Dismetry of the lower limbs, false short leg or true short leg?

By Dr. Ilio Iannone

In the medical field there is often a lot of confusion in the prescription of the increase in cases of dysmetria of the lower limbs. All this is due to the lack of clarity and difficulty in recognizing between a real shortening of the lower limb or its false shortening due to other components.

The prescription of the increase is often made very lightly and without the appropriate clinical evaluations.

It is absolutely essential to ascertain whether a real short leg is actually present, which requires the permanent use of a rise, or of another phenomenon for which its use - in addition to being useless - can be harmful.

The only diagnostic tool currently used is the radiographic measurement of the cotyloid line. However, there are several components that cause a false limb shortening:

Prosthesis of the heel or knee, greater on one side than the other, causes a decrease in the distance from the ground to the cup; lowering the latter leads to a false short leg.
The tilting of the iliac bone can influence the height of the cup: an anterior tilting lowers the cup causing a false long leg, a posterior tilting raises the cup causing a false short leg.
Abnormal pelvic ossification.
The rotation of the pelvis that generally lowers the cup from the propulsive side.
Lumbar scoliosis.
Visceral fixations.
Muscle retractions of psoas, piriformis (piriformis syndrome), etc.

For these reasons it is advisable to carefully evaluate the patient before prescribing an increase through instrumental examinations and evaluation tests.

Scansioscintigrafia e RX
Patient observation

When standing, it is necessary to assess whether there is consistency between the inclination of the pelvis and an apparently more deformed lower limb. Evaluating the sitting position it is possible to eliminate the influence of the lower limbs on the tilting of the pelvis: if in this position the pelvis is perfectly aligned with respect to the standing position, the cause of the tilting is to be attributed to the lower limb.

Osteopathic tests that assess the tilt of the pelvis.

In light of these aspects, the increase requirement should only be applied after numerous investigations. This solution must never be too thick and it is preferable to consider a few mm less than the actual need. It must be positioned below the sole of the foot and not only below the heel, since this would favor the shortening of the triceps sural.