Leg length inequality in humans: a new neurophysiological approach.

In conditions where there is moderate or severe pain, such as in low back pain, sciatica and osteoarthritis affecting the hip, the patient often reports the sensation that the two legs are of unequal length. This sensation cannot be explained as a result of fracture or other trauma that might cause a real change in length of the legs. There is confusion as to whether this 'leg length inequality' causes the pain or vice versa. It is argued here that the sensation occurs when there is pressure on the sensory nerves, especially the dorsal spinal roots. This causes pain but, more relevantly, causes an increased discharge in muscle spindle nerves, this in turn signaling an increased length of the associated muscles. This idea is testable using percutaneous electrodes.