When it comes to the topic of "short leg", we must make a crucial distinction between what is called an anatomical or "true" short leg, and a functional short leg. Understanding the difference is important because clinically, you address them very differently.An anatomical or "true" short leg is a measurable difference in the distance between the lateral hip bone landmark ( greater trochanter) and lateral ankle bone ( lateral malleolus). It is an unchanging anatomical constant. A true short leg can be the result of one of the long bones of the leg or one of the pelvic bones to grow to the same extent as the opposite side. This can also happen with the cartilage of the knee and ankle, but less commonly. Trauma of some sort to the growth plate is probably a fairly common cause, and since all kids and teenagers get banged up a bit along the way, those injuries, if mild, may not be recalled as significant. In which case a teenager will typically start developing a short leg during their growth spurt and have a permanent differential by the time they reach young adulthood. As mentioned last week, the gradual development of a short leg during growth affords more opportunities for the body to compensate for it by increasing the size of another bony landmark.Adults can also acutely develop a true anatomical short leg. For some reason I have seen more such cases in the past 3 months than I have seen in the past 10 years. Lower extremity fractures can drop a leg by a solid inch or more, and knee replacements can suddenly lengthen your leg by almost an inch as well, especially if the knee had any difformity in the first place. I even had a case last fall of someone who had a foot injury that resulted in a permanent dropped arch and caused a new short leg. Acute onset leg differential in adults affords little opportunity for the body to compensate and is typically going to be symptomatic. This gets especially ugly in our senior population who may have underlying degenerative lumbar disc issues that do not like sudden mechanical disruption. Patients who develop persistent lumbar pain after a joint replacement, especially if the symptoms are aggravated by walking, should always be checked for a new leg differential.
