Management of Leg Length Inequality

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Management of Leg Length Inequality

http://www.medscape.com/viewarticle/423194

J South Orthop Assoc 10(2):73-85, 2001. J. McCarthy, MD, and G. Dean MacEwen, MD

Abstract

Leg length inequality is common. Treatment objectives include obtaining leg length equality, producing a level pelvis, and improving function. Clinical assessment should include determination of a level pelvis with the patient standing using a set of blocks of various heights to estimate the amount of leg length inequality. Radiographic measures include the teleroentgenogram, orthoradiograph, and computed tomography (CT). A prediction of the ultimate leg length inequality at skeletal maturity will be needed to determine treatment. Our guidelines for treatment of leg length inequality are as follows: <2 cm -- no treatment or a lift in the shoe; 2 to 6 cm -- an epiphysiodesis or shortening procedure is considered; 6 to 15 cm -- a lengthening procedure is considered. A leg length inequality of 15 to 20 cm -- may require a staged lengthening, lengthening combined with epiphysiodesis, or amputation. Numerous complications of limb lengthening procedures occur frequently, even in experienced hands.

IntroductionLeg length inequality is common, 23% of the general population having a discrepancy of 1 cm or more.[1] The prevalence of leg length inequality requiring a corrective device, such as a lift, is approximately 1 in 1,000.[2] In this review, we discuss the etiology, functional effects, assessment, and treatment of leg length inequality.

The first published report of lengthening was by Codivilla[3] in 1905. He achieved lengthening by incremental maximal lengthening under anesthesia. There were numerous problems with stabilization of the fragments as well as the sequelae of sudden large lengthenings, including sudden death. In 1939, Abbott and Saunders[4] reported on their lengthening procedure using external fixation and incremental distraction, much as we do today with a monolateral fixator. Wagner[5] developed a technique of open lengthening, in which the tibia or femur was divided and rapid lengthening was done until the desired length was achieved. The distraction gap was then bone grafted and plated. Although originally popular, this technique fell out of favor because of the need for multiple operations (at least three, including plate removal) and the extremely high rate of complications.

The Ilizarov technique and variations thereof are used most often today.[6] The procedure is named after Gavril Abramovich Ilizarov, a Russian physician who first used his technique to treat injured World War II veterans. Lengthening is usually done by corticotomy and gradual distraction with a ring fixator and fine wires.

Etiology

The numerous causes of limb length inequality can generally be divided into two broad categories: congenital and acquired. Congenital limb length inequality is due to limb hypoplasia syndromes, the most common of which is longitudinal deficiency of the fibula; hemihypertrophy syndromes, such as Klippel-Trénaunay-Weber syndrome; or skeletal dysplasias. Acquired causes include anything that injures or slows the growth of the physis, such as a bony bar due to trauma or infection; shortening, such as that from a femoral fracture with comminution or overriding bone fragments; and any systemic condition that results in asymmetric innervation or vascularization.

Functional Effects

The functional effects of leg length inequality on gait have been studied by several authors. Gait asymmetry requires a leg length inequality of at least 2 cm (3%).[7,8] Minor leg length inequalities (<2 cm) do not seem to alter the kinematics or kinetics of gait.[9] Larger inequalities are associated with greater mechanical work,[10] and equalizing limb length improves the symmetry of gait.[11]

The effect of gait asymmetry on back pain, scoliosis, and knee and hip arthrosis is less clear. The association between leg length inequality and back pain has not been established.[12-15] There does not appear to be an increase in the incidence of back pain in patients with small leg length inequalities,[12,14] though Tjernstrom and Rehnberg[16] have reported improvement in back pain in patients who have had lengthening for correction of large (3 to 14 cm) leg length inequalities. Before resorting to a limb equalization procedure, we suggest a trial of a shoe lift in a patient with a leg length inequality and back pain to determine whether equalizing limb length will improve the back pain.

