MIAMI — To successfully evaluate the child who presents with a limb discrepancy, identify the etiology, understand normal limb growth, estimate the ultimate deficiency, and guide the family regarding intervention, Dr. Christopher A. Iobst recommended at a pediatric update sponsored by Miami Children's Hospital.
“Many people have a slight discrepancy in their leg lengths. Leg length discrepancies below 3% are generally not a concern,” Dr. Iobst said. One of the options, therefore, is to do nothing but observe and monitor the child.
“Some kids do fine with a minor discrepancy, others freak out and want something done to correct it. Realistically, any discrepancy greater than 1.5 cm should be treated,” said Dr. Iobst, attending physician in the department of orthopedic surgery at the hospital.
Options include an operation on the shoe or an operation on the child. Shoe lifts correct a length discrepancy without surgery, but most kids don't like wearing shoes with a noticeable lift, Dr. Iobst said. Up to 1 cm can be added inside a shoe. “I don't like prescribing lifts greater than 5 cm because they become dangerous.”
Operations on the patient include techniques to either lengthen or shorten the affected limb. Epiphysiodesis or ablation of the physis is the most common surgery Dr. Iobst performs to shorten a limb. The number of growth plates permanently destroyed depends on the degree of the limb discrepancy.
Epiphysiodesis can be performed as a percutaneous, outpatient procedure. The surgery can be done through a small incision with minimal soft-tissue disruption. “The problem is, I am reducing their overall height, so if they are already [short], they may not want to do this.”
To lengthen a limb, the bone is cut and gradually distracted to produce new bone. For example, with the Ilizarov technique, an external frame is placed around the leg and slowly adjusted to promote natural bone healing and bone growth.
An attendee asked about pain management during limb lengthening. “When we apply fixators and the frame, we leave it alone for 5–7 days at first so the bone starts to repair the fracture we caused,” Dr. Iobst said. “It's not as painful as it looks. We are lengthening about 1 mm/day, so it's not as noticeable to them in terms of pain.” He added that most patients discontinue pain medication by 2–3 weeks.
Immediate physical therapy is essential to postoperative success. “We want them weight bearing as soon as possible.” Patients are instructed on daily pin care and to come for weekly follow-up visits.
“They have to be in these frames a long time. It can take 6–9 months for new growth,” Dr. Iobst said. The duration of wearing the fixator could be shortened by combining the use of an external fixator and an intramedullary nail. “We can save a patient anywhere from 3 to 6 months by using [a] rod along with an outside frame,” he said. “Once the length is achieved, screws are placed in the rod to hold it, and the frame is removed.”
“My practice is pediatric, and these rods go through the growth plates, so one adaptation is to place a plate (instead of a rod) that protects the growth plates when the frame is removed,” Dr. Iobst said.
Hydroxyapatite-coated pins or screws put directly into bone to stimulate growth are another option in development. Researchers are also assessing the Taylor Spatial Frame, which is fitted and adjusted via computer.
When evaluating a child with a leg length discrepancy, most of the time the abnormal limb is obvious, Dr. Iobst said. But sometimes you cannot immediately tell. Many pediatricians were taught to measure from the spine of the pelvis down to the ankle, he said. “Throw away the tape measure—it is a very unreliable way to measure leg lengths. Overall length can vary by as much as 3 cm just by incorrectly positioning the lower extremity by 10 degrees.”
At Miami Children's Hospital, Dr. Iobst and his colleagues place blocks under one foot to normalize the pelvis. If it is difficult to tell if the pelvis is horizontal, use the underwear line as a reference, Dr. Iobst suggested. A radiographic assessment can be helpful, such as a standing anteroposterior view of bilateral lower extremities taken from the hips down.
A scanogram is another option. This imaging modality takes three scans at intervals along the lower extremities. “This gives an accurate length determination, but it's my second choice,” Dr. Iobst said. “You can miss an anomaly in the areas not scanned.”