For decades, physical therapists, osteopaths and chiropractors have manipulated the spine in countless patients with low back pain. Despite proposed theories to explain the effects and prediction rules to forecast who will receive benefit, little evidence has been produced to tell us what is actually occurring when the back is manipulated. A prospective case series, published in last months edition of Spine , investigated the immediate and short-term effects of a high-velocity, low amplitude spinal manipulation on those with low back pain.
The authors of this case series recruited fifty-one participants with complaints of low back pain and analyzed several variables over a three-session period. The participants completed an Oswestry disability index (ODI), numeric pain rating, Fear Avoidance Beliefs Questionnaire (FABQ) and pain body diagram at the beginning of each session. Associations between the subjective scores and objective measurements were examined later using linear regression.
Next, the authors objectively measured spinal stiffness and multifidus function pre- and post-manipulation. Spinal stiffness of L3 was measured in each participant while lying in a prone position . A mechanized indentation instrument was used to obtain objective levels of stiffness. The instrument worked by having a probe produce an indentation three times at L3, and then a mean level of stiffness was calculated from the three measurements. A slope of the force displacement was then used to calculate global stiffness (representing the stiffness of tissues throughout the indentation) and a terminal stiffness (representing the stiffness at the end of indentation). The level of L3 was chosen in this experiment because the motion of L3/4 was less likely to be painful and does not differ from L4/5 motion (the level from which multifidus measures were to be taken). Also, previous studies have demonstrated the effects of lumbar spinal manipulation are non-specific and would likely affect L3/4.
Following stiffness measures, multifidus thickness (of the more symptomatic side) was assessed next via ultrasound. The examiners performed this by having the patient produce a submaximal contraction in a prone position (which has been shown to have reliability).
Following both of these measures, a physical therapist or chiropractors performed a lumbar spinal manipulation. Following the manipulation, immediate measurements of spinal stiffness and multifidus thickness were reexamined. This regimen was performed in sessions one and two. On session three, a final measurement of stiffness and multifidus thickness was taken without a manipulation.
The results of this study showed significant immediate decreases in global stiffness and less initial terminal stiffness of the lumbar vertebrae following spinal manipulation, regardless of the patients perceived outcome. ODI score improvements were also related to those with a greater decrease in stiffness. An immediate increase in multifidus recruitment occurred following the spinal manipulation and an immediate change was associated with those who fit the clinical prediction rule for manipulation, indicating the likely responder correlated with greater immediate increase in lumbar multifidus recruitment.
This study was necessary for several reasons. As therapists, we often perform manual techniques on patients. Despite having theories to support use, there is still alot that is not understood. This study provided some preliminary evidence to support the notion that manipulation helps improve stiffness as well as activation of lumbar musculature. The mechanisms behind the effects are likely a multifactorial combination of mechanical and neurophysiological and much further research needs to be conducted to not only further examine the immediate effects, but also the long-term effects on these variables. This study also further supports the use of the clinical prediction rule for determining responders to lumbar manipulation (a review of this is provided below) and helps guide us in understanding, why some respond to manipulation better than others.
Clinical Prediction Rule for Lumbar Manipulation:
1. Duration of symptoms < 16 days
2. No symptoms distal to the knee
3. FABQ work subscale < 19
4. At least 1 hypomobile segment
5. Greater than or equal to 35 degrees of hip IR (in at least 1 hip)
Fritz JM, Koppenhaver SL, Nawchuk GN, et al. Preliminary Investigation of the Mechanisms Underlying the Effects of Manipulation. Spine 2011: 36; 1772-1781.
