Leg-Length Discrepancy from Old Ankle Sprains: Pelvic Tilt, Back Pain, Knee Pain, and How to Measure at Home

Many people with long-standing lower back pain or stubborn knee pain are shocked when a physical therapist or chiropractor says, “Your pelvis is a little rotated. Your right leg is functionally shorter.” That sounds like a hip problem. But very often the story actually starts at the ankle. A past ankle sprain can stiffen certain joints in the foot and ankle, change your walking pattern for years, and quietly create a leg-length discrepancy that is just a few millimeters. That small difference is enough to tilt your pelvis and load your spine unevenly over thousands of steps per day. Over time, that becomes chronic lower back pain, sacroiliac region tightness, outer hip soreness, and inner knee stress on one side.

Here is the critical point: in most adults, the two thigh bones and shin bones are basically the same length. The problem is not always that one actual bone is shorter. The problem is how one leg stands and loads compared to the other. That is called a functional leg-length discrepancy. Functional leg-length discrepancy can come not from birth or fracture, but from years of compensation after an ankle sprain. Recurrent ankle sprains and chronic lateral ankle instability are known to change gait mechanics, limit ankle dorsiflexion (the ability to pull the foot upward), and alter how long the stance phase lasts on that side. Those adaptations can make one leg behave as if it is shorter.

If you have:

• One-sided lower back pain that gets worse after standing,
• Knee pain mainly on one side when going downstairs,
• A shoe that wears out faster on the outer heel on one side,
• A sense that one hip hikes up or rotates forward,

then you are in the exact cluster of complaints seen in people with mild pelvic tilt due to subtle leg-length asymmetry.

This article will walk you through how an ankle sprain can create that pattern, how a tilted pelvis irritates the spine and knee, and how to measure leg-length discrepancy at home (safely) before you rush to buy heel lifts or blame “slipped discs.”

After a typical lateral ankle sprain (rolling the ankle outward, stretching the ligaments on the outer side), scar tissue and protective muscle guarding can restrict dorsiflexion. Dorsiflexion is what lets your shin move forward over your foot when you walk. If dorsiflexion is restricted, you will do one of two things unconsciously: you will shorten the time you spend on that foot, or you will externally rotate that leg and toe it out so you can still move forward.

Shortening stance time effectively makes that leg act shorter. Imagine walking while slightly tiptoeing on one side: your heel may lift sooner, and your pelvis drops a little on that side at mid-stance. That “dropped” side tricks the body into thinking that leg is shorter, even though the bones are normal length.

The peroneal muscles (outer calf muscles that prevent the ankle from rolling again) often stay overactive after an ankle sprain. When they stay tight, they hold the foot in a slightly everted or pronated position. Mild over-pronation on one side can collapse the arch more on that side, which can either make that leg functionally longer (arch collapse increases contact time) or, paradoxically, cause the opposite leg to act longer because you unload the injured side early. The exact direction depends on how you compensated, which is why two people with the same ankle injury can present very differently.

The common thread is asymmetry: one side moves differently than the other at the foot and ankle, so the pelvis stops being level.

If one leg behaves shorter, the pelvis tilts downward on that side. To keep your eyes level with the horizon (your brain is obsessed with level vision), you then side-bend and rotate through the lumbar spine. That repeated spinal side-bend becomes your new “neutral,” and the small spinal joints, the sacroiliac joints, and the muscles of the lower back are now working asymmetrically all day. Over months to years, this can lead to local inflammation and chronic pain in the lower back and buttock region. Pelvic tilt patterns like this have been associated with nonspecific lower back pain in observational studies.

When your pelvis is not level, you are basically walking in a tiny sideways slope all the time. That creates:

Uneven compression on the lumbar facet joints

Facet joints are the small joints in the back of the spine that guide motion segment by segment. Side-bending plus rotation jams one side more than the other. Over time, that can cause localized soreness, pinching with extension, or even pain that wraps into the buttock or upper hamstring.

Constant tension in quadratus lumborum and gluteus medius

Quadratus lumborum is a deep low-back muscle that hikes the hip up. Gluteus medius is the side-hip stabilizer. On the “long leg” side (or the side that is acting longer), these muscles have to work harder to keep you upright. Chronic overuse here is a classic source of dull, achy back pain that gets worse by the end of the day.

Stress at the sacroiliac joint

The sacroiliac joint is where the spine meets the pelvis. Asymmetrical loading is a known driver of sacroiliac region pain, especially in people with even mild leg-length discrepancy.

This is why someone with a “mysterious” one-sided low back pain can often trace it not to a disc bulge, but to a gait compensation that started with an ankle sprain that never fully rehabilitated.

