Leg length discrepancy is when one of the legs is shorter than the other and this causes imbalance and misalignment in the body and in the entire kinetic chain while walking. Besides a postural imbalance, leg length discrepancy can cause over pronation (in the longer leg) or over supination (in the shorter leg), low back pain, hip pain and increased muscle activity on the shorter side. There are 2 types of leg length discrepancies: 

Structural

Structural leg length discrepancy is the physical or anatomical shortening of one of the legs. This discrepancy could be congenital or acquired as a result of an accident, surgery, fracture or a degenerative disease. 

Functional

Functional leg length discrepancy is when one of the legs behaves as if it were shorter, but it is actually not. This behaviour is caused by a unilateral asymmetry of the lower leg that could be caused by the biomechanics of the leg or a shortening in the muscles, misalignment in the mechanical axis of the leg or joint contracture. An abnormal motion of the foot can also cause functional shortening of the leg. 

Podiapro makes corrective insoles with compensation for leg length discrepancy after evaluating the nature of the discrepancy and its effects on the patient.