Apologizing for adding yet another doctor into the mix, I suggested a rheumatologist—a joint specialist—who then sent Mr. McCoy for a procedure in which an anesthetic, followed by cortisone, was injected directly into the ball-and-socket part of the hip joint. This, too, failed to relieve the pain.
We had not yet addressed the slight disk bulge that appeared on the MRI of Mr. McCoy’s lower back. I didn’t think it was the culprit, but we had no other leads. Disk bulges are notoriously tricky to interpret because they are common in people both with and without pain; in fact, they appear on MRIs of people without back pain roughly 50 percent of the time. So it isn’t easy to decide whether a bulge justifies the discomfort, expense, and radiation exposure of additional tests, or even surgery.
Mr. McCoy’s neurosurgery appointment wouldn’t happen for another two months. While he waited, I suggested he return to the physical therapist for a cane and some hip exercises.
When I saw him a month later, in January, I had to blink a couple of times. He wasn’t limping. He wasn’t using a cane. He was smiling.
What he told me was so utterly unexpected, so simple, that I was at a loss for words. “I have a short leg,” he explained. “The physical therapist measured my legs, and my right one is about half an inch shorter. He gave me a heel lift and it’s working like a charm.”
I had not learned about leg length discrepancy (LLD) in my training, and it seemed that none of the other clinicians Mr. McCoy saw had considered it either. But leg length discrepancies are common. According to some studies, up to 70 percent of people have a slight difference in the length of their legs; one person in a thousand has a difference of nearly an inch. In most cases, the difference goes undetected.
There are two kinds of LLD. Structural discrepancies, which can be congenital or the result of a fracture or hip replacement surgery, involve an actual difference in the length of the bones. Functional discrepancies, on the other hand, are caused by muscle weakness or stiffness in the pelvis, ankle, or foot—the legs are the same size but function as if one is longer. Mr. McCoy probably had a lifelong mild leg length discrepancy that never bothered him until he hurt his hip. The pain changed the way he walked, and all of a sudden the discrepancy mattered.
My patient’s LLD was small enough that it had never caused an obvious limp, at least until now. But there was another clue that nobody had noticed. “I looked at the soles of his shoes, and one was more worn,” the physical therapist told me. “If the right leg is shorter, you tend to walk on the outer part of that foot, to extend the leg. On the other side, to make the longer leg feel shorter, you flatten out that foot. You can learn a lot from the soles.”
One common method used to check for a structural leg length discrepancy involves running a tape measure from a point on the pelvis to the ankle bone several times and then averaging the numbers. To check for a functional discrepancy, a physical therapist will measure from the belly button to each ankle bone. Some doctors recommend taking a special X-ray to verify the measurement; others believe that the degree of accuracy achieved with an X-ray is not worth the radiation exposure and is not necessary with small discrepancies.
Physical therapists often give a patient with hip pain and a small LLD a heel lift or even an insert from a sneaker to try for a week or so. What makes the treatment tricky is that a heel lift doesn’t always work. As with those incidental disk bulges on MRIs, a leg length discrepancy may have nothing to do with the pain; since a slight difference in leg lengths is so common, it would be easy to make the mistake of treating the pain with a heel lift when there is another reason for it, like arthritis or bursitis. And some people have had an LLD for so long that they’ve compensated by holding their pelvis at a certain angle. In those situations, a heel lift that is used for more than a week may end up causing pain rather than relieving it.
For some people, the search for relief from hip pain never ends. Luckily, that wasn’t the case with my patient. The heel lift did more than match the length of his legs. It lifted his spirits.
Anna Reisman is an internist in West Haven, Connecticut. The cases described in Vital Signs are real, but names and certain details have been changed.