HOW DIGITAL CASTING IS APPLIED TO BACK BRACES
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When a new method is introduced, it is always met with both suspicion and infatuation. We will be reviewing this technology, which is no longer "new", and comparing it to the plaster casting technique used with orthopaedic back braces (spinal orthotics).
With thermoplastics being used to make orthopaedic appliances that are custom-fitted to a patient's shape, the only way to obtain a mould of the body part in question was take an imprint with plaster strips. This method was so deeply embedded in everyone's mind when it comes to moulding that any new technique was brushed aside. Although this method is effective, is it truly the only valid one?
WHY DO WE NEED AN ALTERNATIVE TO CASTING?
To provide relief for patients, especially children, from the constraints of plaster casting. Plaster casting is a tedious, oppressive and messy method that carries risks for patients with respiratory disorders.
But we also need to improve the quality of the finished device because the possibilities are endless when it comes to modifying and adjusting the mould.
Some have argued that digital casting will primarily benefit companies but this holds no weight because the investment required is high. The only motivation is that the activity will thrive in the medium and long term through careful management of the various technologies being used.
CONSTRAINTS OF MOULDING
The moulding process has to reproduce the volume and the desired correction at the same time. This is where it gets challenging! It is literally impossible to do everything at once because the various parameters (contours for attachment, corrective pads, static position related to straightening, etc.) interact with each other. The two options can be summarised as follows:
- The cast is made in its corrected configuration. In this scenario, the pressures placed on the patient change the volume due to compression and movement of soft tissues. The volumes must be restored when the positive mould is retouched.
- This cast is made so that it exactly matches the patient's shape. In this scenario, the corrections will have to be made when the positive mould is retouched.
CAN WE DO AS WELL OR BETTER THAN WITH PLASTER?
Critics of the digital casting technique state that plaster is very accurate. But actually, it is not. Volume reproduction is affected by the tightness of the plaster strips, and their tension can create bridges above hollow areas.
The irregular thickness of the plaster that wraps around the patient does not truly represent the moulding process. In other words, we think the cast is good, but when we remove the positive from the mould, it isn't what we had expected.
At this stage, the positive mould cannot be cut into, so retouching it gets very complicated.
On the other hand, the laser scanner captures the patient's shape in three-dimensions, with all of its bumps and hollows. It does not apply any pressure and does not alter the volume and contours.
But the bean bag itself places local and regional pressure. The magnitude of the pressure can be evaluated by comparing the volume at the edge of the bag and the patient. Once the mould has been virtually reconstructed, various parts of the mould can be straightened or the spinal curves can be modified easily while maintaining the volume.
Casting is carried out either by unrolling circular plaster strips around the patient or by splinting one side and then the other after the patient turns around. In both cases, everything happens at the same time. This can be nearly impossible to manage and the mould often needs to be touched up afterwards.
Orthotech's approach: Digital casting system
Because a camera system is used to digitally scan shapes and volumes, it would seem impossible to perform pressure or static corrections in the frontal and sagittal planes during moulding. To get around this limitation, the patient is placed in an evacuated bean bag. This technology is currently being used to design brace seats and to immobilise patients in emergency situations.
Since the material is malleable but can be made rigid any time, corrective pads can be added and the static positions in both planes (frontal, sagittal) can be adjusted. This bean bag is now the extra set of hands that was missing during plaster casting.
All we need to do is scan the patient while on the bean bag and then scan the patient's imprint on the bag, once he/she gets up. This provides anterior and posterior views of the patient's three-dimensional shape that are combined to build a full mould. This mould is then virtually corrected on a computer using an extraordinary set of sculpture tools that provides the user with tactile feedback about the contours and hardness of the mould.
Various factors affect the moulding process. Through comparative studies, we have been able to show that digital scanning provides better control over all the parameters, during and after moulding, which leads to a higher quality device in the end.
But the success of any method depends on the skills and experience of the person using it. Many years of practice and development have allowed us to master this technology, thereby increase our satisfaction, and more importantly, that of our patients.
IN-HOUSE TESTING: Beyond our daily assessments, we also compared the two techniques by making two Garchois braces from the two different moulding methods. These back braces were both offered to a young female patient with Rett syndrome, without telling her how they had been made. She immediately told us that she preferred using the brace produced using the digital casting method. This brace provided better balance during walking (lordosis maintained) and reduced the scoliosis curvatures that were slightly better than with the cast.
To reassure the purist, we still work with plaster casts. But we immediately scan them for retouching to improve the quality and save us from doing needless work.