Leg length discrepancy is a difference in the length of your right and left legs. It is extremely common: most studies find that about 90 percent of people have some measurable difference, and the average is roughly 5 millimeters. Small discrepancies are usually harmless, while larger differences can affect gait, load joints unevenly, and sometimes contribute to pain; treatment depends on size and symptoms.
What is leg length discrepancy?
Leg length discrepancy (also called limb length inequality) refers to one lower limb being longer than the other. It can be anatomic, where bones are actually different lengths, or functional, where muscle tightness, pelvic tilt, or joint contracture makes one leg act shorter without a true bony difference.
Clinicians often distinguish between small differences, which most people tolerate without issues, and larger differences that may alter walking mechanics and loading in the hips, knees, and spine.
How common is leg length discrepancy?
Multiple reviews of healthy populations show that leg length differences are the rule, not the exception. The distribution is centered near a few millimeters.
Systematic reviews report that roughly 70 to 90 percent of people have an anatomic leg length difference, with a mean near 5 mm and most under 10 mm (Knutson, 2005); clinical summaries echo that differences under 1 cm are common and usually well tolerated (StatPearls).
Bigger discrepancies exist but are much less common. Differences over 2 cm are unusual in the general population and more likely to cause symptoms or warrant targeted management (AAOS OrthoInfo).
What causes leg length discrepancy?
Causes fall into two broad groups:
- Anatomic causes: congenital differences in bone growth, childhood conditions that affect the growth plate, fractures that heal shortened or lengthened, and surgeries that change bone length.
- Functional causes: pelvic tilt, hip or knee contractures, foot mechanics, or muscle imbalances that make one side effectively shorter during standing or walking.
In children, growth plate injuries or conditions can create progressive discrepancies as the child grows. In adults, degenerative joint disease, spinal curvature, or prior orthopedic injuries are common contributors (PM&R KnowledgeNow).
What problems can leg length discrepancy cause?
Small differences, especially under about 1 cm, often cause no symptoms. As the gap increases, the body may compensate with pelvic tilt, altered stride, or toe-walking on the short side, which can contribute to:
- Low back, hip, knee, or foot pain in some people
- Gait asymmetry and fatigue
- Uneven foot loading, calluses, or plantar fasciitis
- Exacerbation of scoliosis or joint wear in susceptible individuals
Associations between larger discrepancies and pain or osteoarthritis are reported, but not everyone with a discrepancy develops symptoms; many remain asymptomatic, especially with small differences (StatPearls).
How is leg length discrepancy measured?
Clinicians start with a physical exam to estimate true and functional differences. Common bedside measures include tape measurement from the anterior superior iliac spine to the ankle and block testing under the short limb to level the pelvis.
When precise measurement matters, imaging is used. Standing long-leg radiographs or a calibrated scanogram can quantify bone lengths and total limb length under weightbearing conditions, which is important for deciding on treatment in larger discrepancies (AAOS OrthoInfo).
When does leg length discrepancy need treatment?
Treatment is guided by the size of the difference, symptoms, and patient goals.
- Small differences, typically under 1 cm: usually no treatment. Consider activity modification or targeted physical therapy if there is muscle imbalance or overuse symptoms.
- Symptomatic differences around 1 to 2 cm: a shoe insert or lift on the short side can level the pelvis and reduce asymmetry. Evidence suggests lifts can reduce pain for some adults, but overall research quality is limited and individualized trials are reasonable (Cochrane Review).
- Larger differences, usually over 2 cm: in growing children, guided growth procedures can slow the longer limb or lengthen the shorter one; in skeletally mature patients, surgical lengthening or shortening may be considered for substantial, disabling discrepancies (AAOS OrthoInfo).
People with orthotics, prosthetics, or complex spine or hip disorders should be assessed in a multidisciplinary clinic to balance limb length with overall alignment.
What does this mean for everyday activity and exercise?
If you feel fine, a small leg length difference is usually not a problem and does not need to be “fixed.” If you notice persistent one-sided pain, recurrent overuse injuries, or a visible pelvic tilt, an evaluation can clarify whether a functional or anatomic difference is contributing and whether a simple lift or targeted therapy might help.
For runners and walkers with symptoms, a gradual trial of a partial lift, added in small increments up to the measured discrepancy, allows your body to adapt while you monitor comfort and performance. Reassess with your clinician, since overcorrecting can create new issues.