Przejdź do treściFeeling that one leg is shorter does not always mean that the bones are actually different in length. Pelvic position, a hip or knee contracture, scoliosis, foot deformity or the way a painful limb is loaded can produce a similar impression. Before using a shoe lift, it is therefore important to establish what is actually being measured.
Two different situations: anatomical and functional discrepancy
An anatomical leg-length discrepancy means that the bony segments of one limb are genuinely different in length. It may be developmental or follow a fracture, bone deformity or surgery. A functional discrepancy occurs when bone lengths are similar, but the position of the pelvis, spine or joints makes one leg behave as though it were shorter or longer.
For example, a knee that cannot fully straighten effectively shortens the limb in standing. A hip contracture, pelvic tilt or collapse of the foot can also change functional limb height. This is why assessment should not begin and end with a tape measure between two points on the skin.
What does the orthopaedic examination look for?
The examination starts with standing and walking, pelvic and spinal alignment, and the position of the feet. Hip and knee extension are checked because a contracture can mimic shortening. It also matters whether both legs are loaded equally and whether the perceived asymmetry changes when the pelvis is levelled.
One useful screening method is the block test: blocks of known height are placed progressively under the apparently shorter side until the pelvis is approximately level. A systematic review found this to be the most useful clinical method among those assessed, but it does not replace imaging when an exact measurement is needed for an important treatment decision.
Gait adds another layer of information by showing whether the asymmetry actually affects function. More: Why Does an Orthopaedic Surgeon Watch How You Walk?
Why can home measurements be misleading?
Bony landmarks are covered by soft tissue, and even a small change in pelvic position or tape direction can alter the result. Measuring from the waistband, navel or floor does not show which segment of the limb is responsible for the asymmetry. Hip rotation, knee flexion and foot position can also change the measurement.
A home observation can be a good reason to seek assessment, but it is not enough to justify a permanent lift. If the apparent discrepancy is caused by a contracture or pelvic tilt, mechanically “levelling” the height may not address the real problem.
When is a standing full-length X-ray useful?
If the exact size of the discrepancy could change treatment, a standing radiograph that includes the entire lower limbs may be useful. It allows the femur and tibia to be measured separately and shows alignment and joint position under load. In the systematic review by Alfuth and colleagues, full-length standing anteroposterior radiography appeared to be the most valid and reliable imaging method among those assessed for anatomical leg-length discrepancy.
Not everyone needs this test. If a small asymmetry causes no symptoms and would not change management, additional imaging may add little. After a recent injury, standing should not be forced simply to obtain a measurement. More about imaging under body weight: Why Do Weight-Bearing X-Rays Show More?
Does every discrepancy need to be corrected?
No. The number of millimetres is only one part of the decision. The cause, symptoms, age, ability to compensate and effect on walking also matter. Reviews of treatment indications emphasise that evidence for rigid thresholds is limited and that management should not be based on a single measurement alone.
A shoe lift can be helpful in a properly selected situation, but it is not a neutral experiment for everyone. Rapidly correcting the full measured difference in someone who has adapted to an asymmetry for years can itself provoke symptoms. The amount of correction should therefore follow the examination and the aim of treatment, not a home tape measurement.
What if the sensation started after hip surgery?
After hip replacement, a perceived leg-length difference has to be distinguished from an actual change in bony length. Previous contractures, pelvic position, gait and soft-tissue tension can influence the sensation, although a true anatomical difference is also possible. There is no single interpretation based only on the name of the operation: the actual procedure, the examination and, when relevant, appropriately performed imaging all matter.
A sudden sense of shortening after an injury or operation together with severe pain, deformity or inability to bear weight requires urgent assessment. In other situations, the first step is to establish whether the problem is anatomical, functional or mixed before trying to correct it.
The key point
“One leg is shorter” is a description of a sensation or observation, not a diagnosis. The pelvis, spine, joint range of motion, feet and gait should be assessed before deciding whether precise imaging measurements are needed. Treatment makes sense when it addresses the real cause and a meaningful functional problem.
References
- Alfuth M, Fichter P, Knicker A. Leg length discrepancy: A systematic review on the validity and reliability of clinical assessments and imaging diagnostics used in clinical practice. PLoS One. 2021;16(12):e0261457.
- Vogt B, Gosheger G, Wirth T, Horn J, Rödl R. Leg Length Discrepancy—Treatment Indications and Strategies. Deutsches Ärzteblatt International. 2020;117(24):405–411.
Content prepared by: Tomasz Poboży - orthopaedic surgeon.