limb length discrepancy

Contrary to popular belief and to findings in anatomy books, the human body is not symmetrical in appearance. One of the biggest potential problems in human asymmetry is when one leg is shorter than the other. Most of us are not symmetrical in regards to the length of our limbs. Limb length discrepancy (LLD) sometimes referred to as short leg syndrome is a problem of various origins which can lead to a multitude of problems.

In many situations this is a condition first noticed in adolescence. As the child begins to walk, the parents will notice what they perceive to be an abnormal gait. The initial complaint may be of flat feet particularly with one foot appearing flatter than the other.

In other cases parents will state that their child experiences pain in one or both legs, severe enough to disrupt daily activities. This may be the classic "growing pains". There is some skepticism as to whether or not this is a real clinical entity. The thought here is that the osseus (bone) structures of the legs are growing at a faster rate than the corresponding muscles. Thus the muscles are over-stretched and therefore over worked in daily activity and pain ensues.

Most people have very small limb length discrepancies and probably will never require treatment as these differences are easily compensated for in gait. Obviously, the greater the difference in limb length the greater the potential for problems. In some individuals the difference in leg length will not become evident until later in life for the simple reason, the younger we are, the more adaptable the human body is to stresses placed on it and as we age we become less adaptable and then begin to experience the consequences of a limb difference.

Various authors offer up what they consider pathological limb length discrepancy. I have seen some claim that differences of as little as 6 mm particularly in athletes should be treated. Personally, I think there are too many variables involved to actually measure a difference that small.

It seems there may somewhat of a consensus that limb discrepancy of 1 to 1.5 cm in difference may be enough to cause gait issues and thus require treatment. The greater the difference in limb length, the greater the compensation needed to "equalize" the gait cycle.

HOW DO WE MEASURE LIMB LENGTH DISCREPANCY

Measuring the lower limbs can have a fair amount of error and inaccuracies and differ between two clinicians measuring the same patient. The most accepted method is for the patient to be lying supine (on their back). Using a steel tape measure, the length from the anterior superior iliac spine (the bony lump in front of your pelvis) to the lower part of the medial malleolus (the lowest part of the inside of your ankle) is measured. This is done on both limbs and any difference in length is noted.

A second method is to measure from the umbilicus (belly button) to the medial malleolus of each ankle.

The problem with each of these measurements is that they do not account for any discrepancy in the ankle joint itself or the foot.

An alternate method is to take radiographs of each limb, with the patient standing, and measure the difference on the x-ray itself.

The last consideration is whether or not the pelvis is level. Conditions such as scoliosis or severe muscle spasms can "lift" one side of the pelvis and create a relative limb length difference.

TYPES OF LIMB LENGTH DISCREPANCY

There are two main types of limb length discrepancies.

Structural or anatomical type. This is a true difference in length of either the femur (upper leg bone) or the tibia (lower leg bone) on one leg compared to the other. This difference may be congenital or post surgical such is the case in hip surgery where the operated side becomes shorter compared to the other limb. Trauma such as severely broken bones particularly where hardware has to be inserted may create an inequality.

Functional As the name implies, this is due to a malfunction usually at the level of any of the joints from the hip down to the foot. A typical example would be someone whose one foot excessively flattens out resulting in a situation where that limb may appear shorter.

Both types of discrepancies may occur together making the actual cause more difficult.

Some authors refer to a third type of discrepancy known as environmental. This is the result of walking or running on uneven surfaces such as runners who run in the street which in most cases tend to be slightly "banked" for improved water drainage. A shoe that is more worn out on one foot compared to the other would also be another source of environmental limb length discrepancy. This type of diagnosis may be made in individuals who complain of foot or leg pain when doing certain activities, eg: running.

HOW DOES LIMB LENGTH DISCREPANCY CAUSE PAIN IN THE FOOT, ANKLE OR LEG

In anyone with a discernible limb length discrepancy this creates an abnormal placement of the foot when it hits the ground in the gait cycle which will lead to an abnormal motion in the pelvis. The body then tries to compensate resulting in movement that is not "normal" and this may lead to pain. Typical types of compensation may include excessive plantarflexion of the ankle (the foot pointed downwards) on the shorter limb. The foot on the shorter leg may also supinate in an effort to try and functionally lengthen the leg. This excess supination may lead to pain on the outside of the heel as well as the outside of the foot.

