Causes. Leg length discrepancies can be caused by poor alignment of the pelvis or simply because one leg is structurally longer than the other. Regardless of the reason, your body wants to be symmetrical and will do its best to compensate for the length difference.
Date of Onset. When the Social Security Administration (SSA) refers to a disability applicant's Date of Onset, they are referring to the date that a Social Security Disability applicant became disabled. When you fill out your Social Security Disability claim forms, you will be asked to provide the date your disability began.
The combined effect of these rules is that you usually shouldn't select a disability onset date that is more than 17 months prior to the date you apply for SSDI. There is nothing to be gained from trying to prove that your disability began ten years ago if Social Security won't make payments that far back.