Unequal leg length
Unequal leg length (also termed leg length inequality, LLI or leg length discrepancy, LLD) is where the legs are either different lengths or appear to be different lengths because of misalignment. The condition has been estimated to affect between 40% and 70% of the population, with at least 0.1% having a difference greater than 20 mm. Classification. There are two main types of leg length inequalities: Diagnosis and workup. Unequal leg length in children is frequently first suspected by parents noticing a limp that appears to be getting worse. The standard workup in children is a thorough  physical examination, including observing the child while walking and running. Also, at least in United States, standard workup in children also includes X-rays to quantify actual length of the bones of the legs. On X-rays, there is generally measurement of both the femur and the tibia, as well as both combined. Various measuring points for these have been suggested, but a functional method is to measure the distances between joint surfaces: A leg length difference can result from a pelvic torsion. Abnormal (gravity drive) pronation will drive the innominate bones forward (anteriorly). The forward rotation of the innominate  will shorten the leg (See Rothbart 2006). The more pronated foot will have the more forwardly rotated innominate bone. And will be the side with the functionally short leg. In adults, leg length discrepancy is believed to cause low back pain as a result of increased pelvic obliquity and lumbar scoliosis. Treatment. The most common treatment for discrepancies in leg length is the use of a simple heel lift, which can be placed within the shoe. In cases where the length discrepancy is moderate, an external build up to the shoe is usually more comfortable. In severe cases, surgery can  be used to make the longer leg shorter (or impede its growth), and/or make the shorter leg longer via limb lengthening. Measurement challenges. Although prone "functional leg length" is a widely used chiropractic tool in their Activator technique, it is not a recognized anthropometric technique, since legs are usually of unequal length, and measurements in the prone position are not entirely valid estimates of standing X-ray differences. Measurements in the standing position are far more reliable. Another confounding factor is that simply moving the two legs held together and leaning them imperceptibly to one side or the other produces  different results. Clinical measurement of leg length conventionally uses the distance from the anterior superior iliac spine to the medial malleolus. Projectional radiographic measurements of leg length have two main variants: On X-rays, the length of the lower limb can be measured from the proximal end of femoral head to the center of the plafond of the distal tibia. References. Rothbart BA 2006. Relationship of Functional Leg-Length Discrepancy to Abnormal Pronation. Journal American Podiatric Medical Association;96(6):499-507