A Guide To Detecting And Treating Limb Length Discrepancy

Limb length discrepancy (LLD) can cause a variety of symptoms. There are a variety of common clinical techniques clinicians can use to help detect LLD. Radiographic imaging provides the best method for measuring LLD. Treatments vary but can lead to significant improvement of symptoms. Indeed, the detection and treatment of LLD can be a very satisfying aspect of a clinical biomechanics practice.

In cases of LLD, gait evaluation normally shows the dominance of one side or leg. As the patient walks down the hall, there is a tendency to lean to one side. One can see this on every step or every third or fourth step, but the lean is always to the same side. The head cups from center to the dominant side and then back to the center, but it does not go to the other side. The dominance may be to the longer or shorter side. The dominance to one side should disappear as one puts lifts in to correct LLD. Remember that dominance is a clue that a LLD may exist.

What is my normal standing examination? With the patient barefoot or shoeless, I palpate the anterior superior iliac spine (ASIS), the iliac crests (IC) and the greater trochanters (GT). Try to keep your fingers parallel to the ground as you find the same spot on each side. Sometimes, you will need to ask the patient if you and the patient are on identical spots. Especially when it comes to evaluating for LLD in obese patients, the ASIS is impossible to locate well. Crouching or kneeling to get one’s eyes level with the palpated landmark is vitally important.

Then one can place blocks of varying millimeters under the foot on the side considered shorter to seek evenness. It is great when all three landmarks show the same side is short. However, even then, it may take different heights to level the three landmarks. For example, a short left leg may show a 9 mm difference at the ASIS and a 6 mm difference at the greater trochanters and iliac crests.
One will often find a pelvic asymmetry. For example, one may see the IC high on one side, the ASIS low on that side, and the GT high, low or level. It is important to keep in mind that these quick clinical screens are just that. Fortunately, one can routinely determine the dominance in gait after the standing exam and start treatment at the first visit. When one notes pelvic asymmetry, radiographic evaluation is usually necessary. Be advised that tape measure examination is very inaccurate.

What Should You Look For In The Gait Analysis?
Leg or side dominance in gait is a useful clue that a LLD may exist. While watching the patient walk, see if one or more of the following occur.
• Head leans to one side
• Shoulder drops to one side
• Arm swing is greater on one side
• Arm position is further from body on one side
• More asymmetrical excessive pronation on one side

These findings are the basis of gait analysis for LLDs. There are several common patterns with LLDs.

Pattern A: Typical adult pattern (long left leg noted)
• Head leans/tilts to the left
• Shoulder drops to the left
• Trunk mass leans to the left
• Arm swing is greater on the right
• Arm position is further from the body on the right
• Excessive foot pronation on left

Pattern B: Typical youth pattern (long left leg noted)
• Head leans/tilts to the right
• Shoulder drops to the right
• Trunk mass leans to the right
• Arm swing is equal or greater on either side (right or left)
• Arm position is further from the body on the left
• Excessive foot pronation is equal or greater either side (right or left)

Understanding these two common patterns is easy if you call pattern A “compensated” and pattern B “uncompensated.” The complexity comes in recognizing partially compensated patterns and the involvement of pelvic asymmetries and scoliosis.

In the compensated pattern of a long left leg, the body attempts to level itself by increasing pronation of the left foot, dropping the arch and increasing left knee flexion. The eyes must be level so the head goes to the left as the left shoulder does. The compensation of a long left leg also causes a shift in trunk mass to the longer side with more compressive forces into the left hip socket. With excessive pronation increased on the left leg to flatten the arch, right arm swing increases to balance that motion. If there is more motion in the left leg, there will be more motion in the right shoulder as the patient moves in equal and opposite motions. As the trunk mass leans to the long left leg, the right arm moves further away from the body to help with balance.

In the uncompensated pattern of a long left leg, the body essentially falls to the short leg. This is a typical pattern that one sees in youths following growth spurts, adults who have never compensated or following hip replacements, knee injuries that limit extension and other injuries/surgeries.

With the majority of patients having at least a 3 mm short leg, our adolescent growth patterns do not leave us with equal leg lengths. As the body falls to the short right side, the head tilts to the right, the shoulder drops on the right, the trunk mass shifts to the right and the left arm moves further from the body to balance. This collapse on the right may produce greater foot pronation on the right or not, and therefore may produce greater arm swing on the left or not. If there is increased foot pronation on the right, there is foot breakdown.

Why The Standing AP Pelvic X-Ray Is Crucial
The most important part of the examination for LLD will be the standing AP pelvic X-ray with the patient in normal stance. Make sure the patient is standing with his or her feet in a normal angle and base of gait. Both knees should be equally straight and the patient should stand upright with good posture. The X-ray shows the hip height difference at the acetabulum, any pelvic asymmetries, the sacral base levelness and the lumbar spine. One X-ray is packed with very important information. The X-ray must be standing so there is a reference to walking and running activities.

Normally, the X-ray will agree with one’s clinical impression but frequently it will not. By using the hip height difference at the acetabulum, one can be sure of the exact LLD. I will always take this X-ray with the shoes and orthotics (if the patient has them) on when the orthotics have been designed to correct heel position (as with most custom-made functional foot orthotics). The two standing X-rays (barefoot versus shoes/orthotics) may reveal a significant difference.

What You Should Know About Lift Therapy
The utilization of lift therapy can produce dramatic clinical successes. Normally, the practitioner is correlating some pain syndrome (i.e. hip or low back pain) with abnormal functioning produced by LLD. Before noting a symptom response, one should initiate lifts. After taking the history, it is important to note common pain syndromes associated with LLD. These syndromes include but are not limited to:
• low back pain made worse with walking or running;
• hip pain made worse with walking or running;
• a history of multiple one-sided problems (i.e. left shin splints in 1996, left knee pain in 1998, left plantar fasciitis in 2002);
• overuse problems developing on one side only (Achilles tendonitis, plantar fasciitis, runner’s knee, foot stress fractures); and/or
• neurological problems (i.e. tarsal tunnel syndrome, Morton’s neuroma) with possible low back involvement.

