Taking a Good Cast

 


Photo of CastsImproving Negative Casts For Prescription Foot Orthoses
By: Jeffrey A. Root, President
Root Laboratory, Inc.
March, 2006

The Importance of Good Casting

The process of utilizing prescription foot orthoses in the treatment of foot related pathology can be broken down into several basic steps.  These steps include, but are not limited to:

1. An examination

2. A diagnosis

3. A treatment plan

4. Casting

5. Writing an appropriate orthotic prescription

6. Filling the prescription (the lab's responsibility)

7. Dispensing and evaluating the orthoses

8. Follow-up

9. Treatment plan evaluation and modification, if necessary

It is obvious that the practitioner plays a major role in influencing patient outcomes, which is why foot orthotic therapy should only be performed by licensed and qualified healthcare professionals.  Achieving good patient outcomes requires success in every step of the treatment process outlined above.  Treatment failures can occur as a result of a problem in just one of the above steps.  Therefore, achieving consistently good patient outcomes requires significant education, experience, and skill.

Two very important factors in successful foot orthotic therapy are the quality of the cast of the foot and the nature and quality of the laboratory workmanship which is performed to the cast of the foot.  There are three basic rules that always affect foot orthotic quality:

1. A good quality foot orthosis can not be manufactured from a poor quality cast (the garbage in, garbage out rule).

2. A poor quality foot orthosis will be manufactured from a good quality cast when good laboratory technique is not employed (the quality in, garbage out rule).

3. A good quality foot orthosis is the result of a good cast and good laboratory technique (the quality in, quality out rule).

A custom foot orthosis is a device that is designed to brace, support, or protect the foot or a part of the foot. The biomechanical benefit derived from a custom foot orthosis is largely related to the shape and physical properties of the device. The shape of an orthosis is determined by the original cast of the foot and by any shape modifications made to the cast during the manufacturing process. While modification of the cast influences the shape and is critical in the production of an orthosis, the fundamental shape of an orthosis is first governed by the patient’s individual foot anatomy and the physiological position in which the foot is casted.  The importance of a good quality cast of the foot can not be overstated!  So, what is a "good quality cast" and how does one produce it?

The shape of any foot is somewhat variable and is directly influenced by the relative position of the osseous segments. The subtalar and midtarsal joints are responsible for major changes in the plantar contour of the foot. Since the plantar contour of the foot is directly influenced by the position of the joints of the foot, it is important to understand the reasoning behind positioning of the joints during casting. It is equally important to understand how to achieve specific joint positioning and alignment in casting so that the plantar contour of the cast will be therapeutically optimal.

The neutral position of the subtalar joint (STJ) is frequently considered the most desirable position in which to cast the foot. When the STJ is placed in the neutral position and when the midtarsal joint is fully pronated, the angular relationship between the plantar plane of the forefoot and the plantar plane of the rearfoot can be measured in both the foot and a cast of the foot. These measurements can be used to compare the foot to the cast and can help verify the accuracy of the cast.  The plantar plane of the heel is considered to be perpendicular to a line bisecting the posterior aspect of the heel. While it is not necessary to bisect the heel for casting purposes, heel bisection is an important clinical skill and has many applications in biomechanics and foot orthotic therapy.  As a result, the following method for heel bisection is presented in an effort to increase consistency and improve the general reliability of heel bisections.

 

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Note: There are 6 pages total...




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