How To Evaluate For Leg Length Discrepancy

Author(s): 
By David Levine, DPM, CPed

Small, seemingly inconsequential leg length differences (LLD) can lead to symptomatic biomechanical asymmetry. Without careful examination, subtle LLDs can go undetected as can the etiology of the pathology they create. Differences in leg lengths vary from the subtle to the obvious. Once one identifies LLD, practitioners also need to know how to treat it. Understanding the patient’s lifestyle and activity level will help you determine when to address his or her LLD. Whether it is a difference in appearance of the two feet or a difference in function, asymmetry is often obvious if we know what to look for and why to look for it. For example, a patient may present with hallux limitus. While there are many causes of hallux limitus, if the finding is asymmetric and no trauma was involved in the deformity, then looking for a LLD would be worthwhile. Another example is assessing the range of motion within each foot. If there are joints that move or feel different between feet, then a LLD may be present. Since the foot is the mobile adapter for the body, it will compensate for the differences more proximally. Asymmetry is often the first clue that the patient has a LLD. Understanding the prevalence of LLD and how these differences can contribute to pathomechanics will yield important clues in helping you provide successful treatment outcomes for your patient’s biomechanical problems. Addressing the injured joint or chief complaint only without looking at the interrelationship between the injury and the rest of the body can allow some problems to slip by without being properly identified. The injury, ache or pain may improve with the prescribed treatment, but then may resurface if the underlying cause is a LLD that was not properly identified. This may then lead to a pattern of injuries, injuries that may perhaps affect one side of the body from the back down to the foot. The LLD assessment can be an easy addition to your biomechanical exam. Integrating this assessment into your diagnostic work-up will yield beneficial results. There are many types of LLD such as congenital, developmental and acquired. Congenital leg length discrepancies can have several causes with the most common one being hemihypertrophy. This condition involves one side of the body developing faster than the other. This is an isolated finding most of the time but can, in some instances, affect the kidneys as well. Other causes of LLDs in children include trauma, neurologic conditions and talipes equinovarus. When there is significant LLD in children, leg lengthening procedures (including recent advances in external fixation) are within the realm of possibility for some patients. When one sees LLD among adult patients, it may be due to leftover differences that were never addressed or identified at a younger age, arthritic processes and surgery such as joint replacement. LLDs can be a challenge to treat, but even more challenging to identify. The challenging cases are not necessarily those that have a large difference from one side to the other. In these cases, the difference is usually known and of longstanding duration. Fine-tuning may be needed but these patients come in with the awareness and knowledge that a difference exists. The more challenging cases are the adults of any age who come in with a mechanically related chief complaint that needs to be solved. One of the best ways to determine whether a LLD is present is to ask the patient. Since your patient is the one who has the difference, a little savvy prompting and asking the right questions will give you important clues. Does the patient favor one leg over the other when standing? Does the patient find it generally uncomfortable to stand? Do certain activities such as washing dishes aggravate the condition? If the answers to these questions provide information consistent with an imbalance, then you know where to direct your examination. What Can Observation And Gait Analysis Tell You? There are several ways to detect LLD. The simplest way is through observation and palpation. Simply have the patient stand in front of you, facing forward. Place your hands on their iliac crests and see if they are even. Bear in mind this is not always accurate because you may be applying different amounts of pressure on each side, making it appear as though a LLD is present when it is not. To confirm LLD, do the same thing with the patient facing away from you. When patients are obese, this technique may prove to be to be invalid because anatomic landmarks become obscured. Some practitioners like to measure each lower extremity. For example, they may measure from the anterior superior iliac spine or the navel down to the medial malleolus. This works well if someone has a structural difference in which one tibia/fibula or femur is truly longer. However, in the majority of cases of LLD in general, the legs will actually measure the same lengths, but will function as though they are different because of a pelvic tilt or curvature in the back or other variable. The challenge of this technique is correlating the measurements that you take when the patient is in a supine position to observations made when he or she is standing or walking. Sometimes the opposite of what you measure will occur when the patient stands or walks due to a pelvic tilt or curvature in the back. Gait analysis is another way to obtain clues of LLD. Watching your patient walk back and forth in a hallway gives you the opportunity to look for a head or shoulder