Considering the Height Compensation

If a height compensation is required, it can be realised, for example, through the orthosis. A height compensation at the orthosis provides the advantage that patients may wear ready-made shoes. The following text describes which steps must be considered when modifying a height compensation, in addition to the steps of the usual modifying technique. One part of the modifying technique is, for example, Making the Negative Cast with e-Cast, where you can find all information regarding the positioning of the plumb line - which is also used in this tutorial - under the subitem “Determining the Ideal Position”.

And, if the final model is finished, you can see how to further proceed with the orthosis by using the online tutorial Producing a Height Compensation.

Fase 1/9

For the following work steps, the plumb line is used as a reference.

Check the individual normal posture in the sagittal plane with the help of a laser plumb bob. The plumb bob should fall as follows:

  • from the body’s centre of gravity,
  • across the greater trochanter,
  • centrally through the ap measurement at knee height,
  • to the rear third of the front half of the supportive area.

With extension deficits, the knee joint does not serve as a reliable point of orientation. If this is the case, approximate the above-mentioned fixed points as closely as possible.

Write down if the plumb line falls through or before the knee’s pivot point.

Note: take the length difference of the feet into account, if present.

Note: if the patient is unable to stand (even with assistance), mark the plumb bob reference area (orange) on a stencil and write down the values.

Fase 2/9

When producing a height compensation, it is essential to create a leverage ratio that is similar to the contralateral side. To do so, the following steps are necessary:

  • compensate the volume under the heel and in the forefoot area (blue hatching),
  • set the heel back (pink hatching),
  • define the mechanical rolling-off line (j),
  • consider the heel-to-toe drop (x),
  • consider the toe spring (y).

Note: mark the plumb and rolling-off line of the healthy/unaffected foot on the shoe’s insole (or a copy) and use the insole as a guidance for all further steps.

Fase 3/9

Modifying the Positive Cast

  • position the aluminium clasp or similar
  • Prolong the forefoot up to k. k stands for the inner shoe dimension and j marks the mechanical rolling-off line.
  • fill the form with plaster
  • create a smooth transition
  • let the model harden

Also consider the online tutorial Making the Positive Cast and Modifying the Positive Cast KAFO.

Fase 4/9

In order to define the toe spring, determine the trochanter (B) first. Tie a string to a pen. The string’s length (R) should match the distance from the trochanter (B) to the rolling-off line (C) (R B - C).
Hold the string at the trochanter (B) and place the pen at the rolling-off line (C). Use the pen to draw the circle line on the positive cast.

Fase 5/9

Modify the forefoot area of the foot piece corresponding to the drawn marking.

Note: modify the bottom and the top of the foot piece parallel to one another. This way, the screw clamp can easily be attached in the later work steps.

Fase 6/9

Mind the parallelism when modifying the foot piece. Modify the heel, the rolling-off area and the forefoot area parallel to the axis/axes.

Fase 7/9

Modified positive cast from below:

  • j is the mechanical rolling-off line
  • k is the point where the aluminium clasp had been positioned
  • l is the inner shoe length (the heel protrudes; pink hatching)
     

Fase 8/9

Modified positive cast from lateral:

  • j is the mechanical rolling-off line
  • k is the point where the aluminium clasp had been positioned
  • l is the inner shoe length (the heel protrudes; pink hatching)
     

Fase 9/9

Modified positive cast from lateral while standing:

  • the toe spring y must be modified
  • it begins at the mechanical rolling-off line j

The toe spring is essential for:

  • the foot piece’s fitting in the shoe
  • making a physiological terminal stance possible → knee remains extended longer → body's centre of gravity remains at one height → energy is saved
  • making a physiological swing phase possible → functional shortening of the leg → swinging freely without compensating (e.g. vaulting, circumduction) possible → energy is saved
     

Last Update: 16 February 2023

 


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