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Casting

To be considered a custom-made foot orthotic, each product must be created from a 3-D cast, then manufactured from raw materials.  Currently there are several different 3-D casting methods, each with advantages and disadvantages.  These are as follows:

  • Direct Mold
  • Plaster Paris Slipper Cast
  • Foam Box
  • Laser Scanner
  • Contact Digitizer

Note: Pressure plates have previously been viewed or believed to be an appropriate casting method by many; however, they do not produce a 3-D cast.  For full information see the Insurance section.

Ottawa Foot Orthotics uses two of these methods, Plaster Paris Slipper Cast and Foam Box due to their mobile versatility and success rate.

Plaster Paris Slipper Cast

Plaster casting is one of the most common and popular casting techniques among Pedorthists.  This method of casting is performed non-weight bearing.  Several positions are possible with the most common being the patient lying face down on a bed or plinth, while using the figure four position to insure correct alignment.  An abbreviated version can be used while the patient is standing on one leg with the other knee rested on a chair relaxed in a 90 degree angle at the knee and ankle allowing for the correct casting position.  The casting process is as follows:

  • The Pedorthist will acquire a warm bucket of water to moisten the plaster bandage along with some towels.
  • Strips of plaster bandage are cut to appropriate length.
  • Lotion is rubbed onto the foot prior to applying cast to ease the removal of the plaster cast after bandages have dried.
  • The plaster bandage is moistened and applied to wrap around foot, ensuring a high ridge required for deep cast while pouring the plaster positive cast.
  • The thumb is placed on the fourth and fifth metatarsal heads to lock that lateral (outside) column of the foot.
  • The Pedorthist then using the other hand’s forefinger and thumb, feel the sub-talar joint while moving the thumb on the cast adjusting the foot to the correct position while maintaining a 90 degree ankle positioning.
  • Audible tapping for the cast will reveal if the cast is ready to be removed.
  • By pulling the skin around the heel and foot the cast should be easily slid off the foot courtesy of the lotion on the foot that was applied prior to the plaster bandages.
  • The thumb print under the fourth and fifth metatarsal heads is then removed and any additional modifications are performed as seen fit by the Pedorthist.

Plaster paris slipper cast creates an extremely accurate and direct impression of the foot.  This method of casting is especially valuable when attempting to capture the rearfoot and forefoot alignment including any boney prominences.  However, cast dressings or modification must be taken into account before manufacturing a patient’s custom-made foot orthotics.

Maintaining correct position while slipper casting during drying process.

Correctly aligned completed Slipper Cast ready for manufacturing.

Foam Box

Patient can be casted in two different positions, semi-weight bearing (sitting) and full weight bearing (standing).

Semi-weight bearing

  • Patient sitting with hip, knee, and ankle at 90 degrees.
  • Foot placed into sub-talar joint neutral position (for optimal range of motion).
  • While maintaining sub-talar joint neutral, the Pedorthist will push the patients foot into the foam, creating an impression into the foam.

Note: Patient is advised to NOT help push their foot as it will alter their foot position and impression.

  • The foot is removed and cast is checked for correct alignment and positioning.

Weight bearing

  • Patient is standing, maintaining their balance on either a wall or chair.
  • The Pedorthist positions and maintains the foot in sub-talar joint neutral.
  • The patient then slowly applies pressure creating an impression in the foam, while the Pedorthist controls and assists the patient, maintaining correct positioning.
  • The foot is removed and cast is checked for correct alignment and positioning.

Foam box casting method is used for patients who may not be able to maintain the correct position required for plaster paris slipper cast for the duration of the required time. This provides a less aggressive, custom-made foot orthotic for certain types of diabetic and arthritic patients (can also use plaster paris slipper cast for these conditions as well – at the Pedorthists discretion).

Maintaining Correct position while applying the correct pressure to create the cast.

Correctly aligned completed Foam Box cast ready for manufacturing.