By Dr. Mark Hinkes, DPM Unequal limb length (ULL) is a clinical problem that is more common than most clinicians realize and is one for which most patients are rarely evaluated. Common problems associated with unequal limb length include instability in gait, falling, low back pain, sciatica, joint pain, IT Band Syndrome, chronic muscle strain, tendonitis, and failure of diabetic foot wounds to heal. Unequal limb length may be the result of a difference in the length of the leg bones caused by a birth defect, a leg fracture, infection, damage to a growth plate of the bone or as a result of hip or knee joint implant arthroplasty or genu valgum of one leg. ULL may also occur when the legs themselves are the same length, but due to neuromuscular injuries in the pelvis or upper legs, one leg or hip is held higher and tighter than the other. The unequally tightened muscles cause the legs to seem to be different lengths.

How do unequal limb length problems affect the foot?

Problems caused by ULL typically demonstrate unilateral pathology on the foot on the longer leg. Problems such as heel spur, plantar fasciitis, nerve entrapment syndromes in the heel and forefoot, hallux abducto valgus, digital deformities and ankle or sub talar joint pain are commonly seen. If ULL is unrecognized or undiagnosed, it can be a contributing factor in delaying the healing of diabetic foot ulcers. This problem is especially common under the first metatarsal, where 19% of all diabetic foot ulcers occur and the first or great toe where 24% of all diabetic foot ulcers occur.

How does ULL affect diabetic foot ulcer healing?

When there is an unequal limb length, the foot on the longer leg will tend to pronate or flatten out in an attempt to equalize the unequal limb length. This creates abnormal pressure against the medial side of the foot, and especially under the first metatarsal and great toe. As the foot rolls in and flattens, this causes continued pressure against the ulcer. In essence the ulcer site is not "offloaded," one of the necessary components of wound healing. Even if the patient is in an offloading surgical shoe and permitted to bear weight, the continuous pressure against the ulcer via pronation due to ULL delays the healing.

How much difference in ULL does it take delay healing of a diabetic foot ulcer?

Typically the difference in limb length in the average patient is small, ranging from 1/8" to 1/4". However, in some cases the difference can be 3/8" up to an inch or more.

Two quick ways to identify unequal limb length:

Measure your patient for a limb length inequality:

1. Have your patient lie supine on your examination table or chair.
2. Measure the distance from the umbilicus to the medial distal tibia on both sides.
3. Measure the distance from each ASIS to the medial distal tibia on each side.
4. The difference between the two measurements is the limb length inequality.

"Eyeball" your patient for a limb length inequality:

1. Have your patient sit on your treatment chair with their buttocks even all the way to the back on the chair.
2. Have them bring their legs together and then relax them.
3. Line up the legs and check to see if the level of the knees and ankles correspond.
4. Then while standing directly in front of the feet dorsi-flex them and look down to check the position of the bottom of the calcaneus bone of each foot relative to the other foot.
5. If there is a limb length inequality it should be plainly evident with this maneuver.
6. This will give you an "eyeball" estimate of the unequal limb length of the legs.

Here is how to figure the amount of correction needed to treat unequal limb length:

1. Based of your evaluation of the amount of ULL, place a piece of self-adhering felt under the calcaneus of the shorter leg.
2. Have the patient stand with equal weight on both feet and the feet spread apart about 12 inches.
3. Ask the patient if they feel "jacked up" on the side with the pad, if they feel level, or if they cannot tell any difference. Patients may take some time to sense any difference, especially if they are neuropathic.
4. Have the patient walk for a reasonable distance while concentrating to see if the pad feels comfortable or if it feels too high,
5. Ask the patient if there is any positive affect on any joint, musculo-skeletal, or low back pain, especially on the contralateral side. Don't be surprised if they report that there is some pain relief with the use of the pad.
6. A pad of 1/4" thickness will compress to about 3/16" after that patient walks on it, and padding of 1/2" will compress to about 3/8". Be mindful of the true thickness of the pad. If the original pad is 1/4" thick and it feels too high, remove half the thickness of the pad or replace the pad with a new 1/8" pad, and have the patient walk again.

A Happy Ending

Once the limb length issue is addressed, most diabetic foot ulcers go on to heal without delay and do not tend to reoccur as the abnormal pressure against them has been removed and the site is offloaded. The body can usually compensate for mild ULL differences, but not always. In these cases, an adhesive felt pad placed under the insole of the heel of the shoe on the short limb will act as a lift and can be a temporary solution. A more permanent solution is to fabricate a custom foot orthotic and have the lift added to the heel of the orthotic. Crepe material works best for this lift. In this way, the correction remains inside the shoe and out of sight.

For cases where the difference is greater than 1/2 inch, a modification to the sole of the shoe may be an option to correct the problem. Podiatrists have an advantage in this area of wound care as they have special training in clinical podiatric biomechanics. This science is a powerful tool that quantifies human locomotion function, and helps to understand issues of gait and ambulation and how foot structure affects its function. So in the case of a patient with diabetes who has a foot or great toe ulcer that fails to heal, faulty biomechanical function as a result of unequal limb length should be considered. A podiatry consultation may be appropriate for a biomechanical evaluation and fabrication of orthotics with a heel lift to control abnormal pronation due to ULL and prevent a recurrence of the ulcer.

About the Author

Dr. Mark Hinkes is the former Chief of the Podiatry Service and Director of Podiatric Medical Education for the Veterans Affairs Medical Centers in Nashville and Murfreesboro, Tennessee, part of the Tennessee Valley Healthcare System. He was Chairman of the Preservation Amputation Care and Treatment (PACT) Program for more than a decade. He is Board Certified by the American Board of Foot and Ankle Surgery, and the American Professional Wound Care Association, and is a Fellow of the American College of Foot and Ankle Surgeons. Dr. Hinkes spends time consulting, lecturing, and writing about foot health issues on his website, www.dr-mark.net. His most recent book, Healthy Feet for People with Diabetes, is a practical self-care guide designed for patient education.