Diagnosis and Clinical Findings

A diagnosis of leg-length inequality can be made by a pediatrician at a regular visit in infancy or early childhood or by a pediatric orthopaedic surgeon at a referral for an obvious limp in an older child. The initial diagnosis of LLD is made on physical examination, with gait asymmetry being the most common complaint. The traditional measurements of real and apparent leg-length inequality (measuring with a tape measure from the medial malleolus to the umbilicus or iliac crest) have led to inaccurate measurements. A more reliable method of clinically testing for limb length inequality is simple visual assessment of the posterior iliac crest level while the child is standing with his or her knees and hips in an extended fashion. Blocks of various sizes can then be placed under the short limb until the pelvis is level to give an estimate of the leg-length inequality (Fig. 668-2). Physical examination can also identify joint contractures and angular deformities that cause errors in clinical and radiologic measurements.

Figure 668-2 Physical examination using blocks under the short leg until the pelvis is perfectly squared.

Radiographic Evaluation

Coupled with clinical examination, radiologic evaluation is used to guide the appropriate treatment decisions. Four different techniques are the most commonly used (Fig. 668-3): teleoroentgenogram, orthoroentgenogram, scanogram, and CT. Whichever method is initially used should remain consistent in all future studies in order to maximize accuracy and validity.

Figure 668-3 A, Teloroentgenogram. B, Scanogram. C, Orthoroentgenogram. D, CT length study.

A teleoroentgenogram, or full-length standing anteroposterior (AP) view, is a single-exposure radiograph on a long cassette that shows both lower extremities while the child is standing leaning against the x-ray plate, with his or her hips, knees, and ankles fully extended. A ruler is then placed on the film and direct measurements (factoring in a 6% magnification error) of the length discrepancy are made. This technique is primarily indicated for young children. Some advantages are that angular deformities can be easily assessed. This method applies one amount of exposure to the whole leg that is denser at the hip than at the ankle, thus causing difficulties in reading the film itself. For example, it might be too light at the hip or too dark at the ankle. Because the ankle is against the film plate and the hip is as much as 6 or 7 inches from the plate, and the x-ray beam at the level of the knee aiming at an angle to both the hip and ankle, the hip, and then is projected several centimeters larger than the actual measurement of the limb. Owing to the inverse distance square laws, this method uses a very large amount of x-irradiation.

An orthoroentgenogram requires placing the patient and ruler on a long x-ray cassette and making 3 exposure radiographs of the hip, knee, and ankle, starting above and ending below the specified (hip, knee, and ankle) location. For the hip exposure, the area that the radiograph spans is from the pelvis to the mid-femur; for the knee exposure, the area spanned is from the mid-femur to the mid-tibia; and for the ankle exposure, the area spanned is from the mid-tibia to below the foot. This technique produces both an accurate measurement of the bone length and a frontal plane assessment of the deformity. The child must lie perfectly still for the 3 individual exposures, which is often very difficult for younger children.

A scanogram consists of 3 small separate exposures of the hips, knees, and ankles, with a radiographic ruler for direct measurements on the small film cassette containing low radiation. Although there is no magnification error, two disadvantages of this method are that the child must remain perfectly still for the 3 single exposures and angular deformities cannot be assessed.

CT potentially offers the most accurate method of limb measurement if it accounts for both the limb deformity and the axis of the limb not necessarily being in the projected plane of the screen on which the measurements are actually being produced. However, the measurement points chosen by the radiologist are not necessarily the ones needed or used on previous films.

In the presence of flexion deformities of the hip and knee, separate radiographs of the isolated femurs or tibias in the plane of the x-ray plates may also be taken and patched together for whole limb assessment. Skeletal age can be determined by measuring an AP radiograph of the hand and wrist, which are then compared with the specific standards in the Greulich and Pyle Atlas. The range of variability using this approach is approximately 9 mo, so it is most accurate when multiple data points have already been collected. Although more accurate techniques are available, most of them are time-consuming and impractical for routine clinical application.

Treatment

There are many different options, surgical and nonsurgical, for treating leg-length discrepancy. To determine the appropriate treatment, the child’s age, overall health, past medical and surgical history, tolerance to medications and procedures, the expectations and preferences of the clinician and the child and family, and the cause of LLD and its severity, must be carefully reviewed. The goal of treatment is not always equal leg length. If a child has a neuromuscular condition that involves muscle weakness or paralysis of the shortened leg, some physicians believe the appropriate treatment is to undercorrect such length by 1-2 cm during surgery. This inequality can help the child clear the floor during the swing phase of the routine walking cycle. Treatment can range from observation, a shoe lift or custom orthosis, a limb-shortening procedure, a limb-lengthening procedure (gradual or acute), temporary (plate and screw) or complete (drill or graft) epiphyseodesis, or a combination of these choices.

In addition to the actual quantitative amount of discrepancy predicted at skeletal maturity (if not already reached), both the likely adult height of the child, projected from family members and growth charts, and the requests of the child and his or her family are essential to take into consideration before any final treatment decisions are made.

Discrepancy >2.0 cm generally may observed or treated by a small shoe lift, if symptomatic. A lift of up to 1 cm may be placed inside the normal shoe, whereas a lift >1 cm should be attached to the sole or heel of the shoe.

