On Wedge Angles and Stuff

Suppose you needed help trying to read something written in Italian. You have an English-Italian dictionary, but also English-French and French-Italian dictionaries. Would it make more sense to use the English-Italian dictionary, or translate them from Italian to French and then from French to English? Obviously, the less direct pathway that goes through two dictionaries would introduce more mistakes, because meanings lost in the translation would be compounded by passing through two languages instead of one.

Something like this happens, I submit, when the chiropractor tries to get from the language of motion restriction to that of dynamic thrusting, but only by way of the intermediary language of bony misalignment. That is, the doctor could go directly from a perceived motion restriction to a thrust intended to diminish that restriction, as many do, but some feel compelled to construct what I recently heard called a "bones-in-space" mental image. Suppose, for example, a doctor, finds restriction in right lateral bending at L2 on L3. What added benefit is derived from imagining a proverbial "open wedge" (i.e., divergent disc angle) on the right, and only then delivering a right-to-left thrust aimed at reducing this supposed wedge? Given all the vagaries involved (for openers, demonstrated non-reproducibility of the palpatory procedure; uncertainty as to whether the thrust actually reduces the purported restriction; and lack of evidence that the patient would be made better off by that thrust), what added benefit is derived from piling on another, particularly huge vagary, the one that has lateral bending restriction associated with an open wedge? (Probably about the same amount of added benefit there is getting from English to Italian by way of French, instead of directly.)

One can appreciate how nice it would be if lateral bending restriction did usually go along with open wedges, so that one finding usually predicted the other. As Drs. Sam Cooke and Louie Armstrong put it, "What a wonderful world it would be!" In such a world there would be good concordance between static and dynamic analysis, and usually at least two criteria supporting the chosen thrust. Instead of being forced to choose between "sticky-joint and crooked bone" paradigms (Stonebrink), we could have our cake and eat it too ... indeed, use the same examination procedure as both a floor wax and a dessert topping!

Unfortunately, according to Aldous Huxley, "Maybe this world is another planet's hell," one in which there is no automatic concordance of static and dynamic analysis, at least in the assumed direction. Information is so often lacking about fixation, palpation and manipulative biomechanics that we sometimes take refuge in the comforting thought that we can go about thinking and doing whatever we please with impunity. You know the refrain: "Lack of evidence is not evidence of lack," and more of that kind of stuff. However, every now and then this profession does actually find something out; a research finding does suggest that changes in clinical practice are necessary and that continued basking in the glow of ignorance is no longer acceptable.

Enter Haas and Peterson. They investigated whether measured segmental lateral flexion malposition, as seen on neutral lumbopelvic x-rays, correlates with lateral bending restriction, as measured by stress x-rays (Haas M, Peterson D. A roentgenological evaluation of the relationship between segmental motion and malalignment in lateral bending. Journal of Manipulative and Physiological Therapeutics 1991;15(6):350-360). The results: there is indeed a statistically significant relationship between wedging and lateral bending, but in the opposite direction from what is commonly believed. They found increased bending toward the side of the open wedge, as measured from the initial start point of the segment to the end range.

Now: the investigators considered various ways of interpreting their data, including measuring motion from an "ideal neutral segmental position" instead of the actual (tilted) segmental position. Measured this way, there was increased bending away from the side of the open wedge. This manner of interpreting the data may seem at first to validate the traditional belief that perceived lateral flexion restriction predicts an ipsilateral open wedge, but not really. The tactile sense of the motion palpator can only discern spinous process movement from the de facto starting point of the patient, which is not an "ideal neutral" position, but rather whatever it happens to be, crooked or not.

Therefore, motion palpation, as it is usually performed, for lateral bending restriction ("since palpable lateral flexion asymmetry is uncorrected for misalignment") predicts an open wedge on the wrong side. (Why hasn't a summit conference of leading palpators looked into the matter further, like what would have been called by leading astrophysicists if Neil Armstrong had found the moon to be made of green cheese, previous theories and measurements notwithstanding?)

I only saw one letter to the editor concerning the study, noting the small size of the outcome relative to the reported measurement error, and raising a question about the timing of the measurements (Ebrall PS. A roentgenological evaluation of the relationship between segmental motion and malalignment in lateral bending [letter; comment]. J Manipulative Physiol Ther 1993;16(3):197-9). Haas addressed each issue easily. Despite the lack of obvious design flaws in the study, it would be premature to simply toss out one of the profession's more time-honored beliefs. After all, it would be very nice if perceived lateral restriction really predicted open wedges on the side of the anointed thrust. Moreover, it is unclear what would replace the intricate, even Byzantine, rules we currently teach chiropractic students about "which way the spinous processes go" and what it means during the various palpatory procedures. This currently occupies about two years in the curriculum, not only serving as a guarantor of concordant examination findings, but furthermore seeming to constitute an important rite of initiation into the profession.

