Leg Length Inequality

Leg length inequality is common, with estimates of up to one-third having a 2-cm or less discrepancy mea­sured between the length of their legs (6,303). There are two basic types of leg length discrepancies: true and apparent.

Radiographic measurement is the most reliable. The scanogram technique avoids magnification by tak­ing separate exposures of the hip, knee, and ankle so that the central x-ray beam passes through the joints, giving true readings from scale (Fig. 14.23) (304,305). CT scanogram is still the standard, reducing errors from angular deformity (306). If the examination is done specifically for this purpose, economic cost can be competitive (multiple sections unnecessary) and radia­tion exposure less with microdose technique (307,308). Causes of true leg length discrepancy are many and can be classified by growth retardation versus growth stimulation (6,20). Growth retardation has included conditions such as congenital hemiatrophy, develop­mental hip dysplasia, Legg-Calve'-Perthes disease, slipped femoral capital epiphyses, polio, achondropla­sia and dyschondroplasia, and severe burns. Causes by growth stimulation include congenital giantism, Wilm's tumor vascular abnormalities such as Klippel- Trenaunay-Weber, thrombosis or femoral or iliac veins,

Figure 14.23 The scanogram technique avoids errors of magnification and is preferred for children who can remain still for three exposures.

and traumatic arterial venous aneurysms. Tumors such as giant cell, neurofibromatosis, and bony fractures can cause other growth retardation or growth stimu­lation. The child with true hemihypertrophy needs to be screened every four months for the possibility of Wilm’s tumor (6,309) up through the age of 8 and every 6 to 12 months through the age of 10. Eighty percent of Wilm’s tumors present prior to the age of 8, with an average age at presentation of 3 years. The tumor may be associated also with aniridia (lack of an iris in the eye) and secondary metastases to the skeleton. A firm, nontender abdominal mass may be palpated. Damage to the growth plate with trauma and epiphysiodesis, including fractures with marked-over riding of frag­ments, tend to cause more growth retardation.

Treatment objectives include obtaining leg length equality, producing a level pelvis, and improving func­tion. Leg length discrepancy of less than 1.5 cm is usually just observed. Shoe lifts can be utilized for dif­ferences up to 3 cm. Horizontal alignment of the iliac crest or sacral base in the standing position should also be witnessed with appropriate shoe lifts in place. Early attention should be given by the age of 7 or 8 to observe and record the pattern of growth and appro­priately time the growth plate arrest.

The Greulich-Pyle norms for skeletal maturation of the hand (310) and the charts of Green-Anderson (311) are used for prediction of future growth and the timing of surgery when stapling epiphysiodesis of the longer side is considered for true discrepancies between 3 and 6 cm. Stapling techniques across the physis produce a tethering effect and can be removed later once equal­ization has been achieved (312,313). Surgical epiphysi- odesis is an all-or-nothing procedure that completely and permanently arrests physeal growth. The prin­ciple is to produce a symmetrical bony bridge that tethers the physes and prevents future growth (314). Epiphysiodesis is most commonly performed two to three years prior to maturity (girls age 11 or 12 years; boys age 12 or 13 years).

Shortening procedures can also include removal of a section of bone for limb equalization performed in adults or adolescents who are no longer growing (11).

Skeletal age (year)

Figure 14.24 Grafts showing total leg length vs. skeletal age for girls. It provides useful analysis of leg length data, allowing a projection into the future on the basis of present status.

Skeletal age (year)

Figure 14.25 Grafts showing total leg length vs. skeletal age for boys. It provides useful analysis of leg length data, allowing a projection into the future on the basis of present status.

Figure 14.26

(A) Sequential metaphyseal lengthening. (B) Elongation through the active metaphysis promotes osteogenesis and strength by the large cross­sectional area across the lengthening gap.

A

Elongation through the metaphyses promotes osteogen­esis because metaphyseal bone is so active and promotes strength by the large cross-sectional area. The length­ening process begins approximately 5 to 10 days after surgery. Lengthening of 1 mm per day or approximately 1 inch per month is recommended (6,11). External fixators are worn until the bone is strong enough to support the patient safely. This usually takes about three months for each inch. A normal lifestyle during treatment is encour­aged. Some children even go swimming with the external fixator in place. Complications include pin tract infec­tions (most common), fracture, axis deviation, delayed union, and soft tissue contractures. A child whose fam­ily is not capable of sustained follow-up may be a poor candidate for limb lengthening. Significant patient and family education needs to occur, including preoperative and postoperative phases, preparing the child and family both physically and emotionally for the long treatment. Counseling services may prove helpful. Rehabilitation services are most helpful, including frequent physical therapy visits for any successful long-term outcome.