tilt. There may be an appearance of one side vaulting over the other or one side stepping into a hole. These findings might be hard to see or isolate with confidence, just using your eyes. A better way may be to record a patient’s gait with video. Doing this allows you to play back the patient’s gait in slow motion and enables you to discern a lot more detail. Enhancing this approach further with multiple camera views can be extremely helpful as well. Gait analysis can also include pressure mapping. This not only enables you to identify the pressure distribution on each foot for symmetry, but facilitates measuring forces as well. The force at heel contact should be close to equal between feet as should other characteristics such as the center of force and duration of time spent on each foot. If the pressure mapping shows a consistent difference between feet, then one can diagnose a LLD with a high degree of certainty. Since there is not one reliable test to determine the presence of LLD, it is helpful to have as many clues as possible. Palpation, visualizing gait, measuring certain parameters during gait and even asking your patient are all ways to obtain the information you need to go forward with a treatment plan. From the simple clues you pick up with your ears to clues you pick up with your hands to clues you see, every clue helps when making a decision on how to address the problem. Think of the patient who presents with an asymmetric finding of a bunion on only one foot. If you diagnose the LLD prior to performing surgery, you will come out further ahead than if you ignore it and see the bunion recur. What You Should Know About X-Rays And LLD Employing X-rays can also be helpful when trying to detect a structural difference in leg lengths such as when the legs are truly different in length or when a curvature of the spine exists. However, when it comes to patients who have a functional LLD, X-rays will be of little to no help. In cases of functional LLD, the patients’ legs may actually measure the same length from the iliac crests down to the foot, but they may function as though they are not the same length. Therefore, taking X-rays does not shed much light in diagnosing a functional LLD. However, in cases in which there is a contribution from the back or hips, one may use X-rays to detect a tilt in the pelvis and give proof of one side being higher than the other, forcing the person to function as though there is a LLD. When there are biomechanical imbalances following hip or knee joint replacement surgery, obtaining an X-ray may be useful in actually measuring the difference. When there are cases in which an implant did not fit perfectly or if it was too long or short, one can see these differences in standing radiographs. Detecting LLDs With Different Thicknesses Of Crepe There is also a very simple test that you can use to detect a LLD. Have a few different thicknesses of crepe available in your exam rooms. Have 1/8-inch, 1/4-inch, and 3/8-inch pieces available. Then ask your patient to stand on the 1/4-inch crepe with either foot. It doesn’t matter which side you start with. Then switch it to the other side after a few moments. You may need to do this with a few different thicknesses to get a good idea. In this exam, you are not trying to determine how much of a difference is present. All you are trying to determine is if a LLD is present at all. If your patient does have a LLD, your patient will invariably feel a difference when standing on the crepe between sides. It will feel noticeably different between the right and left sides. In these cases, one can diagnose a LLD with confidence. Pertinent Pearls On Using Lifts To Treat LLD Even when you have detected a LLD and tell the patient, he or she may not be surprised. Patients may either have been told about it before or noticed it themselves when getting pants hemmed. They may have noticed that one pant leg usually needs to be adjusted more than the other one. The interesting patients are those who knew about the LLD but never did anything to address it. Long term imbalances will not only contribute to chronic pain, but lead to pathomechanical changes in the body from the back down to the foot. In general, people can discern 1/8-inch increments in LLD. When it’s less than this, it is hard to tell whether a lift is necessary. Since there isn’t an exact way to measure, using the 1/8-inch rule works well. Therefore, a lift needs to be 1/8, 1/4, 3/8 and so on. If the difference is small, then starting with a simple 1/8-inch heel lift is adequate. Most shoes will accept this amount without causing much, if any, heel slippage. Lift up the insole and place the lift underneath the heel. One should use a firm material such as crepe. Using firm material allows the lift to maintain its thickness. If the material is soft, then you will lose track of how much lift you are actually providing since it will compress with time. If a 1/4-inch lift is needed, then there are choices, but one of the choices is superior to the others. The easy choice is to use a 1/4-inch heel lift in the same way as the 1/8-inch lift. The problem with a 1/4-inch heel lift is that it will raise the heel too high inside the shoe, altering the shoe fit enough so one shoe will fit different than the other. In addition, you create asymmetry when only one heel is elevated. A similar option is to put in an extra insole measuring 1/4 inch inside the shoe. This will also have a negative effect on shoe fit, causing one shoe to be tight while the other fits properly. Also keep in mind that not all shoes can