Facts About Leg Length Discrepancy
by Dr. Christine Foss
Does Leg Length Discrepancy (LLD) matter? Usain Bolt, the world’s fastest runner, has an LLD of 1⁄2 inch. The question remains whether this has aided his speed or if he could have been even faster with the correction of the LLD. Although poorly documented in the past, chiropractors have long recognized that leg length plays a vital role in pelvic position and patient outcomes. In fact, we examine this before adjusting the majority of our patients. However, the crucial question lies in what emerging research reveals about the effects of leg length discrepancy.
Insights into Leg Length Discrepancy
Current research indicates that only 10% of the population possess precisely equal lower limb lengths, implying that the remaining 90% exhibit some degree of LLD.(1) In fact, if LLD were quantified and classified into mild, moderate, and severe categories, it could potentially enhance the significance of research findings and their clinical application. However, even a minor LLD of 1 cm could have long-term effects along the kinetic chain. For application in clinical practice, we can certainly classify it as follows.
LLD Categories by Severity of Kinetic Chain Effects
- <1 cm – mild
- >5 cm – moderate
- >9 cm – severe
In a comprehensive study by Harvey et al., a direct correlation was found between an increase in LLD and a rise in the grade of osteoarthritis (OA). For instance, a 1 cm LLD revealed a 53% incidence of knee OA on the shorter leg and 36% on the longer one. In contrast, an LLD of >2 cm presented a 68% incidence of knee OA on the shorter leg and 37% on the longer one. This study also uncovered OA at an increased incidence with as little as 0.5cm LLD.(2) This underscores the importance of detecting and rectifying LLD as soon as possible.
In a longitudinal study spanning 29 years conducted by Tallroth et al., it was discovered that 70% of patients requiring a total knee arthroplasty had an LLD greater than 5 mm.(3) Interesting to note that his research detailed that only 5% of the patients who needed a total knee replacement had no LLD.(1,3)
Identifying the Source of LLD
As we evaluate and rectify LLD, it’s crucial to be aware of its root cause in order to design an appropriate care plan or shoe insert. During the initial exam, a leg-length screening that includes assessments for the items listed below ensures a correct determination of the LLD’s source.
- Spinal curvature
- Hip dysplasia and OA status
- Pelvic obliquity
- Hip angle of inclination
- Hip anteversion/retroversion
- Femoral and tibial length discrepancy 7. Foot hyperpronation and supination 8. Foot structure and function
What Are the Known Ramifications of LLD
A detailed analysis of Usain Bolt's gait reveals that the shorter leg appears to strike the ground with increased force, while the longer leg spends more time in contact with the ground. Thus, the shorter leg side is likely to experience higher impact forces. In addition, since the longer leg side exhibits more compensatory gait features, it has a higher incidence of knee and hip replacements, as noted in the literature.(1)
LLD is often associated with compensatory pelvic obliquity.(4) This is not the end of the road for compensatory options for the human body in motion. We can see changes up the kinetic chain to the neck in some patients.
Let’s Take Action
Understanding the body’s long-term adaptations and LLD compensatory strategies enables us to see how they can potentially lead to pathology somewhere along the kinetic chain. It’s crucial to address LLD in the clinical setting at the earliest to prevent this progression.
Steps for Leveling Your Patient and Sidelining Long-Term Compensatory Pathology Ramifications of LLD
- The first and most important step is evaluating the feet for a navicular drop, using patterns and standing weight distribution. Secondly, watch your patient walk, run (if applicable) and squat.
- Measure LLD. (See below)
- True Leg Length Measurement - Measure the true leg length of the patient from the right ASIS prominence to the right medial malleolus. A second measurement from the left ASIS prominence to the left medial malleolus. Compare each measurement. Take note if one leg is shorter. Document the difference. (Can also be performed supine.)
- Apparent Leg Length Measurement - Measure the apparent leg length of the patient from the umbilicus to the right medial malleolus. A second measurement from the umbilicus to the left medial malleolus. Take note if one leg is shorter. Document the difference. (Can also be performed supine.)
- Place a custom flexible orthotic in the shoe and correct a proper leg length, if necessary, with a heel lift. Getting the foundation of the body level and the plantar vault lifted and functioning optimally is critical.
Heel Lift Placement Measurement - A third measurement is suggested to be used pre- and post-heel lift placement. This will ensure that the heel lift has leveled the pelvis to the needed extent. This measurement is taken from the right ASIS to the floor at the center of the right medial longitudinal arch. A second measurement is taken from the left ASIS to the center of the left medial longitudinal arch. Post heel lift placement, this number should be close to equal. (Performed Standing.)
- Align the pelvis.
- Implement core stability exercises to assist in holding the adjustment.
*Keep in mind the incremental height increase protocol for heel lift placement. Therefore, as you introduce a heel lift, your measurement may not be equal until patient tolerance allows.
*It is essential to take these measurements before and after placing your patient’s orthotics to assess the correction in the standing position.
A Note on Heel Lifts
Employing a heel lift should be executed under clinical guidance, especially when addressing a non-correctable leg length discrepancy. It’s advisable to gradually increase the heel lift height over several weeks. This will give the kinetic chain time to adapt correctly and slowly into a more normal pattern.
Using the Foot Levelers Shoe Heel Lift Pack, doctors can closely monitor patient progress and response and progressively provide the necessary lift. Notably, some patients may feel best when not completely level or level even to our preference. Prioritizing patient response and comfort is key to achieving success with heel lifts.
- Gordon, J. Eric MD*,†,‡; Davis, Lauren E. MPH*. Leg Length Discrepancy: The Natural History (And What Do We Really Know). Journal of Pediatric Orthopaedics 39():p S10-S13, July 2019. | DOI: 10.1097/BPO.0000000000001396
- William F. Harvey, Mei Yang, Theodore D.V. Cooke, et al. Association of Leg-Length Inequality With Knee Osteoarthritis: A Cohort Study. Ann Intern Med.2010;152:287-295. [Epub 2 March 2010]. doi:10.7326/0003- 4819-152-5-201003020-00006
- Tallroth K, Ristolainen L, Manninen M. Is a long leg a risk for hip or knee osteoarthritis? Acta Orthop. 2017;88:512–515.
- Resende RA, Kirkwood RN, Deluzio KJ, et al. Biomechanical strategies implemented to compensate for mild leg length discrepancy during gait. Gait Posture. 2016;46:147–153.