How do we determine if someone is unstable? From a pure physics model, instability is a state that is not in equilibrim, or in which a small change has a large irreversible effect. Synonyms are unsteadiness, inconstancy (which is a great word).
I found capricious, fickle, mercurial, and unstable as synonyms of inconstancy. While all these words mean "lacking firmness or steadiness," inconstant implies an incapacity for steadiness and an inherent tendency to change.
When I watch a patient walk, I want to make observation Numero One: Are they stable? If they are, it is good to move on to another part of their examination. If I find instability, I want to begin to address the instability right at day one. Posts 1 and 2 of Limb Length Discrepancy have talked about the signs in gait of instability related to a short leg. These signs can be head tilts, shoulder drops, asymmetrical arm swing, dominance (lean) to one side, uneven belt line, and asymmetrical lower extremity motions like more pronation on one side. You see these gait signs and it is implied that one of the biggest causes of instability in the human skeletal structure is present. You are witnessing a state of equilibrium out of equilibrium.
Other causes of instability that Podiatrists can help with dramatically are: excessive pronation and its effects, excessive supination and its effects, weak muscles and their effects, tight muscles and their effects, and various lower extremity problems that produce limping, require casts or braces, etc. The simple fact of surgery on the foot or ankle will produce a temporary or permanent imbalance in this state of equilibrium that will make us unstable. This instability can be helped by the compensations within the body, or the compensations just lead to a further breakdown in the body's equilibrium sought. A better fix for all of the instabilities we find is in correction of these biomechanical faults. In the case of short leg syndrome, it is lifts.
The next post we will talk about the pros or cons of various types of lifts. But today, the focus will be on separating structural, from functional, from combination short legs. Let's review the most important landmark in our evaluation of limb length discrepancy.
Hands parallel, find the top of the greater trochanter first on one side and just stabilize the other side. Then, find the other side. Ask the patient if you are on the exact same spot (they will know). Here, the left side is so much higher. Put lifts of 1/8 inch material, like grinding rubber, under the short side until the two sides look even. That will be your limb length measurement. Also, remember your eyes should be at the level of the body part you are measuring.
Here are two pieces of 1/8 inch grinding rubber I commonly use as my lifts, but also use in my evaluation to get the greater trochanters level.
Let us say we find 1/2 inch long left leg on this patient. We had used 4 (one-eighth inch) lifts under the apparent short side to level the greater trochanters. When we had first observed the various landmarks, all 4 landmarks were higher on the left side. This is not always true, but we would need a post on the study of pelvic tilts. I then had the patient walk with 1/2 of the measurement or 1/4 of an inch. The patient both looked and felt better. What you will find with 3/8 inch or more limb length discrepancy that all 4 measurements should agree that one side is longer than the other. By this I mean, that foot compensations (long leg pronates to lessen the hip discrepancy), or pelvic tilts (anterior superior iliac spine drops on the long leg) can not change that the one side is higher.
When you are dealing with 1/4 inch difference, again let's say left is longer, then both pelvic tilts and long leg compensations can make the picture more confusing. But, for today, let us finish this discussion. As podiatrists, if we measure limb length discrepancy, it can be purely structural with the patient falling to the short side in gait. It can be functional, meaning that there is no structural limb length discrepancy, only one side functions as a short leg. The classic example of this is unilateral flatfoot from PTTD. This side drops the talus and the whole leg. Therefore, if we see the signs of LLD in gait, we have to look for a symmetry or asymmetry in our RCSP or arch collapse findings.
Here is a patient with everted heels primarily due to genu valgum. The 9 degree asymmetrical positioning is over 1/2 inch functional short left leg (1/16 inch equivalent to one degree change).
Then what is the third type of limb length discrepancy. It is called combination limb length discrepancy. There is both a structural component and a functional component. This is probably the vast majority of limb length discrepancies. As a doctor trying to help my patients, I am always measuring as things change. I am looking for patterns of a more stable gait, better RCSP, leveling of the pelvis, and of course improvement in the symptoms that the patient initially presents with. Do I always get everything perfect? Of course, not! But, I can count on one hand the patients I have not helped in some way. Next week, I will begin to delve into LLD treatment.
