Leg Discrepancy

Leg Length Discrepancy Leg length discrepancies are common in childhood. The causes of leg length discrepancy are extensive. Common Causes of Leg Length Discrepancies Congenital Proximal femoral focal deficiency Coxa vara Hemiatrophy–hemihypertrophy (anisomelia) Development dysplasia of the hip Developmental Legg–Calvé-Perthes disease Neuromuscular Polio Cerebral palsy (hemiplegia) Infectious Pyogenic osteomyelitis with physeal damage Trauma Physeal injury with premature closure Overgrowth Malunion (shortening) Tumor Physeal destruction Radiation–induced physeal injury Overgrowth

CLINICAL MANIFESTATIONS AND DIAGNOSIS. Signs and symptoms associated with leg length discrepancy usually are related to the underlying cause. Approximately 65% of the growth of the entire lower extremity comes from the distal femoral (37%) and proximal tibial (28%) physes. Thus, growth disturbances about the knee can have the most adverse effect on leg length. Determination of the skeletal, or bone, age allows for a relatively accurate assessment of remaining growth. Bone age is determined from an anteroposterior radiograph of the left hand and wrist. It is possible to estimate the ultimate discrepancy at maturity. The clinical methods available are less accurate than the radiographic techniques, but they are useful. The most common clinical measurement is leveling the pelvis. Blocks of various thickness may be placed beneath the foot on the involved side until the iliac crests are level. The thickness indicates the amount of discrepancy. Adult sitting height is approximately 52% of total height in the male and 53% in the female. Thus, two times the predicted length of the normal leg at maturity gives a close approximation of the anticipated adult height. This height plays an important role in determining equalization. Lengthening procedures are more applicable in predicted short adults, whereas shortening procedures are generally used for predicted normal height or taller individuals. In either case, acceptable body proportions must be maintained. Children with neuromuscular disorders such as spastic hemiplegia benefit from 1–2 cm of shortening on the involved side to improve the swing phase of gait and increased toe clearance. Only extremities that are neurologically normal should be considered for complete equalization of leg lengths. Angular deformities and limitation of motion are important considerations in children with unequal leg lengths. This is especially true when lengthening procedures are being considered. A child with a dysplastic acetabulum may subsequently experience a