Leg-length discrepancy does not just hit the spine. The knee on the longer-acting side tends to take more compressive load in standing and walking. That means:

• More pressure on the medial (inner) knee if the pelvis drops toward the other side and the knee caves slightly inward to hold you up.
• More pressure on the lateral (outer) knee and iliotibial band if your strategy is to toe out and lock the knee straighter on one side.

Either pattern can irritate the patellofemoral joint (the joint behind the kneecap), which is one of the most common sources of front-of-knee pain in adults who stand a lot. Patellofemoral pain has been linked to altered lower limb alignment, altered hip control, and uneven ground-reaction forces.

If your knee pain is always on the same side and you cannot remember one clear knee injury, you should absolutely consider whether you are dealing with pelvic tilt and functional leg-length asymmetry.

You do not need an MRI to get suspicious. Watch for these:

1. You always stand with weight on the same leg.
   If you catch yourself always leaning on your left leg with the right knee a little bent, or vice versa, that is not random. That is your body offloading the side that does not want to bear full, even weight.
2. Your hips look uneven in the mirror.
   Stand in front of a mirror with your feet shoulder-width apart. Place your hands on the tops of your pelvic bones (the bony points at your waistband, called your iliac crests). If one side is clearly higher, that suggests pelvic tilt.
3. One foot points out, the other points forward.
   Chronic toe-out on just one side is common after ankle sprains because it is mechanically easier for a stiff ankle to roll forward if it is already turned out. That rotation also shortens functional stride length on that side.
4. Old photos show a pattern.
   Look at candid standing photos from the last few years. If your torso always leans slightly to the same side or one shoulder always drops, that is your compensation caught in the wild.

Important note: Home screening is not a medical diagnosis. But it can tell you, “Yes, this is worth getting professionally assessed.”

This is simple and surprisingly informative, and versions of it are used clinically.

1. Stand barefoot on a hard floor in front of a mirror.
2. Notice which side of your lower back or pelvis feels tighter or higher.
3. Now take a thin book or a couple of magazines (start with about 5 millimeters thickness) and place them under the foot of the side that felt lower or “shorter.”
4. Stand again. Ask yourself two questions:
   • Does your lower back feel more level or more relaxed?
   • Does your knee on the other side feel less compressed?

If the answer is “yes,” try adding or removing a little more height until you find the smallest lift that makes you feel most even. That approximate thickness gives you a rough idea of the functional difference that your body is dealing with. Clinical studies have shown that even a small heel lift can reduce low back pain in people with leg-length discrepancy by improving pelvic alignment, though results vary from person to person and not everyone benefits.

If you feel dramatically better with just 5 to 8 millimeters under one heel, that is a strong clue that asymmetrical loading is relevant.

Very important: this is only a screening tool. Do not immediately wear a random lift in your shoe all day. Sudden correction can shock your knees, hips, and back if they have adapted for years. Any lift change should be gradual and ideally guided by a clinician who can watch your gait.

1. Wear a snug T-shirt and shorts.
2. Ask someone to take a straight-on photo of you from behind while you stand naturally, feet hip-width apart.
3. Draw (mentally or digitally) a horizontal line connecting the top edges of your pelvis.
4. Draw a second horizontal line connecting the back pockets or waistband.

If those two “should be horizontal” landmarks are tilted, you are likely seeing pelvic tilt. Pelvic tilt can be a downstream effect of leg-length discrepancy. Observational gait research correlates pelvic obliquity (pelvis not level in walking) with side-dominant lower back pain.

This one looks at the original villain: the ankle.

• Stand facing a wall, barefoot.
• Put one foot forward so your big toe is about the length of your thumb away from the wall.
• Keeping your heel down, try to drive your knee straight forward to touch the wall.
• Move the foot back little by little until you just barely can still touch the wall without the heel lifting.

Measure the distance from your big toe to the wall for each ankle.

If one ankle is clearly tighter (less distance before the heel pops up), that ankle is not allowing your shin to glide forward the same amount. Limited dorsiflexion after ankle sprain is a well-documented long-term finding and changes gait mechanics years after the original injury.

That side is often the “short-acting” leg.

While most mild functional differences are mechanical and manageable, you should not self-manage if you have any of the following:

• Recent trauma (fall, accident) followed by sudden, clear leg-length difference.
• Numbness, weakness, or shooting pain down one leg.
• A history of fracture in the hip, femur, tibia, or ankle.
• Visible scoliosis in a child or teenager (tilted shoulders, rib prominence).
• Progressive limping or dragging one leg.

