Actual structural leg length discrepancies are very rare.
Most uneven leg length is functional. This means that the muscles of the waist, back,and hip, in conjunction with other muscles, are pulling one leg shorter than the other.
While this can be a part of and a cause of many other functional imbalances, it is most often readily corrected by a client and practitioner working together with very specific neuro-muscular reeducation techniques.