The foot on the longer leg will tend to pronate to functionally decrease the length of the limb. Also noted is forward displacement of the tibia forcing excessive knee flexion. A foot that excessively pronates causes more internal rotation in the lower leg compared to the uppper leg and the result is excessive torquing of the knee joint. Excessive pronation will cause excess pressure on the inside portion of the heel bone potentially creating conditions such as plantar fasciitis and tarsal tunnel syndrome.

Compensation is not limited to just the foot, but it all starts from there. Depending on the position of the foot as it plants itself on the ground other compensation may take place at the ankle, knee and hip joints as well as the lower back. The degree and nature of compensation varies from individual to individual and is affected by not only the degree limb length difference, but also age, sex, individual flexibility, body type including weight along with lesser variables.

Limb length abnormalities not only adversely affects gait, but can be evident in posture when simply standing primarily on the musculature of the lower extremity. Some of the conditions that may be the result of limb length discrepancy include the following:

• low back pain usually on longer side first
• sacroiliac pain
• sciatica
• disc herniation
• vertebral impingement
• hip and knee pain
• osteoarthritis
• iliotibial band syndrome
• plantar fasciitis
• posterior stress syndrome
• bunions
• contracture of the achilles tendon
• metatarsalgia on the short limb

HOW DO WE TREAT LIMB LENGTH DISCREPANCY

A person can exhibit a discrepancy in their limbs, either structural or functional and it may be nothing more than an incidental finding and as such may not require treatment, while others will have discrepancy and will be part of the source of their musculo-skeletal complaint. Unfortunately, there is no consensus as to how much limb length discrepancy is "too much" and so there are limited guidelines when to treat, other than when there is pain related to the condition.

People who are athletic as well as older individuals with a multitude of anatomical limiting conditions such as arthritis, previous hip surgery, or muscle weakness, where in essence they stress their bodies more, will tend to have lower tolerances to the amount of discrepancy they can get away with. In these situations the energy expended to perform even simple tasks such as walking is increased which makes these humans inefficient machines. Obviously, for an athlete that can be the difference between success and failure in their particular sport, while for an older individual it can make simple walking, going from point A to point B an arduous task.

Treating this condition, in most cases becomes one of trial and error. From an anatomical standpoint treatment may include:

• stretching of tight muscle groups
• strengthening of weak muscle groups
• increasing range of motion in restrictive joints, both done with exercises and perhaps physical therapy.
• heel lift- Once all anatomical deficiencies are addressed and resolved as well as possible, the next step is to add a heel lift to the shorter limb. This should be done in increments starting with a small heel lift possibly 1/8 inch. After a short period of time, perhaps two weeks, if symptoms have not resolved, adding another 1/8" would be advised. Continuing to add height until symptoms begin to resolve. Keep in mind, the added heel lift is usually done in conjunction with treatment on the actual painful area.

If the actual discrepancy is greater than 3/4 inches, a simple heel lift to accommodate the difference may not be the best option and in these cases a tapered heel lift or even an orthotic with a heel lift built into it may be necessary. Tapering the lift through the foot leads to better accommodation of the large difference in each limb.

The final point worth mentioning is that particularly in functional limb length discrepancies, ongoing evaluation is imperative because over time as the body "adjusts" itself from a combination of heel lift therapy and treatment of any anatomical defects, the size of the heel lift will need to be adjusted to reflect those changes as the limbs become closer to symmetrical.

Herman Tax DPM. Podopediatrics. Williams and Wilkins, Baltimore, MD, 1980

David Edward Marcinko DPM. Medical and Surgical Therapeutics of the Foot and Ankle. Williams and Wilkins, Baltimore, MD, 1992

REFERENCES

OrthoInfo

Children's Hospital of Philadelphia

Pediatric Orthopedic Society of North America

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