left; L5 = fifth (lowest) lumbar vertebra. The first image (c) was taken before the left lumbar side-posture spinal adjustment; the second (d) is after. Notice that the gap of the left facet joint (i.e., the white space between the two dark hamburger-bun shapes directly above the L) is larger after the adjustment. Figure copied from Cramer, et. al (2002). The Effects of Side-Posture Positioning and Spinal Adjusting on the Lumbar Z Joints. Spine 27: 2459-2466.