Leg Length Inequality: Does it Matter?

17 September 2019

One of the most common questions in practice regarding a patient’s anatomy is “do you think that having one longer leg is the cause of my back pain”? This is a fair question and unfortunately there is no black and white answer. Many other chiropractors have a fascination and obsession with the measurement and documentation of leg length inequality. From experience with communicating and observing many other chiropractors, leg length inequality appears to be the primary point of care when it comes to the treatment and management of athletes and non-athletes. This forms the cornerstone of practice and it leads to a seemingly quick and easy solution to the problem. The rationale and solution is to purchase a heel lift to “rebalance the alignment of the spine, pelvis, hips and knees” in the hope of eradicating low back or hip pain. However, we know that human beings are not entirely symmetrical in their structure. For example, the diaphragm on the right sits much higher than the left due to the pressure of the liver exerting upon it and the right lung consists of 3 lobes compared to the left lung (2 lobes).

So how much leg length inequality warrants the use of a heel lift or other treatment interventions?

Some studies suggest a heel lift is indicated for a leg length discrepancy (LLD) equal to or >20mm magnitude. Other studies suggest that an LLD of at least 0.5 cm to be of significance. Of course, this depends on how well a person can transition between a left-handed to right-handed posture under many different variables and constraints. Furthermore, strength, endurance and postural control is not to be overlooked in conjunction with the assessment of LLD. I do however, like to stick with the research guidelines and administer a heel lift if the LLD is greater than 20mm. If the difference is less than 20mm and hip and/or low back pain is present, I will still provide a heel lift only in the event that an intervention to improve skill, postural control, strength and endurance has failed the patient.

What is the cause of my Leg length discrepancy (LLD)?

LLD falls into one of two categories:

(i) anatomic (fracture or trauma to the immature epiphyseal growth plate, degenerative disorders, post-hip or knee arthroplasty, or idiopathic developmental abnormalities)

(ii) functional (joint contractures, adaptive shortening of soft tissues, ligamentous laxity, axial malalignment or abnormal foot mechanics).

A third category - environmental, has been proposed and is related to repeated exposure to uneven ground (e.g. consistently running on one side of a crowned road) but may be less commonly seen in the clinical setting. Functional complications include gait and balance problems or associated muscle joint disorders (LBP, fracture).

How is leg length discrepancy measured?

Two methods are used to measure LLD: the direct method which measures the distance between two anatomical points (ASIS and medial or lateral malleolus as seen in video) while lying in a supine position (using a tape measure) and the indirect method measuring LLD in a standing position, where lifts are used to level the pelvis, preferably using a pelvic levelling device (we use heel lifts in the clinic). The most accurate measure we can provide is a standing x-ray to determine whether the leg length is coming from a pelvic tilt, bone length (femur or tibia) or other various joint disorders.

Does leg length discrepancy play more of a risk factor low back/hip pain during standing for long time periods?

Compensation for LLD in standing can occur in many ways. The longer leg is often compensated for by pronation of the foot on the longer leg. In addition, supination and/or plantar flexion of the foot of the shorter leg can be used as a compensatory mechanism. The knee and hip can also compensate by extension of the shorter limb and/or flexion of the longer limb. If the leg is left uncompensated, the anterior and posterior iliac spines are lower on the side of the short leg, which, in turn, may result in a sacral base unleveling and/or scoliosis. A greater amount of pressure is transmitted through the hip of the longer leg due to both a decrease in the area of contact of the femoral head on the acetabulum, as well as an increase in tone of the hip abductors secondary to an increased distance between origin and insertion. To compound this decrease in contact area, there may be an increase in axial loading through the long leg. it has been reported that a 10 mm lift on one leg resulted in a significant shift in the mediolateral position of the centre of pressure towards the longer leg. 10 mm lift on one leg resulted in a significant shift in the mediolateral position of the centre of pressure towards the longer leg.

Is leg length discrepancy alone the cause for my low back pain, hip pain or premature hip and knee osteoarthritis?

