Detecting And Treating Leg Length Discrepancies

Author(s): 
By Mark A. Caselli, DPM, and Edward C. Rzonca, DPM
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.

Comments

VERY HELPFUL, THANKS

P.Mitchel,C.Ped

If patient has a verified structural LLD of 6-8 mm, would you recommend orthotic height for the full 6-8 mm or 3-4 mm?

I have heard that many DPM's recommend half the height of LLD? Why or why not?

Thanks for the reply.

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