When someone has a leg length inequality often it is indicated to use a heel lift. Commonly this is attached to the heel post of a functional foot orthosis (for the shorter limb) as part of a customized orthotic prescription. There are limitations on the amount of lift or correction that can be achieved using heel lifts, the biggest factor is to do with shoe fit, particularly shoe depth, and if you add too much of a heel lift the person will tend to walk out of their shoe or you’ll get excessive heel slippage.
The maximum amount of heel lift attached to the heel post of an orthotic device is about 1/4”, more than that can cause a pelvic iniquity. This amount of lift will also fit in most standard shoes, but not smaller dress shoes.
An alternative to attaching a lift to the heel post of foot orthoses is to make a 3/8” detached tapered lift that extends from the heel to the ball of the foot. This is placed in the shoe of the shorter limb and the orthotic is placed on top of it. These lifts are customized for right or left. This amount of a lift will only fit in deep shoes like Athletic footwear or boots.
More than 3/8” needs to go on the outside of the shoe, and should extend the full length of the shoe, tapering at the toes, think of a platform shoe but just on the shorter side.
Another factor to consider is if the leg length inequality is functional or structural. Functional leg length inequality is where the limbs are actually the same length but one appears to ‘function’ as a shorter limb because of the position of the back and pelvis.
A true structural leg length inequality is where there is an actual difference in the length of the limbs, this has a number of causes and it can be congenital but a common cause is after trauma, like an accident causing a fracture of one limb or damage to a growth plate on one side. Surgery can also be a cause. Especially in older patients, leg length inequality can be an unintended consequence of having a hip replaced.
So you have done an evaluation on your patient and have determined that there is a structural leg length inequality and you feel that your patient would benefit from having a heel lift but you want to know how much of a lift you should use? How much to add depends on the severity, the shoe it needs to go into and the age of the patient. The general rule is to start with no more than half the difference. For example if you have a patient that is 1” shorter on the right, you could recommend the 3/8” lift but you need to explain to the patient that it will require very deep shoes. Or go with a 1/4” lift on the orthotic and have the sole of the shoe modified to add another ¼” to 1/2”. Remember, many patients – particularly women because of cosmetic considerations, are reluctant to have shoes modified unless there is a significant difference in their limb length.
Another factor to consider is if someone has had a limb length inequality for a long time they may have ‘compensated’ for it and a large amount of change in a heel lift may not be tolerated well. In this case you can ramp up the amount of lift gradually to help improve their function and improve any symptoms associated with the leg length inequality.