Management of Leg Length Inequality

James J. McCarthy, MD, and G. Dean MacEwen, MD

Disclosures

J South Orthop Assoc. 2001;10(2) 

In This Article

Methods of Assessment

Objectives

Treatment objectives need to be carefully considered. The decision to treat depends not only on the expected leg length inequality, but also on the disability that it may or may not cause. Usually the goals are to obtain leg length equality (typically within 1 cm), produce a level pelvis, and improve function. Some patients may actually benefit from a small leg length inequality, such as children with hemiplegic cerebral palsy, polio, or other neuromuscular disorders who can use the leg length inequality to aid in clearance in the swing phase of gait.[21] The decision to shorten versus lengthen a limb will depend on the patient's actual or predicted height and the degree of leg length inequality. General guidelines for the treatment of leg length inequality are outlined in the Table .

There are other less common indications for limb equalization techniques. Prosthetic fitting can be improved with limb equalization techniques.[22,23] Shortening, usually by epiphysiodesis, can be done when an amputation has left a stump that is too long to accommodate a prosthetic foot or to equalize knee height. Usually a minimum of 6 cm of leg length inequality (at maturity) is needed to accommodate an ankle/foot or knee prosthesis, and 10 to 12 cm is ideal. Limb lengthening may be beneficial in extremely short amputations to aid in the control and security of the prosthesis. For standard prosthetic fitting, a residual limb length of 12 to 15 cm in the femur or tibia is necessary.[24]

The use of limb lengthening for apparent leg length inequality can be considered. If a patient has significant foot or pelvic asymmetry, limb equalization techniques may be used to produce a level pelvis and decrease the limp.[25] Lengthening in achondroplasia and other dysplasias is controversial and often involves multiple procedures, staged throughout childhood.[26] The goal in these cases is to increase height, not to reduce leg length inequality.

Surgical treatment of leg length inequality can be done at the tibia, femur, or pelvis. The choice of which bone to treat depends on the source of the inequality and the preference of the patient and surgeon, as well as any underlying conditions. Typically the part of the extremity (tibia or femur) that is short is lengthened, or the opposite side is shortened. There are specific reasons why this general rule may not be followed, such as a distal or proximal unstable joint. A tibial lengthening may be considered for a patient with hip dysplasia even if the patient's leg length inequality is in the femur, in an effort to prevent hip subluxation during lengthening. Typically, if an acute shortening is done, the femur is shortened. Knee height asymmetry does not appear to be a significant disability if kept less than 4 cm.[20]

Numerous radiographic and clinical measurements have been used to assess leg length inequality. Clinical assessment should include determination of a level pelvis with the patient standing. Any significant leg length inequality should be apparent, though the location of the inequality may not be apparent. Care must be taken to ensure that the patient is standing with both knees and hips extended and in neutral abduction/adduction. A set of blocks of various heights can be placed under the shorter leg and the position of the pelvis examined to estimate the amount of inequality. This is a more accurate method of determining leg length inequality than using a tape measure.[27] A standing anteroposterior (AP) radiograph of the pelvis, with an appropriately sized block under the shorter limb, will document these findings.

The Galeazzi test, typically used to assess hip dislocation, can also be used to assess a disorder that results in a significant leg length inequality. The examination is done with the patient supine and the hips and knees flexed. The test is positive if the height of the knees is asymmetrical (Fig 1). It is also helpful in determining whether the leg length inequality is primarily from the femur or the tibia and in assessing leg length in someone with knee or hip flexion contractures.

Figure 1.

Galeazzi test.

Various radiographic studies have been used to determine leg length inequality. The teleroentgenogram is a single exposure AP radiograph of the lower extremity with a ruler. This is subject to magnification error of 5% to 10% at the outer border of the film but has the advantage of showing coronal (angular) deformities and is not subject to movement errors.[20] Orthoradiography incorporates three separate exposures (of the hip, knee and ankle) in an effort to avoid magnification errors. Scanography uses a similar technique, but exposure size is reduced and all three exposures are on one film cassette. Both orthoradiography and scanography are subject to movement errors, and angular deformities cannot be assessed. All the techniques are inaccurate if the patient has knee or hip flexion contractures, or if they are simply flexing the knee or hip asymmetrically at the time of exposure. Lateral radiographs, or separate (prone) radiographs of the femur and tibia with a ruler, can be obtained to assess leg length in patients with knee flexion contractures.

The use of CT to assess limb length has increased. It uses less radiation and is more accurate than conventional radiographic techniques in patients with knee or hip flexion contractures.[28] Ultrasonography is now being used as well, primarily as a screening tool.[29]

Once the current leg length inequality has been measured, a prediction of the ultimate leg length inequality at skeletal maturity will be needed to determine treatment. The three methods typically used to do this are the arithmetic method, the growth remaining curve, and the Moseley straight-line graph.[30] The multiplier method has also been recently described, in which an arithmetic formula is used to determine limb inequality at maturity.[31]

The simplest is the arithmetic method.[32] This method assumes growth of the distal femur to be 1 cm per year, growth of the proximal tibia to be 0.6 cm per year, and skeletal maturity at age 16 for boys and age 14 for girls.

The growth-remaining graphs relate chronologic age to limb length to determine a child's growth percentile. Using this, the remaining growth of the tibia or femur can be determined graphically.

In an effort to combine this information into one graph, Moseley[30] incorporated the same data into one straight-line graph. The advantage of this technique is that several measurements can be plotted on one graph. The Moseley straight-line graph relies on determination of bone age as estimated from a left hand/wrist film.[33] When these three techniques were evaluated, there was little significant difference between them.[34]

There are several sources of error in determining leg length inequality at skeletal maturity. Error can occur from radiographic technique, patient position, determination of skeletal maturity, and measurement. Additionally, growth inhibition may not be constant with age and may worsen or improve with time, leading to underestimation or overestimation of the leg length inequality at maturity.[35]

We use the Moseley straight-line graph and attempt to obtain at least three data points, separated by no less than 6 months, to predict leg length inequality at skeletal maturity. This method is then confirmed by the arithmetic method. We tend to delay slightly (3 to 6 months) from our estimate of when to perform an epiphysiodesis, so that we lessen the risk of making the current longer leg ultimately the shorter leg.

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