Walk the line!

We have said it before and we’ll say it again: “Prosthetic alignment cannot be seen, it can only be measured!” Humans are born with balancing capabilities. When using a prosthesis, a patient will take one step and immediately adapt to the prosthesis to maintain equilibrium, irrespective of the prosthetic alignment.

Cameras take photographs of the patient’s alignment, which are then sent to a tablet or computer.

This happens fast and secretly and it is not humanly possible to see or feel the patient’s forces transferring to Mother Earth. But adapting to the prosthesis alignment is the wrong way round. The prosthesis should adapt to the patient’s alignment. For a better understanding of the importance of prosthetic alignment, consider this:

A bakkie weighing 1 500 kg can carry a load of 1 000 kg, or roughly 70 percent of the vehicle mass. If an average three-kilogram below-knee prosthesis carries an 85 kg man, it carries 2 750 percent of the device mass! If the alignment is even slightly incorrect, it places unnecessary stress on all muscles and also on 76 different areas of the spine and pelvis as well as 62 lower limb joints.

This, in effect, will make it harder for the amputee to walk and balance, leaving them tired, uncomfortable and prone to injuries, and wondering where this lower back pain, neck spasm or other aches and pains come from – or why the skin is continuously breaking down on their stump.

Let’s go back to the basics. Alignment can be defined as the relative position of different body parts or prosthetic components to one other. Natural alignment allows us to stand and walk using the least amount of effort and without losing our balance. This is also the main goal of prosthetic rehabilitation.

Lines on the photographs indicate the measured forces with millimetre accuracy.

Measuring and achieving the correct device alignment is imperative, yet  it is impossible to achieve by estimating it with the human eye. To solve all these problems, Ottobock has launched its new 3D LASAR Posture device, which raises prosthetic alignment to a whole new level.

Prosthetists who make use of this technology can offer their prosthetic (and orthotic) patients a level of comfort, accuracy and mobility that is unparalleled by measuring from the point where the patient makes contact with the floor. The device uses four cameras positioned around the patient, who stands on a hyper-sensitive measuring plate. An image is sent to a computer or tablet.

The measured forces are presented as lines positioned with millimetre accuracy over the patient’s image. The device captures the weight and also the force (leverage) path simultaneously displayed for both limbs. Reciprocal influences and adjustment inputs can be seen clearly and immediately on the screen. In layman’s terms, this diagnostic marvel will provide the following info:

• Leg length discrepancies;

• Weight carried, percentage-wise, in both limbs;

• Accuracy of component placement;

• Accuracy of component alignment;

• Prosthetic socket design accuracy and functionality;

• Influence of flexion contractures on the residual limb and whether the prosthetic alignment accommodates these contractures;

• Prosthetic influence on the sound limb and vice versa, and torque forces influencing both limbs.

All this and more can be viewed in 2D or 3D. The elimination of alignment deviance has never been so easy and accurate. To conclude, this device tells you everything you always wanted to know about alignment but could not observe before!


Heinrich Grimsehl is a prosthetist in private practice and a member of the South African Orthotic and Prosthetic Association (SAOPA). email: info@hgprosthetics.co.za

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