2/96 BioMechanics 1996 Desk Reference: Orthoses: Foot/Prefabricated: Lower Limb Length Discrepancies

BioMechanics
1996 Desk Reference

Orthoses: Foot/Prefabricated:
Lower Limb Length Discrepancies

Effective treatment of limb length discrepancies can include full-length lifts, orthoses—or a combination of both—and surgery in severe cases.

by Guido La Porta, DPM

Clinicians treating lower extremity musculoskeletal pathology must be on the lookout for limb length inequality. Limb length inequality is, in my experience, the most consistent finding during examination for lower extremity musculoskeletal complaints. Patients who present with unilateral signs and symptoms such as hyperpronation, halux valgus, metatarsalgia, Achilles tendinitis, and knee pain are prime candidates for length inequality as a primary or contributing etiology.

Limb length discrepancies of greater than 2cm frequently come to the attention of practitioners when patients present with compensatory gait and spinal deformities. While the incidence of limb length asymmetry in the general population is currently unknown, patients presenting with less than 2cm discrepancies probably are much more common than those presenting with greater than 2cm discrepancies.

Categories and Compensations

Limb length discrepancy is subdivided into structural and functional categories. A structural asymmetry is an actual shortening of the skeletal system between the head of the femur and the ankle joint mortise. Functional discrepancy is secondary to abnormal or altered lower extremity mechanics. A third category of environmental discrepancy, secondary to either poor footwear or training maneuvers, also has been suggested. Regardless of the etiology, limb length asymmetry usually manifests itself as lower extremity injury or low back pain. A decision to treat asymmetry less than two centimeters should be based on symptoms, activity level, or degree of compensation.

The body compensates for limb length asymmetry with three classic positions. Type I compensation presents with lumbar and cervical scoliosis; the pelvis tilts downward on the short side and the head and shoulder tilt downward on the long side. The long side demonstrates hyperpronation and increased arm swing. Type 2 compensation presents with lumbar scoliosis; the pelvis tilts downward on the short side and the head and shoulder are level. Type 3 compensation presents with no sound column compensation. The head and shoulder tilt toward the shorter side. Type 1 compensation is more common in adults while Type 3 is more common in children.

Measurement

Clinical measurements of limb length discrepancy are accomplished by either the direct or indirect method. The direct method involves measuring the distance from the anterior superior iliac spine to the medial malleous. Variations of the direct method include using the lateral mallelous, umbilicus, or xiphoid process. The direct technique, however, can be inaccurate due to joint contracture, pelvic obliquity, and difficulty in finding landmarks. As such, the indirect method is often preferable. This method involves palpation of the iliac crests while the patient is weightbearing. The anterior and posterior superior iliac spines should be measured to obtain consistent values. Although pelvic height differences may influence this measurement, palpation of the top of the greater trochanter should alert the clinician to this possibility. By using different landmarks, the clinician should be able to differentiate between leg length inequality, pelvic rotation, and pelvic height differences.

A more accurate measurement can be obtained using radiographs or computed tomography. These tests, however, require proper positioning and involve some expense. Although clinical measurement maybe more feasible, the more accurate diagnostic tools are necessary when surgical intervention is planned.

Treatment

Structural inequalities up to 10 mm may be treated with lifts within the shoe. Full-length lifts (as opposed to heel lifts) are recommended as heel lifts may produce secondary pathology such as stress concentration and Achilles tendon shortening. Length inequalities greater than 10 mm may require a combination of in-shoe lifts and modification to other portions of the shoe. A thorough musculoskeletal evaluation is required as there is sure to be muscle imbalance in long-standing deformity. Lifts should be instituted in stages to allow mechanical changes to occur gradually.

Functional inequalities—especially those caused by hyperpronation—may be treated with functional orthoses. Although prefab devices are very useful, certain pathology involving Tibules Posterior dysfunction or knee pain may require custom-made devices. Symptoms primarily related to poor shock absorption may be effectively treated by soft tissue supplements such as Plastazote.

Larger inequalities that do not respond to mechanical therapy, and are functional and/or cosmetic concerns, may require surgical intervention. Surgical intervention may involve the use of immaculate distraction with internal fixation or gradual distraction with external fixation. Larger inequalities are more amenable to gradual distraction techniques and may also involve simultaneous lengthening of the shorter extremity and shortening of the longer extremity. The tibia is more frequently lengthened than the femur.

The current interest in limb length discrepancy has been fueled in part by the introduction of the Ilizarov method of gradual distraction to augment standard surgical techniques. The Ilizarov principle of gradual distraction is not fixator specific. While lengthening without associated deformities may respond well to simple linear fixators, complex multiplanar deformities are best handled by Ilizarov frames which allow correction in all three body planes simultaneously.

The clinician who treats lower extremity musculoskeletal pathology must have a high index of suspension for leg length inequality. This entity is very common and may present as a structure of functional pathology. Inequalities as seemingly insignificant as 3mm may have a profound impact on the active athletic population. Effective treatment may be provided by the use of full length lifts, orthoses, or a combination of both. Surgical intervention is reserved for severe cases and may involve either immaculate or gradual distraction.

Guido LaPorta, DPM, is a founding member of the American Academy of Podiatric Sports Medicine, and a diplomate and past president of the American Board of Podiatric Surgery.

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