Leg Length Discrepancy
We tend to think of ourselves as symmetrical beings, with perfectly equal right and left sides. Upon closer examination, it’s easy to see minor differences from side to side. While in the ideal world we would each have two legs that function identically, the reality is that our legs are different. This difference is referred to as a limb length inequality or leg length discrepancy. The average human has a slight variance in leg length of up to 5 mm between the right and left sides. For the vast majority, this mild difference in length is not bothersome; our brains do a wonderful job compensating for minor differences.
There are two main classifications of leg length discrepancies:
1. Structural leg length discrepancies, which involve a difference in bone length.
2. Functional leg length discrepancies, which involve short or tight musculature, which impacts leg symmetry by shifting the pelvis up on one side.
Before treating limb length inequality, Dr. McClanahan determines the root cause of the problem so as to address the issue, not the symptom. Structural limb length inequalities are typically congenital (i.e., present from birth), or as a result of injury. For example, a fractured bone that results from a motor vehicle accident may heal in a shortened position. Surgery and joint replacements can also affect overall leg length.
Functional limb length inequality is more often the result of habitual movement patterns. For example, favoring a certain leg while standing, or constantly crossing legs a certain way can tilt the pelvis up on one side. Muscle tightness higher up in the body can also contribute to a functional leg length inequality, such as tight hip or back muscles that lift or tilt the pelvis.
In rare cases, leg length discrepancies can exceed 5 mm. The larger the discrepancy, the more likely the body will be unable to fully compensate, causing a variety of symptoms. In addition to causing altered gait or limping, larger limb length inequalities can be associated with back, hip and leg pain.
Different providers have various methods for determining limb length. It’s common for legs to be evaluated with tape measures while the patient is standing or lying down. Providers will also frequently determine leg length by visually assessing posture. Unfortunately, these methods have been proven unsuccessful and unscientific at accurately determining leg length. In addition, they do not establish if the difference is due to a structural or functional discrepancy. Dr. McClanahan recommends evaluation of limb length via a Scanogram, or a standing X-ray. These tests involve radiographic images that measure the distance from the pelvis through the talus, a key ankle bone. This method helps to accurately determine overall limb length as well as where the limb is short.
Once limb length difference and type has been determined, Dr. McClanahan uses different treatment techniques for structural vs. functional discrepancies. Functional limb length inequalities can be treated by addressing the tight muscles that are impacting pelvis orientation. Structural limb length inequalities exceeding 5 mm can be treated with the use of a full foot lift, like Clearly Adjustable. Clearly Adjustable liners lift the whole foot evenly to maintain an even weight distribution across the foot. Dr. McClanahan does not recommend using a heel lift; lifting the heel only can overload the forefoot causing poor structural alignment throughout the foot. If the shoe lift for a structural limb length inequality exceeds what can be comfortably placed within a shoe, it’s possible for a cobbler to add material to the shoe’s outsole. Both full foot lifts and cobbled lifts do unfortunately add weight to a shoe and can come at a considerable cost.
If you think you may have a shorter limb, or were previously diagnosed with a leg length difference via an unscientific form of assessment, Dr. McClanahan recommends one crucial step before you seek treatment: Get a Scanogram to determine the type and severity of the leg length discrepancy. This will more accurately establish how to proceed with treatment, and will, ultimately, allow your body to move better with each step.