Nonetheless, it would seem at minimum imprudent to simply ignore the study, since if its conclusions are correct, it would invalidate this fairly cherished treatment protocol. It is dangerous to proceed without knowing what is going on, but more dangerous to proceed despite knowing what is going on. No less an authority than Yogi Berra, tying it all together, opined: "If you don't know where you're going, you'll end up someplace else." If patients are truly made better off by having their open wedges closed, and if the thrusts we perform can actually close these wedges, then perhaps patients are not most optimally treated by thrusting on their side of diminished bending. That, alas, would be their closed wedge side. Are patients being ravaged all around the world by being adjusted according to defunct formulas?

Not really. If the motion palpator were correct most of the time, then he or she would be doing the wrong thing most of the time. Oddly enough, the saving grace is that motion palpation is very unreliable by almost all accounts (see, for example, Troyanovich SJ, Harrison DD. Motion palpation: it's time to accept the evidence. Journal of Manipulative and Physiological Therapeutics 1998;21(8):568-571), and thus provides the wrong wedge listing only about half the time, to the extent that listings matter at all (I think they do). Therefore, the palpator would be doing the "wrong" thing only half the time. How rare it is to find virtue in the unreliability of a diagnostic test!

We would still like an explanation as to why nominal lateral bending (i.e., excursion) is restricted toward the closed wedge side. One explanation, of course, immediately suggests itself: perhaps the superior vertebral segment cannot flex to the side because it has already done so, although not necessarily to end range. Perhaps lateral bending is greater toward the open wedge side simply because it can be, i.e., there is more room to go in that direction. From this point of view, it would be hard to predict in any one case whether a thrust intended to increase bending toward the "restricted" side is indicated or not, since we don't know a priori whether the restriction has occurred near end range or significantly before.

Haas and Peterson do report that the magnitude of the misalignment, on average, occupied from 1/4 of the unilateral ROM in the upper lumbars to 1/2 the ROM in the lower lumbars. This suggests that restriction often occurs long before end range. Therefore, however paradoxical it may seem, it may be warranted to thrust on the closed wedge side, if indeed there is restriction in that direction as determined by some reliable means.

In this ultra-bizarre clinical scenario, the traditionalist motion palpator, incorrectly surmising an open wedge on the restricted side, might wind up doing the right thing anyway, since restriction would actually occur on the closed wedge side long before end range had been obtained. Maybe hypertonic muscles on the open wedge side undergo an eccentric contraction in a futile attempt to close that wedge, thus restricting motion toward the closed wedge side (or something like that). Perhaps hypertonic muscles on the closed wedge side, having undergone concentric contraction, nevertheless surrender motion toward the open wedge side freely, at least to the "ideal neutral point," but relatively little beyond that (or something like that). Then, I guess, the appropriate thrust should be on the open wedge side after all! Personally, I usually duck all the intricacies of this type of segmental analysis by thrusting so as to enable left-right symmetric, multisegmental participation in lateral bending movements, as best I can determine by careful observation of the global lateral bending behavior of a sitting patient.

As if they had not uncovered paradoxical data enough, Haas and Peterson had reason to speculate, as an aside, that the phenomenon of hard endfeel, a palpatory experience of more importance than segmental range of motion according to some, may occur when moving in the direction of greater motion. Therefore, "it may be prudent for the clinician not to assume that palpation of segmental lateral flexion restriction is synonymous with the direction of appropriate manipulation" (Haas and Peterson).

I'm afraid there are no shortcuts. Experiments will have to be done to determine whether thrusting on one or the other side of a proven lateral flexion restriction affects the range of motion, and furthermore whether the subject is made any better off by whatever the outcome. In the meantime, it might be wise to interpret the practice of thrusting so as to reduce restriction carefully and cautiously. And avoid the lateral bending restriction=open wedge rule like the plague. It is bad enough not knowing whether thrusting on the "restricted" (or possibly end range) side to increase that motion is indicated. The uncertainty is not made better by presuming an open wedge; not only because it probably isn't there, but because doing so adds yet another false indication to perform that possibly ill-advised thrust.

Perhaps I worry too much. After all, "The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts" (Bertrand Russell). But then again, "If we weren't all crazy, we would go insane" (Jimmy Buffett).