When a gait evaluation demonstrates some or all of the six common findings for compensated or uncompensated LLD, place the patient in a normal angle and base of gait, and note any significant (observable) asymmetry of foot pronation. Palpate the three landmarks at the pelvic area. Many practitioners palpate the posterior superior iliac spines (PSIS) at this time. They are part of my pelvic asymmetry exam. If the ASIS, IC and GT are all higher on one side, one can be pretty confident that it is the longer leg. Use two pelvic landmarks and one femoral landmark. If only two of the three are higher, then X-ray evaluation is a must before using lifts.

I use 3 mm sheets of plastic under the short leg until the landmarks are level. Due to the inaccuracy of this technique, it is common that each landmark is slightly higher than the other two. One can normally feel comfortable within 3 mm. Since most athletic shoes only can accommodate for approximately 9 mm, if the initial evaluation shows 10 mm or more, begin lift therapy initially and build up to 9 mm over a six-week course of lift therapy.

There are many decisions to make when utilizing lifts. Fortunately, the process is normally slow and one can easily pace decisions. “Start low, go slow” is the lift therapy mantra. If one only measures a 3 mm LLD and a 3 mm lift eliminates leg dominance, the process is fairly simple. If one measures a 6 mm or more discrepancy, start lift therapy by adding 3 mm every two weeks. Always watch the patient walk before and after a new lift elevation. The gait should remain smooth from heel contact through propulsion. There should be less leg dominance. There should be no increase in shoe instability as the foot is lifted higher on the shoe. In addition, the patient should feel better.

At times, the added lift will not go well for the body. I tell patients they are fighting the lift. One may observe more jerking at the hip, some dragging of the shoe or a harder time moving through into propulsion. One will have to decide if the lifts are for athletic shoes only or if you need to place lifts into dress shoes as outer sole lifts.

Most patients help you decide upon these aspects due to their pain and inconvenience. The more pain they have, the more inconvenience they will tolerate. Most shoe repair stores will put lifts on the outer soles of dress shoes, carefully blending in the color so it is less obvious. In regard to midsole lifts with added forefoot flexibility tapered to the toes, only more select shoe repair stores will do this but they can be found.

Other Considerations With Lift Therapy
Heel lifts are far easier to use but not as effective. Heel lifts are inherently unstable since they produce more knee flexion and ankle instability.

For athletics, full foot lifts are crucial. The lift must extend into the metatarsal area as this area may be the only weightbearing surface over 50 percent of the time. A heel lift in an athletic patient who is up on the ball of his or her foot most of the time makes no sense. One should taper the lifts at the ends or cut them at the sulcus in order to avoid jamming the toes. When the LLD is over 6 mm, one can taper the lifts not just at the ends but starting at the midfoot. For example, a 12 mm lift may have all 12 mm under the heel with a slow taper forward, leaving 9 mm at the midfoot, 6 mm under the metatarsals and no lift at the end. This 50 percent rule of heel to metatarsal (in this case 12 mm/6 mm) is very commonplace and tends to allow smooth foot motion forward in lifts necessary with LLDs over 6 mm. This type of tapering is also very important in midsole and outer sole lifts.

Be sure to keep lift therapy separate from orthotic therapy. Attaching lifts to rearfoot posts normally does not make sense in LLDs over 3 mm if at all. Rearfoot posts for orthotic devices tend to be harder than most lifts. Applying lifts to rearfoot posts tends to increase the impact/contact phase shock. Lifts made of cork/rubber products are usually quite durable and shock absorbing. I keep a copy of the full length or sulcus length lift in the chart for future use. Again, be sure to keep the lift separate from the orthotic when utilizing both lifts and orthotics.

Using leather lifts is a good way to record pressure. There will be slightly more pressure on the side of the lift since the lift pushes the orthotic up into the foot more. In situations in which there was a marked increase in the pressure on one side before the lifts, the leather can help document a tendency to even out this pressure.

For the normal biomechanical patient, lift use can start on the first visit. If orthotic therapy is in use, level the amount of the lift the patient has built up to when the orthotics are dispensed for one month. Doing so makes sure the symptoms produced by the orthotics are separate from those produced by the lift. If the clinician is using asymmetrical orthotics for different foot function (i.e. right foot supinates, left foot pronates), carefully evaluate if that changes LLD landmarks. This may affect how much lift one finally uses. This also applies to similarly functioning feet (i.e. both pronators or both supinators) in which the orthotic correction is intentionally or inadvertently unequal.

For example, this could be the case when both feet pronate severely. Correction attempts symmetry but the right foot is controlled perfectly and the left foot partially. Therefore, since foot function affects hip height, orthotic therapy may affect the final results of how much lift one utilizes.

In Summary
A clinical biomechanics practice should increasingly consider lift therapy as a vital aspect of addressing LLDs. Many symptoms are related primarily to LLDs. Gait evaluation that documents leg dominance should heighten the practitioner’s suspicion. Palpable pelvic and hip landmarks with the use of measurement blocks should point toward leg length, pelvic asymmetry or both. Obtaining standing AP pelvic X-rays in normal stance is crucial when it comes to chronic pain patients, pelvic asymmetry or LLD over 6 mm.

Lifts should start low and increase slowly. Full length (or sulcus length) lifts are much preferable to heel lifts. Lift therapy should remain separate from orthotic therapy since each may require experimentation. Follow-up is crucial as one may need to alter the lift height changes to ensure that gait remains smooth and symptoms are responding.