Discrepancy between 2 and 5 cm is usually treated by either an epiphysiodesis or an acute shortening in skeletally immature and mature children, respectively. Epiphysiodesis refers to either a temporary or permanent arrest of growth at one or more of the physes. This simple and minimally risky procedure must be performed at a precise time during growth to prevent under- or overcorrection. Roughly 65% of growth comes from the lower extremity—the distal femur (37%) grows about 9 mm/year, whereas the proximal tibia (28%) grows about 6 mm/year. Boys typically continue growing until they reach 16 yr of age, and girls continue growing until they reach 14 yr of age. However, not all children grow at the same time, so a careful analysis of each child’s personal rate of growth is crucial. Serial measurements of length over the growth period can accurately help to determine the best time for epiphyseodesis.

Certain techniques can be used to determine the appropriate timing of epiphysiodesis. These consist of the Menelaus method [estimated discrepancy = current discrepancy + (years remaining × discrepancy per year)], the Green and Anderson method (Fig. 668-4), the Moseley straight-line graph method (Fig. 668-5), and the Paley multiplier method (Fig. 668-6). The most common surgical technique used is the percutaneous drill epiphysiodesis. In this outpatient procedure with very few complications, the physis is either ablated with a drill and curette under high image intensification or screws are inserted across the physis. Temporary epiphyseodesis can also be obtained using plates and screws across a growing physis. Once the amount of correction has been achieved, the staples or screws and plates are removed, thus allowing growth to resume. After skeletal maturity and for corrections of 2-5 cm, acute shortening can be performed at the femur or tibia and fibula by resection and internal fixation. This method is rarely used for correction of >3 cm because of permanent weakness of the surrounding muscles.

Figure 668-4 Growth-remaining charts for girls and boys. To use this chart correctly, both the discrepancy at maturity and the percentage of growth retardation of the short limb should be calculated.

(Redrawn from Anderson M, Green WT, Messner MB: Growth and predictions of growth in lower extremities, J Bone Joint Surg Am 45:1–4, 1963.)

Figure 668-5 The Moseley straight-line graph is used to assess leg-length inequality and to accurately predict lengths of each extremity at skeletal maturity. It allows simultaneous correlation of the normal leg, short leg, and bone age of the child. The reference slopes shown here are used as a guide in determining when the appropriate treatment should actually be performed. Certain techniques can be used to determine the appropriate timing of epiphysiodesis.

(From Moseley CF: A straight-line graph for leg-length discrepancies, J Bone Joint Surg Am 59:174–179, 1977.)

Figure 668-6 The Paley multiplier method is used to assess leg-length inequality at maturation. It is also applicable for shortening specific conditions in which growth retardation is consistent.

(From Paley D, Bhave A, Herzenberg JE, et al: Multiplier methods for predicting limb-length discrepancy, J Bone Joint Surg Am 82;1432–1446, 2000.)

Discrepancy >5-8 cm may be treated with lengthening of the short limb. This technique would not be used if the discrepancy were secondary to overgrowth of a limb, in which case a limb-shortening method would be favored in order to preserve the original body proportions. Children with expected discrepancies >5-6 cm, though, often require one or more limb-lengthening procedures conducted several years apart with or without an epiphysiodesis of the longer limb. The most common technique used for limb-lengthening involves placing an external fixator, either a monolateral or a ring fixator (Fig. 668-7). An external fixator is then applied to the limb to be lengthened and an osteotomy is performed, through which distraction is obtained. The usual rate of lengthening is about 1 mm per day (i.e., approximately 30 mm per month), and it takes approximately 1 mo in the external fixator for each centimeter lengthened. A maximum of about 15-25% of the original length of the bone may be gained during each lengthening session depending on the etiology. More length is achieved from the normal bone shortened by physeal injury, whereas less is achieved from congenital deficiencies. Simultaneous correction of angular, translational, and rotational deformities can also be obtained with both the circular and the newer generation of monolateral fixators. Complications include pin tract infection or wound infection, hypertension, joint subluxation, dislocation of the hip and knee, muscle contracture, premature consolidation, delayed union of bone, stiffness of adjacent joints, implant-related problems, slight over- or undercorrection of the bone’s length, and fatigue fractures following the removal of the lengthening apparatus. To prevent some of the complications, regular follow-up visits to the clinician’s office, meticulous cleaning of the area around the pins and wires, careful adjustment of the frame several times weekly, and physical rehabilitation to further stretch and maintain joint flexibility are essential to improving the quality of care.

Figure 668-7 A, The Ilizarov device. B, MAC device (MultiAxial Correcting, Biomet). This ring fixator is used to demonstrate bone lengthening and angular correction by distraction osteogenesis.

Children with projected discrepancies >18-20 cm (requiring >3 limb lengthenings), especially when there are coexisting deformities or deficiencies of the ipsilateral foot (Fig. 668-8), might benefit from early amputation, rotation of the ankle to function as a knee, and prosthetic fitting for the best long-term function. The other alternative would be multiple reconstructive procedures throughout childhood and adolescence. The potential impact on the child’s psychosocial development, combined with his or her emotional and physical challenges and future restrictions of activities or abilities must be kept in mind when formulating an individualized treatment plan in these complex cases.

Figure 668-8 A, Extension prosthesis in leg-length discrepancy. B, Extension prosthesis in compensation.