Limb Length Discrepancies in the Pediatric Patient

Pediatric Orthopedic Surgery, Hospital for Special Surgery


Causes

A spectrum of congenital conditions affecting the femur may be diagnosed at birth, including congenital short femur and proximal femoral focal deficiency (PFFD). In some cases, such as fibular hemimelia, (a shortening or absence of the fibula) and posteromedial bow of the tibia (bowing of the tibia), the lower leg bones (the tibia and the fibula) may be affected.

Other causes of limb length disparities are infection of the bone or joint, which can occur at any time during childhood, including the weeks immediately following birth. Fractures that involve damage to the growth plate (the area at each end of the bone where new bone develops, adding length to the bone) can also result in the cessation of growth or growth arrest and subsequent limb length discrepancy. This can occur due to any injury or condition.


Figures 1 & 2: X-ray images of pediatric limb length discrepancy before and after surgery

Treatments

Treatment decisions for patients with limb length discrepancies are based not only on the extent of the disparity at the time of diagnosis, but also on predicted increases in discrepancies over time. In order to make this prediction, the orthopedic surgeon takes into account the following factors:

  • growth plate location
  • the age of the patient (i.e., the amount of growth remaining)
  • in the case of trauma or infection, the extent of injury to the growth plate

In patients who have congenital limb anomalies of the leg, the predicted increase in limb length discrepancy can be calculated by comparing the short unaffected leg with the long unaffected leg; the percentage of growth arrest tends to remain constant during childhood. Use of growth charts in the equation help make the predictions more precise.

In addition to these factors, the patient and family’s preferences and ability to follow up on needed care can play a role in treatment selection.

At Hospital for Special Surgery, recommendations are made according to the following guidelines:

  • When the discrepancy between the limbs is small (less than two centimeters) use of a shoe lift is appropriate.
  • For those patients in whom the discrepancy ranges from 2-5 centimeters, a surgery called epiphysiodesis may be appropriate. This procedure slows the growth of the opposite leg or arm by altering the activity of the growth plate, thereby allowing the affected limb to “catch up” by the end of growth.
  • For discrepancies greater than three centimeters, however, limb lengthening may be an effective treatment choice.

The Ilizarov Procedure

Originally developed in Russia more than half a century ago, the Ilazarov Method of limb lengthening was first introduced in the United States in the late 1980s. Since that time, it has developed into a highly sophisticated and well-tolerated treatment option.

To initiate limb lengthening, the orthopedic surgeon performs an atraumatic osteotomy, a procedure in which a small incision is made in the metaphysis, a section of the bone that has the greatest metabolic turnover, and therefore yields the fastest formation of new bone tissue. During surgery, great care is taken to protect both soft tissue and the blood supply to the bone.

External fixators are placed with pins and wires along the affected bone to set the stage for the next part of the process, distraction osteogenesis.

Distraction osteogenesis describes the process of very gradual separation of the bone at the site of the incision and the formation of new bone tissue. Beginning approximately one week after surgery, the physician - and then later the parents and/or patient - adjust the fixator according to a precise schedule, usually three or four times per day.

As the bone is distracted (or pulled apart), new bone forms at the gap as part of the healing process. The rate of distraction is very slow, with a standard increase of one millimeter (.0394 inches) per day.

In pediatric patients, the orthopedic surgeon may use either a monolateral fixator, a rail system that runs along one side of the limb, or a Taylor Spatial Frame, a circular fixator based on the original Ilazarov frame (seen above).

The Taylor Spatial Frame allows simultaneous correction of the limb length discrepancy, as well as any angular or rotational deformity. Prior to its development, children with multiple deformities and leg length discrepancies required separate consecutive treatments for each element of deformity.

Rehabilitation after Limb Lengthening

Physical therapy plays a crucial part in the entire limb lengthening process. Patients meet with physical therapists before undergoing surgery and during their post-operative hospital stay - usually a period of 3 to 5 days.

HSS therapists design the post-operative rehabilitation program and continue to oversee therapy throughout treatment. (Even those patients who live far away from the hospital benefit from this process, as HSS therapists work with local physical therapists.)

Most patients see their physical therapists three times a week and are required to do home exercises for a minimum of four times a day. Physical therapy helps ensure that the surrounding soft tissues remain flexible as the patient’s bone length increases and that muscle strength is maintained.

Depending on the planned lengthening, treatment typically continues for 30 to 60 days. Following this stage of treatment, the frame remains on for an additional period of consolidation. This allows the regenerative bone to mature until it is capable of full, independent weight-bearing.

When the surgeon has determined that this process is complete, the patient returns for removal of the frame, a day surgery that is usually performed with the patient under sedation.

Safety of Limb Lengthening

In the hands of experienced orthopedic surgeons, limb lengthening has become a highly predictable surgery with an excellent safety profile. The most common complications are those involving soft tissue, where tightening or contractures can occur if soft tissue lengthening doesn’t keep up with bone lengthening. However, an appropriate physical therapy program should prevent or minimize this problem.

Irritation or superficial infection may also occur around the pin sites, but this is usually minor and easily treated with oral antibiotics. Moreover, owing to the gradual nature of the process, pain is usually minimal.

Depending on existing and predicted discrepancy, limb lengthening procedures may be repeated up to two or three times during childhood. The preferred lengthening for a given procedure is 5 or 6 centimeters, an amount associated with the lowest number of complications, but there is no specific limitation on additional surgeries, except for what’s appropriate and reasonable for family and patients.

At HSS, this surgery is complemented by a staff of dedicated pediatric anesthesiologists and pediatricians. The physical therapy team has specialized training in the care of such patients.

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