Detecting And Treating Leg Length Discrepancies
Chronic overuse problems that persist despite appropriate care are the hallmarks of a leg length discrepancy (LLD) in an athlete. While the symptoms associated with LLDs are diverse and, at times, vague and confusing, you should suspect limb length asymmetry when athletes have back or lower extremity complaints. Leg length asymmetries appear to be the third most common cause of running injuries and occur in 60 to 90 percent of the population. In regard to classifying LLD, the two major categories are structural and functional. The one minor category is environmental. Structural discrepancies result from an actual anatomic shortening of one or more of the bones of the lower extremity. This can occur from a growth plate injury during childhood or adolescence, fractures or genetic and acquired conditions that affect bone growth. Structural leg length differences can also result from spinal abnormalities such as scoliosis. Functional leg length differences usually occur as a result of muscular weakness or inflexibility at the pelvis or foot and ankle complex. They include pelvic obliquity, adduction or flexion contractures of the hip, genu varum, valgum or recurvatum, calcaneovalgus, equinovarus and rearfoot pronation. Environmental factors such as drainage crowns built into roadways, banked running surfaces, and excessive wearing of shoes can create a situation that mimicks a leg length difference. These environmental factors can also either accentuate or correct structural and functional length differences depending on how the athlete is running on a given surface. Know The Compensations And Symptoms Of LLD The spine, pelvis and lower extremity are all involved in the compensation of leg length asymmetry. Leg length asymmetry causes the center of gravity to be shifted to the short leg side. Most commonly, the compensations associated with limb length asymmetry include pelvic tilt (to the short side), lumbar scoliosis (convex to the short side), knee flexion (increased on the long side), genu recurvatum (on the short side), subtalar joint pronation (on the long side), and ankle plantar flexion and foot supination (on the short side). The most common symptom associated with LLD is backache. Other symptoms affecting the lower extremity with a structural discrepancy usually appear first on the long leg side and include flank pain, arthritis of the knee, psoasitis, arthritis of the hip, patellar tendinitis, patellofemoral pain syndrome, plantar fasciitis, medial tibial stress syndrome and metatarsalgia. Symptoms affecting the short extremity include iliotibial band syndrome with lateral knee pain, trochanteric bursitis, sacroiliac discomfort, Achilles tendinitis and cuboid syndrome. If the patient just has a functional LLD, the symptoms will usually appear on the short side first and include plantar fasciitis, medial tibial stress syndrome, patellofemoral pain syndrome, illiotibial band syndrome, ipsilateral sacroiliac discomfort with contralateral low back pain, and secondary psoasitis. Essential Diagnostic Tips When it comes to ruling out LLD, your exam must be organized and systematic so you don’t overlook any clues that are suggestive and consistent with a short leg. To assess for asymmetry, palpate the iliac crests while the patient is standing. Be on the lookout for a pelvic side shift, lateral spine curvature (noting the convexity), frontal plane leg deviation (genu varum and valgum), sagittal plane leg deviation (hamstring and/or ankle equinus), transverse plane leg deviation (excessive femoral anteversion demonstrated by “squinting patella”), and/or unilateral foot pronation. If you see any of these, be sure to note whether it is occurring on the left or the right. Proceed to perform gait analysis so you can evaluate for asymmetries during ambulation. Dynamic gait findings should support static measurements. Evaluate the three cardinal body planes (frontal, sagittal, and transverse) while looking at each body segment. Analyze the head and neck for any tilt to one side or the other. It is common to see a tilt to the short side. Evaluate the shoulders for any tilt and be aware that it is most common to see tilts to the long leg side for balance. Note the arm swing for symmetry of motion. Also be sure to evaluate the spine for any curvatures or deviations. Watch the patient’s hips for any asymmetries in motion as the hip will drop to the short side. Evaluate his or her knees for any varum, valgum, flexion or recurvatum. Keep an eye on the position the heel makes to the ground at contact and his or her midstance as there is usually an increase in heel eversion on the long side. Since LLD produces an asymmetry, you’ll find the timing of the gait parameters will also be deviated. You may notice an early heel off on the short side. The long side will have a shortened swing phase while the short side will have a longer swing phase. The long side will have a longer stance phase while the short side will have a shorter stance phase of gait. Once you’ve identified LLD, you need to categorize the asymmetry as a structural or functional problem. A structural short leg manifests as a pelvic obliquity