My 88-year old mother says she feels her pelvis clunk when she stands on one leg. She says it doesn’t hurt but it feels unstable. Have you ever heard of something like this in the older adult? Does it mean anything to you?

Your mother may be experiencing a condition called separation of the symphysis pubis. This problem is more commonly referred to as symphyseal diastasis.

The entire pelvis is formed by the sacrum (wedge-shaped bone at the base of the spine), the coccyx (tailbone at the bottom of the sacrum), and the hip bones. The upper (socket) portion of the hip is made up of the ilium (pelvic crest), ischium (bones you sit on), and pubis (birth canal ring).

The pubis symphysis is in front of the body where the two pelvic bones come together. A disruption of the connective tissue between the two pelvic bones at the symphysis pubic can cause pelvic instability.

Standing on one leg can cause disruption or movement of the pubis on one side up or down. Since this area is connected together by soft tissue, there is a certain amount of normal give. But it shouldn’t be felt or perceived in any way. The clunk your mother feels is not normal. It may be a symptom of pelvic instability.

Trauma such as a car accident, childbirth, or a fall is the most common cause of pelvic instability. In older adults with osteoporosis (brittle bones), stress fractures can occur that also lead to disruption of the symphysis pubic and pelvic instability.

The diagnosis of pelvic instability is difficult. X-rays are usually taken in the standing (on two legs) position and supine (lying on the back). But these views don’t always show pelvic instability even when it’s present.

A more accurate assessment of this particular problem is with the single-stance X-ray. The single-leg X-ray, a simple, inexpensive, diagnostic tool, can be very helpful. A significant shift in the bones can best be seen by comparing the position of the symphysis pubis when standing first on one leg and then on the other (single-stance).

A history of preceding trauma, older age, or abnormal motion in the pelvic area is reason enough to order this type of X-ray view. Damage to any part of the pelvic ring can result in disruption of any other portion of the ring. A positive single-leg stance X-ray signals the need for further evaluation.