OVERVIEW OF CASTING TECHNIQUES
Once the cast dries , the clinician cuts the cast , usually where the channel tube was inserted , which allows the cast to come off easily . The socks come in many different heights . The most common used for orthosis being the slipper sock , which ends below the malleoli and covers the toes . Casting with the sock requires less manipulation of the wet plaster than with the strips , which allows for a tidy end .
Once the clinician becomes familiar with the medium , this technique is very fast . Like plaster casting , the clinician can use advanced casting techniques and use a laser cast scanner after the negative is off the foot .
Advantages of plaster sock casting :
• Easy to manipulate the subtalar joint into a neutral position .
• Can load the lateral column and neutralize longitudinal axis to provide good mid-foot and forefoot stability .
• Good visual confirmation of foot position .
• Cast is one unit , less manipulation of wet plaster .
Disadvantages of plaster sock casting :
• Need to modify positive model of cast to compensate for soft tissue expansion during weight bearing .
• Requires water and creates a mess .
• Storage required for casting materials due to different cast foot sizes .
Common errors :
• Poor positioning of the subtalar joint : either too much pronation or too much supination .
• Insufficient or excessive loading of the lateral column .
• Allowing the metatarsal heads to elevate ( and the toes to sag ), which distorts the position of the first ray .
Laser foot scanner casting
Computer-generated laser foot scanner is the technologically advanced medium for casting in non-weight bearing . This technique also uses CAD / CAM software to obtain the 3-D cast . With any laser scanner , the clinician produces a digital image of the foot / cast using laser or white light .
The laser foot scanner is not used regularly in pedorthic clinics . The pedorthist must either give up a hand to hold the device or work around a bulky piece of equipment to hold the foot in position . Most commonly , a cast laser scanner is used in lieu of the laser foot scanner .
Advantages of laser foot scanner casting :
• Accurate plantar contour measurement .
• On-screen cast modifications with software .
• No distortion by operator or materials between scan and fabrication of orthosis device .
• Quick and clean scanning and manufacturing .
• Cast storage and duplicate orthoses greatly simplified using available software .
• Positive perception by client of the procedure .
Disadvantages of laser foot scanner casting :
• What you cast is what is manufactured ; a poor cast is a poor orthosis .
• Expensive , especially if equipment fails .
Misconceptions :
• Office scanners provide diagnostic information .
• Result is more exact because it ’ s done with computers .
• Technology replaces the skill of the practitioner .
• CAD / CAM technology is only for large institutions due to cost .
As you can see , there are many different options of casting . Most pedorthists become great at casting either a semiweight bearing or a non-weight bearing cast . Then they become good at the other weight-bearing methods . This way ,
the clinician can achieve any result they and their client like . Research indicates that introducing an orthosis will not necessarily change foot alignment to the degree we had originally thought , and that the use of an orthoses is mainly to provide comfort to the client . 6 So it is the client ’ s comfort level , which they associate with alleviation of pain that determines if a pedorthist is doing his or her job well . The first step in orthosis fabrication is a great cast ! ■
References
1
Trotter LC , Pierrynowski MR : “ Ability of foot care professionals to cast feet using the non-weight bearing plaster and the gait-referenced foam casting techniques .” JAPMA 98 : 1 , 2008 .
2
McPoil TG , Hunt GC : “ Evaluation and management of foot and ankle disorders : present problems and future directions .” JOSPT 21 : 6 , 1995 . 3 Decker W , Albert S ( 2002 ) Contemporary Pedorthics . Seattle , Washington : Elton- Wolf Publishing . 4 Michaud , T . C . ( 1993 ) Foot Orthoses and Other Forms of Conservative Foot Care . Baltimore , Maryland : Williams & Wilkins . 5 Nigg BM : “ Impact forces and movement control - Two new paradigms .” PAC Conference April 15 – 17 , 2005 . 6 Nicoll KD : PEDS 6012 Advanced Orthosis Systems . University of Western Ontario , 2010 .
* This is a periodical of the Pedorthic Association of Canada . Originally printed in Pedorthics Quarterly , Fall 2010 . Printed by Kendrick Printing , ISSN 1922-9429 .
Kim Nicoll has been a Certified Pedorthist since 2003 . She has helped develop and taught the Advanced Orthosis Systems course at the University of Western Ontario since the onset of the pedorthic diploma program . Kim is now turning a new leaf and going back to school to increase her practical knowledge in Traditional Chinese Medicine .
14 Pedorthic Footcare Association www . pedorthics . org