in which the iliac crest is low on the same side and becomes level with the use of a heel lift. A functional short leg secondary to foot pronation manifests as a pelvic obliquity in which the iliac crest is low on the same side and becomes level by placing the subtalar joint in neutral position. What The PronationTest Will Tell You You can use the pronation test to determine its effect in contributing to the LLD. Have the patient stand with his or her knees extended and the feet in the angle and base of stance. Have him or her place the subtalar joint in the neutral position. Palpate the iliac crests and record any discrepancies. Allow the patient to pronate. Re-evaluate the iliac crests as to their position and note any changes you see. Performing this test helps you determine one of three conclusions: • pronation has no effect on limb length; • pronation is causing a functional short leg; or • pronation is compensating for the long leg. Depending upon your findings, the pronation test enables you to decide whether orthoses or heel lifts are indicated in treating the LLD. If subtalar joint pronation has no effect on limb length, there will be no change between the iliac crests with neutral and pronated subtalar joint positions. If the iliac crest on the ipsilateral side is lower in pronation than in neutral subtalar joint position, then the subtalar joint pronation is causing a functional leg length asymmetry. In this situation, an orthosis with appropriate posting would be indicated to correct the LLD. If the iliac crest becomes more level when you examine it in the pronated position, then subtalar joint pronation is compensating for a structural LLD. Using a heel lift on the opposite extremity is indicated in this instance to correct the anatomic asymmetry along with decreasing the amount of compensatory long leg subtalar joint pronation. How To Determine The Amount Of LLD Once you’ve diagnosed and classified the LLD, you can proceed to quantify the discrepancy by either a direct or indirect method of measurement. The direct method involves measuring the distance between the anterior superior iliac spine to the medial malleolus. Unfortunately, the direct method is difficult to reproduce and fails to take into account functional LLDs. The indirect method is superior to the direct method. The indirect method of limb length evaluation involves reducing the pelvic tilt and leveling the sacral base by placing a material of a known thickness under the short leg while the patient is standing. The indirect method is reproducible and accurate in quantifying the amount of leg length discrepancy. In some cases, you may need to confirm the diagnosis with a roentgenograph. Top Treatment Insights The treatment for LLD often depends on whether or not symptoms are present. If the body is compensating for a length difference without causing biomechanical stress in other areas, correcting the difference may alter the patient’s body mechanics in such a way as to cause an injury. If the discrepancy is causing symptoms, you do need to address it in order for a full recovery to take place. Treatment also depends on the classification of the asymmetry. If your patient has a functional asymmetry due to unilateral foot pronation, you can correct it by emphasizing a properly posted orthotic. When it comes to environmental asymmetry secondary to improper foot gear or canted running surfaces, you can recommend new or appropriate foot gear or a change in the geometry of the running surface. You can use heel lifts to treat structural limb asymmetry. The purpose of the heel lift is to level off the sacral base and correct the compensatory scoliosis caused by the short leg. You can determine the amount of heel lift needed via the indirect method of evaluating a structural shortage. Again, have the patient stand with his or her subtalar joint in neutral. Place a material of known thickness under the short limb until the iliac crests are level. The thickness of the heel lift under the short leg is the amount of the patient’s limb length inequality. Initially, you want the amount of heel lift to be about half of the anatomic discrepancy because the superstructure is being realigned in a gradual manner. With feedback from the patient, you can determine the final amount of lift that will produce the best results regarding the underlying symptoms. Approximately a 1/4- to 3/8-inch heel lift can fit into the average adult shoe. If more correction is required, the patient may need an addition to the outside of the shoe. Editor’s Note: This article reflects the views of the authors and is not necessarily the views of the Department of Veterans Affairs of the Hudson Valley Health Care System in Montrose, N.Y. Dr. Rzonca is a Diplomate of the American Board of Podiatric Orthopedics and Primary Podiatric Medicine. He is a Staff Podiatrist within the VA Hudson Valley Health Care System in Montrose, N.Y. Dr. Caselli (pictured at right) is a Professor in the Department of Orthopedic Sciences at the New York College of Podiatric Medicine. He is also a Staff Podiatrist within the VA Hudson Valley Health Care System in Montrose, N.Y.
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