Limb Length Discrepancy
Differences in limb lengths are extremely common. Many times, the reason for the difference is unknown (a term called idiopathic). Many of us have differences in our limb lengths, and it is of little consequence. In a normal size person, differences up to 3/4" are generally well tolerated and do not need any treatment. A smaller person, however, may not be able to tolerate such a difference; on the contrary, someone of a taller stature may be able to tolerate a greater difference.
Limb length discrepancies can be any of the following:
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Diagnosis can often be made by history and physical exam alone, but a radio graph can be particularly helpful. Based on the reason for the limb length difference, your physician should be able to both discuss the current difference of the limb lengths. Often times, projections can be made into the future if the difference in the limb lengths will worsen over time. For those differences due to congenital reasons, the difference will always worsen with time as the limbs grow at different rates. However, in other circumstances, such as a limb length difference due to a prior infection in the growth area, this is much more challenging to predict future limb length differences as the rate of growth does not stay proportional over time.
Treatment is based on the cause of the limb length inequality, as well as the projected difference between the limb lengths once your child is fully grown. In general, if the difference is projected to be less than 2 cm (about ¾”), then no treatment is required. For those limbs projected to be between 2-5 cm (about ¾” – 2”) different in length at skeletal maturity, the recommendation is usually a well-timed epiphysiodesis of the longer limb (see below). Lastly, for those limbs projected to greater than 5 cm different at skeletal maturity, the recommendation is lengthening of the shorter limb.
Difference less than 2 cm: In general, most people tolerate a 2 cm difference without symptoms. However, this is not the case for everyone. The taller a person, the greater the difference in limb lengths he/she can likely tolerate. In other words, someone who is 6’5” tall will tolerate a 2cm or less difference in limb lengths better than someone who is 4’10” tall. Therefore, think of 2 cm as a guideline rather than a rule.
The best way to tell if back and/or hip pain is due to a known limb length discrepancy is to even out the legs, and the easiest and least invasive way to make that determination is with a shoe lift. Therefore, if your child was fully grown, had a 2 cm difference in their limb lengths and had hip pain that was alleviated with a shoe lift, then it would make sense to either continue with the shoe lift forever (which is a very reasonable option), or undergo a surgery to lengthen the shorter limb by 2cm to obviate the need for a lift. The latter scenario is rarely necessary, but may happen from time to time.
Difference between 2-5 cm: Once a difference in limb lengths is greater than 2 cm, then the majority of people will develop symptoms at some point in his/her lifetime, and therefore, recommendation is equalization of limb lengths as close as possible. If the difference is projected to be less than 5 cm, and your child is still growing, the easiest solution is to stop the long limb from growing at the appropriate time and allow the shorter limb to catch up. The way in which physicians stop the long limb from growing is with a procedure known as an epiphysiodesis. This is a surgery performed as an outpatient procedure in which your physician literally drills a hole in the growth plate of the bone to prevent it from growing anymore. It is a fairly simple procedure to perform with minimal risk. The more difficult part is to determine the correct time in which to perform the surgery. There are many natural history studies and growth charts at your surgeon’s disposal that aid with the decision. In addition, the more times your child is seen prior to the surgery, the more accurate the predictions typically can be determined.
In order for an epiphysiodesis to be effective, your child still has to have enough growth remaining for the short limb to catch up once the long limb stops growing. If your child has little to no growth remaining, then epiphysiodesis is not an option. In that case, if the difference is closer to 2 cm, and especially if your child is on the taller side, then it may be best just to observe if your child develops any symptoms. However, if the difference is greater than the 2 cm (3/4”), then it may be best to perform a limb lengthening surgery to equalize the limb lengths.
Difference greater than 5 cm: Once the difference is determined to be greater than 5 cm, then it becomes less practical to shorten the longer limb with an epiphysiodesis. With a large discrepancy, in general, the recommendation is to lengthen the shorter limb. However, lengthening has a very high complication rate, and there are certain instances in which lengthening is not a good option. Your surgeon can discuss contraindications of lengthening in detail at a scheduled appointment. If your surgeon has recommended a lengthening surgery, there are several ways in which to lengthen the bone, but all are lengthened by the same principle – the bone is cut in half surgically and gradually distracted, typically at a rate of 1mm per day. The device applied to perform the distraction is where the difference lies. Currently, there are only a few options available in which to distract the bone. In general, this include a variety of external fixators in which a device is applied outside the skin and pins and wires are drilled into the bone (please see photo). There is also a nail that is designed to lengthen from the inside and is known as an ISKD nail (intramedullary skeletal kinetic device). It is important that you discuss all the options with your surgeon to determine which lengthening device, if any is appropriate for your child.
Below are online resources available to you and your child.
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