It has been reported that the incidence of scoliosis is higher in patients with leg length inequality.[17,18] If the leg length inequality caused the scoliosis, it would be expected that the scoliosis would compensate for the inequality (with the convex of the curve toward the short leg), but in one third of the cases the opposite is true.[19]

The effects of leg length inequality on the lower limbs are largely speculative. Tjernstrom and Rehnberg[16] reported few lower extremity complaints in patients with a leg length inequality. The longer limb will place the hip in slight adduction, about 4° to 5° for a 2 cm leg length inequality, but only with equal weight on each limb and symmetric joint positions. There is no evidence that leg length inequality leads to early hip or knee arthrosis.[20]

Methods of Assessment

ObjectivesTreatment 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]

Measuring TechniquesNumerous 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.

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]

Assessment TechniquesOnce 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.

Treatment Methods

Treatment of leg length inequality involves many different approaches, such as orthotics, epiphysiodesis, shortening, and lengthening, which can be used alone or combined in an effort to achieve equalization of leg lengths.

OrthoticsLeg length inequality of 2 cm or less is usually not a functional problem. Often, leg length can be equalized with a shoe lift, which usually corrects about two thirds of the leg length inequality. Up to 1 cm can be inserted in the shoe. For larger leg length inequalities, the shoe must be built up. This needs to be done for every shoe worn, thus limiting the type of shoe that the patient can wear. Leg length inequalities beyond 5 cm are difficult to treat with a shoe lift. The shoe looks unsightly, and often the patient complains of instability with such a large lift. A foot-in-foot prosthesis can be used for larger leg length inequalities. This is often done as a temporizing measure for young children with significant leg length inequalities. The prosthesis is bulky, and a fixed equinus contracture may result.

EpiphysiodesisEpiphysiodesis is a reliable procedure that inhibits growth with few complications. This obviously cannot be done on skeletally mature patients, and the final leg length inequality and the degree of growth inhibition need to be predicted and are subject to errors. Because the procedure effectively shortens the longer leg and is usually done on the uninvolved side, it may be unappealing to the patient and family.

One of the most useful indications for epiphysiodesis is in conjunction with limb lengthening for large leg length inequality. By performing an epiphysiodesis, a second or third lengthening may be avoided. If a patient has a 10 cm limb length inequality and has gained 7 cm by lengthening, an appropriately timed epiphysiodesis can result in limb length equality for the final 3 cm discrepancy, without the need for a second lengthening.

Phemister[36] described another technique for epiphysiodesis. He removed a section of the epiphysis, then rotated it 90° and replaced the bone. Currently, the most common technique is the percutaneous drill epiphysiodesis, done with the aid of image intensifier. This technique has been reported to result in physeal closure in 85% to 100% of patients,[37-40] with few complications.[41] et al[41] compared the Phemister technique with the percutaneous technique and found the results to be similar. They preferred the percutaneous technique because of the ease of the procedure and decreased morbidity. Staple epiphysiodesis can be done, but it results in more complications and is more invasive. Often the staples are prominent or they back out.[42] Staple epiphysiodesis has the theoretical advantage of allowing for growth after staple removal. Percutaneous epiphysiodesis using transphyseal screws have also been used in an effort to provide a reversible method of inhibiting growth with less morbidity. This technique has been used primarily in the ankle for correction of angular (valgus) deformity.[21,43] We use epiphysiodesis commonly to correct predicted leg length inequality up to 5 or 6 cm.

ShorteningShortening techniques can be used after skeletal maturity to achieve leg length equality. Shortening can be done in the proximal femur using a blade plate or hip screw, in the mid-diaphysis of the femur using a closed intramedullary (IM) technique (Figs 2 and 3), or in the tibia. Shortening is an accurate technique[44] and involves a much shorter convalescence than lengthening techniques.[44,45] Quadriceps weakness may occur with femoral shortenings, especially if a mid-diaphyseal shortening of greater than 10% is done.[46] If the femoral shortening is done proximally, no significant weakness should result. Tibial shortening can be done, but there may be a residual bulkiness to the leg, and risks of nonunion and compartment syndrome are higher (Fig 4).[47,48] If a tibial shortening is done, shortening over an IM nail and prophylactic compartment release are recommended. We limit the use of shortenings to 4 to 5 cm leg length inequality in patients who are skeletally mature.

