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What is Unequal leg length and explain in detail?
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 (0.79 in).

Classification
There are two main types of leg length inequalities:

Structural differences are caused by the legs themselves being measurably different in length, usually due to differences in the length of the femur in the thigh or the tibia and fibula bones in the lower leg.  This may be a birth defect or it may occur after a broken leg, serious infection, or local damage to one of the growth plates in a leg.
The other, more common, type is seen when the legs themselves are the same length, but due to neuromuscular injuries in the pelvis or upper leg, one leg or hip is held higher and tighter than the other (hypertonicity in the musculature of the pelvis or leg).  These unequally tightened muscles cause the legs to seem to be different lengths, even though careful measurement would show equal lengths of the actual leg.  This is called leg length alignment asymmetry (LLAA) and can be seen while lying down.

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:
Femur length: The superior aspect of the femoral head and the distal portion of the medial femoral condyle.
Tibial length: The medial tibial plateau and the tibial plafondA 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