accept the addition of an added insole. The best way is to put a 1/4-inch lift on the shoe. This approach is the best because it actually raises up the short side while having no effect on shoe fit. It can also be done on any type of shoe whether it is a dress shoe or athletic shoe. In fact, on a woman’s dress shoe, you can do the opposite in some cases. Instead of adding a 1/4-inch lift to the shorter side, you can remove 1/4 inch from the long side. Keys To Facilitating Patient Compliance With Lifts Patients initially ask whether they have to modify all of their shoes and the initial answer is no. Discussing the mechanics of the body and how a LLD affects it will warrant doing a trial lift with just one shoe to start. After trying it for a few weeks, reevaluate your patient to see if it was effective. Some aches and pains may have occurred as the patient adjusted to it. In the most successful cases, there will be no break-in period because it will feel right from the start. In fact, sometimes it is like watching a flower blossom. Equalizing leg lengths will allow the patient to stand up straighter with better posture. Like any treatment modality you recommend, you have to believe in it in order for the patient to want to try it. With a shoe lift or any shoe modification for that matter, you have to believe it will help your patient function better. One way to do this is through gait analysis. Doing gait studies before and after shoe modification is an excellent way to actually quantify that what you are doing for your patient will be of benefit. How is a lift added to a shoe? Skilled shoe repair technicians can do this easily. There are some shoes that will need to have additional material added to the sole. This is best in a woman’s dress shoe. In fact, in dress shoes, one only adds material to the heel and ball of the foot. No matter the type of shoe that you add a lift to, the lift must be beveled from the ball of the foot forward in order to aid propulsion. If you pay no attention to this and add a solid piece of crepe, then the shoe will be uncomfortable and will slip off the heel as the propulsive phase of gait begins. The shoe won’t bend when it needs to, making it uncomfortable to wear and often forcing the patient to give up on it. In many shoes, a more aesthetically pleasing way to add a lift is to put the additional material on the midsole. This way the shoes will continue to have the same soles and call less attention to the difference in leg lengths. In Conclusion There are many asymmetric deformities that we see each day in our practices, whether these deformities are due to Charcot arthropathy in only one foot or hallux limitus. Treating the symptoms is certainly appropriate and necessary, but in order to get better long-term results, it’s important to identify as many of the contributing biomechanical factors as possible. Doing so will go a long way toward achieving better outcomes and more satisfied patients. Dr. Levine is the director and owner of Physician’s Footwear in Frederick, Md. CE Exam #120 Choose the single best response to each question listed below: 1. The most common cause of congenital leg length discrepancies (LLD) is: a) talipes equinovarus b) hemihypertrophy c) trauma d) neurologic conditions 2. X-rays are of little to no help in detecting: a) LLD among obese patients b) structural differences in leg lengths c) functional LLD d) none of the above 3. LLD in adults may be the result of … a) arthritic processes. b) surgery such as joint replacement. c) leftover LLD that was never addressed or identified at a younger age. d) all of the above 4. Gait analysis … a) gives you the opportunity to look for a head or shoulder tilt. b) is the only reliable test to determine LLD. c) enables you to identify pressure distribution on each foot via pressure mapping. d) a and b e) a and c 5. What is an obstacle to observing and palpating to check for LLD? a) There are none. It is the simplest test to check for LLD. b) obesity c) when practitioners apply different amounts of pressure in placing their hands on the iliac crests. d) b and c e) none of the above 6. X-rays are helpful … a) in detecting structural differences in leg lengths. b) in detecting LLD cases in which there is a curvature in the spine. c) in detecting biomechanical differences following hip or knee joint replacement surgery. d) all of the above e) none of the above 7. What is the most reliable approach for determining LLD? a) gait analysis b) measuring each lower extremity c) observation and palpation d) there is no one reliable test e) none of the above 8. No matter what type of shoe you add a lift to, the lift must … a) be incorporated with additional material in the sole. b) be incorporated with additional material to the heel and ball of the foot only. c) be beveled from the ball of the foot forward in order to aid proplusion. d) none of the above 9. When trying to determine LLD, the challenge in measuring each lower extremity is … a) correlating the measurements taken in a supine position to those taken when the patient is standing and walking. b) when legs actually measure the same lengths but function differently due to a pelvic tilt or curvature in the back. c) a and b d) none of the above Instructions for Submitting Exams Fill out the postage-paid card that appears on the following page or log on to www.podiatrytoday.com and respond electronically. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam. Responses will be accepted up to 12 months from the publication date.

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