LengtheningLengthening is usually done by corticotomy and gradual distraction. This technique can result in lengthenings of 25% or more, but typically lengthening of 15%, or about 6 cm, is recommended.[49] The limits of lengthening depend on patient tolerance, bony consolidation, maintenance of range of motion, and stability of the joints above and below the lengthened limb.

Numerous fixation devices are available, such as the ring fixator with fine wires, monolateral fixator with half pins, or a hybrid frame. The choice of fixation device depends on the desired goal. A monolateral device is easier to apply and better tolerated by the patient. The disadvantages of monolateral fixation devices include the limitation of the degree of angular correction that can concurrently be obtained; the cantilever effect on the pins, which may result in angular deformity, especially when lengthening the femur in large patients; and the difficulty in making adjustments without placing new pins. Monolateral fixators appear to have a similar success rate as circular fixators, especially with more modest lengthenings (20%).[50]

About 30 days in the fixation device per centimeter of length gained are necessary for both lengthening and consolidation. In general, femoral lengthenings heal faster than tibial, as do lengthenings in younger patients (less than 14 years of age). Treatment of dysplasias, such as achondroplasia, is associated with fewer complications than treatment of limb length inequality.[51,52] The level of the corticotomy does not seem to have a significant effect in the tibia, and mid-diaphyseal appears to be the best in the femur.[51]

Other techniques, such as the Wagner technique, acute lengthening, and physeal distraction, are used much less commonly to obtain limb length equality. The Wagner technique involves immediate and more rapid lengthening followed by bone grafting and plating. When comparing these techniques, Arron and Eilert[53] and DalMonte and Donzelli[54] found that the Ilizarov technique resulted in fewer complications and does not require an additional procedure for plating and bone grafting. When we reviewed our results of lengthening in children with fibular hemimelia, we found that the use of the Ilizarov technique resulted in fewer procedures but increased pain scores and a slightly higher complication rate than the Wagner technique.

Acute correction is difficult to obtain and is limited to about 3 cm. Acute lengthening can be done in the mid-diaphysis of the femur or through an innominate osteotomy. The latter may be indicated for a patient with primary pelvic asymmetry.

Lengthening has also been done through physeal distraction. Although this is a less invasive technique in that no corticotomy is necessary, it can be painful if the physis acutely separates, and it may lead to premature physeal closure and septic arthritis. Currently, we do not routinely perform either acute lengthenings or lengthening through physeal distraction. Experimental methods of producing lengthening, such as transfer of cultured chondrocytes,[55] vascular surgery,[56] and periosteal sleeve resection[55] are being studied.

Large leg length inequalities can be treated by staged lengthenings or by simultaneous ipsilateral femoral and tibial lengthenings. Additionally, lengthenings can be combined with appropriately timed epiphysiodesis in an effort to produce leg length equality. Staged lengthenings are often used for congenital deficiencies such as fibular hemimelia, in which 15 cm or more may be needed to produce leg length equality. We typically plan for the final lengthening to be completed by age 13 or 14 years, and allow at least 3 years between lengthenings.

Lengthening of both the tibia and femur simultaneously requires aggressive therapy and treatment of soft tissue contractures. Curran et al[57] reported the need for surgical release of soft tissue contractures in 3 of 8 patients treated with simultaneous ipsilateral femoral and tibial lengthenings.

Lengthening over an IM nail can be done in an effort to decrease the amount of time the fixator needs to be worn and to prevent angular malalignment (Figs 5 and 6). This technique requires that the patient be skeletally mature and it carries a higher risk of osteomyelitis (up to 15%). Additionally, if premature consolidation occurs, a repeat corticotomy is more difficult.[58-60]

In this technique,[59] an IM rod is placed in standard fashion. Reaming must be at least 1.5 mm greater than the rod diameter (2 mm is preferable), and the rod should have minimal bowing (to allow for easier distraction). The corticotomy is made before the IM rod is placed and can be done with an IM saw. The fixator is placed with the pins either posterior (Fig 6) or anterior to the rod. A true lateral view is needed to ensure that there is separation between the rod and half pins. A technique of using a guide wire and cannulated drill will help prevent unnecessary drill holes. If the rod is left short, the distal half pins can be inserted below the rod, although this can produce a stress riser below the IM rod. Initially, the rod is locked proximally. After the distraction period, the rod is locked distally and the fixator is removed. Care must be taken to ensure that there is ample rod length for stability distally after distraction. Lengthening over an IM nail will obligatorily lengthen the anatomic axis of the femur, and if significant femoral lengthening is planned, it will medialize the mechanical axis.

