Orthopedic and osteopathic use of this test is usually about hip and gluteus medius function. It is possible, though, to make great use of the test to observe how various parts of the lumbar spine and pelvic joints are working.
It is good to use this test after the standing 'looking' part of the exam, either before or just after we have asked the patient to actively move in various directions. We can start by saying that when it comes to gleaning information about the functioning of a patient's lumbar spine from this test, we are not so much interested in how 'wobbly' the patient is. In fact, it is perfectly possible for a patient to be quite wobbly on either leg and yet - from a spinal point of view - balance well (as long as it is the same type of 'wobbliness' on each leg).
So many factors (neurological, learning patterns, problems with other areas in the lower extremities, etc.) affect wobbliness.
But what we are looking in this article is predictions about asymmetrical functioning in the lumbar spine. So a key concept to focus on when observing this test is to realize that when a patient lifts his knee (say to waist height) it is required - in perfect balance - that the lumbar spine side-bends towards to the lifted leg.
ANY failure of the lumbar spine to side-bend in a particular direction (and, of course, lateral flexion is the key movement - along with extension - of this area of the spine) will therefore affect the way the patient balances.
You can observe this. With the patient's right knee (for example) at waist height, how well does the lumbar spine bend to the right, with a nice apex of the concavity (convex on the standing leg) at L3-4? In fact, you are just as much interested in the way the patient's lumbar spine laterally flexes during this balance test as you are in the way they balance on the grounded leg.
Observe the grounded leg and the position of the trunk above it. Clearly, in advanced hip disease, or in paralysis of the gluteus medius (e.g. polio, or L4-5 motor affected radiculopathy) we observe the trunk dropping towards the lifted leg. But in the vast majority of cases, we are interested in more subtle clues than this. A failure to bend to the right in the lumbar spine will thus variably produce the following signs;
- A hitch or adjustment in stance as the patient commences the right leg lift
- A lean to the left of the trunk, so as to reduce the effort required by the left hip abductors
- A straight, not right sidebent, lumbar spine
- In more subtle cases, and where the patient is quite fit and coordinated, they might 'hide' these signs - you will need to look very carefully in these cases)
And, of course, comparison of both leg balances will provide a lot of information that you can use to predict the problems you are likely to find in the rest of the active and passive exams.
Thinking further afield, it is possible to also make predictions from this test as to how the lower extremities will be affected by an asymmetrical pattern of balance (caused by a side-bending failure in the lumbar area).
For example, if balance on the left leg is poor, and a patient takes up running (having previously been sedentary) then we can infer that 'collateral' strains will go through the left knee (the grounded leg) during the whole stance phase of running, whereas it is at heel strike on the right leg when an abnormal 'jolt' will go through the system. Whether symptoms will emerge to trouble the patient will, of course, depend on many other factors.