What Is Leg Length Discrepancy?
Leg length discrepancy (LLD) means one leg is longer than the other. This is extremely common—most people have some asymmetry, often without knowing it.
The question isn't "do you have it?" but "is it significant enough to matter?"
Types of LLD
Structural (True) LLD
Actual bone length difference:
One femur or tibia shorter than the otherFrom birth, injury, or bone diseaseMeasurable on X-rayFunctional (Apparent) LLD
Legs are the same length, but appear different due to:
Pelvic tilt or rotationScoliosisMuscle imbalancesJoint contracturesFoot abnormalities (flat foot vs high arch)Why This Matters
Structural LLD: May need physical correction (heel lift)
Functional LLD: Address the underlying cause, not just add a lift
How Common Is It?
Studies suggest:
Up to 90% of people have some differenceMost are less than 1 cmDifferences under 2 cm rarely cause problemsDoes It Cause Problems?
The Complicated Truth
Small differences (< 1 cm):
Most studies show no significant link to pain or injury. The body compensates well.
Moderate differences (1-2 cm):
May or may not cause issues. Individual variation is huge.
Large differences (> 2 cm):
More likely to cause problems, though not guaranteed.
What Research Shows
LLD is associated with some conditions (low back pain, hip arthritis)But many people with LLD have no symptomsAnd many people with pain have no significant LLDCorrelation isn't causationSymptoms (When Present)
Common Complaints
Low back pain (usually on longer leg side)Hip painKnee painPelvic tilt or asymmetryGait abnormalityPostural changesOften Asymptomatic
Many significant LLDs cause no symptoms at all. The body is remarkably adaptable.
Diagnosis
Clinical Measurement
Methods:
Measuring tape (ASIS to medial malleolus)Block test (stand on blocks until pelvis level)Visual observation of pelvic heightLimitations:
Clinical measurements have significant errorCan be off by 0.5-1 cm or moreImaging
X-rays:
Standing full-leg X-rayMost accurate for structural LLDDone if considering treatmentFunctional Assessment
If functional LLD suspected:
Assess pelvic mobility and positionTest hip and ankle flexibilityCheck for scoliosisEvaluate muscle imbalancesTreatment
First: Determine if Treatment Is Needed
Questions to ask:
Is the LLD causing symptoms?Is there a functional component to address first?What's the actual measurement?Address Functional Issues First
If pelvic dysfunction:
Manual therapyStretching tight musclesStrengthening weak musclesMay resolve "apparent" LLDIf joint restrictions:
MobilizationStretchingMay equalize leg lengths functionallyHeel Lifts (For Structural LLD)
When to use:
Structural LLD greater than 1 cmAssociated with symptomsFunctional causes ruled out or addressedHow to use:
Start with half the measured differenceGradually increase if neededAllow weeks to adaptMay need full lift eventuallyIn-shoe vs shoe build-up:
Small lifts: in-shoe insertLarger lifts: shoe modificationPhysical Therapy
Address compensatory patternsStrengthen weak areasStretch tight areasImprove mechanicsSurgery (Rare)
Indications:
Large discrepancy (usually > 2-3 cm)Significant functional impactGrowing children may benefit from guided growth proceduresOptions:
Bone lengtheningBone shorteningEpiphysiodesis (growth plate arrest in children)Should You Get Checked?
Worth Investigating If
Persistent one-sided painVisible pelvic tiltShoe wear asymmetryHistory of leg fracture or childhood hip problemProbably Not Needed If
No symptomsNormal functionNo history of leg/hip problemsLiving With LLD
If You Have It
Doesn't mean you'll have problemsAddress it if symptomaticMany athletes perform at high levels with LLDFocus on Function
Symmetry isn't everythingMany "perfect" spines and legs have painMany asymmetric bodies are pain-free
Leg length discrepancy is incredibly common and usually unimportant. Small differences are normal variations. If you have symptoms that might be related, get properly assessed—but don't assume a minor LLD is the cause of your problems. Address functional issues first, use lifts judiciously, and remember that the body is remarkably good at adapting to asymmetry.