These expert panelists share their approach to limb length discrepancies and the roles that orthotics and orthotic modifications can play in addressing these discrepancies. They also offer pearls on conservative care for Morton’s syndrome.
What method do you use for assessing limb length discrepancy and how do you determine if the degree of discrepancy is contributing to the presenting pathology?
As Joseph D’Amico, DPM, notes, most experts and texts indicate that a limb length discrepancy of 1 to 1.5 cm is extremely common and does not produce pathological effects in the average individual. However, he says almost everyone agrees that discrepancies greater than 1.5 cm and certainly those over 2.0 cm produce pathomechanical consequences and symptomatology.
“Determining the importance, degree of abnormality and correction for leg length discrepancies remains one of the most controversial issues in medicine today,” notes Lou Pack, DPM.
Acknowledging how comprehensive the subject of limb length discrepancy is, Dr. Pack says physicians often focus on the best method of measuring length differences but emphasizes it is more important to focus first on whether those differences are structural or functional.
“If we don’t, those measurements, as accurate as they may be, may at times be worthless,” says Dr. Pack.
J. David Skliar, DPM, cautions that limb length discrepancy measurement is only meaningful when the patient is standing with equal weight on both limbs (if possible) in an anatomical stance position. Both he and Dr. D’Amico suggest palpating the anterior superior iliac spine or posterior superior iliac spine, and then have the patient place his or her thumbs in the same position, which can help achieve a more accurate visual impression of which side is elevated.
One should place index cards under the short limb’s heel in increasing numbers until the pelvis appears level. At this point, Dr. Skliar says one should remove the index cards and measure the thickness of the cards with a standard ruler.
Similarly, Dr. Skliar advises that the simplest way of determining if the limb length discrepancy is related to presenting pathology is to place a temporary lift of at least half the measured shortening to the patient’s shoe. If there is considerable pronation to the same foot, he says one should use an inversion strapping with the heel lift.
Furthermore, the limb length discrepancy should correlate with a clinical examination of the subject’s gait, according to Dr. Skliar. He notes that if the center of gravity shifts to the short side, the longer limb may be externally rotated or the corresponding foot may be pronated with or without genu valgum. The shoulder of the longer limb is usually lower, yielding what he notes would appear to be a longer arm length.
Dr. D’Amico assesses limb length via computer assisted gait analysis two weeks after dispensing the orthotic. He says parameters that are particularly important to be symmetrical include: calcaneal stance duration, single limb support, stance, swing, midstance and propulsive phases of gait.
In his biomechanical examination, Dr. D’Amico notes the position and symmetry of the limbs first while the patient is seated. Then with the patient standing, he places his hands on the superior brim of the pelvis and notes any asymmetry. In this manner, one can easily observe discrepancies of less than ½ inch, according to Dr. D’Amico.
Dr. D’Amico and Dr. Skliar recall seeing Richard O. Schuster, DPM, place a large carpenter’s level across the patient’s knees while he or she was seated to assess below knee shortages and then recheck it with the patient in neutral subtalar position.
Before rendering definitive therapy, Dr. Pack routinely sends limb length discrepancy patients for further consultation including a visit to a physical therapist, chiropractor or kinesiotherapist. He says these clinicians may diagnose things that he would never have considered as possible etiologies for the discrepancy, like tightened muscles in the shoulder region.
In some cases, it is obvious that correcting a leg length discrepancy has eliminated symptoms. In other cases, Dr. Pack thinks such correction can be preventative.
Dr. Pack believes any degree of abnormality decreases sports performance, increases the risks of injury and can later cause arthritic changes, adding that optimizing leg length equalization is far more important than physicians often realize. Although he has seen many patients with large differences who appear to be symptom-free, others with small degrees of abnormality have significant symptoms. Ideally, all leg lengths should be as equal as possible, according to Dr. Pack.
If a discrepancy is significant, how do you address it and what orthotic modifications do you employ?
All panelists emphasize the use of heel lifts. For a significant discrepancy, Dr. Skliar will determine the need for an additional heel lift, with or without an orthotic. He says one should recognize that a heel elevation greater than 1/2 inch cannot usually occur within the shoe itself and adding an elevation to the outside heel would be necessary. If there is excessive pronation on the longer side, he suggests using a corrective pair of orthotics with the heel lift incorporated on the short limb side.
If a structural deformity is present and/or if one has treated functional leg length abnormalities but the treatment has not maintained corrections, Dr. Pack advises placing small, incremental lifts under the insoles or custom orthotics on the shortened side. He prefers to have the lifts extend at least from the heel to the ball of the foot unless fit is an issue, in which case he will use a heel lift. Dr. Pack says one should use additional corrections until the patient feels overcorrected or that the symptoms are exacerbated. While he incorporated lift corrections into the devices themselves in the past, Dr. Pack no longer does so because functional abnormalities can cause leg lengths to change at any time.
