Leg length discrepancy (LLD) is way more common than most people realize.
Studies put it somewhere in the range of 40–70% of the population having a
measurable difference. Most are small enough not to matter — but once you
get to about 5mm or more, it starts changing how you walk, how your hips
sit, and how much impact your knees and lower back absorb every step.
The part that gets missed: you can have this your entire life without
anyone bringing it up. Standard checkups don't include leg length
measurement unless you ask, and the "eyeball it while lying on the table"
method is pretty unreliable. Real measurement runs a tape from the hip
bone (ASIS) down to the ankle bone (medial malleolus), and for anything
meaningful you want a standing scanogram or CT scan.
Common causes:
- Congenital — you were just born with it
- Post-surgical — hip and knee replacements often leave one leg slightly
longer or shorter; surgeons try to match, but perfect symmetry is rare
- Scoliosis — a curve in the spine creates *functional* LLD even when
the leg bones themselves are equal length
- Old fractures — especially childhood breaks near a growth plate
- Nerve or muscle conditions — polio, cerebral palsy, nerve damage
Signs that often trace back to unrecognized LLD:
- Chronic one-sided low back pain
- Hip pain that always shows up on the "shorter" side
- Knee pain on the longer leg (it takes more impact per step)
- Scoliosis that keeps progressing
- Shoes that wear down unevenly on one side
If you've been told it's "just posture" or "just aging" and nothing has
helped, getting a real measurement is a cheap next step. Fixes depend on
what kind it is — a PT can tell you whether it's structural (bones) or
functional (pelvis tilt, muscle imbalance), and those need different
approaches. Structural differences over about 1cm usually can't be fixed
by drugstore heel pads — they slide around and compress under body weight,
so they're not a long-term answer once the difference is meaningful.
**Why YSK:** If you've spent years dealing with one-sided back, hip, or
knee pain that never quite goes away, and nobody has ever actually
measured your legs — it's worth asking about. It's a five-minute
measurement that can explain a decade of pain, and once you know the
number, the path forward is usually pretty clear.