It is difficult to determine whether the shorter or longer limb is the culprit and causing long-standing hip and knee pain. However, according to research, it does seem that the longer leg is at more risk for developing knee and hip osteoarthritis (OA) (the longer being more frequent than the shorter limb). Furthermore, hip or knee arthroplasty due to primary OA had been done 3 times more often to the longer leg than to the shorter.

In a study, twenty-seven of these subjects had severe idiopathic hip arthrosis, with the arthrosis occurring on the longer leg in 24 of the 27 subjects. 79 of these hip patients with hip arthrosis were prescribed shoe lifts, 56 of which became symptom-free after treatment. The reason may be that the longer leg is accompanied by superior migration of the same side pelvis greater amount of pressure transmitted through the hip of the longer leg due to the decrease in area of contact of the femoral head on the acetabulum, and therefore less cartilage surrounding the acetabulum is in contact with high ground reaction forces. Secondly, an increase in tone of the hip abductors secondary to increase distance between origin and insertion also contributes to greater internal muscle forces. stress fractures occurring in the tibia, metatarsals, and femur were found in the long leg 73% of the time. The increased incidence of stress fractures on the longer limb appears consistent with the greater forces emitted through the longer leg described under hip pain.

Premature OA and pain on the short leg side may be due to increased distance from the short leg to the grounds surface in running creating far more acceleration forces at that hip or knee. In addition, because the shorter leg attempts to lengthen itself, less ankle, knee and hip flexion will occur at initial contact to mid-stance causing an increased impulse (increased force due to less time for absorption).

What are the gait (walking and running) characteristics that are manifested by leg length discrepancy? And, does this gait cause pain or degeneration in the long term? Without going into much biomechanical detail, an individual with an LLD will attempt to shorten the long leg and lengthen the short leg to minimize center of mass oscillation, prevent energy wasting and improve running efficiency and economy.

Below are just a few compensations the body makes when an LLD is present. Keep in mind this is not an exhaustive list!

  1. Lean torso to short leg side (hip adduction to longer side)
  2. Circumduction of longer lower extremity
  3. Hike torso on long leg side
  4. Increase plantar flexion and ankle inversion on short leg side during stance phase
  5. Reduced hip and knee flexion on short leg side during stance phase
  6. Increase hip and knee flexion on longer side during stance phase
  7. Increased dorsiflexion and eversion on the longer side during stance phase

As you can see these compensations allow a more economical smooth efficient gait pattern in the presence of a LLD. Problems arise when variability is hindered during fatigue, poor strength-endurance of postural control, whereby the preservation for continually adjusting for LLD far exceed those adjustments needed under the above-mentioned conditions.

So, what is the management plan for an LLD and how long should it take for me to perceive any positive benefits including pain reduction and increase in performance?

To use heel lift depends on a person's internal mode networks, postural control, adaptability, relative strength and absorption ratios (strength profiles), cardio-respiratory endurance, history of training, current training status, acute:chronic workload ratio and how much mileage they are performing in an average week. We must also keep in mind that certain phases of gait might be more problematic or require different rate limiters. For example, a wedge-shaped heel lift from heel to metatarsal heads, will not affect the entire stance phase of the gait cycle since during the terminal stance, after heel rise, weight bearing is solely on the forefoot. Heel lifts will affect only certain parts of gait phases. Furthermore, given our intelligent design, the motor control system may clearly distinguish itself from a passive artificial environmental constraint (shoe-lift or heel lift) and retard it's biomechanical effects, as the internal models strongly preserve consistent kinetics and kinematics during the stance phase of gait. In other words the long leg might still maintain the force-time ratios and the degree of hip and knee flexion during the mid-stance phase.

First, we will test the heel lift to see if LLD is reduced during quite standing but most importantly, if running with the heel reduces pain or increased comfort, then LLD is more likely to be the mechanism behind your symptoms. If it’s made no difference, then we can rule LLD as being a cause of your symptoms.

So if you're concerned after being told you have a leg length discrepancy or you know someone who has also been told they have a leg length discrepancy, we can firstly provide all the assessments to confirm this and give you some clarity. Secondly, we will issue you with a temporary heel lift to take home and see what effect it has - it's worth a try!

Click here to book online or call the clinic for an appointment or to discuss your experience with this issue on (02) 9317 2288.