The first issue at hand when discussing leg length discrepancy is whether or not leg lengths are being accurately measured.
According to the American Academy of Orthopedic Surgeons (AAOS), a leg length discrepancy of 1/5 inch to 3/5 inch is normal (1).
Most doctors and physical therapists use a measuring tape and bony prominences on the pelvis and the ankles to determine the absolute lengths of the legs. Then, by subtracting the two, it can be determined whether or not there is a difference.
Research has consistently shown that this is an inaccurate and unreliable way to measure leg lengths. In a 1991 review article by S.T. McCaw and B.T. Bates, the authors describe how tape-measured leg lengths can be off by up to half an inch (2). To think that dentists work on a precision of microns… one would hope that precision in regards to leg lengths discrepancy is a must!
What are the Real Causes of Leg Length Discrepancy?
Leaving aside genetic and traumatic factors, the real reason for a leg length discrepancy is an asymmetry of pressure on the lower limbs during growth. This is knows as DELPECH’s law which states that any increased pressure on a limb will slow the growth of the limb. The opposite is also true which is that any decrease in pressure will stimulate growth. There are many factors that can cause a child to lean more to one side than the other. One of the most common causes is an eye muscle discrepancy.
The control of human balance depends upon the integration of sensory information not only from the skin, muscles and vestibular system (inner ear) but also from the visual system. An eye muscle discrepancy influences body perception, which in turn modifies the load distribution of the feet causing a change in the position of the feet and the overall center of gravity.
Leg Length Discrepancy and Injury
From a purely mechanical perspective, it seems obvious that a leg length discrepancy will cause the body to be off-balance, just like a car with one wheel larger than the others. Recent studies suggest that an asymmetry in plantar pressure can affect gait (4). Another study confirms that plantar pressure is used by the nervous system for human balance and control (5).
Proprioception and kinesthesia are the sensory feedback mechanisms for motor control and posture. We can then conclude that when the input provided to the nervous system by the feet and the eyes are uneven, the brain will contract muscles unevenly causing articulacy constraints. A simple articulary constraint (asymmetrical feet) can cause an X-Ray to show a difference of several millimeters.
Symptoms of Leg Length Discrepancy
Here are some of the conditions (symptoms) linked to a leg length discrepancy (cause) (6):
- Stress fracture
- Meniscus ruptures (knee pain)
- Back Pain
- Coxarthrosis (hip pain)
- Osteoarthritis
Correcting a leg length discrepancy can have a huge impact on sports that involve both feet on the ground and can help with injury prevention. Postural imbalances affect muscle tone along with muscular chains. Posturology is a precise science that studies the postural system and is a methodological treatment system that can pinpoint specific causes of the body’s orthostatic misalignments and deficiencies. Posturology addresses and corrects leg length discrepancies using unique neurological protocols that address the functioning of the body as a whole.
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1.https://orthoinfo.aaos.org/topic.cfm?topic=a00259
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1478813/pdf/brjsmed00025-0014.pdf
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1771854/pdf/bjo08701146.pdf
4. https://www.mdpi.com/1424-8220/15/8/20392
5. https://www.ncbi.nlm.nih.gov/pubmed/10465703
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1478813/pdf/brjsmed00025-0014.pdf