A number of designs for totally implantable IM devices are being explored. Such a device would offer the advantages of producing immediate axial stability, preventing angular deformity, and eliminating pin tract infections and scarring. The Albizzia nail uses a ratcheting mechanism that elongates with a rotational maneuver.[61] The biomechanics of this device and standard IM nails are similar and have been well studied.[62] A motorized, programmable IM nail has been developed and is currently under clinical investigation.[63,64] With all IM nails, significant angular correction must be achieved acutely, and even placing the nail in a patient with significant angular deformity may be impossible. The patients need to be close to skeletal maturity to prevent avascular necrosis of the femoral head (in the femur) or proximal tibial physeal closure, and the IM canal must be large enough to accommodate the IM nail.

Complications

Numerous complications of limb lengthenings occur frequently, even in experienced hands. Complication rates vary significantly from reported studies and seem to depend on degree of lengthening, definition of complication, and the surgeon's experience.[65] Complication rates from most series, including ours, are about one per procedure, and many of these require operative treatment.[51,57,66] Fortunately, the ultimate objective often can still be obtained. The most common complication is pin site infection. Depending on how it is diagnosed, treated, and reported, this complication may occur in nearly every patient. Numerous pin care protocols have been developed. Some authors are showing good success with a shower regimen after the incisions have healed. We use this in combination with standard cleaning of the pin sites and oral antibiotics if there is excessive discharge, redness, or swelling. Most patients have periosteal reaction around the pin sites, which may be an early indication of loosening.[67]

In femoral lengthenings, knee range of motion uniformly decreases by an average of 37°, but at follow-up the mean loss in range of motion is usually minimal.[68] Other more ominous complications include fracture, osteomyelitis, or joint subluxation. The incidence of these more serious complications is about 25% with an experienced surgeon.[65]

Other less commonly considered effects of limb lengthening include muscle weakness,[69,70] pain, and possible physeal inhibition. The later effect is extremely important if lengthenings are planned for younger patients with open physis. Hope et al[71] found little difference in growth velocities before and after lengthening, but Viehweger et al[72] found growth inhibition in the tibia after lengthenings in children. Review of our patients has shown no significant decrease in the rate of growth after lengthening, though these have largely been femoral lengthenings. Unlike pain associated with conventional surgery, pain due to lengthening seems to continue beyond the postoperative period and through the lengthening and consolidation phases,[73] until the fixator is removed.

The use of somatosensory evoked potential monitoring may be helpful in preventing neurologic injuries, especially of the peroneal nerve.[74] The use of ultrasound and/or electrical stimulation, while not routinely prescribed, may decrease the time to consolidation.[75]

Side Bar: Editorial Perspective

The problem of leg length inequality is an ancient one. From the obvious congenital malformations resulting in hugh discrepancies to the more subtle leg length discrepancies causing minor limps, the problem is actually extremely common. For many years, the orthopaedic community has wrestled with the inherent difficulty of lengthening the short leg, but in more recent years, shortening of the long leg has received equal attention and, because of its simplicity, some large measure of success. This article by McCarthy and MacEwen reviews the past 40 years of experience in the prediction, diagnosis, and management of leg length discrepancy. It summarizes the classification of leg length discrepancy, clearly advises the method of treatment best suited to the deformity, and warns us about the significant difficulties inherent in the art of limb lengthening.

Reprint AddressReprint requests to J. McCarthy, MD,

Shriners Hospitals for Children, Philadelphia,

3551 N Broad St, Philadelphia, PA 19140.