Keys To Recognizing And Treating Limb Length Discrepancy
- Volume 27 - Issue 5 - May 2014
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If the scoliosis is present with the spine flexed and extended, it indicates a structural deformity and any limb discrepancy would be secondary. If the scoliosis is present only when the patient is standing (spine extended) and disappears when seated (flexed), then it is a functional scoliosis secondary to the primary LLD.1,14 With the pelvis dropped toward the shorter limb, there is a compensatory tightening of the iliopsoas muscle contralateral to the scoliotic convexity in an attempt to counteract lateral spinal deviation.1 This process flexes the hip, consequently flexing the knee, internally rotating the femur and increasing subtalar pronation, all effectively shortening the longer limb.
As a result of its anatomic configuration, the iliopsoas is incapable of effectively compensating for the lumbosacral scoliosis and may contribute to the formation of a proximal compensatory contralateral scoliotic curve. Continued spasm and adaptive iliopsoas shortening maintains and progressively magnifies this entire cycle of sequential internal derangement.
Additionally, the femoral head on the longer limb is being wedged into the acetabulum, thereby forcing the anterior pelvis posteriorly and proximally, further complicating this situation.22,23 A typical compensatory mechanism for a short right limb, whether it is a structural or functional LLD, would be right pelvic drop, lumbar and cervical scoliosis with iliopsoas contracture, left shoulder drop and head tilt. Fingertips would be lower on the longer side. Variations on this theme can and do occur, and depend on the individual compensatory mechanisms that are available.
Halliday and Karol examined the results of a three-dimensional kinematic and kinetic analysis along with Cybex strength testing of 35 children over 7 years of age with congenital or traumatic LLDs ranging from 0.6 cm to 11.1 cm.24 When it came to milder discrepancies, they found that the hip and knee of the longer limb was flexed to equalize limb lengths and level the pelvis and trunk.24 Some children decreased their normal hip and knee flexion, and vaulted over the longer limb while others laterally swung the longer limb during swing phase. Those with more severe discrepancies demonstrated equinus function on the shorter limb.
Each child walked in a different way as the concept of mechanical efficiency during gait suggests, traveling a certain distance using the least amount of energy possible.24 With equal leg lengths, there is minimal vertical translation of the center of mass, which is 4 percent of the height of the individual. With LLDs in which no compensatory mechanisms are in place, large vertical translations in the vertical center of mass would be visible with secondary gait inefficiency and fatigue. Researchers observed inefficient gait patterns in nine of the 35 children tested. This group was comprised of toe walkers and those in whom the limb discrepancy was 5.5 percent or more.
According to Subotnick, angle of gait variations in running result from limb length discrepancies.25 Short limb findings include external rotation for increased stability, posteroinferior pelvis imbalance and overstriding. The foot on the short limb is subject to a greater force for a shorter period of time in comparison with the contralateral extremity. Overstriding produces posterior central heel wear due to heel contact in front of the center of gravity, increasing the need for “braking” to avoid foot slap, thereby increasing anterior tibial activity with possible anterior tibial stress syndrome.25