Locking and Specificity in Spinal Manipulation

This essay is by Jim Meadows, BScPT, MCPA, FCAMPT. It is the sixth in a series on clinical reasoning in physical therapy.

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The question posed is this: is it possible to make the force of a manipulation specific to a given segment? But more than this we should ask whether it is necessary to do so. It calls into question the purpose and the need for specific and axial locking in manipulation. There is debate about whether it is necessary to lock joints prior to manipulating, or whether a regional approach to manipulation is not only simpler but adequate.

Let’s first define locking and what it accomplishes (at least what its proponents purport it accomplishes). Locking is moving the segments to their end of range to make them stable — to transmit or accept forces effectively and safely. There are many methods of locking, some sensible and others less so, including ligamentous, articular, neutral, axial and so on, but they are not particularly relevant to this discussion.

Locking has three main purposes that I can see, and a fourth that is certainly debatable:

1. It forms a rigid lever when the joint that is to be manipulated is distant from where the force is to be applied. The best example is manipulating any lumbar segment above L5/S1 when the force is applied to the innominate.
2. It protects joints above or below the target segment from the force of the manipulation.
3. It makes the force specific to the target segment.

There can be little debate that locking segments provides a more rigid lever to transmit forces than does leaving the segments unlocked. There are a few ways of dissipating forces, including the production of heat and the production of movement. The first is really not a significant factor in manipulation — the heat generated is probably unmeasurable — but the second is very significant. If the intervening segments move, then energy is lost in making them move and less is delivered to the target segment. So to generate optimal effect, the amount of force applied has to be considerably higher than it need be if the segments are locked. But this particular issue does not impact on the debate, as with regional manipulation the intervening segments are locked or the applied force couldn’t move the target segment.

Does locking protect the segments above and below the target segment from the applied force? Only if the locking takes into account the particular sensitivity of the segments in question. The common and accepted wisdom is: “you can lock a hypermobile joint but you shouldn’t thrust through it, and you cannot lock an unstable segment.” The first statement may well be true — it is certainly prudent — but the second I would reject unless it is qualified. I would say that an unstable segment may not be lockable in the direction of its instability. So if a segment were unstable into extension (or more accurately posteriorly), there should be no reason why it couldn’t be locked into flexion or any other direction that does not involve a posterior shear. But the bald statement that locking protects joints and/or segments is flawed unless the direction of sensitivity is taken into account in the locking process.

If there is one guiding principle to doing anything, it should follow Einstein’s statement that “things should be as simple as possible but no simpler.” Certainly simplicity is a wonderful thing — it reduces complex issues to manageable proportions — but over-simplification reduces them to the point where the simplified model no longer resembles reality.

As far as protecting joints or segments beyond the target segment (that is, on the far side of the segment from the applied force), it is unlikely that locking helps very much at all, and may in fact put segments at more risk than if they were left unlocked. To limit how much force reaches those segments, I can either very carefully adjust the amount of force applied to the point where it optimally affects the target segment but not those distal to it (extremely ambitious for anyone other than an expert), or I can have the force dissipate by leaving those segments unlocked and in neutral, allowing them to move.

Now to deal with the question posed: can we be specific with our locking techniques? There are two aspects to this. First, can we make the force specific to the target segment only, or even maximally? Second, can the lock make the manipulation produce a specific movement?

On the first point: I would say this is patently untrue. If we are pushing on a rigid lever, that force is felt throughout the lever — and in fact the force will be stronger where the lever is close to the applied force than where it is further away. So if we lock L5/S1, L4/5 and L3/4 to lever the force to L2/3, these segments will feel the force more strongly than L3/4, but they will not move if the lock is effective.

On the second point: can we move the joint in a specific direction? Maybe — but only if it is set up at the end of that range before the manipulation is applied. The lock must do double duty: it must act as a rigid lever, and it must barrier the target joint at the end of its abnormal range so that the manipulation can push it into that range.

Conclusion

As far as I can see, it is not possible to make the force of a manipulation specific to any segment unless you are exceptionally skilled — and probably a little self-deluded — but by setting the lock up to barrier the target joint you may be able to move it in the desired direction.

Is regional manipulation all we need? Is the simpler method as simple as necessary, or is it too simple and does it miss effects? That question is for another time, but whatever the answer, it shouldn’t be based on belief systems or traditions — it should be based on rational and scientific arguments.

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Also in This Series

• Script Focused Deduction: Mimicking the Expert
• Clinical Reasoning: Methods and Tools
• Heuristics and Axioms
• Methods of Clinical Reasoning
• The Pathoanatomical Diagnosis