Keys To Recognizing And Treating Limb Length Discrepancy
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
As a one-limb single plane deformity, limb length discrepancy is capable of producing a number of compensatory changes that are ineffective in correcting the original deformity and may magnify the problem throughout all body planes. The nature of compensation is individually unique and determined by age, site, severity, flexibility, body type, weight and other variables.
A Closer Look At The Clinical Significance Of Limb Asymmetry
Since limb length asymmetry is such a common situation, we often regard it as normal. However, nothing could be further from the truth.
The musculoskeletal system is built to function most efficiently when neuromotor control is intact and there is adequate but not excessive joint ranges of motion in an aligned, symmetrical lower extremity complex. Since the foot represents the foundation for this complex, it is critical that it be properly aligned and function in the appropriate symmetrical, adaptive or stabilizing manner at each stage of the gait cycle.14,26,27 According to Von Baeyer’s 1898 “Closed Chain of Links,” postulate defects or deficiencies in one segment affect the entire chain.20
Perhaps the most obvious effects of LLD are on posture. Limbs with length discrepancies are obviously less efficient during gait but there are increased demands on postural musculature in an imbalanced musculoskeletal system during stance as well.1