The proper treatment of low back pain due to tilting of the pelvis (pelvic obliquity) requires the physician to differentiate anatomical leg length deficiency from a functional leg length inequality caused by a muscular imbalance.3 This examination involves the comparative measurement of the leg lengths with both static and functional components.
Static, or Anatomical Leg Length Difference
This biomechanical evaluation may be performed first, with the patient lying on the back. The doctor then measures and compares length of each leg. If there is a difference in leg length, it is considered an anatomical leg length discrepancy.
Functional Leg Length Difference
In addition, the leg lengths are measured and compared in both a back lying position (supine) and a seated position. This biomechanical test determines functional leg length inequality. If one leg measures longer than the opposite leg while the patient is in the supine position but that same leg measures longer in the seated position, the patient is demonstrating a functional leg length discrepancy. This asymmetrical leg length condition or functional short leg often causes a mild tilting of the pelvis and a postural imbalance. Further examination will frequently reveal tenderness upon palpation of the iliopsoas muscles, especially on the side of the short leg while in the supine position.