If a discrepancy is significant, Dr. D’Amico employs the necessary amount of heel elevation to produce functional symmetry as documented on computer assisted gait analysis. Elevations of over 1/2 inch require a tapering to ¼ inch at the metatarsal region and then 1/8 inch distally, according to Dr. D’Amico. If a ½-inch lift cannot remediate a discrepancy, then he would refer the patient for physical therapy evaluation and probable sacroiliac mobilization. The patient would then return to Dr. D’Amico for reassessment of the situation.
What is your view of the incidence and significance of Morton’s syndrome, especially the short first metatarsal phase, in the production, perpetuation or aggravation of mechanically induced foot disorders? How can one conservatively manage this?
In one of his first published articles, Schuster performed a survey analysis of the incidence of Morton’s syndrome (as evidenced by a short first metatarsal) in a non-patient control group in contrast with a 1,000 patient population, notes Dr. D’Amico.1 In the adult control group, 33 percent had a short first metatarsal in comparison to 79 percent in the adult patient population group. Dr. D’Amico adds that Schuster concluded that the short first metatarsal phase of the Morton theory is “definitely one of the contributing factors in many orthopedic foot disorders.”
Calling Morton’s syndrome “a very insightful concept of forefoot hypermobility and subsequent excessive pronation,” Dr. Skliar says Morton described three osseous foot abnormalities that are visible on a dorsal-plantar X-ray of a foot that exhibited biomechanical problems.2 They are, in descending frequency: a short first metatarsal; hypermobility of the first segment (i.e. a cleft between the metatarsal base and the internal cuneiform with the base of the second metatarsal bone); and a posterior placement of the first metatarsal sesamoids. As Dr. Skliar explains, any of these three findings could present alone or in any two combinations, or all three could present together.
Dr. Skliar notes that Morton’s syndrome almost always results in a hypertrophy of the mass of the second metatarsal and/or sometimes a relative flattening of the second metatarsal head, or lateral bowing of the fifth metatarsal. In more advanced cases, he notes there can be a possible lowering of the navicular, a positive Helbing’s sign of the tendo-Achilles, abduction of the forefoot or internal limb rotation.
What Morton described is what podiatric physicians now recognize as a partial or complete compensation for what Root described as a forefoot varus and/or equinovarus, notes Dr. Skliar.3 However, he notes Morton attributed the underlying mechanism to “ligamentous laxity” acting on the sagittal plane rather than recognizing that it is a frontal plane problem. Compensation occurs at the rearfoot at the subtalar joint and involves the other two planes.
For Morton’s syndrome, Dr. Skliar suggests conservative management with rigid orthotics from the heel to metatarsal head. He advises posting at the heel and forefoot to accommodate the total varus influences of the forefoot, rearfoot and limb.
Dr. Pack sees Morton’s syndrome quite often as a contributing symptomatic factor in the adult patient population. He usually finds that incorporating a metatarsal pad or bar into a custom foot orthotic can treat the problem quite easily.
“The significance and incidence of Morton’s syndrome has been underemphasized as a major contributing factor in the production of pathologic foot function and subsequent deformity,” says Dr. D’Amico. “The presence of this deformity in any of the pathologic foot types only adds to the severity of dysfunction and deformity potential that is taking place.”
Dr. D’Amico notes that identifying this entity is relatively simple and one can address it by adding a Morton’s extension to the first metatarsal segment. As he notes, this restores a normal metatarsal parabola and the potential for improved function, providing one has identified and neutralized any accompanying structural deficiencies as well.
Dr. D’Amico is a Professor and Past Chairman in the Division of Orthopedics at the New York College of Podiatric Medicine. He is a Diplomate of the American Board of Podiatric Medicine, and a Fellow of the American Academy of Foot and Ankle Pediatrics. Dr. D’Amico is in private practice in New York City.
Dr. Pack is a Fellow of the American College of Foot and Ankle Surgeons and a Diplomate of the American Board of Podiatric Surgery. He is a Founding Fellow of the American College of Rheumatology and a Fellow of the Academy of Ambulatory Foot and Ankle Surgeons. He is in private practice in Georgia. Dr. Pack is a former Clinical Instructor of Medicine at Emory Medical School and a Consultant to the U.S. Navy SEALs.
Dr. Skliar recently retired from practice. He is a Fellow and Past President of the American College of Foot and Ankle Orthopedics and Medicine. He is a Professor Emeritus of the New York College of Podiatric Medicine and an Assistant Professor in the Division of Orthopedics at Barry University.
1. Schuster RO. Survey analysis of the Morton syndrome. J Natl Assoc Chirop. 1952; 42(5):35-41.
2. Morton D. The Human Foot, Hafner Publishing Co., 1964.
3. Root ML. Normal and Abnormal Function of the Foot, vol. 2. Clinical Biomechanics Corp., 1977, p. 298.