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hip dislocation if femoral lengthening is attempted. Thus, any significant angular deformities or joint abnormalities should be corrected either before or simultaneously with leg length equalization. RADIOGRAPHIC EVALUATION. Radiographic evaluations are the most accurate methods of assessing leg lengths. Four different types of radiographic techniques are available. The teleoroentgenogram is a single exposure of both lower extremities. Its primary indication is for young children, usually younger than 5 yr. There is a small amount of magnification error present, but it has the advantage of demonstrating any associated angular deformity. The orthoroentgenogram consists of three separate, slightly overlapping exposures of the hips, knees, and ankles on a long cassette. Bone length is measured directly on the radiograph. There is less magnification, and it is relatively accurate and will demonstrate angular deformities. The scanogram is a simple, accurate method of assessment. It consists of three narrow exposures of the hips, knees, and ankles on a standard cassette with a radiographic ruler laying next to the extremity. Thus, minimal magnification is present, and accurate measurements can be made. However, angular deformities cannot be fully visualized and, if present, can lead to errors in measurement. Computed tomography is the most accurate technique and will also show angular deformity. TREATMENT. The psychological status of the child as well as the parents is an important consideration in treatment selection. Some equalization techniques are simple and safe, whereas others, especially lengthening procedures, are complex with high complication rates and require strict cooperation by the child and parents. Discrepancies of greater than 2 cm at skeletal maturity usually require treatment because these often cause the patient to limp. Equalization can be achieved by nonsurgical and surgical methods. In general, the goals are to maintain adult height (5'6" in males, 5'0" in females) and adequate body proportions. Shortening procedures are preferred, and lengthening procedures should be used cautiously. Orthotics and Prosthetics. Orthotic devices are generally indicated for discrepancies between 2–3 cm in skeletally mature individuals. A heel lift is frequently all that is necessary to provide the patient with a normal gait. Because of normal pelvic rotation during the gait cycle, complete equalization is not necessary. The smallest lift that will allow the patient to walk without a limp is all that is necessary. Prostheses are necessary for severe discrepancies or uncorrectable deformities. Extremity-Shortening Procedures. Three procedures are used to shorten the longer extremity. Epiphysiodesis is indicated in children who have 5 cm or less predicted discrepancy at maturity, have adequate remaining growth for satisfactory correction, and have a predicted relatively normal, corrected adult height. It requires accurate timing to achieve equalization of the leg lengths at maturity. The disadvantages of epiphysiodesis include shortened stature, surgery on the unaffected extremity, the possibility of an angular growth deformity, and the irreversibility of the procedure itself. Percutaneous epiphysiodesis under fluoroscopic control currently is the most popular technique. This is an outpatient procedure that is effective and has a low complication rate. Epiphyseal stapling is performed to slow the rate of physeal growth. Three staples inserted extraperiosteally on each side of the physis are required to retard growth adequately. Once equalization has been achieved, the staples are removed, allowing normal growth to resume. Stapling on one side of the physis can be used to correct angular deformities about the knee. Bone resection is indicated for ultimate discrepancies of 5–6 cm in adults or adolescents who have inadequate remaining growth to undergo an epiphysiodesis. The femur can be shortened up to 6 cm and the tibia-fibula, up to 3 cm before irreversible muscle weakness occurs. Extremity-Lengthening Procedures. The advantages of lengthening are equalization of significant leg length discrepancies; maintenance of ultimate adult height; preservation of normal body proportions; surgery on the affected limb; correction of existing angular deformities; and elimination of orthoses. The disadvantages are that they are technically difficult to perform and have a significant complication rate. Common complications include pin tract infection, wound infection, hypertension, hip and knee subluxation, ankle equinus, loss of correction, delayed union, metal failure, and fatigue fractures after metal removal. Transiliac, or pelvic lengthening, osteotomies can provide a gain of up to 3 cm in length. They are generally reserved for those

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individuals with mild discrepancies who have ipsilateral shortening with acetabular dysplasia, an asymmetric pelvis, or possibly decompensated scoliosis. The callotasis technique allows for progressive lengthening of the femur or tibia. An osteotomy is performed after application of an external fixator lengthening system. There is no initial lengthening. After 7–10 days, lengthening is begun at 1.0 mm/day (0.25 mm every 6 hr). This allows elongation of the forming callus. Significant lengthening of the bone can be achieved with this technique. Once the desired length has been achieved, the callus is allowed to consolidate. The lengthening device is removed after consolidation. The entire process requires approximately 1.0 mo per centimeter lengthened. The advantages of this procedure over previous lengthening techniques is that it requires only one procedure, allows greater lengthening, and has a lower complication rate. Occasionally, a combination of a transiliac, femoral, or tibial diaphyseal lengthening and possibly leg-shortening procedures such as epiphysiodesis is necessary to equalize leg lengths. The combination of femoral diaphyseal lengthening and contralateral epiphysiodeses is very useful for discrepancies of 8–10 cm when a single lengthening is insufficient for complete correction. Aaron A, Weinstein D, Thickman D, et al: Comparison of orthoroentgenography and computed tomography in the measurement of limb-length discrepancy. J Bone Joint Surg 74A:897, 1992. Anderson M, Green WT, Messner M: Growth and predictions of growth in the lower extremities. J Bone Joint Surg 45A:1, 1963. Barry K, McManus F, O'Brien T: Leg lengthening by the transiliac method. J Bone Joint Surg 74B:275, 1992. Canale ST, Russell TA, Holcomb RL: Percutaneous epiphysiodesis: Experimental study and preliminary clinical results. J Pediatr Orthop 6:150, 1986. Gruelich WW, Pyle SI: Radiographic Atlas of Skeletal Development of the Hand and Wrist, 2nd ed. Stanford, CA, Stanford University Press, 1959.

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