These signs may point to structural leg-length discrepancy (true bony length difference), nerve involvement, or other causes such as hip pathology, and those require proper examination and sometimes imaging. Persistent structural leg-length discrepancy greater than about 2 centimeters is associated with gait asymmetry and higher risk of osteoarthritis in the longer limb knee, so it is not something to ignore.

A clinician such as a physical therapist, sports medicine physician, or chiropractor may use:

• Visual pelvic level check in standing and in lying.
  They palpate the iliac crests and compare heights. This is quick but can be subjective.
• Block testing.
  Similar to the book test you did at home, but more standardized. They add specific-height blocks under the suspected short side until the pelvis levels. That height is recorded.
• Tape-measure testing
   They measure from the bony point at the front of your pelvis (anterior superior iliac spine) down to the inner ankle bone. This estimates true bony length. Small errors are possible, but it is widely used in clinic.
• Standing X-ray scanogram or low-dose imaging 
  When it really matters (for example, planning surgery, custom orthotics, or understanding a scoliosis driver), doctors can get standing long-leg imaging that measures femur and tibia length precisely while you are weight-bearing. Research considers standing imaging the gold standard for detecting true structural leg-length discrepancy.

Most people with low back pain do not jump straight to imaging, because many mild functional discrepancies improve with conservative care: ankle mobility work, glute and hip strengthening, and gradual lift correction.

You can begin addressing the root cause instead of just chasing back pain with painkillers.

Gentle calf stretching with the knee bent (to bias the deeper soleus muscle) and controlled ankle dorsiflexion drills can gradually improve ankle glide. Restoring dorsiflexion after chronic ankle sprain has been shown to normalize walking mechanics and reduce asymmetrical loading up the chain.

Do not force through sharp pain. The feeling should be strong stretch, not pinch.

If one hip is always working overtime to hold you level, you want both sides strong and symmetrical. Side-lying leg lifts, step-downs, and single-leg balance work train gluteus medius, which supports pelvic alignment during standing and walking. Better hip control reduces pelvic drop and reduces stress on both the sacroiliac joint and the knee. Weak hip abductor strength has been associated with patellofemoral pain and dynamic knee valgus.

Several times a day, especially when cooking, brushing your teeth, or talking on the phone, check: are you hanging on one hip with the other knee soft and bent? Reset so both feet are planted evenly, knees unlocked, ribs stacked over pelvis. You are retraining your baseline alignment.

If your at-home stack test was dramatic (you felt immediate relief in your back with a tiny lift), you can speak with a clinician about a gradual lift plan. The keyword is gradual. Adding too much height too fast can overload the opposite knee or irritate the Achilles tendon. A healthcare professional can help you decide:

• how much lift,
• which shoe,
• how many hours per day initially,
• and how to reassess symptoms.

There is evidence that appropriately prescribed heel lifts can reduce chronic low back pain related to leg-length discrepancy by improving pelvic symmetry, but it is not universal. Some patients feel dramatically better, others feel no change, and a small group feel worse if the guess is wrong.

In most people, no.

Most mild pelvic tilt from functional leg-length discrepancy is a load-management issue, not a catastrophic joint failure. Think of it like driving a car with slightly uneven tire pressure. You will get weird wear patterns. You may hear noise on one side. But if you correct the pressure and rotate the tires, the car is still perfectly usable.

Similarly, many people notice that once they improve ankle mobility, strengthen hips, and stop always leaning to one side, their daily baseline pain drops. The spine, hips, and knees are extremely adaptable. They just do not like sneaky, one-sided stress for years.

However, do not ignore persistent one-sided pain that is getting worse. If you have progressive numbness, weakness, night pain that wakes you, unexplained weight loss, fever, or recent trauma, that moves you out of the “mechanical asymmetry” story and into “go see a clinician now” territory.

A “short leg” is not always a birth defect or a hip problem. Sometimes it is a story that began the day you rolled your ankle, limped for a few weeks, never fully restored ankle motion, and then spent years walking with a tiny built-in twist.

That twist can tilt the pelvis, tighten one side of the lower back, overload one knee, and create chronic pain patterns that seem random — until you trace them back to the ankle.

You can screen yourself at home:

• Try the stacked magazine test under one heel.
• Photograph your pelvic level from behind.
• Compare ankle mobility side to side.

If those tests strongly point to asymmetry, do not panic. It means you finally have a mechanical explanation. The next step is not endless pain medication. The next step is restoring ankle mobility, balancing hip strength, correcting long-standing posture habits, and — if appropriate — gradually using a small lift under guidance.

When your foundation (the ankle and foot) becomes symmetrical again, the pelvis levels, the spine stops side-bending all day, and the knee no longer carries extra load every time you go downstairs. That is how you break the cycle.