Lower extremity asymmetry includes inequalities in length and size. Leg length inequality may be structural from abnormalities in any of the bones, nerves, or vasculature in the pelvis or limb, or functional as a result of contractures. Discrepancies in extremity size can also occur from a wide array of congenital, developmental, or acquired conditions that speed or slow growth. A thorough clinical history and careful physical examination are crucial to determining where the abnormality originates and its potential etiologies. The underlying etiology typically will dictate the course and outcome of the limb inequality.

• Timing of limb asymmetry is important: limb aplasias, hypoplasias, hyperplasias, and clubfoot are congenital, whereas discrepancies that become more evident as the child grows are usually acquired. Developmental dysplasia of the hip, and hemihypertrophy or hemihypotrophy are exceptions, as they may not be noted at birth.

• Risk factors for developmental dysplasia of the hip include firstborn status, female gender, breech position, positive family history, and oligohydramnios.

• Family history of any bony anomalies is helpful in elucidating if there is an underlying dysplasia, hemangioma, or other anomalies in the bony matrix that would affect growth.

• Skin abnormalities overlying the spine or progressive asymmetric deformities in the limbs may indicate the presence of spinal dysraphism or a tethered cord.

• Inflammatory processes, such as rheumatoid arthritis and hemophilia, can be associated with bony overgrowth.

• Hypotonia, weakness, or paralysis of a limb occurring in those with cerebral palsy or other neurologic disorders often results in growth inhibition from actual discrepancies or apparent ones due to contractures and posturing.

• Disorders or events that cause diminished blood flow to the leg, such as vascular injury, can result in growth interference.

• A medical and family history significant for cutaneous, arteriovenous malformations (AVMs) warrants evaluation for internal AVMs and underlying syndromes, such as Osler–Weber–Rendu.

• Vascular malformations on the limbs can stimulate growth in the limb that involves all growth plates, not just those adjacent to them.

• Tumors typically may cause shortened limbs in multiple ways, such as direct destruction and growth inhibition or postirradiation therapy; however, certain ones, such as Wilms tumor, may accompany accelerated growth.

• Infection and trauma history are important to elicit as they can cause leg length discrepancies by either impeding growth through physeal disruption or increasing growth by stimulating blood flow to the limb.

• Perform a careful and complete head-to-toe examination to determine whether the asymmetry is confined to the lower extremities or exists elsewhere, which may indicate an underlying syndrome.

• Utilize body proportions to determine which limb appears to be the affected one—the pathologic one may be smaller, shorter, larger, or longer depending on the etiology; then evaluate limb segments to ascertain the exact location of the anomaly.

• The true leg length is determined by using a tape measure to measure from the anterior superior iliac spine to the tip of the medial malleolus and the apparent leg length from the umbilicus to the medial malleolus, which can help determine whether the inequality is structural or functional, respectively.

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