A patient came into our Lakewood Ranch office last fall convinced she had a disc problem. Same left-sided low back pain for three years. Two rounds of physical therapy. A course of NSAIDs. She had tried it all. What the exam turned up was simpler and, frankly, more actionable: her left leg measured 11 millimeters shorter than her right, and her pelvis was tilted to compensate. Her spine was doing exactly what a tilted base forces it to do. Once we understood that, the path forward was much clearer.
Leg length discrepancy is more common than most patients realize. Research estimates that roughly 70 percent of the population has some measurable difference between leg lengths. For most people the difference is small enough to be irrelevant. But in our experience with non-surgical back pain care in Lakewood Ranch, differences of 6 millimeters (about a quarter inch) or more are frequently a contributing factor in chronic one-sided back pain, SI joint dysfunction, and even hip or knee pain on the longer-leg side. The threshold is not a bright line; it depends on how much compensation the rest of the body has been asked to do over time.
Structural vs functional: two completely different problems
Before anything else, a clinician needs to establish which type of leg length discrepancy they are dealing with. The two look similar on the surface but require different approaches.
Structural leg length discrepancy means the bones themselves are different lengths. The femur (thigh bone), the tibia (shin bone), or both, physically measure shorter on one side. This can be congenital, the result of a childhood growth plate injury, a fracture that healed slightly short, or a hip replacement where the prosthetic leg is positioned differently than the original. A true structural short leg does not disappear when the patient lies down or changes position.
Functional leg length discrepancy is far more common and occurs when the bones are equal length but an imbalance in the soft tissue or joints makes one leg appear shorter. Classic drivers include a rotated pelvis, a pronated (flat) foot on one side that effectively lowers the arch and drops that limb, a tight iliopsoas that hikes one hip, or sacroiliac joint restriction that shifts the pelvis asymmetrically. Functional LLD often improves dramatically with the right manual treatment because you are removing the mechanical distortion, not compensating around a permanent anatomical difference.
The distinction matters because the interventions are different. A structural short leg needs a heel lift to level the pelvis. A functional short leg needs whatever is causing the distortion addressed first, before any lift is considered. Putting a heel lift under a functional short leg can actually make the problem worse by reinforcing a pattern the body had already developed to cope with something else.
What an uneven pelvis actually does to the spine
The pelvis is the foundation the lumbar spine sits on. When one side drops even a small amount, the lumbar spine has a choice: lean with it (creating a lateral curve) or compensate upward (creating a compensatory curve in the thoracic spine or neck). Most bodies do a combination of both. Over months and years, this compensation loads the facet joints and discs unevenly. The side taking more compression tends to be where the pain shows up, though not always. Some patients hurt on the high side of the pelvis where muscles are chronically stretched and strained.
Common patterns we see:
- Low back pain consistently on one side, often worse after standing or walking for 20 to 30 minutes
- A belt that sits noticeably crooked despite being fastened at the same hole
- One shoe wearing down at the heel faster than the other
- A hip that feels higher or more prominent on one side when standing
- Pain that shifts or worsens when going from a flat surface to walking on a beach or uneven ground
- Recurrent muscle spasms on the same side that keep returning a few weeks after treatment settles them
None of these signs alone proves a leg length discrepancy, but in combination they are worth a careful clinical look.
"Most of my patients are surprised when they see their standing X-ray. They thought their posture was normal. The film shows the pelvis tilted three or four degrees and the L3-L4 disc space measurably narrower on one side. That image makes the whole picture click."
How a chiropractor evaluates leg length
There is no single perfect test, and experienced clinicians use several together to build a picture.
Supine (lying face up) leg check. With the patient flat on the table, the clinician observes the relative position of the medial malleoli (the inner ankle bones). One ankle sitting higher than the other suggests a length difference, but this test is sensitive to pelvic rotation and table position, so it is a starting point, not a conclusion.
Prone (face down) leg check. With knees bent to 90 degrees, the clinician observes the heel positions. Changes between supine and prone position can suggest whether the issue is structural or functional.
Standing postural assessment. Observing the iliac crests (hip bones) from behind while the patient stands on a level surface. A lower crest on one side is a clear sign worth investigating further. Placing calibrated lifts under the short side until the crests level tells us both the magnitude and whether a lift helps the patient's symptoms.
Weight-bearing (standing) X-ray. This is the gold standard for structural leg length discrepancy. A full-spine standing film lets us measure femoral head height bilaterally and calculate the actual leg length difference in millimeters. It also shows any resulting lumbar curve and allows us to measure its degree. In our Lakewood Ranch office, we take weight-bearing films when clinical findings suggest a structural component.
The SI joint and sciatica connection
The sacroiliac joint sits at the junction of the pelvis and the sacrum, one on each side. When the pelvis tilts chronically due to leg length discrepancy, the SI joints are loaded asymmetrically. The joint on the high side tends to compress; the joint on the low side tends to gap and become hypermobile over time. Either pattern can produce significant pain in the low back, buttock, and sometimes down the leg in a pattern that closely mimics sciatica.
The distinction is important for treatment. True disc-driven sciatica involves nerve root compression and typically produces sharp, electrical, or burning pain that follows a dermatomal pattern (the specific strip of skin that nerve root supplies). SI joint referral is usually a duller, more diffuse ache in the buttock and posterior thigh that rarely drops below the knee. For more on this distinction, see our piece on SI joint pain versus disc pain.
When leg length discrepancy is contributing to both an SI joint problem and apparent sciatica, addressing the pelvis level often reduces both the SI joint irritation and the nerve tension simultaneously. Many patients who have been treated for sciatica repeatedly without lasting relief find that correcting the pelvic tilt was the missing piece.
What actually helps
The answer depends entirely on what type of discrepancy is present and how much compensation the body has built up over the years.
For functional LLD, the primary approach is removing the cause. That typically means:
- Chiropractic manipulation to restore motion to the restricted SI joint or lumbar segments maintaining the compensatory pattern
- Soft-tissue work (manual therapy, shockwave, or Class IV laser) on chronically tight hip flexors, quadratus lumborum, or piriformis muscles holding the pelvis in rotation
- Corrective exercises targeting gluteus medius and deep stabilizers that help maintain the corrected position between visits
- Gait reassessment, particularly if pronation on one foot is a driver
For structural LLD, a calibrated heel lift is the standard starting point. We begin conservatively, typically at half the measured difference, and watch how the spine responds over 4 to 6 weeks. Going to the full measured amount too quickly can actually cause new symptoms by overcorrecting a spine that has adapted over years. Gradual progression gives the soft tissue and discs time to remodel.
In cases where significant disc compression has developed on the lower side over years of uneven loading, non-surgical spinal decompression can help restore disc height and reduce nerve irritation while the postural correction is in progress. The two approaches work well together because the lift addresses the cause while decompression addresses the tissue consequence.
What does NOT help, in our experience: treating only the muscles with massage or stretching while the pelvic tilt stays in place. Many patients report that their symptoms return within days or weeks of any manual therapy because the structural driver is still there. The spine goes right back to the position the uneven base is putting it in.
When imaging changes the picture
Most functional leg length discrepancy does not need imaging before treatment begins. The clinical exam is sufficient to identify the pattern, and a trial of manual care will usually confirm or challenge the working diagnosis within a few visits.
Imaging is more useful in these situations:
- You want a precise millimeter measurement for fitting a custom orthotic or heel lift
- Symptoms have not responded to conservative care and you want to rule out a structural cause
- There is a history of fracture, hip surgery, or childhood limb-length surgery that makes structural inequality likely
- The patient has neurological symptoms (weakness, numbness, loss of reflexes) that need a disc or nerve root explanation
Standing AP pelvis films and full-spine standing radiographs are the most informative for leg length measurement. Lying-down MRI measures disc pathology well but is a poor tool for measuring functional leg length inequality because gravity is removed from the equation.
If imaging reveals a complicating factor beyond what conservative care can address, we coordinate a referral appropriately. For most patients with leg length discrepancy as the primary driver, the conservative path is both safe and effective when the right pieces are addressed in the right order.
